Goldschmidt Conference Abstracts 2008 A1070

Emergence of a habitable planet KEVIN ZAHNLE

1, NICK ARNDT2, CHARLES COCKELL

3, ALEX HALLIDAY

4, EUAN NISBET5, FRANCK SELSIS

6 AND

NORMAN H. SLEEP7

1NASA Ames Research Center (Kevin.J.Zahnle@nasa.gov) 2LGCA, Grenoble (arndt@ujf-grenoble.fr) 3Open University (c.s.cockell@open.ac.uk) 4University of Oxford (alex.halliday@earth.ox.ac.uk) 5Royal Holloway, U. of London (e.nisbet@gl.rhul.ac.uk) 6Universite Lyon (franck.selsis@ens-lyon.fr) 7Stanford University (norm@pangea.standford.edu)

We address the first several hundred million years of Earth's history [1]. The Moon-forming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over ~1000 yrs. As it cooled the Earth degassed its volatiles into the atmosphere. It took another ~2 Myrs for the magma ocean to freeze at the surface. The cooling rate was determined by atmospheric thermal blanketing. Tidal heating by the new Moon was a major energy source to the magma ocean. After the mantle solidified geothermal heat became climatologically insignificant, which allowed the steam atmosphere to condense, and left behind a ~100 bar, ~500 K CO2 atmosphere. Thereafter cooling of the surface was governed by how quickly CO2 was removed from the atmosphere. If carbonate subduction were efficient, this could have taken as little as 10 million years. In this case the faint young Sun suggests that a lifeless Earth should have been cold and its oceans white with ice. But if carbonate subduction were inefficient the CO2 would have mostly stayed in the atmosphere, which would have kept the surface near ~500 K for many tens of millions of years. Hydrous minerals are harder to subduct than carbonates and there is a good chance that the Hadean mantle was dry. Hadean heat flow was locally high enough to ensure that any ice cover would have been thin (<5 m) in places. Moreover hundreds or thousands of asteroid impacts would have been big enough to melt the ice triggering brief impact summers. We suggest that plate tectonics as it works now was inadequate to handle typical Hadean heat flows of 0.2-0.5 W/m2. In its place we hypothesize a convecting mantle capped by a ~100 km deep basaltic mush that was relatively permeable to heat flow. Recycling and distillation of hydrous basalts produced granitic rocks very early, which is consistent with preserved >4 Ga detrital zircons. If carbonates in oceanic crust subducted as quickly as they formed, Earth could have been habitable as early as 10-20 Myrs after the Moon-forming impact. [1] Zahnle, Arndt, Cockell, Halliday, Nisbet, Selsis & Sleep (2007) Space Sci. Rev. 129, 35-78.

Trace metal pollution in the sediments of an urban river:

An impact of anthropogenic activities H.M. ZAKIR

1,2 AND N. SHIKAZONO

1 1Laboratory of Geochemistry, School of Sci. for Open &

Environ. Sys., Faculty of Sci. & Tech., Keio University, Hiyoshi 3-14-1, Yokohama 223-8522, Japan (sikazono@applc.keio.ac.jp)

2Dept. of Agricultural Chemistry, Faculty of Agriculture, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh (zakirhm.ac.bau@gmail.com)

The banks of Old Nakagawa River in Tokyo, Japan is a

location where a significant amount of different types of industrial units were available at the time of second world war (USAMS, 1945-46) and the people of that area informed that in some locations a huge amount of industrial metal contained waste was deposited about 30 years ago. The landscape of the area favour deposition of trace metals in sediments, and still it receives significant amount of various waste from different types of industries and residential areas. The association of Cd (76-98 %) and Zn (48-67 %) were found highest with AEC (adsorbed/ exchangeable/ carbonate) phase; Cu (45-60 %) and Pb (44-73 %) with amorphous Fe oxyhydroxide phase, and the maximum fractionation of Cr was in both crystalline Fe oxide (12-60 %) and amorphous Fe oxyhydroxide phase (15-60 %). For retention by amorphous Fe oxyhydroxide minerals, the observed stoichiometric gradient was: 1.52 for Cu, 1.23 for Pb, 2.25 for Cr and 3.09 for Zn. Corresponding values for association with crystalline oxides, and sulfides and organics were an order of magnitude greater than those for amorphous oxyhydroxide, indicating a greater affinity of trace metals for these phases. The total concentration ranges of Cd, Cr, Cu, Pb and Zn in Old Nakagawa River sediments were 2.86-16.95, 551.7-3953.1, 340.6-1565.3, 136.9-385.9 and 931.4-3650.1 µg g-1, respectively. The observed order of potential trace metal mobility in the aquatic system was: Cd > Zn > Pb > Cu > Cr. Organic carbon contents in sediment samples were comparatively high (mean 5.48 %), and the X-ray diffraction (XRD) study detected the presence of several clay minerals, those are likely to be major host of trace metals in sediments. According to the enrichment factors (EFc), most of the sites have several times higher values of trace metals than the standard. [1] USAMS (US Army Map Service) 1945-46. US Army map service city plans for the Tokyo area. Sheet 9- Honjo. Reproduced from compilation manuscript by overprints. UT Library online.

Goldschmidt Conference Abstracts 2008 A1071

Records of past climate events: A Hitchhiker’s Guide to the

Earth system R.E. ZEEBE

SOEST-Ocean, University of Hawaii, 1000 Pope Rd., MSB 504, Honolulu 96822 HI, USA (zeebe@hawaii.edu)

A prerequisite for making informed predictions about

future climate change is to understand the fundamental climate system-carbon cycle feedbacks underlying the response of the Earth System to perturbations. Unfortunately, the time period of modern observations is too short to provide a complete picture of all those feedbacks. Paleoclimatic studies provide information on a variety of time scales and therefore have a unique opportunity to contribute to comprehending the Earth System. In this keynote talk, I will review selected past climate events, which may guide our understanding of climate, biogeochemical cycles, and ecosystem functioning. Of particular interest here are abrupt events such as the onset of the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma ago), which, in terms of pace and magnitude, may be comparable to the current anthropogenic perturbation. One of the most intriguing aspects of the PETM is that the current generation of climate models appears unable to explain the magnitude of global warming during the event. Archives of those and other past climate events represent chapters of a “Hitchhiker’s Guide to the Earth System” that is invaluable to our present civilization, which, on geologic time scale, has arrived on this planet only a blink of an eye ago.

Finding needles in the haystack: Coordinated analyses on planetary

materials T.J. ZEGA

1*, C.M. O’D. ALEXANDER2, H. BUSEMANN

3, G.D. CODY

2, A.L.D. KILCOYNE4, A.N. NGUYEN

2, L.R. NITTLER

2 AND R.M. STROUD

1 1Naval Research Laboratory, Washington DC, USA

(*correspondence: tzega@nrl.navy.mil) 2Carnegie Institution of Washington, Washington DC, USA 3PSSRI, The Open University, Milton Keynes, UK 4ALS, Berkeley National Laboratory, USA

Primitive meteorites, interplanetary dust particles (IDPs), presolar grains, and the recently returned Stardust samples from comet Wild-2 provide a wealth of information on the chemical and physical processes that shaped our solar system and galaxy. Here we report on coordinated analytical studies of these materials using secondary ion mass spectrometry (SIMS), focused ion beam scanning electron microscopy (FIB-SEM), transmission electron microscopy (TEM), and X-ray absorption near-edge spectroscopy (XANES).

Figure 1 illustrates our coordinated approach to studying insoluble organic matter (IOM) in primitive meteorites. SIMS analysis of a fragment of IOM from the GRO 95577 CR2 chondrite reveals large anomalies in D (Fig. 1a) and 15N. These isotopic anomalies suggest that GRO 95577 contains remnants of presolar organic material. We used the FIB-SEM to extract, in situ, electron-transparent sections of the IOM in order to investigate its structure and composition at higher spatial scales. Bright-field imaging with TEM reveals that the organic material occurs in both monolithic and nanoglobular forms (Fig. 1b). XANES spectra show that this organic material contains aromatic, carbonyl, imine, and nitrile functional groups. The 15N enrichments correlate with a higher abundance of imine and nitrile functional groups, suggesting that they could be molecular carriers of the 15N anomaly. The implications of these results for solar and interstellar processes will be discussed.

Goldschmidt Conference Abstracts 2008 A1072

Na2O vs Sr in lunar samples

Sr (ppm)200 300 400 500 600 700

Na 2O

(wt%

)

0

1

2

3

4SaU 169 IMBA12 High-Th IMBsMIL 05035 (basalt)FAN (A16 + A14)A14 KREEP Basalt

TerrestrialContamination?

Refinement of kaolin and silica sand by microbial removal of iron

impurities A. ZEGEYE*, C.I. FIALIPS, M. WHITE,

D.A.C. MANNING AND N. GRAY

School of Civil Engineering & Geosciences, Drummond building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK (*correspondence: Asfaw.Zegeye@ncl.ac.uk)

Kaolin clay and silica sands are minerals used in a wide

range of industrial applications, particularly in paper, ceramics and glass manufacturing. These minerals are formed by the mechanical and chemical breakdown of rocks and, depending on the geological conditions of deposition they are often associated with iron (hydr)oxides that are either adsorbed to the mineral surfaces or admixed as a separate iron bearing phase. Unfortunately, iron (hydr)oxide impurities in raw kaolin and silica sands dramatically affect their quality and value. Several physical and chemical refining methods are currently being used to remove as much iron impurities as possible from these raw minerals, including magnetic separation, alkali and acid treatments. However, because of technological and environmental disadvantages associated with these processes, microbial leaching is now being considered as an alternative method.

In this study, we have examined the Fe(III) removal efficiency from kaolin and silica sand by a series of iron-reducing bacteria from the Shewanella species (S. alga BrY, S. oneidensis MR-1, S. putrefaciens CN32 and S. putrefaciens ATCC 8071). The microbial reduction of Fe(III) was achieved using batch cultures under non-growth conditions. The rate and the extent of Fe(III) reduction was monitored daily for 5 days as a function of the initial Fe(III) content, Shewanella species and temperature. The bacterially-treated minerals were analysed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS) to observe any mineralogical transformation. The whiteness and ISO brightness of the kaolin was measured by spectrophotometry.

All Shewanella species were able to couple the oxidation of lactate to the reduction of Fe(III) associated with the kaolins and silica sands. However, there are differences among species with respect to the rate of reduction and extent of Fe(II) production. S. putrefaciens ATCC 8071 is the most effective, with an increase in kaolin whiteness from 57.7% to 67.8%, and a decrease in yellowness decreased from 10.1% to 6.3% at 20°C. ISO brightness increased from 76% to 80%.

Determination of Sr concentrations in lunar plagioclase by electron

microprobe analysis R.A. ZEIGLER, B.L. JOLLIFF, R.L. KOROTEV AND

P.K. CARPENTER

Dept. Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, St. Louis, MO, 63130

We have measured Sr concentrations in plagioclase in a

variety of lunar samples to investigate how variations might correlate with rock type, petrogenetic history, or reservoir. Sr concentrations in lunar plagioclase are relatively low (a few 100s of ppm), thus it is not typically measured because its analysis requires fairly severe analytical conditions.

Analyses were done on the JEOL 8200 electron micro-probe at Washington University. Sr was simultaneously counted on four wavelength-dispersive spectrometers (one high intensity). Nominal conditions were 15 keV, 100-200 nA, 20-50 µm beam diameter (to prevent Na volatilization), and 150-300 second count times (per spectrometer). Analytical uncertainties (99% CI) were ± 11-18 ppm.

Sr concentrations vary considerably, from 200 to 650 ppm, correlating positively with Na2O (Fig. 1). We see increasing Sr concentrations from the core to the rim of normally zoned plagioclase grains, reflecting crystallization trends. Different lunar samples or sample suites also define different trends in Fig. 1, representing differences in initial composition, i.e., reflecting different reservoirs. For example, the three KREEP samples in this study (SaU 169 IMB, Ap12 IMBs, KREEP basalts) all have different trends; does this then indicate three different reservoirs of KREEP? Different suites of lunar samples tend to populate different regions of Figure 1 (or define distinct trends, e.g., MIL 05035), suggesting that with more study, Sr concentrations could be used to identify the provenance of plagioclase mineral grains in polymict samples.

Figure 1: Na2O vs. Sr in selected lunar samples.

Goldschmidt Conference Abstracts 2008 A1073

Some first-order observations on magma transfer at volcanic arcs

G.F. ZELLMER*

Institute of Earth Sciences, Academia Sinica, 128 Academia Road Section 2, Taipei 11529, Taiwan (*correspondence: gzellmer@earth.sinica.edu.tw)

The viscosity of lavas erupted at volcanic arcs varies over

orders of magnitude. A comparison of the relative abundance of viscous lava dome eruptions indicates that the average viscosity of arc lavas also varies considerably between arcs. It will be shown that for continental or transitional arcs with little within-arc crustal deformation and without underlying slab windows or tears, average lava viscosity is anti-correlated with average surface heat flux (R2=0.77). The latter may be influenced by crustal thickness and crustal magma throughput. To constrain the relative contributions of these parameters, variations of average lava viscosity with average crustal thickness and plate convergence rate are assessed. While crustal thickness appears to have little effect on average lava viscosity, a good anticorrelation exists between average lava viscosity and plate convergence rate (R2=0.71), with the exception of two arcs that show significant intra-arc crustal deformation. If plate convergence rate is a good proxy of the rate of melt generation within the mantle wedge, these first-order observations indicate that where the rate of mantle melting is high, crustal magma throughput is rapid and efficient, resulting in low viscosity melts migrating through a hot overriding crust; in contrast, where the rate of mantle melting is low, crustal magma transfer is slow and inefficient, resulting in high viscosity melts that may frequently stall within a cool overriding crust prior to eruption. Uranium series geochemical evidence from dome lavas is presented and lends support to this interpretation. This leads to a general model of eruptive style dependence on crustal magma transfer processes. Finally, the observed average viscosity variations of some arcs with underlying slab windows or tears and/or significant intra-arc crustal deformation will be discussed with reference to their geochemical characteristics.

Recent bimodal magmatic processes and their rates in the Torfajökull-

Veidivötn area, SE Iceland G.F. ZELLMER

1*, K.H. RUBIN2, K. GRÖNVOLD

3 AND

Z. JURADO-CHICHAY2

1Institute of Earth Sciences, Academia Sinica, 128 Academia Road Section 2, Taipei 11529, Taiwan (*correspondence: gzellmer@earth.sinica.edu.tw)

2Department of Geology and Geophysics, SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822, USA (krubin@hawaii.edu, zinzuni@soest.hawaii.edu)

3Volcanological Institute, University of Iceland, IS-101, Reykjavik, Iceland (karlgr@hi.is)

Historical eruptions of bimodal composition eruptions

from Torfajökull central volcano and the neighbouring Veidivötn fissure swarm in southeastern Iceland provide insights to the nature and timing of basalt and rhyolite genesis and eruption at an active divergent plate boundary. This study focuses on lavas and tephras of the last two regional eruptions in 871 and 1477AD, using samples that approximate mafic and felsic endmember compositions relative to regional mixing trends. Whole rock and mineral U-Th-Ra isotopic compositions indicate both rapid petrogenetic timescales and limited compositional variation in the basalt and rhyolite magma sources. Torfajökull rhyolites show the greatest 230Th excesses (≤ 17%) at only slightly lower (230Th/232Th) activity ratios than co-eruptive Veidivötn basalts. Both magma types display small but significant 226Ra excesses (≤ 10% and ≤ 60% in rhyolites and basalts, respectively). Trace element and U-series isotopic data are consistent with crustal melting dominated by young (≤ 60 kyrs), metasomatized mafic protoliths similar in composition to the Veidivötn tholeiites as source of the 871 and 1477 Torfajökull rhyolites. Young protolith ages are inconsistent with previous models that call on old materials as source rocks for Icelandic rhyolites (e.g., old silicic segregation lenses or isostatically subsided lavas). Zero-age U-Th and few-ka Ra-Th mineral - whole rock isochrons suggest crystallization shortly prior to eruption, consistent with petrographic and compositional indicators that the crystals are phenocrysts, and the data suggest that the rhyolite melts are of Late Holocene age.

Goldschmidt Conference Abstracts 2008 A1074

Evidence for an Earth-Moon impact event 800 Ma ago

N.E.B. ZELLNER1, J.W. DELANO

2 AND T.D. SWINDLE

3 1Department of Physics, Albion College, Albion, MI 49224,

USA (nzellner@albion.edu) 2Univerity at Albany (SUNY), Albany, NY 12222, USA

(jdelano@atmos.albany.edu) 3University of Arizona, Tucson, AZ 85721, USA

(tswindle@U.Arizona.Edu)

Lunar Impact Glasses Lunar impact glasses offer the potential for providing

compositional information about local and remote areas of the Moon [1-3] and may also place constraints on the impact history in the Earth-Moon system.

Previous workers have reported 40Ar/39Ar ages of ~800 Ma on lunar samples, such as rock fragments (Apollo 12; 4) and impact glasses (Apollo 14, 16; 5, 6). We present additional 40Ar/39Ar ages on Apollo 14 and 17 impact glasses. When all of these data are viewed collectively, there is a suggestion that there may have been an increase in the impact flux at ~800 Ma. Results

Of the 62 glasses for which an age has been determined by these authors, 8 have diverse compositions with ages ~800 Ma, as shown in Figure 1. This age is similar to the best current estimate for the age of the Copernicus impact event (~800±15 Ma; [4, 7]).

Figure 1; Refractory element compositions of lunar samples (including impact glasses) with ~800 Ma ages.

The higher frequency of impact glasses with this age is

consistent with a transient increase in the impact flux at this time. Perhaps the Copernicus impact event was only one of numerous large events (and many small local events) that occurred. [1] Delano (1991) GCA 55, 3019-3029. [2] Zellner et al. (2002) JGR 107(E11) 5102, doi,10.1029/2001JE001800. [3] Delano et al. (2007) MAPS 42, 6, 993-1004. [4] Barra et al. (2004) LPSC 35, 1365.pdf. [5] Zellner et al. (2003) LPSC 34, 1157.pdf. [6] Borchardt et al. (1986) PLPSC 17th, p. E43-E54. [7] Bogard et al. (1994) GCA 58, 3093-3100.

Early Mesozoic high pressure metamorphism in the Lhasa Block,

Tibet: Implications for the growth of the Cimmerian subcontinent

L. ZENG1*, J. LIU-ZENG

2 AND K. XIE

2 1Institute of Geology, Chinese Academy of Geological

Sciences, Beijing 100037, China (*correspondence: changting1970@yahoo.com)

2Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100871, China

The traditional Lhasa Block is part of the Cimmerrian

subcontinent which was accreted to the southern margin of the Laurentia continent at Mid-Mesozoic [1, 2]. The east-west trending Sumdo-Jiaxing eclogite belt, ~200 km east of Lhasa, provides information to constrain how the Cimmerian subcontinent was assembled. This eclogite belt consists of two types of eclogites: kilometers long and several hundreds meters wide massive blocks and sub-meter size subparallel layers or lentoids. Both are enclosed within late Paleozoic quartzite and carbonates. Bulk-rock major and trace element data indicate that these eclogites have preserved an N-MORB type geochemistry [3]. P-T estimations show that they experienced high pressure metamorphism at ~2.6 GPa and ~650oC. Sm-Nd whole rock isochron on 11 data yields an age of 239±16 Ma. Petrography and trace element data suggest that this age represents the timing of high pressure metamorphism. These data show that the Sumdo-Jiaxing oceanic block was subducted to a depth of ~75 km and underwent high pressure metamorphism at ~239 Ma. Such an early Mesozoic event of subduction of oceanic crust within the Lhasa Block suggests that (1) at least one oceanic basin existed concurrently with the Paleo-Tethys and (2) the Cimmerrian subcontinent was assembled by a number of smaller continental or oceanic blocks that were scattered within the Paleo-Tethyan Ocean. [1] Dewey, Shackleton, Chang & Yiyin (1988) Phil. Trans. Roy. Soc. London, series A, 327, 379-413. [2] Hsu, Pan, Sengor et al. (1995) Int. Geol. Rev. 37, 473-508. [3] Zeng, Liu & Xie (2007) Eos, Trans. AGU, 88(47) Fall Meet. Suppl. Abstract T23D-1637.

Goldschmidt Conference Abstracts 2008 A1075

The solubilities of the quaternary system Li2CO3+Na2CO3+K2CO3+H2O

at 273 K Y. ZENG*, G.L. CEN, Z.Y. ZHENG AND X.F. LIN

Department of Geohemistry, Chengdu University of Technology, Chengdu, P. R. China, 610059 (*correspondence: zengy@cdut.edu.cn)

The salt-water system phase diagram is the direction for

the comprehensive and utilization of saline brines. System Li2CO3 + Na2CO3 + K2CO3 + H2O is one of the basic systems for carbonate alkaline brines.

Experimental Method

The isothermal evaporation method was used [1]. The experiments were done at (273.15 ± 0.1) K, and a thermostatic evaporator was used for evaporation. The composition of solution was determined by analytical method. The crystals were analyzed by X-ray diffraction.

The densities of solution were also determined by specific gravity bottle method [1] and used for the mass fraction calculation of components. Discussion of Results

The phase diagram consists of five univariant curves, two invariant points and four crystallization fields corresponding to single salt Li2CO3, Na2CO3·10H2O, K2CO3·3/2H2O and double salt KNaCO3·6H2O. Double salt KNaCO3·6H2O is formed in this system, which was also founded in the Harvie’s study at 298 K [2]. Whereas, Na2CO3·10H2O is the only crystal form for sodium carbonate, the heptahydrate and unihydrate sodium carbonate are not found.

Figure 1: The phase diagram of the system K2CO3 + Na2CO3

+ Li2CO3 + H2O at 273 K.

The work was supported by the National Nature Science Foundation of China (No. 40673050). [1] Zeng et. al. (2005) J. Chem. Eng. Data, 50, 928-931. [2] Harvie et. al. (1984) Geochim. Cosmochim. Acta. 48, 723-751.

Fractionation of multiple sulfur isotopes during phototrophic

S oxidation A.L. ZERKLE

1*, J. FARQUHAR1, D.T. JOHNSTON

2, R.P. COX

3 AND D.E. CANFIELD

4 1Department of Geology and Earth Systems Science

Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA (*correspondence: azerkle@umd.edu)

2Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

3 Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark

4Nordic Center for Earth Evolution and Institue of Biology, University of Southern Denmark, Odense, Denmark

Here we report multiple sulfur isotope measurements

(33S, 34S, and 36S) of sulfur compounds associated with the oxidation of H2S and S0 by the anoxygenic phototrophic S-oxidizing bacterium, Chlorobium tepidum. We measure small inverse isotope effects during H2S oxidation, and slightly larger normal isotope effects during S0 oxidation, resulting in the net production of sulfate that is slightly depleted in heavy isotopes from the starting sulfide. Utilizing the fractionation factors for phototrophic S oxidation processes that we calculated from these experiments, we present a steady-state box model of the isotopic composition of ocean sulfur reservoirs. Our model indicates that, although the isotopic effects associated with phototrophic S oxidation are small, this process can significantly alter the overall isotopic composition of the system through the redistribution of mass. The trends produced in our models suggest that phototrophic S oxidation has the potential to mask the isotopic signal of sulfur compound disproportionation if greater than 33% of elemental sulfur in the system is re-oxidized to sulfate. This result has important consequences for interpretation of ancient S isotope records during periods of widespread photic zone euxinia, such as proposed for the mid-Proterozoic.

Goldschmidt Conference Abstracts 2008 A1076

The solubility of Au in H2O-H2S gas mixtures

D. ZEZIN*, A.A. MIGDISOV, AND A. E. WILLIAMS-JONES

Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec, Canada, H3A 2A7 (*correspondence:zezin@eps.mcgill.ca)

Magmatic-hydrothermal systems commonly contain high

proportions of vapor and, in some cases, the vapor phase may be dominant. Moreover, there is increasing evidence that this phase can transport appreciable concentrations of metals. In the case of gold, there is also evidence that it may even partition preferentially into the vapor over the liquid. In a previous study, we demonstrated that neutral solvated sulfide gaseous complexes of Au significantly enhance the solubility of gold in the vapor phase [1]. It is also known from other studies that the formation of hydrated species may positively influence the solubility of metals in liquid-undersaturated vapor. Therefore, it is reasonable to propose that the preferential partitioning of gold into vapor relative to liquid is due to the increased stability of hydrated complexes of Au involving reduced sulfur in H2O-H2S gas mixtures. We report here the results of an experimental study designed to test this hypothesis

The experiments were carried out in titanium alloy autoclaves at temperatures from 300 to 365°C and total pressures (estimated from the independently measured PVTx properties of H2S-H2O gas mixtures) up to 300 bars. The results of the study show that the solubility of Au in H2O-H2S gas mixtures increases with temperature and fH2S. The solubility of Au at 300-350°C and fugacities of H2O up to about 100 bars appears to be controlled dominantly by sulfide or bisulfide complexes of Au solvated by H2S. However, at greater fugacities of H2O, solvation of complexes of Au with reduced sulfur by water molecules is pronounced and increases the solubility of Au by more than one order of magnitude over that in pure H2S. Based on the results of our experiments, we propose that there may be as many as four molecules of H2O in the hydration shell of gaseous sulfide or bisulfide Au species at 350°C. Thus, with increasing pressure, the solubility of Au in the aqueous vapor containing H2S will rapidly increase and, at conditions typical for natural hydrothermal systems the formation of hydrated sufide/bisulfide complexes may be sufficient to explain the concentration of gold to economic levels.

[1] Zezin D.Yu. Migdisov Art.A. Williams-Jones A.E. (2007) The solubility of gold in hydrogen sulfide gas, An experimental study, GCA 71, 3070-3081.

Electrical conductivity of MgO at high pressure and high temperature

B. ZHANG1,2, X. WU

1, J. XU1 AND T. KATSURA

3 1School of Earth and Space Science, University of Science and

Technology of China, Hefei 230026, P. R. China (zhangbh@mail.ustc.edu.cn)

2School of Materials Science and Engineering, Hefei University of Technology, Hefei, Anhui 230009, P. R. China

3Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori-ken 682-0193, Japan

Periclase (MgO) has been the subject of extensive study

because it is relevant as an end-member of magnesiowüstite (Mg,Fe)O, which is proposed to be the second most abundant phase in the lower mantle. The electrical conductivity of MgO has been measured in a KAWAI-type multianvil high-pressure apparatus at 20 GPa and in the temperature range 700-1700K. A MgO+5% Cr2O3 octahedral pressure medium with 10 mm edge length was used, the edge length of tungsten carbide anvils was 31 mm and their truncated edge length was 4.0 mm. All of the reproducible and reversible conductivity data were fitted to Arrhenius equation σ=σ0exp(-∆H/kT) by a Levenberg-Marquardt nonlinear procedure, where the activation enthalpy ∆H=∆E+P∆V with activation energy ∆E and activation volume ∆V. As a result, the preexponential factor, activation energy and activation volume were calculated to be σ0=8745±2 S/m, ∆E=1.057 eV, and ∆V=0.292 cm3/mol, respectively. Comparing the previous magnesiowüstite (Mg1 xFex)O and perovskite-magnesiowüstite assemblages data, the large activation energy and positive activation volume were inconsistent with the small and large polaron conduction mechanism. As a result, the ionic mobility, the diffusion coefficient of the Mg vacancy and the self-diffusion coefficient of Mg ion were estimated in this study, which suggested that the ionic conduction caused by the migration of MgMg

x via VMg”, can be the conduction mechanism in periclase (MgO) at high temperature and pressure.

This work was supported by funds from the Natural

Science Foundation of China (No. 40537033, 40374025) and Program for New Century Excellent Talents in University (NCET-05-0553). We gratefully acknowledge financial support from COE-21 Collaborative Research Program at ISEI, Misasa, Japan.

Goldschmidt Conference Abstracts 2008 A1077

Sulfur isotope constraint on the Chipu Zn-Pb deposit

CHANGQING ZHANG1, LI LI

1, JINJIE YU1

AND ZHIHONG LI2

1Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037

2Institue of Geology, Chinese Academy of Geological Sciences, Beijing, 100037

Result

Chipu large scale Zn-Pb deposit is located on the southwest margin of Yangtze craton, China. It is one of the most important deposits in this area. The sulfur isotope is measured on sphalerite and galena. Ores are enriched in heavy sulfur. The ranges of δ34S for the samples of shpalerite and galena are from 8.6‰ to 13.2‰ and 11.9‰ to 15.1‰ with an average of 10.71‰ and 13.23‰, respectively. Our results are shown in the figure below.

Figure 1: Distribution of δ34S from Chipu deposit. Discussion of Results

The characteristic of enriched in heavy sulfur is obviously different from mantle-derived sulfur with δ34S values of about 0 per mil. However it is similar to those of about 17 per mil for the host rock of Dengying Fmantion. The sulfur in the ore-forming fluids of this deposit came mainly from the carbonate strata. Reduced sulfur can be derived from the thermochemical reduction of sulfate (TSR) by organic matter, which yields sulfur isotope fractionations less than about 0 to 15 per mil of the isotopic value of the sulfate source [1]. The homogenous temperatures of fuild inclusion in shalerite are from 127 to 288°C [2], which are sufficient to overcome the kinetic constraints of accounting for sufficient production reduced sulfur locally within the ore deposit. In addition, there are many bitumen in or near the orebody. So we propose that Chipu Zn-Pb deposit is interpreted to have involved reduced sulfur derived by TSR. This will be a important evidence for researching on the genesis of this deposit. [1] Leach et al. (2005) Economic Geology 100th Anniversary Volume, 561~607. [2] Zhang et al. (2007) Acta Petrologica Sinica 23, 2541-2552.

Framework of Mesozoic magmatism and crust-mantle interaction in the Dabie Mountain and middle-lower Yangtze River belt, central China

CHAO ZHANG* AND CHANGQIAN MA

State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China (*correspondence: halfrock@gmail.com)

Integrated methods including in situ zircon dating,

petrology and geochemistry have been taken to investigate the massive magmatism in the Dabie Mountain and adjacent areas, which gain the result that Mesozoic magmatism began from late Jurassic and reached its peak at early Cretaceous. Zircon LA-ICP MS age of Zhangbang pluton, a small scale granitic pluton in southern Dabie Mountain, is 150.3±2.0 Ma, which is at present the earliest Mesozoic magmatic record and approximately 20 million years prior to the peak. In situ zircon Hf analyses performed on LA-MC-ICP MS obtain εHf(t) values of about -29 and Hf crustal model ages of around 3.05 Ga. These greatly old model ages are similar to ages of the continental core of the South China Craton and the basement rocks of the Dabie Mountain, which suggests its magmatic protolith is mainly earlier Precambrian metamorphic complex. Statistic analyses of accurate chronological and geochemical data of igneous rocks show that the magmatic movement and crust-mantle interacton in the Dabie Mountain and the middle-lower Yangtze River belt occurred almost simultaneously with a rough duraiton from 150 Ma to 115 Ma. The thickening of the orogenic crust started after ~ 150 Ma and finished at ~ 130 Ma, and was followed by the striking thinning and collapse. However, there are some significant differences in magmatic composition and magmagenesis between Dabie Mountain and middle-lower Yangtze River belt, including εNd(t) values which are usually between -10 and -25 in the former while not less than -10 in the latter, suggesting a model that mantle-derived magma played a more important part in the latter than that in the former. An implication could be drawn that the extents of upwelling of asthenosphere and delamination of lithosphere in late Mesozoic were much more intense in the middle-lower Yangtze River belt than those in the Dabie Mountain.

This work is supported by National Natural Science

Foundation of China (No. 40334037), Scientific Collaboration Project (No. 2007DFA21230) and Fund for Creative Research Groups (No. 40521001).

Goldschmidt Conference Abstracts 2008 A1078

Characteristics and evolution of geothermal field in the Bozhong Sub-

basin, Bohaiwan Basin, China CHENG ZHANG, XINONG XIE, XIURONG GUO

AND XUEBIN DU

Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China (zhangch@cug.edu.cn)

Based on the analysis of tectonic evolution, characteristics

and evolution of the geothermal field in the Bozhong sub-basin of the Bohaiwan basin in eastern China have been summarized by means of measured temperature data, vitrinite reflection gradient and numerical simulation.

Measured formation temperature data show that the present geotemperature field has a good correlation with the depth, but temperature gradients are different in various areas and layers. Temperature gradients decrease from the Shahejie Formation to the Dongying Formation in the Paleogene System and increase from the Guantao Formation to the Minghuazhen Formation in the Neogene System. Temperature gradients in the uplifts (about 3.0~4.0°C/100m) are higher than that in the depression (about 2.5~3.5°C/100m) that maybe result from the effect of lower rock thermal conductivity in the depression and the hot fluid flow along main faults in these uplifts.

The paleo-geothermal gradient, calculated from the vitrinite reflection gradient, is about 3.5~5.8°C/100m and observably higher than that in nowadays, which indicates not only the thermal field in the study area was continued cooling during the post-rifting period in the Neogene (25Ma ~ nowadays), but also there occurred higher maturity of organic matters and more active fluid flow in this sub-basin during the syn-rifting period in the Paleogene (50 ~ 25Ma). The numerical simulation similarly shows the higher paleo-geothermal gradient and the rapid thermal mature of source rocks. The source rock in the 3rd member of the Shahejie Formation in the deep depression center had matured in 27.4Ma at latest and had entered producing-gas stage from producing-oil stage in a short time.

Carbonate and its stable isotopes for the reconstruction of hydrological

changes in the Holocene Bosten Lake in China

CHENGJUN ZHANG1 AND FANGQING GUO

2 1School of Resources and Environmental Sciences, Lanzhou

University, Lanzhou, China (cjzhang@lzu.edu.cn) 2 School of Resources and Environmental Sciences, Lanzhou

University, Lanzhou, China (guofq06@lzu.cn) Carbonate content in the Bosten Lake core sediments in

the mid-latitude arid China and the mineral calcite, aragonite and dolomite contents, carbon and oxygen isotopes have been analyzed in this paper, it is shown that calcite and aragonite content, the characteristics of stable isotopes and the correlation coefficient between these carbon and oxygen isotopes have an obvious relation with the hydrological changes in the Bosten Lake that supplies by the ice-snow melt-water. In the period of 8500~8100a B.P., stable isotopes of sediment carbonate are δ13C=0 ~ -4‰, δ18O=-6 ~ -5‰, r=0.04 (coefficient), little aragonite in the carbonate. It implied that climate was cold and a little water inflowed into the lake; From 8100 to 3100a B.P., δ13C=-1 ~ +5‰, δ18O=-6.5 ~ -+2‰, r=0.7. The climate had several cold-warm alternation in the warm background. Lake water enlarged as judged from the result of stable isotopes and calcite, aragonite content; From 3100~2200a B.P., δ13C=0 ~ +1‰, δ18O=-6 ~ -4‰, r=0.1. The temperature fell in this period and made the evaporation down also, so the lake water minished and the ice-snow melt-water took a great influence to the stable isotopes, and let a lower correlation. Although the isotope characteristics in this period was similar with that in the 8500~8100a B.P., the hydrological change was an obvious different; From 2200 a B.P., δ13C=+2 ~ +4‰, δ18O=0 ~ +1‰, r=0.9, aragonite content is 30~40%. It was shown that the temperature ascended in this area, and lake water had been influenced largely by the evaporation.

Goldschmidt Conference Abstracts 2008 A1079

Studies on the Zircon U-Pb-Hf isotopes of host rocks and enclaves

from the Shahewan pluton in Qinling Orogen, central China

CHENLI ZHANG*, JINGLAN LUO AND HONGLIN YUAN

State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, 710069, China (*correspondence: clzhang@nwu.edu.cn)

The Shahewan pluton was intruded into the boundary

between North and South Qinling Belts, providing us an important object to reveal the continent-continent collisional history between North China and Yangtze blocks in Mesozoic. The two group ages from host rocks (209.2Ma-205.4Ma and 198.3Ma-197.6Ma) and enclaves (199.09Ma-199.90Ma and 192.6Ma-187.4Ma) were obtained from this pluton using in situ zircon LA-ICP-MS method, respectively. The age from basic dykes adjacent to Shahewan pluton was slightly older (212.5Ma). Furthermore, they have narrow ranges of 176Hf/177Hf, with the εHf(209.2Ma) of -0.77 and εHf(205.4Ma) of -0.40 from host rocks and εHf(199.9Ma) of -0.63 and εHf(199.09Ma) of -1.23 from enclaves. The εHf(212.5Ma) of the basic dykes is -0.87. In addition their TDM2 are quite similar. In witch the TDM2 of host rocks are from 1079Ma to 1057Ma, enclaves from 1095Ma to 1064Ma and the basic dykes 1090Ma. All these suggest that the Shahewan pluton was mainly formed by the melting of the Neoproterozoic crustal materials in South Qinling basement and granitic magmatic activity was trigged by basic magma derived from the enriched mantle similar to that of middle Neoproterozoic in South Qinling [1, 2], implying the mantle was not much changed from Neoproterozoic to Mesozoic in Qinling. [1] Lu et al. (2003) Earth Sci. Front. 10(3), 69-75. [2] Zhang et al. (2007) Sci. China Ser. D-Earth Sci. 50(09), 1293-1301.

U-Pb SHRIMP-dating of zircons and structures of granitoid plutons in the

Tongling area (Anhui, China) and their tectonic significance

DA ZHANG*, GANGUO WU, YONGJUN DI, WENSHUAN ZANG AND WENCAN LIU

State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, 100083, China (*correspondence: zhangda@cugb.edu.cn)

Key Laboratory of Lithospheric Tectonics and Lithoprobing Techology of Ministry of Education, China University of Geosciences, Beijing 100083, China

In southeastern China, there are numerous Mesozoic

plutons, which are considered to be controlled by a NNE trending tectonic regime (D3 deformation) during ascent and emplacement. Unfortunately, the chronology and structural geology of these plutons are not commonly studied. Thus clearly distinguishing the relationship between the D3 deformation and pluton’s emplacement is hampered because of the shortage of direct isotopic ages and structural evidence.

Chronological and structural information are used to evaluate the emplacement mechanisms of the plutons in the Tongling area and their relationship with regional tectonics. Five zircon U-Pb SHRIMP ages from 5 different plutons in the Tongling area are 142.8±1.8Ma, 144.2±2.3Ma, 151.8±2.6Ma, 146.4±4.3Ma and 148.2±3.1Ma, indicating that the plutons formed at the end of late Jurassic (142.8~151.8Ma). The meso- and microscopic structural analysis indicate that the plutons experienced high temperature magmatic to low temperature solid-state deformation. The magmatic, enclave and magnetic foliation all show the feature of concentric fabrics within the plutons, rather than the preferred orientation of the regional D3 deformation. The S-C fabrics and mylonites, representing the D3 deformation, transect the pluton, which show that the low temperature solid-state deformation occurred during the cooling of the pluton post-emplacement.

From the above results, it is suggested that the crystallization and emplacement of the plutons occurred at the late Jurassic, older than the D3 deformation. Thus the regional D3 deformation didn’t control the formation, ascent and emplacement of the plutons in the Tongling area.

Grant Nos. 40434011 and 40372050.

Goldschmidt Conference Abstracts 2008 A1080

Geochemistry and tectonic setting of basalts in Shilipo native copper

mineralized area, Eastern Tianshan DA YU ZHANG, TAO FA ZHOU*, FENG YUAN

AND YU FAN

School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China (*correspondence: tfzhou@hfut.edu.cn)

Geochemistry of the Basalts

The Shilipo area with native copper mineralization occurring in the Matoutan Group is located in Eastern Tianshan of North Xinjiang. The orebearing basalts are from Low potassium to Calc-alkali series with enrichment of LREE and none Eu anomaly of basalts indicate an inner plate setting (Fig.1) and continental facies volcanic rocks.

Figure1: Zr-Zr/Y diagram(after [1]).

Discussion Wang & Xu [2] suggested the time span of the main post-

collisional stage in northern Xinjiang. Combining with the ages of the orebearing basalts [3, 4], the basalts as well as the native copper mineralization were formed in the extensional regime of a post-collisional tectonic setting.

This research was sponsored by the National Key Basic

Science Research project of China (2007CB411304 and 2001CB409806) and the National Natural Science Foundation of China (40772057).

[1] Dupuy et al. (1992) GCA 56, 2417-2423. [2] Wang & Xu (2006) Acta Geologica Sinica 80, 23-31 (in Chinese) [3] Yuan et al. (2007) Acta Petrologica Sinica 23, 1973-1980 (in Chinese) [4] Yuan et al. (2007) Acta Mineralogica Sinica 27, 118-119 (in Chinese).

A reactive transport model to simulate uranium immobilization

through pH manipulation FAN ZHANG

1, W. LUO1, D.B. WATSON

1*, J.C. PARKER2,

B. GU1, B.P. SPALDING

1 AND P.M. JARDINE

1 1Environmental Sciences Division, Oak Ridge National

Laboratory, Oak Ridge, TN 37831, USA (*correspondence: watsondb@ornl.gov)

2Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN 37996, USA

Saprolite cores collected from around the former S-3

Ponds waste disposal site on the Oak Ridge Reservation in east Tennessee, USA, exhibit low pH and high concentrations of Al, Ca, Mg, Mn, various trace metals such as Ni and Co, and radionuclides such as U and Tc. Because uranium is one of the major contaminants of concern at the site, its behavior was of particular interest. The mobility of uranium depends highly on pH. Groundwater titration experiments showed that when pH was increased from 3.87 to 5.45 with addition of dissolved sodium hydroxide, concentration of aqueous uranium decreased from 50 ppm to less than 5 ppm [1]. However, base additions to the sediments to increase pH are strongly buffered by various precipitation and sorption reactions. This study was undertaken to investigate the geochemical processes that control contaminant mobility and to develop a practical model to predict uranium immobilization under conditions where pH is manipulated for remediation of geochemically complex sites.

The method of Spalding and Spalding [2] was utilized to model soil buffer capacity by treating aquifer solids as a polyprotic acid. Aluminum precipitation and dissolution kinetics was included in HydroGeoChem v5.0 [3] in addition to an equilibrium reaction model that considers aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange capacity. The HydroGeoChem model was successfully utilized to simulate batch titration experiments and comparison of reactive transport model results with pH manipulation column experiments were in close agreement. The model was also calibrated to simulate acidic groundwater percolating through carbonate gravel at the site. [1] Gu et al. (2003) Geochimica et Cosmochimica Acta 67(15) 2749-2761. [2] Spalding & Spalding (2001) Environ. Sci. Technol. 35, 365-373. [3] Yeh et al. (2004) HydroGeoChem 5.0. Oak Ridge National Laboratory.

Goldschmidt Conference Abstracts 2008 A1081

Substrate-controlled crystallization of calcite and aragonite

FANGFU ZHANG1, H. XU

1, G. FARFAN2, J. HUBERTY

1, H. KONISHI AND E.R. RODEN

1 1Department of Geology and Geophysics, University of

Wisconsin, Madison, WI 53706, USA 2Madison West High School, Madison, WI 53726, USA

Both calcite and aragonite are common minerals on the earth surface. Ca-carbonate minerals are very important for balancing Ca and carbon cycles in the earth system. Late stage fibrous minerals that fill or partially fill some voids in Cenozoic basalt from Dust Devil Mine in Lake County, Oregon, were investigated using optical microscopy and X-ray diffraction. XRD patterns indicate the fillings are dominated by aragonite with small amount of calcite. The amount of calcite in the mixture ranges from ~ 3% to ~10 %. The substrate of the aragonite aggregates are hematite-bearing glass matrix. Both texture and associated minerals indicate the aragonite is not biogenic. We propose that hematite substrate can also enhance aragonite formation besides solution composition. Aragonite (~ 90%) and calcite (~10%) was obtained in a Ca-bearing solution; and pure aragonite was obtained in a solution with Mg/Ca ratio of 0.25. The carbonate grew in hematite-free solutions only result in pure calcite. Both natural sample and synthesized samples prove that high-pressure structure phase aragonite can precipitate on hematite surface or in hematite-bearing suspensions. It is proposed that both surface structure and surface acidity of hematite may cause the aragonite formation.

Figure 1: Aragonite crystals (with small amount of calcite) grow at a hematite-bearing surface (Hm). (Image width: ~ 4 mm)

This work is supported by NASA Astrobiology Institute

(N07-5489).

Geochronology of the Altay adakite and the initiation of the Paleo-Asian

Ocean subduction HAIXIANG ZHANG*, X. SHEN AND L. MA

Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institue of Geochemistry, CAS, Guangzhou, 510640, China (*correspondence: zhanghx@gig.ac.cn) Petrological and geochemical characteriustics of andesites

from the Fuyun region, Altay are simiar to those of adakites and, were likely derived by partial melting of the subducted neonatal Paleo-Asian Oceanic crust [1]. LA-ICP-MS zircon U-Pb dating of an adakite has been carried out to give better constraints on the beginning of the Paleo-Asian Ocean subduction in this study. The 206Pb/238U ages of 30 measurement spots range from 436.1 to 449.6 Ma along the accordant line with an average age of 441.3±1.8Ma (Fig. 1). This is the formation time of the adakite, which represents the low limit of the onset of the Paleo-Asian Ocean subduction underneath Siberian plate.

Figure 1: U-Pb consonant diagram of zircon. The tectonic evolution of north Xinjiang and, the

formation and evolution of the Paleo-Asian Ocean are not well agreed due to lack of precise geochronology data [2, 3]. Recent studies based on fossil records suggested that the accretion of the Central Asian Orogenic Belt to south occurred during early Paleozoic [4, 5]. Here we provide precise ischronological data, supporting that the outset of the subduction of the Paleo-Asian Ocean in north Xinjiang started at least in the Early Silurian (441.3±1.8Ma).

This study was supported by the National Natural Science

Foundation of China (No. 40672057 and 40473016).

[1] Zhang et al. (2005) The Island Arc 14, 55-68. [2] Jahn (2001) Episode 24, 272-273. [3] Khain et al. (2002) EPSL 199, 311-325. [4] Xiao et al. (2004) J Geol. Soc. 161, 339-342. [5] Windley et al. (2007) J Geol. Soc. 164, 31-47.

Goldschmidt Conference Abstracts 2008 A1082

Re-Os isotopic variation in melt/rock interaction: Implication for the

Re-Os age of lithospheric mantle beneath the North China craton

HONG-FU ZHANG

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

More attention has been paid to Re-Os isotopic system as

this system behaves as an important method to probe the formation age of the lithospheric mantle. However, if the Re-Os system is affected by the low-temperature alteration and mantle metasomatism or melt/rock interaction is still not very clear. Based on the intergration of the studies on the typical orogenic peridotite massif and mantle peridotite xenoliths in the world, it is found that peridotite Re-Os system is generally unaffected by the low-temperature alteration. However, melt/rock interaction could change the peridotite Re-Os system, i.e. the introduction of the Re and/or Os. Periditite-melt interaction at the low melt/rock ratios (< 1) could result in an obvious increase in peridotite Re abundance and a limited increase in radiogenic Os. The peridotite-melt interaction at the high melt/rock (>> 1) could result in a marked increase in radiogenic Os. At the same time, positive correlations between the Re abundance of the peridotite and moderately incompatible major and trace elements such as Al, Ti, Yb have been interpreted by two stage model of evolution, namely as a result of early stage partial melting and later peridotite-melt interaction. The positive correlation between the Re abundance and the Cr observed in the peridotite further argue for such a suggestion. This result has an important implication for the evolution of the lithospheric mantle beneath the eastern North China craton. Archean lithospheric mantle indeed occurred in the Paleozoic in the eastern North China Craton. However, mantle peridotite xenoliths entrained in the Cenozoic basalts ubiquitously have Proterozoic rather than Archean Re-Os ages. This fact suggests that peridotite-melt interaction indeed exist extensively in the lithospheric mantle beneath the eastern North China craton, leading to the lithospheric mantle becoming younger. Therefore, Re-Os isotopic ages of the Cenozoic mantle xenoliths are not the formation age of the lithospheric mantle, but the result of the peridotite and melt mixing. Re abundance of the Hannuoba peridotites and Sr-Nd isotopes have shown a mixing trend of the peridotites and multiple melts. The negative correlation between their whole-rock Al2O3 contents and olivine Fo can also be interpreted by this peridotite-melt interaction.

Timing of Jinchang porphyry gold deposit, eastern Heilongjiang

province, Northeast China HUAFENG ZHANG*, S. LI AND Z. LI

School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, PR China (*correspondence: nighty@cugb.edu.cn)

Introduction

The Jinchang giant gold deposit, located at the easternmost of the Hunchun block which belongs to the easternmost portion of the eastern Chinese extension of the Central- Asian Orogenic Belt (CAOB), has been discovered and explored since 1990’s [1]. But the timing of gold mineralization of the deposit still remained very poorly constrained. Therefore, we provide new geochronological data of gold-related sericite and pyrite Rb-Sr dating. Discussion of Results

Sericite extracted from two samples of granodiorite and porphyry granite, yield ages of 107 ± 5 Ma (MSWD=0.91) and 110 ± 4 Ma (MSWD=1.04), with initial Sr of 0.7063 ± 0.0047 and 0.7072 ± 0.0034, respectively. Meanwhile, their sericite + pyrite grains yield two well Rb-Sr isochron ages of 104 ± 6 Ma (MSWD=0.18) and 110 ± 3 Ma (MSWD=0.14), with initial Sr of 0.7063±0.0033 and 0.7052 ± 0.0026，respectively. The sericite and pyrite herein extracted from samples of porphyry granite and granodiorite yield similar isochron ages around 110 Ma with similar initial Sr, suggestive of homogenous Rb-Sr isotope compositions between sericite and pyrite minerals in each sample. These results indicate that the gold-forming time is cretaceous of around 110 Ma.

[1] Chen et al. (2000) unpublished internal communicated report in Chinese.

Goldschmidt Conference Abstracts 2008 A1083

Water mass structure along 47°N in the North Pacific: Rare earth

elements influenced by marginal seas JING ZHANG

1*, L.-L. BAI2, M.S. NAHAR

3, M. HONDA4

AND N. HARADA4

1Graduate School of Science and Engineering for Science, University of Toyama, 3190 Gofuku, Toyama, 930-8555 Japan (*correspondence: jzhang@sci.u-toyama.ac.jp)

2(d0470305@ems.u-toyama.ac.jp) 3(msnahar@yahoo.com) 4JAMSTEC, 2-15 Natsushima, Yokosuka, Kanagawa, 237-

0061 Japan (hondam@jamstec.go.jp, haradan@jamstec.go.jp)

The northern North Pacific is along a decreasing gradient

of atmospheric input of Asian dust from west to east. It is almost entirely within the Subarctic High Nutrient Low Chlorophyll region between the Western and the Eastern Subarctic Gyre, and it is influenced by the surrounding marginal seas. The three purposes of this study are 1) to measure the influence of Rare Earth Elements (REEs) from the surrounding marginal seas, 2) to clarify the detailed REE distributions via NPIW/NPDW eastward flow though the Northwest Pacific Seamount Chain, and 3) to clarify water mass structure in the northern North Pacific.

The R/V Mirai (JAMSTEC) carried out the zonal section expedition MR05-04 along 47°N in the North Pacific 13 September - 27 October 2005. Several time-series stations, e.g. KNOT (44°N, 155°E), K1 (51°N, 165°E) and K2 (47°N, 160°E) were included on the western side in this cruise. CTD observations were conducted at all stations, and vertical sampling of REEs and other on-board routine analyses were carried out at 12 selected stations. High precision REE measurements with low volume seawater samples (~200 ml) were successfully made in this study by connecting an ICP-MS (ELEMENT2) with a desolving micro-concentric nebulizer-ARIDUS. The measurement precision (relative standard deviation) for surface seawaters (n=10) was 4~5% for La and Pr and 0.3~3% for the other REEs.

The REE distributions clearly show the influence of the surrounding marginal seas, the Sea of Japan, the Bering Sea, and especially the influence of the Dense Shelf Water formed during sea ice production in the Sea of Okhotsk. The REE patterns characterize the northward North Pacific Deep Water (NPDW), and illustrate the distinctive NPIW/NPDW eastward flow though the Northwest Pacific Seamount Chain.

Isotope geochemistry of the Weishancheng stratabound Au-Ag

ore belt, Tongbai county, China JING ZHANG

1* AND Y.-J. CHEN2

1China University of Geosciences, Beijing 100083, China (*correspondence: zhangjing@cugb.edu.cn)

2Peking University, Beijing 100871, China (yjchen@pku.edu.cn)

The Weishancheng gold-silver-dominated polymetallic ore

belt is located in the northern Tongbai Mountains, which is part of the Central China Orogen, and consists of the Yindongpo large gold, Poshan superlarge silver and Yindongling large silver polymetallic deposits and some small ore occurrences. The ore bodies are hosted in the Neoproterozoic Waitoushan Formation, which consists of mica schist, mica-quartz schist, leptynite, plagioclase-amphibole schist, marble and was folded into the Heqianzhuang anticline.

The δ18Oquartz values of 22 samples range from +8.6‰ to +16.2‰, with a mean value of +13.0‰, and the corresponding δ18OH2O values vary between -0.3‰ and +10.8‰, with an average value of +5.40‰. The δDH2O values have a range of -125.4‰ ~ -65.0‰ with an average value of -96.1‰. The δ13CCO2 values of ore-forming fluids are -9.2‰ ~ +6.7‰ and averaged -3.2‰, and the δ13C values of carbonate strata from the Waitoushan Formation vary between +1.9‰ and +2.9‰. The sulfur isotope analysis on 50 samples (pyrite, galena and sphalerite) shows two peaks: +1.00‰ ~ +4.00‰ and -8.00‰ ~ -12.00‰. Ore minerals have lead ratio ranges of 206Pb/204Pb = 16.7529 ~ 17.2163, 207Pb/204Pb = 15.4166 ~ 15.6380 and 208Pb/204Pb = 38.2502 ~ 39.0500. The K-Ar and 40Ar-39Ar chronology results show that the metallogenesis took place during 100 ~ 140Ma.

The H-O-C isotopic system of the fluid inclusions indicates that the fluids in the early and middle stages were sourced from the metamorphic devolatilization of the ore-hosted strata, while in the late stage much meteoric water entered the fluid system. The C-S-Pb isotope geochemistry suggests that the metallogenic materials came from the Waitoushan Formation. The metallogenesis took place under a tectonic setting changed from orogenic compression to extension, little after the intensive activity of continent-continent collision of Qinling Orogen. The Weishancheng gold-silver ore belt belongs to a typical stratabound orogenic-type metallogenic system in terms of their ore-forming fluid, metal source and geologic characteristics.

This work is supported by the 973-project (2006CB

403506, 2006CB403508) and NSFC (No. 40502012).

Goldschmidt Conference Abstracts 2008 A1084

Phenocryst O isotope constraints on the timescale of basaltic magmatism

JUN-JUN ZHANG* AND Y.-F. ZHENG

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (yfzheng@ustc.edu.cn)

The O isotope ratios of phenocrysts from Cenozoic

continental basalts of alkaline and theoleiitic compositions in eastern China were analysed by the laser fluorination technique. The results show δ18O values of 4.42 to 5.70‰ for clinopyroxene and 4.00 to 5.91‰ for olivine. Most clinopyroxene δ18O values are lower than the normal mantle values of 5.6±0.2‰, with the lowest δ18O values of 4.42 to 4.86‰ in the alkali basalt. In contrast, most olivine δ18O values approach the normal mantle values of 5.2±0.2‰, with a few alkali basalts having distinctly lower or higher δ18O values. There is also O isotope disequilibrium between coexisting clinopyroxene and olivine. The basalts appear to acquire supracrustal components from magma source, which was generated by subducting the 18O-depleted oceanic crust into the asthenospheric mantle. Because O isotope exchange by diffusion is very fast between the minerals and melt at mantle temperatures and thus capable of homogenizing the low δ18O signature with the normal mantle, preservation of the low δ18O values for the phenocrysts suggests very short duration of magma residence at mantle depths.

Quantitative estimates have been made on timescale of O isotope reequilibration during basaltic magmatism. Assuming 6 to 7 km thickness for the subducted oceanic crust and rates of 1000 to 2000 m/Ma for O transport within mafic crust, it is calculated that timescales of 1 to 2 Ma can result in complete O isotope reequilibration between the 18O-depleted subducted oceanic crust and the normal δ18O asthenospheric mantle. Such short timescales require that the low δ18O melts derived from the dehydrated oceanic crust would not transport through the convective asthenospheric mantle, but immediately metasomatize the overlying subcontinental lithospheric mantle.

The O isotope disequilibrium between clinopyroxene and olivine provides a further constraint. By taking the grain radii of clinopyroxene and olivine as effective diffusion radii, timescales of achieving O isotope reequilibration by diffusion exchange at ~1200°C are calculated. The results show that under both anhydrous and hydrous conditions, the timescales required for diffusion reequilibration across both minerals are 1 ka and 0.01 ka, respectively. This suggests the maximum timescale for melting, transport and eruption could be less than 1 ka. In this regard, the low δ18O values would be inherited and then preserved in the most clinopyroxene and few olivine phenocrysts.

Petrography, geochemistry and origin of cement dolomite in the Lower Paleozoic dolomite of the

Central uplift, Tarim basin JUNTAO ZHANG

1, W.-X. HU1, Y.-X. QIAN

2, X.-L. WANG

1 AND J.-Q. ZHU

1Department of Earth Science, State Key Laboratory for Mineral Deposits Research, Najing University, Jiangsu, Nanjing, 210093 (tota.zhang@gmail.com)

2Northwest E&P Company, SINOPEC, Urumqi, Xinjiang, 830011 (qyx9167@sina.vip.com)

3China Academy of Sciences, Institute of Geology and Geophysics, Beijing, 100029 (jqzhu@mail.igcas.ac.cn)

The early Paleozoic strata located in the Central uplift of

Tarim basin are composed of huge dolomite, which have undergone complex tectonic evolvement. Cement dolomite is prevaild in the formation, where two genetically distinct cement dolomites are recognized: rhombus and saddle cement dolomites. They occur in different diagenetic considerations and have different characters. The rhombus dolomite widerspread in the formation is characterized by a clear internal structure and unit extinction under crossed polars. The later cement dolomite shows curved crystal faces and wavy extinction under crossed-polarized light, and exhibits complex internal structure, which is composed of rim, clitellum and core. The frequency of the cement dolomites is more intense along faults. The Ca/Mg values of rhombus cement dolomite is similar to that of matrix dolomite, and the Fe concentrations in this style is very low, most of which below the dectection limit. The saddle cement dolomite has low Ca/Mg values and high Fe concentrations correspondingly. Electron microprobe analyses at the rim, clitellum and core of the saddle cement dolomite show that Ca/Mg values and Fe concentrations are not homogeneous, and the lowest Ca/Mg values at core points, and the highest Fe concentrations at clitellum points, which can reach 4%wt.

Stratigraphic, petrographic and geochemical date suggest that rhombus cement dolomite deposited steadily and that source of Mg2+ was altered seawater in early disagenetic process. However, material source of saddle cement dolomite was hydrothermal dissolution of former dolomite. The formation of saddle dolomite cement, three part of which formed in different fracture phases, is associated with faulting. The deposition of dolomite cement is porosity decrease, but saddle cement dolomite can be regarded as a result of hydrothermal dissolution, while can improve dolomite reservior capability.

Goldschmidt Conference Abstracts 2008 A1085

Application of FTIR spectrometry on studying thermal simulation of brown

coal: Implications for its hydrocarbon generation

K. ZHANG AND S.P. YAO

Department of Earth Sciences, Nanjing University, Nanjing, China (donco.zhang@gmail.com)

Fourier Transform infrared spectrometry (FTIR) is one of

the most powerful and convenient technique for the characterization of coal, kerogen and other sediments in organic geochemistry. This paper describes the use of FTIR spectrometer to study the chemical structures of residue from thermal simulation experiment of brown coal. The coal was collected from Tengchong-Lianghe basin, Yunnan Province, SW China. The method of curve-fitting analysis was used in order to more precisely quantify peak areas of different chemical structures. Analytical results indicate that variation of FTIR spectra corresponds to the stage of hydrocarbon generation relatively well.

In the first stage, when simulation temperature is from room temperature (24°C) to 200°C, FTIR spectra area around 1705cm-1 which represents stretching vibration of oxygenous groups in coal descends fastly. In the meanwhile, we observed there are a lot of CO2 generated. Area around 2950cm-1 and 2920cm-1 represents asymmetric stretching vibration of methyl (ACH3) and methylene (ACH2) changes unconspicuously. The yield of total hydrocarbon is from 20.9mg/gTOC to 41.0mg/gTOC. The HI and S1+S2 of coal show slight change. In the second stage (200-350°C), the sum of ACH3 and ACH2

diminishes, accompanying generation of oil and gas in experiment. The yield of total hydrocarbon is from 41.0mg/gTOC to174.9 mg/gTOC. The HI and S1+S2 is from 172mg/gTOC to 10mg/gTOC and 95.04mg/g to 34.39mg/g, respectively. The ratio of ACH3 and ACH2 increases as a result of the break of long aliphatic chains. In the last stage (>350°C), area around 1600cm-1 which presents stretching vibration of aromatic ring increases because of condensation of aromatic rings. The sum of ACH3 and ACH2 decreases to zero almostly. The yield of total hydrocarbon reaches 238.2 mg/gTOC. The HI and S1+S2 descreases to 4mg/gTOC and 3.69mg/g, respectively.

This work was supported by The National Basic Research

Program of China (Grant No. 2003CB214608).

Geochemical characteristics of Longqiao iron deposit, Anhui, China

LE JUN ZHANG*, T. F. ZHOU, F.YUAN, Y.FAN AND C. DUAN

School of Resources and Environment Engineering, Hefei University of Technology, P.R. China (*correspondence: zljzhang@163.com)

Longqiao iron deposit located in the north margin of

Luzong basin, Anhui Province, China, is a large, high-grade layered magnetite deposit. Iron mineralization is strictly controlled by the stratum of DongMaanshan Group of Middle Triassic. The principal intrusive rocks related to the mineraliztion are plutonic syenite (monzonite) and hypabyssal syenite porphyry.

The main ore mineral in Longqiao iron deposit is magnetite and less hematite. The magnetite decrepitated temperature have two obvious ranges of 360~390°C and 410~450°C.Chemically these different magnetite are characterized by magnetite contains very low V and Ti contents, generally about hundreds ppm, lower about one order of magnitude than that in porphyritic iron ores, Ti/TFe ratios are also declining. Na2O,K2O, MgO and CaO in magnetite and hematite are relatively high comparing with porphyritic ones. The ∑REE, LREE/HREE, (La/Yb)N, (La/ Sm)N and (La/Lu)N ratios have a wide range, and obvious Eu and Ce anomaloes. The magnetite mineralization process can be divided into thermal metamorphic stage and magmatic hydrothermal reworked stage.

Hydrogen- and oxygen-isotope data suggested that the ore-forming fluids in Longqiao iron deposit mostly consisted of magmatic water, mixed in various proportions of meteoric water. The variation of sulfur isotopic composition of the pyrite and anhydrite were not resulted from changes of physicochemical conditions, but rather due to compositional variation of sulfur at the sources. Lead isotopic composition provides similar results.

This research was supported by the National Key Basic

Science Research Project of China (2007CB411405）and the National Natural Science Foundation of China (40672062, 40272048)

[1] Wu et al. (1996) Special Publication.

Goldschmidt Conference Abstracts 2008 A1086

Zircon U-Pb dating, Hf isotopes and trace elements characteristics of the

migmatites in Tianjingping area, northwestern Fujian Province

LI ZHANG, Z.Q. ZHONG, H.W. ZHOU, W. ZENG, H. XIANG, R. LIU AND S. JIN

State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, P.R. China (lizhang@cug.edu.cn) The Tianjingping area in northwest Fujian Province is

located in the northeast Cathaysia Block. Metamorphic basement rock series of the Cathaysia Block, frequently migmatites, are explosed fragmentarily in southern China. Migmatites in this area have previously been assigned to Precambrian metamorphic basement. In this study, we carried out a combined study of zircon U-Pb dating, Hf isotopes and trace elements on the homogeneous granodioritic neosomes of migmatites in the Tianjingping area and obtained not only Paleoproterozic ages but also precise Caledonian ages. Zircons were characterized by zoning, high Th/U ratios (mostly ≥ 0.1), enriched HREE, positive Ce and negative Eu anomalies, and show features similar to magmatic or anatectic zircons. Apparent 206Pb/238U ages for the zircons were 447±2Ma (95% conf., MSWD=0.88), corresponding to a Caledonian event. εHf(t) values ranged from -13.3 to -9.7, indicating a crustal source. Two-stage Hf model ages were from 1.7 to 1.9 Ga, suggesting that protolith of the migmates was formed in the Paleoproterozoic. The granodioritic neosomes had the characteristics of peraluminous calc-alkaline granite, and their REE patterns and trace element spidergrams show features of middle to upper crustal rocks. Together with previous studies, we conclude that the protolith of the Cathaysia basement in the Tianjingping area was formed in the middle-late Paleoproterozoic and expericenced partial melting during the Caledonian period. The rcongnition of Caledonian reworking of the Paleoproterozoic basement in the Cathaysia Block provides new information on the tectonic evolution of the Cathaysia Block in the Caledonian period and the interactions between the Cathaysia Block and the Yangtze Block.

This study is supported by the National Proirity and Development Program of China (2006CB403502), the NSFC of China (NO. 40372094), the Opening Foundation of State Key Laboratory of Continental Dynamics, Northwest Universtiy (NO.06LCD12).

An experimental study of pressure solution in angular quartz sands

under simulated burial conditions LIUPING ZHANG

1*, G. BAI2, Z. JIN

3 AND G. LIU

2 1Key Laboratory of Petroleum Resource, Institute of Geology

and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China (*correspondence: lpzhang@mail.iggcas.ac.cn)

2Basin & Reservoir Research Center, China University of Petroleum, Beijing 102249, China

3Research Institute of Petroleum Exploration and Development, SinoPec, Beijing 100083, China

The size and shape of sand grains are the important

geometrical variables controlling pressure solution in sandstones. But experimental studies of pressure solution in very poorly-rounded quartz sands or sandstones have not been documented. In this study, we conducted two simulation experiments for pressure solution in medium-grained (0.25-0.5 mm) very poorly-rounded quartz sands. The first one was conducted to simulate pressure solution under the conditions of burial depths from 0 to 1700 m and the second, from 0 to 2900 m. Based on the geological characteristics of the Dongying Sag in East China where very poorly-rounded sandstones were deposited, the geothernmal gradient, average density of the rocks and the fluid pressure were set to compute the temperature, lithostatic pressure, fluid pressure and effective pressure at different simulated burial depths. The porosities and permeabilities significantly decreased with the increase of burial depths initially and then dropped slowly with time after the simulated burial depths reached to 1700 m or 2900m. The water in the second experiment was highly supersaturated with silica. The silica content reached a sharp peak when the simulated burial depth increased to 2900 m, but then it decreased quickly in the next 100 hours and afterwards gradually with time. This indicates that pressure solution occurs when burial depth reaches to 2900m. The silica content in the pore water in the first experiment was lower than that in the second experiment but the water was still highly supersaturated with silica. The silica content reached a peak when the simulated burial depth increased to 1700m. It then decreased quickly in the next 50 hours and subsequently slowly with time. Therefore, pressure solution in very poorly-rounded quartz sands can also occur at the shallow burial depth of 1700m. The two simulation experiments also indicate that discontinuous subsidence could result in multi-phased pressure solution and provide SiO2 for multi-phased quartz cementation.

Goldschmidt Conference Abstracts 2008 A1087

Carbon and chlorine isotope fractionation during degradation of

trichloroethene by metals MIN ZHANG, O. SHOUAKAR-STASH, R. W. GILLHAM,

S. K. FRAPE AND R. J. DRIMMIE

Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 (mzhang@uwaterloo.ca) Granular iron has been used in permeable reactive barriers

to treat groundwater contaminated with chlorinated ethenes. In addition to iron, other metals or bi-metals such as Zn and Ni-Fe have been found to be effective in the dechlorination reactions. However, the pathways of chlorinated ethene reaction with metals are not fully understood. The compound-specific carbon isotope technique has been used as a tool to delineate degradation of chlorinated ethenes by iron, and substantial isotope fractionation was observed during the reaction. In this study, we combined carbon isotope with chlorine isotope analysis to examine the reactions between trichloroethene (TCE) and different metals, and to derive additional information on reaction pathways.

In a series of batch experiments, TCE was reacted with granular iron, electrolytic iron, nickle-plated iron, and zinc, and sampled at different times. Granular iron from two different suppliers (Connelly and Peerless) was used. Ni-plated Connelly iron was prepared using an electroless plating method. Electrolytical iron and zinc were from Fisher Scientific and BDH, respectively. In each sample, 10 mg/L TCE solution and a w/s ratio of 5 was used. Complete mixing was provided during reaction.

Under the given experimental conditions, carbon isotope enrichment factors of -15.7 and -7.7‰ were measured for Connelly and Peerless iron, respectively. An enrichment factor of -12.5‰ was obtained for Ni-plated Connelly iron, and -20.2‰ for electrolytic iron. The strongest 13C enrichment was associated with Zn, with an enrichment factor of -31.3‰. Substantial chlorine isotope enrichment was also determined, with enrichment factor ranging between -6.4‰ (zinc) and -1.8‰ (Peerless iron). Overall, the chlorine isotope enrichment factor correlated positively with carbon isotope enrichment factor. However, a constant chlorine enrichment factor of -4.3±0.1‰ was observed among Connelly, Ni-plated iron, and electrolytic iron. The overall positive correlation between carbon and chlorine isotope fractionation and the deviation of Connelly and Ni-plated iron from this correlation is likely controlled by the reductive dechlorination process.

Volatiles in mantle minerals: A xenolith study, Eastern China

MINGJIE ZHANG1, Y. NIU

2, P.-Q. HU1 AND P.-E. FU

1 1Department of Geology, Lanzhou University, Lanzhou

730000, China (mjzhang@lzu.edu.cn) 2Department of Earth Sciences, Durham University, Durham

DH1 3LE UK (yaoling.niu@durham.ac.uk)

Volatiles in nominally anhydrous mantle minerals have long been thought to reside primarily in fluid inclusions. Abundances of volatiles in olivine (Olv), orthopyroxene (Opx) and clinopyroxene (Cpx) from in lherzolite and pyroxenite xenoliths in Cenozoic basalts from eastern China were investigated by combined techniques of grain-size reduction, ameliorative vacuum stepwise heating, mass spectroscopy and infrared spectra measurements, and show that significant amounts of volatiles in these minerals in fact reside in structural defects and vacancies.

Early-stage and late-stage two types of fluid inclusions can be readily identified based on differences in shape, size, distribution and homogenization temperature (HT). Volatiles from different crushing size of Olv, Opx and Cpx separates have been released at three temperature intervals: 400-600°C, 600-1000°C and 1000-1200°C. The total volatile content increases with decreasing crushing size at a given temperature interval. The volatile release peak at 300-600°C disappears in crushing size (0.03mm) close to the size of late-stage fluid inclusions (10-200 µm). The volatile release peak at 1000-1200°C shifts towards small crushing size (0.06-0.03mm). The FTIR absorbance peaks of structural OH- in Olv and Opx have been reduced only after degassing at 1200°C.

Progressively crushing breaks larger size of fluid inclusions and releases volatiles accordingly, but volatiles stored in defects and vacancies of crystal structures are still retained. Ameliorative vacuum stepwise heating technique can effectively separate volatiles with different occurrence modes for analysis. Early-stage fluid inclusions are decrepitated at a temperature range (600-1000°C) similar to HT (861-1074°C), whereas late-stage fluid inclusions are released at lower temperature range (300-600°C) due to their large sizes, irregular shapes and micro-cracks developed along inclusion walls. Volatiles in mineral structural defects and vacancies are released at higher heating temperatures (1000-1200°C) close to mineral formation temperatures (987-1296°C), and are more abundant than volatiles hosted in fluid inclusions. This has important implications for mantle volatile in the storage, distribution and recycling.

This study was supported by NSF of China (40273009, 40772058, 40534020) and NCET(NCET-04-0980).

Goldschmidt Conference Abstracts 2008 A1088

Origin of TTG rocks from anatexis of ancient crust: Geochemical evidence

from granitoid batholith at Huangling in the Yangtze Gorge

S.-B. ZHANG AND Y.-F. ZHENG

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (sbzhang@mail.ustc.edu.cn) Petrogenesis of TTG rocks has been controversial between

melting of subducted slab and thickened lower crust. Previous studies have mainly focused on the issues of major and trace elements without sufficient attention to the difference in the age of involved crust. While reworking of juvenile crust is responsible for the slab melting, reworking of ancient crust corresponds to the melting of thickened lower crust. This latter possibility is illustrated by this study of a composite batholith that is mainly composed of TTG rocks at Huangling in the Yangtze Gorge, South China.

The Huangling batholith is composed of three granitoid suites (Huanglingmiao, Sadouping and Dalaoling). All the granitoids share the TTG characteristics of high Na2O/K2O, Sr/Y, (La/Yb)N ratios, depletion in Nb, Ta, and lack of Eu anomaly. Zircon U-Pb dating indicates they were crystallized in a period of 820 to 800 Ma. Inherited cores yield two groups of U-Pb ages at Paleoproterozoic (1.8-2.0 Ga) and Archean (~2.9 Ga), respectively. Zircon εHf(t) values for inherited cores and syn-magmatic domains are significantly different from each other. εHf(t) values for the syn-magmatic domains range from to -29.7 to -3.6, concordant with whole-rock εNd(t) values of -21.3 to -2.1. Correspondingly, zircon Hf model ages are 2.09 to 3.16 Ga, suggesting their derivation from ancient Paleoproterozoic-Archean crust. εHf(t) values for the inherited cores are consistent with those for Archean TTG gneiss and migmatite in the Kongling complex, suggesting involvement of Archean crust. There are systematic differences in source nature between the different suites: the Huanlingmiao suite has relatively lower εNd(t) and εHf(t) values, higher Sr/Y and (La/Yb)N ratios, stronger depletion in Nb, Ta, and thus is mainly derived from the Archean crust. In contrast, the Sandouping and Dalaoling suites are mainly derived from the Paleoproterozoic crust. δ18O values for zircons are 4.85-6.84‰ for the all rocks, suggesting a limited contribution from supracrustal materials to their sources.

The petrogenesis of the Huangling batholith is interpreted by tectonic collapse of Paleoproterozoic arc-continent collision zone and consequent anatexis of the Paleoproterozoic and Archean mafic rocks at different depths. This demonstrates a decoupling between the TTG formation and the slab subduction.

Permian bimodal volcanic rocks from Central Inner Mongolia, North

China: Geochemistry, Petrogenesis and tectonic Implication

XIAOHUI ZHANG1,2*, H. ZHANG

1, Y. TANG1 AND

S. WILDE2

1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, China (*correspondence: zhangxh@mail.iggcas.ac.cn)

2Department of Applied Geology, Curtin University of Technology, Perth, WA 6845, Australia Zircon U-Pb ages, geochemical and Sr-Nd-Pb isotopic

data are presented for the Late Paleozoic volcanic rocks from central Inner Mongolia, North China. These volcanic rocks show a bimodal distribution in composition, with dominant rhyolite and dacite, subordinate basalt and local andesite. New zircon U-Pb isotopic data constrain their magmatic emplacement at ca. 280 Ma. The mafic samples are characterized by high abundances in Th, U and Pb, slightly enriched LREE patterns and low HFS/LREE ratios. These features, together with their OIB-like isotopic signature, indicate that they were likely derived from high percentage partial melting of a subduction metasomatized asthenospheric mantle in the spinel facies field at depths shallower than 60-70 km. The felsic rocks show an A-type affinity. Combined with their moderately positive εNd(t) values, they are inferred to be generated by the mixing between partial melts of a newly-underplated lower crustal source and an ancient felsic crustal source. The typical magma progression starting with asthenospheric melts then proceeding to lithospheric melts indicates that Early Permian magmatism in Central Inner Mongolia occurred in an extensional setting, most probably related to the post-collisional delamination. Therefore, the occurrence of this unique bimodal magmatism not only demonstrates that the Solonker zone experienced final amalgamation of arc-related terranes by the late-Carboniferous, but also indicates that significant vertical continental growth of crustal continuum through repeated magmatic underplating occurred in the continental interior during post-collisional extension.

This study was financially supported by the Major State

Basic Research Program of the People’s Republic of China (Grant No. 2006CB403504), the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-103).

Goldschmidt Conference Abstracts 2008 A1089

Variations in D/H fractionation associated with microbial

heterotrophy XINNING ZHANG AND A. SESSIONS*

Environmental Science and Engineering, California Institute of Technology, Pasadena CA 91125, USA (*correspondence: ALS@gps.caltech.edu)

Compound-specific D/H measurements are emerging as a

useful tool for paleoclimatology, chemical oceanography, biogeochemistry, and geobiology. To date, most research has focused on describing the distribution of organic D/H ratios in nature, while the biological fractionations that underpin that variability have received less attention, particularly with regard to microbial heterotrophs. Here we describe culture experiments that examine lipid D/H in two aerobic soil bacteria, Cupriavidus oxalaticus and C. necator, with physiologically versatile carbon metabolisms growing on a range of organic substrates. The resulting fractionations (differences in δD values between lipids and water) cover a staggering range of nearly 500‰, even for a single organism, and depend primarily on the nature of the organic substrate being utilized (Fig 1). Organisms grown on oxalate and formate (which do not supply organic H) were strongly depleted in D. Those grown on substrates that are processed by the citric acid cycle (acetate, succinate) were strongly D-enriched, while those processed via glycolysis (fructose, pyruvate) were intermediate. We hypothesize that fractionations accompanying the production of cellular NADPH are the source of these variations, and that lipid δD values could be used as a tracer of metabolic processes in environmental samples.

Figure 1: Lipid/water D/H fractionations for fatty acids from microbial cultures grown on defined substrates.

Microbial mobilization of adsorbed arsenate on AlIII-and FeIII-hydroxide

XUEXIA ZHANG, Y.F. JIA*, L. XU AND R. PAN

Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China, 110016 (*correspondence: yongfeng.jia@iae.ac.cn)

Arsenic is present in aqueous environment predominantly

in the form of AsIII and AsV. Its mobility and bioavailability are largely controlled by its adsorption on the minerals widely occuring in aqueous environment. Microbial reduction of arsenate is considered an important factor in the remobilization of arsenic in groundwater systems. This paper investigated the effect of microbial activity on the fate of adsorbed arsenate on AlIII-and FeIII-hydroxides in anaerobic environment.

The bacteria used in this study were isolated from the arsenic-contacminated soils at an abandoned smelter site. Arsenate-adsorbed hydroxide solids were prepared by equilibrating an arsenate solution with AlIII-, FeIII-hydroxide at the M/As molar ratio of 100:1 in order to ensure a complete adsorption. After inoculation, the slurry was incubated under anaerobic condition and the concentration of AsV, AsIII, FeIII, FeII in both solution and solid phases were monitored with time.

The results showed that the arsenate (i.e. AsV) adsorbed on both AlIII- and FeIII-hydroxides were quickly reduced to arsenite (i.e. AsIII) by the microbes, whereas neither reduction nor release of arsenic was observed in the control. The reduction of AsV to AsIII was also confirmed by direct evidence of XAS measurements. For the AsV-aluminum hydroxide system, alomost all the adsorbed arsenic was released into the solution, indicating that aluminum hydroxide showed little affinity for AsIII. In comparison, little arsenic was released from the AsV-ferric hydroxide system, although the adsorbed AsV was also significantly reduced to AsIII. The reduction of FeIII to FeII was observed after 21 days of incubation. The XRD patterns of the heat treated solid clearly showed the presence of magnitite in the solid.

Therefore, it is suggested from this work that remobilization of the adsorbed arsenate by microbial reduction strongly depends on the type of minerals.

[1] Islam et al. (2004) Nature 430, 68-71.

Goldschmidt Conference Abstracts 2008 A1090

Boundary exchange processes on and along the Kerguelen plateau YAN ZHANG, C. JEANDEL* AND F. LACAN

LEGOS (CNES/CNRS/UPS/IRD), OMP, 14 Ave E. Belin, 31400, Toulouse, France (*correspondence: catherine.jeandel@legos.obs-mip.fr)

The KErguelen Ocean and Plateau compared Study

(KEOPS) took place during the austral summer (19 Jan-13 Feb 2005, R/V “Marion-Dufresne”, 68°-78°E/ 49°-52°S sector). One of the KEOPS objectives was to determine the mechanisms responsible for the bloom occurring on the Kerguelen plateau. Coupled with physical measurements, a multi-proxy investigation was carried out in order to better constrain the sources of iron, as well as the water mass and particle pathways. REE concentrations and radium isotope activities already indicated that dissolution of basalts from the shelf of Heard Island loads significant amounts of iron into the plateau waters [1, 2]. However surface waters are depleted in dissolved iron [3], making us suspect that in addition to the biological consumption, strong scavenging affects these waters.

Here we present dissolved Nd isotopic compositions, measured at 5 stations on and 4 off the Plateau, expressed as εNd=[(143Nd/144Nd)sample/(

143Nd/144Nd)chur]-1)*10,000 where “chur” means a reference. Isotopes bring new insight on the scavenging, mixing and exchange processes at play in this area. At open ocean stations, circumpolar deep waters are characterized by εNd of – 9.9 ± 0.2, value that increases to -8.6 ± 0.3 when the same waters flow along the eastern slope of the Plateau, whereas Nd concentration simultaneously drops by a factor ~2. Both the input of radiogenic Nd (explaining the εNd increase) and its obvious subtraction reveal that strong “Boundary Exchange” is acting along the slope. First estimates yield an input of 5.4x108 for a removal of 1.7 x109 mol/y of Nd, that is a net exchange of -1.1 x109 mol/y, in favor of removal. On the Plateau, most of the values are above -8, the most radiogenic ones (-4.8) being observed at the station nearby Heard Islands. These radiogenic waters are also characterized by less pronounced Ce anomaly than the non radiogenic ones, clearly confirming the recent dissolution of basaltic particles (εNd > -2). These different data allow the estimate of input and scavenging rates on the Plateau, results that are compared to the scavenging rates deduced from Th and Pa at the same locations [4]. [1] Zhang et al. (in press) Deep Sea Res. II. [2] van Beek P. et al. (in press) Deep-Sea Res. II. [3] Blain S. et al. (2007) Nature 446, 1070-1074. [4] Venchiarutti C. et al. (in rev.) Deep Sea Res.

Denitrification coupled to pyrite oxidation and changes in groundwater quality at

Oostrum, the Netherlands YAN-CHUN ZHANG

1*, C.P. SLOMP1, H.P. BROERS

2, H.F. PASSIER

2 AND P. VAN CAPPELLEN

1 1Faculty of Geosciences, Utrecht University, the Netherlands

(*correspondence: yanchun.zhang@geo.uu.nl) 2TNO – Built Environment and Geosciences, Utrecht, the

Netherlands

Denitrification is the major pathway of nitrate removal from groundwater systems, with organic matter or minerals, primarily pyrite, serving as electron donors. Because pyrite oxidation leads to sulfate production, as well as the release of trace metals and changes in pH, it can significantly affect groundwater quality.

This study focuses on the occurrence and effects of denitrification coupled to pyrite oxidation in a sandy aquifer using detailed geochemical analyses of both sediment and groundwater combined with groundwater age dating (3H/3He). Our study site is located in cultivated fields and an adjacent forested area at Oostrum, the Netherlands.

Shallow groundwater in the region has high nitrate levels (up to 500 mg/L) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production and the release of Fe2+ and pyrite-associated trace metals (e.g. As, Ni, Zn, Co). These data and the presence of pyrite in the sediment matrix within the nitrate removal zone indicate that denitrification coupled to pyrite oxidation is the main pathway removing nitrate infiltrating into the aquifer. However, the observed increase in sulfate concentrations below the depth of nitrate depletion is about 50% lower than expected from complete oxidation of pyrite to sulfate. Possible explanations include production of elemental sulfur, additional reactions consuming sulfate, or incomplete denitrification. Comparison of regional sulfate and nitrate inputs between 1940 and 2000 to age profiles of sulfate and nitrate in the aquifer for this period confirm significant nitrate loss and sulfate production in the aquifer. The maximum rate of nitrate removal within the reaction zone is estimated at 0.6 mM y-1.

Pollutant concentrations (e.g. NO3, Cl, As, Ni) in the groundwater of the agricultural areas decreased between 1996-2006, due to decreased fertilizer use. In the downstream forest area, in contrast, pollutant concentrations have increased because of lateral inflow from the adjacent cultivated fields.

Goldschmidt Conference Abstracts 2008 A1091

Diffusivity-viscosity relations YOUXUE ZHANG

Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA

It is widely "believed" that diffusivity of a component or

species in liquids is inversely proportional to the liquid viscosity. Some equations are much celebrated (e.g. the Einstein and Eyring equations) and other less so (e.g. the Sutherland and Glasstone equations) [1]. The equations are often of the form: D = kT/(ηL), where D is diffusivity; k is Boltzmann constant; T is temperature; η is viscosity; and L takes the form of 6πa (Einstein), 4πa (Sutherland), 2a (Glasstone), and λ (Eyring), where a is the radius and λ is roughly the jumping distance of the diffusing species. The difference between the equations is no more than a factor of 10. Comparison of experimental data with the relations show:

(1) The Eyring equation applies well to 18O diffusion in dry jadeite, diopside, dacite, and basalt melts (e.g. [2, 3]) but fails for 18O diffusion in hydrous rhyolitic melt [4]. Because most natural silicate melts are hydrous, the applicability of the Eyring equation is hence limited.

(2) The Einstein equation applies roughly to aqueous solutions [1], but does not apply to the molecular species such as H2O, Ar, and CO2 in hydrous rhyolitic melt [5-8] even when speciation effect is taking into account.

(3) The activation energy (E) for viscosity often decreases with T (e.g. [9, 10]) whereas E for diffusion is often constant, or increases with T (e.g. [11]). The opposite trends in how E depends on T imply that diffusivity and viscosity are not inversely proportional.

In summary, none of the celebrated diffusivity-viscosity relations is generally applicable. The causes of the failures will be explored.

[1] Cussler (1997) Diffusion: Mass Transfer in Fluid Systems. Cambridge Univ. Press. [2] Shimizu & Kushiro (1984) Geochim. Cosmochim. Acta 48, 1295-1303. [3] Tinker et al. (2004) Am. Mineral. 89, 1701-1708. [4] Behrens et al. (2007) Earth Planet. Sci. Lett. 254, 69-76. [5] Zhang & Behrens (2000) Chem. Geol. 169, 243-262. [6] Behrens & Zhang Y (2001) Earth Planet. Sci. Lett. 192, 363-376. [7] Zhang et al. (2000) Geochim. Cosmochim. Acta 64, 3347-3355. [8] Zhang Y, Xu Z, Zhu M, Wang H (2007) Rev. Geophys. 45, RG4004, doi:10.1029/2006RG000216. [9] Hess & Dingwell (1996) Am. Mineral. 81, 1297-1300. [10] Zhang et al. (2003) Am. Mineral. 88, 1741-1752. [11] Perkins & Begeal (1971) J. Chem. Phys. 54, 1683-1694.

Probing the cassiterite (110)–water interface structure with X-ray

scattering method ZHAN ZHANG

1, P. FENTER1, D.J. WESOLOWSKI

2 AND

L.M. ANOVITZ2

1Argonne National Laboratory, Argonne, IL, USA (zhanzhang@anl.gov, fenter@anl.gov)

2Oak Ridge National Laboratory, Oak Ridge, TN, USA (wesolowskid@ornl.gov, anovitzlm@ornl.gov)

In earlier studies we reported the rutile [TiO2] (110)–water

interface structures [1]. Cassiterite [SnO2], which is isostructural to rutile but with a significantly different bulk dielectric constant, has been recently studied both theoretically and experimentally to explore the intrinsic factors affecting the oxide-water interface structures and properties. Yet lack of the direct atomic level structure information hindered the thorough investigation of the systematic behavior, which is important to understand the interfacial processes. The earlier interfacial structure study revealed the structure along the surface normal direction but with ambiguities [2]. In this study, the single crystal cassiterite (110)–water interface structure was measured with high resolution surface X-ray scattering method (crystal truncation rod). 3D interfacial structure, including the relaxations of the atoms on the crystal surface and the adsorbed water molecule distribution at the interface, were determined. The similarities and the differences between the cassiterite-water and rutile-water interfaces and their implications are discussed.

[1] Zhang et al. (2007) Surf. Sci. 601, 1129-1143. [2] Vlcek et al. (2007) Langmuir 23, 4925-4937.

Goldschmidt Conference Abstracts 2008 A1092

Characteristic and the formation conditions of chlorite in Xiazhuang

uranium ore-field, South China ZHANSHI ZHANG*, S. LIU AND J.WU

Key Laboratory of Nuclear Resources and Environment (East China Institute of Technology), Ministry of Education, Nanchang ,330013, China (*correspondence: zhszhang@ecit.edu.cn)

Xiazhuang uranium ore-field was one of the most

important granite-type uranium deposits in China. Chloritization was one of the most important alteration types in Xiazhuang uranium-ore field. So the study on the characteristics included the paragenetic association and the formation conditions would be helpfully to understanding the mineralization of the Uranium in this field. Therefore this paper we focused on the characteristic and the formation conditions of chlorite in Xiazhuang Uranium ore-field by using microscope and electron probe microanalyser (EPMA) methods.

There were three types of chlorite in Xiazhuang uranium ore-field. First type chlorite were the secondary product of biotite or feldspar which usually displayed in the false pattern of biotite or very fine flaky, we named it was I-type chlorite; the second type chlorite had the paragenetic association with pitchblende or rutile which shown there might had close relationships with the mineralization of uranium and most of them shaped irregularly, third type chlorite often displayed in vein and shaped in worm or flaky, we combined the second and third type into II-type chlorite. In Fe/Si dirgram which mostly used for classify and nominate of the chlorite since it been used by Foster [1], I-type chlorite located in the ferroamesite and aphrosiderite region, most II-type located in the same region but few of them distribute in pycnochlorite and diabantite region, which shown the later type had lesser iron and richer silicon. The formation temperature of chlorite varied in 179 ~ 276°C, and mainly ranged in 230 ~ 260°C calculated by the empirical equation which be presented by Battaglia [2].

Cation /Mg diagrams show that AlVI and Fe had a good linear relation with Mg, but not so good between Si and AlIV

with Mg, so do the AlIV with n(Fe)/n(Mg+Fe) and AlIV with n(Mg)/n(Mg+Fe), that might suggested that the chlorite were formatted in multi-geological process. Due to most chlorite had the nAl/n(Al+Mg+Fe) value bigger than 0.35 that suggested that most of the chlorite were derived from argillaceous rock and be formatted in the reduced condition, those Mg enriched chlorite might formatted more lower fO2 and pH conditions.

This study is financially supported by the National Natural

Science Foundation of China (Grant No: 40772068 and No: 40642010).

[1] Foster (1962) US Geology Survey Prof. Paper 414A, 33 [2] Battaglia (1999) Clays & Clay Minerals 47(1) 54-63.

Metallogenic setting of the Dabate Copper–Molybdenum deposit in the

Western Tianshan Mountains, NW China

ZUOHENG ZHANG1, Z. WANG

1, G. ZUO2 AND M. LIU

1 1Institute of Mineral Resources, Chinese Academy of

Geological Sciences, Beijing, 100037, China (zuoheng@hotmail.com)

2Gansu Geological Survey, Lanzhou, 730000, China

The Dabate porphyry Cu (Mo) deposit is a typical porphyry copper molybdenum deposit in the Alatao-Keguqin copper polymetallic mineralization belt which comprises porphyry-skarn copper and porphyry copper deposits in west Tianshan. The copper deposit is temporal and spatial related with Mid-Hercynian hypabyssal acid intrusive rock hosted in Upper Devonian tuffaceous breccia and lava of the Tuosikuertawu Formation. In the southeast part of the district, there outcropped Hercynian dacitic porphyry. The ore related intrusion comprise of granite-porphyry and rhyolitic porphyry. The ore bodies are distributed along the contact zone of the intrusion and the wall rocks.

The SHRIMP zircon U-Pb age of dacitic porphyry which developed in the southeast of the deposit is 315.9±5.9Ma, and the SHRIMP zircon U-Pb age of granite-porphyry is 278.7±5.7Ma. The result of Re-Os dating of molybdenite form the vein ores is 301±20Ma. According to these dating results, combining with regional geological evolution, it may be concluded that the dacite porphry formed in the Biezhentao-Keguqin late Paleozoic inland arc and it is originated from the subduction of Carboniferous Bayingou oceanic crust to south to Sailim-Boluokenu lift, while the mineralization ages may be early Permian and formed during the extension of intraplate and the related magmatic activities were simultaneous with the porphyry mineralization.

This work was supported by the National Natural Science

Foundation of China Program (No.40573028), State 305 Project (No. 2006BAB07B08-01) and Geological Survey Project (No. 1212010561603-3).

Goldschmidt Conference Abstracts 2008 A1093

Major magmatic and metamorphic events in the Trans-North China

Orogen: A geochemical and geochronological synthesis

G. ZHAO1, S. LI

2 AND J. GUO

3 1Department of Earth Sciences, The University of Hong Kong

(gzhao@hkucc.hku.hk) 2College of Earth Sciences, Ocean University of China, (sanzhong@ouc.edu.cn)

3Institute of Geology & Geophysics, Chinese Academy of Science (jhguo@mail.igcas.ac.cn)

The Trans-North China Orogen (TNCO) was a

Paleoproterozoic collisional belt along which the Eastern and Western Blocks amalgamated to form the North China Craton. Recent structural, geochemical and isotopic data show that the orogen was an Andes- or Japanese-type arc at the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction. At 2550–2520 Ma, the subduction caused partial melting of the medium-lower crust, producing granitoid plutons in the granite-greenstone terranes. At 2530–2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, forming greenstone-type mafic-felsic volcanic assemblages. Extension driven by widespread volcanism led to the development of back-arc basins in the orogen. At 2520–2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of TTG gneisses. In the Paleoproterozoic, episodic granitoid magmatism occurred, forming 2360 Ma, ~2250 Ma 2110-21760 Ma and ~2050 Ma granites and volcanics in the orogen. At 2150–1920 Ma, the subduction of an oceanic ridge led to emplacement of mafic dykes that were subsequently metamorphosed to high-pressure granulites. At 1880-1820 Ma, the closing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and formed HP granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of symplectic textures in the rocks.

This study was financially supported by a China NFSC

grant (40730315) and the Hong Kong RGC grants (7055/05P, 7063/06P and 7066/07P).

Neoproterozoic mafic dike swarm in the northern margin the Yangtze

Block was not part of Rodinia J.-H. ZHAO* AND M.-F. ZHOU

Department of Earth Sciences, University of Hong Kong, Hong Kong (*correspondence: jhzhao@hkusua.hku.hk)

The ~800 Ma Huangling mafic dike swarm, located at the

northern margin of the Yangtze Block, has been proposed to be comagmatic with mafic dikes in western North American and central-southern Australia [1]. The dikes are alkaline to sub-alkaline with SiO2 ranging from 43.3 to 57.2 wt.% and MgO from 3.7 to 9.2 wt.%. They exhibit LREE enrichment ((La/Yb)n = 3.3-28.5) with slightly negative Eu anomalies (Eu/Eu*=0.6-1.0). The rocks have arc-related compositions, characterized by enrichment of LILE and depletion of HFSE with positive Pb and negative Ti anomalies in the primitive mantle-normalized trace elemental diagram. They have high initial 87Sr/86Sr ratios (0.7052 to 0.7080) and variably negative εNd(t) values (-4.2 to -10.9). The rocks have highly variable whole-rock εHf values ranging from -0.35 to -11.34. Their 206Pb/204Pb ratios range from 16.96 to 17.97, 207Pb/204Pb from 15.41 to 15.58, and 208Pb/204Pb from 38.08 to 39.66. Initial 87Sr/86Sr values correlate negatively with 206Pb/204Pb, whereas 143Nd/144Nd, εHf and 208Pb/204Pb correlate positively with 206Pb/204Pb, suggesting an EM2 source region. The EM2 signature in the these mafic dikes indicates that their source region was likely lithospheric mantle modified by subducted components during the Neoproterozoic. The linear isotope variations are indicative of strong crustal contamination during magma emplacement. Emplacement of the mafic dikes was a consequence of post-orogenic extension. Available data support a model of asynchronous extension along the northern margin of the Yangtze Block, beginning at about ~800 Ma in the east and ~735 Ma in the west. The tectonic evolution of the northern margin of the Yangtze Block differs from that in the west where subduction was still active at 740 Ma. This conclusion rules out the possibility that the Yangtze Block was located in the center of Rodinia [1]. More likely it lay along the margin of the Neoproterozoic supercontinent [2].

[1] Li et al. (2004) Earth Planet. Sci. Lett. 220, 409-421. [2] Zhou et al. (2006) Precamb. Res. 144, 19-38.

Goldschmidt Conference Abstracts 2008 A1094

Amplitude and timing of the last deglaciation warming in the Okinawa Trough constrained by alkenone sea

surface temperature records M. ZHAO

1*, C.-Y. HUANG2 AND L. XING

3 1Sate Key Laboratory Of Marine Geology, School of Ocean

and Earth Sciences, Tongji University, Shanghai, China (*correspondence: maxzhao@mail.tongji.edu.cn)

2Department of Earth Sciences, National Chengkung University, Tainan, Taiwan

3Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China

We report alkenone sea surface temperature (SST) records

of the last 30 kyr for core DGKS9603 (28o08.87′N, 127o16.24′E; 1100 m water depth) and core CSH-2 (31o13.73′N, 128o43.37′E; 703 m water depth) from the middle and northern Okinawa Trough, respectively. These millennial-scale records reveal deglacial warming of ca. 4°C, in agreement with most previous SST records from the Okinawa Trough. The amplitude is larger than SST changes at similar latitude of the open ocean Pacific, but is similar to SST changes of the western Pacific marginal seas, such as the northern SCS. Comparison with planktonic oxygen isotope records from the same sites reveals that the start of deglaciation warming at ca. 15 ka was synchronous with ice volume changes, and within age model uncertainties, synchronous with the warming in the Greenland ice core record and with the summer monsoon increase in the Hulu Cave record. Our results provide additional evidence revealing the spatial variability of the deglacial warming in the western Pacific: earlier warming (ca. 19ka) in the tropical and sub-tropical open Pacific, Bolling-synchronous warming in the marginal seas, and late warming (ca. 13ka) in the mid-latitude open Pacific. Our result is also consistent with earlier suggestions that the last deglaciation warming in the Okinawa Trough was responding to high-latitude northern hemispheric forcing through atmospheric circulation and monsoons.

Association of A- and I-type granites at the western Yangtze Block, SW China: Implications for generation of A-type granite

X.-F. ZHAO1*, M.-F. ZHOU

1, J.-W. LI2 AND F.-Y. WU

3 1Department of Earth Sciences, the University of Hong Kong,

Hong Kong, China (*correspondence: xfzhao@hku.hk) 2China University of Geosciences, Wuhan 430074, China 3Institute of Geology and Geophysics, Beijing 100029, China

Neoproterozoic magmatism in the Yangtze Block produced voluminous S- and I-type granites, and sparse A-type granites. The Shimian and Daxiangling plutons, which are composed of granite and alkaline-feldspar granite (AFG) respectively, are spatially associated along the western margin of the Yangtze Block. Zircon SHRIMP U-Pb dating shows that both plutons formed at ~800 Ma and are roughly contemporaneous with the TTG gneisses in the area. Geological evidence indicates that TTG rocks are the oldest and the AFG are the youngest.

The granites have high SiO2 (69.3-76.6 wt%), Na2O (2.79-3.80 wt%), K2O (3.94-5.87 wt%), and low Fe2O3 (0.96-3.06 wt%) and MgO (0.12-0.50 wt%). The AFG have higher SiO2 (76.3-79.3 wt%) and lower Al2O3 (10.6-11.9 wt%) and CaO (0.21-0.55 wt%). The AFG also have much higher Zr, Hf, Ga, HREE, and lower Sr than the granites. Both granite suites are slightly peraluminous (A/CNK = 1.00-1.12), and show similar and subparallel patterns on chondrite-normalized REE diagrams and primitive-mantle normalized spidergrams. They all show negative Eu, Nb, Ta, Sr, P, and Ti anomalies. They also have identical whole-rock Nd and zircon Hf isotopic compositions (εNd(t) = +1 and εHf(t) = +5 to +9), similar to those of the TTG. Geochemical features indicate that the granites are I-type, whereas AFG are A-type.

We suggest both the I- and A-type granites were derived from the TTG but under different pressure and temperature conditions. The I-type granites were produced by dehydration melting of TTG rocks as a result of underplating by mantle-derived mafic magmas. The rocks above the I-type magma source may have been converted to charnockites by heating and dehydration. With increasing temperatures, partial melting of the charnockites at temperatures >900°C could have produced the A-type magmas. These granites formed at an extensional active continental margin. A-type granites with mantle-like isotopic signatures may be reworked or recycled from juvenile crustal rocks. The association of A- and I-type granites described here suggests that A-type granites cannot be formed by direct melting of tonalites.

Goldschmidt Conference Abstracts 2008 A1095

A composite M- with W-type of REE tetrad effect in a North China

alkaline complex ZHENHUA ZHAO

1*, Z. BAO1, S.-G. LEE

2 AND Y. QIAO

1 1Guangzhou Institute of Geochemistry, Chinese Academy of

Sciences,Guangzhou 510640, China (*correspondence: zhzhao@gig.ac.cn)

2Environmental Geology Division,Kigam,Dajeon, Korea

A new type of REE tetrad effect, an MW-type, was recognized in the Dongping altered alkaline complex, north China. Systematic studies have revealed that the chondrite-normalized REE patterns of these rocks are different from the M- and W-type of tetrad effects defined by Masuda et al. (1987) and combine characteristics of the two types. The first four elements (La, Ce, Pr, Nd) exhibit a clear convex curve(M-type) while the third and fourth sets of four elements (Gd, Tb, Dy, Ho and Er, Tm, Yb, Lu) define two distinct concave curves (W-type) on chondrite-normalized plots. The second four elements (Pm, Sm, Eu, Gb) show a transition form M- to W-type (Fig.1).

Figure 1: Chondrite normalized REE pattern of alkaline rocks. Different analytical methods such as ICP-MS and isotope

dilution thermal ion mass spectrometer were carried out in three laboratories in China, France and Korea to confirm the REE concentrations of the samples. The same results were obtained within reliable errors. In situ analysis of U-Pb dates and REE concentrations in 30 individual zircons extracted from the same altered rocks has provided evidence about the generation of this new MW-type of tetrad effect. Their isotopic ages show a continuous age spectrum from 394 Ma to 217 Ma with mean age 389.8 Ma. The chondrite-normalized REE patterns of most zircons display features typical of hydrothermal zircons, including weak positive Ce anomalies and relatively low enrichments of HREE. These data suggest that the new MW-type of tetrad effect is likely to be caused mainly by the interaction of aqueous liquids with alkaline rocks.

This work was supported by the National Science

Foundation of China (40773018).

Nature of the subcontinental mantle beneath southern Tibet revealed by

mantle xenoliths entrained by ultrapotassic rocks

ZHIDAN ZHAO1*, X. MO

1, Y. NIU2, D. ZHU

1, C. SUN1,

G. DONG1 AND S. ZHOU

1 1State Key Laboratory of Geological Processes and Mineral

Resources, and School of Earth Sci & Mineral Resources, China University of Geosciences, Beijing 100083, China (*correspondence: zd-zhao@163.com)

2Department of Earth Sciences, Durham University, Durham DH1 3LE, UK (Yaoling.Niu@durham.ac.uk)

The nature of the subcontinental mantle of Tibetan Plateau

is not well-known, although lots of postcollisional volcanic rocks in Tibet have been inferred to be generated by low degrees of partial melting from the upper mantle. The key problem is that mantle-derived xenoliths and megacrystals hosted in potassic and ultrapotassic volcanic rocks are rarely found in the hinterland of Tibetan plateau. Here we firstly report our major and LA-ICP-MS trace element data of the minerals of the mantle xenoliths hosted in the Sailipu volcanic rocks (trachyandesite, with an age of ~17 Ma, have typical ultrapotassic features that similar to that found in southern Tibet). The xenoliths, ranging in size from 0.5cm to 1.5cm in diameter, can be divided into two groups. The first group is pyroxenites (Opx+Cpx), and the second is olivine pyroxenites (Ol+Opx+Cpx±Phlogopite±Spinel). The compositions of olivine (Mg#=89-90, CaO=0.05-0.12%, TiO2<0.03%, NiO=0.29-0.80%), Cpx (Mg#=88-91, Al2O3= 5.5-7%), Opx (TiO2=0.05-0.15%, Al2O3=2-5%) and spinel (Mg#=58-76, Cr#=10-44, Cr2O3=9-35%, MnO=0.09-0.24%, FeO=11-18%, Al2O3=29-57%, MgO=16-21%) show similar features to that in the Cenozoic mantle xenolith in eastern China. The calculated temperatures of the xenolith are 990-1140°C at the given pressures of ~1.6-2.0GPa. This P-T condition is similar to that in Kenya and other rift-related upper mantle regimes, implying the regional extension beneath southern Tibet in Miocene, athough India were colliding with Asia during that time. Multi-stage metasomatic processes could be found by the trace element compositions in phlogpite, cpx and spinel. Both Cpx and phlogopite are rich in LREE, Th and U (phlogopite extremely rich in Rb and Pb). The secondary spinel along with neighboring phlogopite suggest that a ultrapotassic, host-rock like metasomatic agent that enriched in REE, Rb, Pb, Th, U, K, H2O, should have played an important role in modifying the upper mantle beneath southern Tibet.

Goldschmidt Conference Abstracts 2008 A1096

Element mobility in mafic and felsic ultrahigh-pressure metamorphic rocks during continental collision

ZI-FU ZHAO* AND Y.-F. ZHENG

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (*correspondence: zfzhao@ustc.edu.cn)

In order to decipher element mobility in ultrahigh-pressure

(UHP) eclogite-facies metamorphic rocks during subduction and exhumation of continental crust, major-trace elements and Sr-Nd isotopes were systematically investigated for two continuous core segments of about 3 m length from the Chinese Continental Scientific Drilling (CCSD) project in the Sulu orogen. The segments are composed of lithological transitions between UHP eclogite and granitic gneiss. The eclogite exhibits a large variation in major and some trace elements such as LILE (e.g. Rb, Ba and K) and LREE, but a relatively limited range in HFSE and HREE. This suggests high mobility of LILE and LREE but immobility of HFSE and HREE during continental collision-zone metamorphism. Some eclogites have andesitic compositions with high SiO2, alkalis, LREE, and LILE but low CaO, MgO and FeO contents. On the other hand, some eclogites appear to have geochemical affinity to refractory rocks formed by melt extraction as evidenced by strong LREE and LILE depletion and the absence of hydrous minerals. These results provide evidence of melt-induced element mobility in the UHP metamorphic rocks. In particular, large variations in the abundance of such elements as SiO2, LREE and LILE occur at the contact between eclogite and granitic gneiss, indicating their mobility between different slab components. Petrographic observations also show the presence of felsic veins on small scales in the UHP metamorphic rocks, demonstrating the occurrence of hydrous melt in local open-systems during the continental collision. As a whole, nevertheless, the protolith nature dictates the geochemical differences in both eclogite and granitic gneiss between the two core segments because mass transport during the subduction-zone metamorphism is principally dictated by the lithological differences at contact. The eclogite and granitic gneiss from the first core segment have high εNd(t) values, whereas those from the second core segment show relatively low εNd(t) values in concordance with majority of UHP metaigneous rocks outcropped along the Dabie-Sulu orogenic belt. Thus contrasting origins of bimodal igneous rocks were involved in the continental collision, demonstrating that the subducted continental crust is the magmatic product of active rifting margin during supercontinental breakup in the middle Neoproterozoic.

Occurrence of Rare Earth Elements in Huaibei coals, Anhui Province

L. ZHENG1, G. LIU

1 AND C.-L. CHOU

2 1CAS Key Laboratory of Crust-Mantle Materials and

Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

2Illinois State Geological Survey (Emeritus), Champaign, IL 61820, USA Our previous research indicated that rare earth elements

(REEs) enriched in the Permian coals from the Huaibei Coalfield, Anhui Province, China, and the average ∑REE is high up to 141µg/g. Especially in No.5 and 7 coals that influenced by igneous intrusion, REE contents are obviously higher than other coals.

Method

The six-step sequential extraction procedure was used in this study, and these tests measured the fractional amount of REEs in various density fractions that was soluble in a series of increasingly aggressive solvents and acids. According to the procedures, modes of occurrence of REEs in the Huaibei coals were classified as water-leachable, ion-exchangeable, organic-bound, carbonate-bound, silicate-bound, and sulfide-bound.

Discussion and Results

The results indicated that: (1) water-leachable and ion-exchangeable REEs is not abundant in Huaibei coals, and these REEs fractios show a near 1:1 abundance suggesting a common origin; (2) silicate-bound REEs dominated coal seams 3, 4, 5, 7, and 10, respectively accounting 84%, 71%, 94%, 89%, and 77% of the REEs in these seams; (3)a part amount of REE may be in the organic matter of coal, and average organic-bound REEs accounted 7% of the REEs in these coals; (4)carbonate-bound REEs contributed 17% of REEs in coal seam 4, which shown more abundant carbonte minerals.

This work was supported by the Natural Science

Foundation of Anhui Educations and Natural Science Foundation of Anhui Province.

Goldschmidt Conference Abstracts 2008 A1097

Determination of trace elements in sedimentary rock samples by Inductively Coupled Plasma

mass spectrometry P.-X. ZHENG

1, Y. ZHOU2, T.-F. WANG

2, Y.-Y. ZHANG2

AND L. LIU3

1College of EarthSciences, Jilin University, Changchun, China (yiwei@jlu.edu.cn)

2Center of Analysis and Testing, Jilin University, Changchun, China (Zhou_yan@jlu.edu.cn)

3Museum, Jilin University, Changchun, China In the gas oil exploration area, there are more than C, H,

O, N, S elements in the rock samples. Some macroelement and microelement also exist. It’s important to use the content of elements and the ratio variation judging the sedimentary environment, resuming the ancient water medium and ancient salinity.

A method for the determination of trace elements in sedimentary rock was proposed by Iductively Coupled Plasma Mass Spectrometry (ICP-MS). The ICP-MS (Agilent 7500a) running conditions: RF power 1350W; Carrier gas flow rate 1.2L/min; Spray chamber temp 2°C; Sample flow rate 0.1ml/min; Sample depth 7mm.

In the determination of the method, we analyse 30 elements including trace elements and rare earth elments. The sample was dissolved in mixed acids with pressurized sample digestion and an appropriate amount of mannnitol was added to prevent boron from volatilization. The detection limits of the method for the elements were 0.0001-0.003mg/L. The method has been applied to the determination of these elements in National Standard Reference Materials including GBW 07105-GBW 07108. The results obtained were in agreement with the certified values with recovery of 90.3%-110% and precision of less than 5% RSD(n=3).

So this technique has a lot of advantages, such as high accuracy and precision, low limit, and high analytic speed, etc. We draw a conclusion that using ICP-MS, we can get satisfactory results.

Isotope fractionation of Hg during volatilization and photoreduction in

freshwater W. ZHENG*, D. FOUCHER AND H. HINTELMANN

Department of Chemistry, Trent University, 1600 West Bank Dr, Peterborough, ON K9J 7B8, Canada (*correspondence: wangzheng@trentu.ca)

The knowledge on isotope fractionation of mercury (Hg)

during different biogeochemical processes is crucial for tracking the source and pathway of Hg in the environment. Volatilization and photoreduction, the two important processes leading to the degassing of Hg from surface water into atmosphere, were investigated in our study. Volatilization was simulated by reducing Hg(II) using SnCl2 and collecting volatilized Hg(0) vapor in trapping solutions (316 µM KMnO4, 0.9 M H2SO4). Photoreduction was conducted by exposing natural water with elevated Hg concentration to sunlight. Isotope ratios of Hg in both gaseous and aqueous phases in both processes were characterized by MC-ICP/MS.

The fractionation of Hg isotopes in volatilization experiments followed a typical Rayleigh model with lighter isotopes enriched in the volatilized phase and heavier isotopes in the dissolved phase. Fractionation factors of 1.00044 and 1.00047 were determined from two independent experiments. Only mass dependent fractionation was found during volatilization. However, photoreduction yielded both mass dependent and mass independent fractionations of Hg isotopes in our study. Higher enrichment of odd-number isotopes (199Hg and 201Hg) versus even-number isotopes (200Hg and 202Hg) were found in the aqueous phase (unreduced Hg). Our current results also suggest larger fractionation of Hg isotopes in photoreduction than in volatilization, which allows differentiation of Hg undergoing different processes. Further investigations will be focusing on the pattern and cause of mass independent fractionation of Hg during photoredution and fractionation by photoreduction with simultaneous volatilization.

Goldschmidt Conference Abstracts 2008 A1098

Mercury accumulation in salt marsh ecosystem of Yangtze estuary

X. ZHENG, L. ZHOU AND J. ZHAO

Key laboratory of Geo-information Science of Ministry of Education, East China Normal University, Shanghai, China, 200062

Salt marsh belongs to some of the most productive natural

ecosystems of the world. The salt marsh ecosystem of Yangtze estuary is the important food supplier of the fish and bird, including the migratory bird in East Asia. Due to the industrialization along the shore of the estuary, huge amount of pollutant are emitted into this region. Large part of them is sinking, cycling in the estuary and accumulating in the salt marsh ecosystem. Mercury is the one of the most harmful heavy metal in environment due to its high mobility, biomagnification capacity. While until recent there are few researches on the mercury in Yangtze estuary. In this work we investigate the mercury accumulation in the typical salt marsh of Yangtze estuary.

The research site lies in the Chongmin Dongtan national nature reserve. The mercury concentration in atmospheric wet deposit, in water over the sediment, in the surface sediment, in the sediment in rhizophere of the vegetations, including three species of vegetations (two native species and one invasion species), in four types of large zoobenthoses have been investigated.

The results shows: 1) the mercury concentration in the wet deposit is a few times larger than in the water over the sediment, which implicated that the wet deposit could be a very important mercury input source in Yangtze estuary; 2) mercury concentration in the sediment of rhizophere is larger than in the surface sediment; 3) for salt marsh vegetation the mercury concentration in leaf is larger than that in stem and in stem larger than in root, which implicate that some part of the mercury accumulates to the ecosystem in Yangtze estuary is through the leaf respiratory; 4) the concentration in the invasion species is lower than the native species, which is different from the behavior of the other heavy metal elements, which demonstrates higher concentration in the invasion species than native ones; 5) the mercury concentration in animals general shows two times larger than the surface sediment, especial helice tridens tientisinesis accumulating magnificent mercury.

3He distribution on the moon YONGCHUN ZHENG

1, ZIYUAN OUYANG1 AND

D.T. BLEWETT2

1National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China (zyc@bao.ac.cn)

2Hawai'i Institute of Geophysics and Planetology, University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822, USA The distributions of the TiO2 concentration and the

regolith maturity Is/FeO are derived from the Clementine multi-spectral lunar digital image model (DIM) of the Moon in five spectral ranges (415, 750, 900, 950, 1000 nm wavelengths) [1, 2].

Abundance of 3He in the lunar regolith at a given location depends on surface maturity, and titanium content, because ilmenite (FeTiO3) retains helium much better than other major lunar minerals [3]. The abundance of 3He in the lunar regolith is determined by:

3He (ppb)=0.2043 [(Is/FeO) × TiO2]0.645

We have developed a map of 3He abundance of the Moon (Fig. 1) based on a combination of TiO2 content and Is/FeO index. The highest 3He abundances occur in the farside maria (due to greater solar wind fluence received) and in higher TiO2 nearside mare regions. The highest concentration of 3He is observed in the western regions of Mare Tranquillitatis. For the Earth should shields the Moon's near side from the solar wind for a portion of each solar orbit, solar wind-implanted particles are more abundant on the far side.

Figure 1: Map of 3He abundance on the Moon.

[1] Lucey et al. (2000) JGR 105(E8) 297-305. [2] Pieters et al. (2006) Icarus 184, 83-101. [3] Taylor (1993) Proc. 2nd Symp. 3He & Fusion Power. 49-56.

Goldschmidt Conference Abstracts 2008 A1099

Geochemical and petrological evidence for dehydration melting in ultrahigh-pressure metamorphic rocks during exhumation

YONG-FEI ZHENG*, Z.-F. ZHAI AND Q.-X. XIA

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (*correspondence: yfzheng@ustc.edu.cn)

The important possibility of generating hydrous melt

or/and supercritical fluid phase in deep continental subduction zones is increasingly being examined. Although some degree of dehydration melting was suggested in some of ultrahigh-pressure (UHP) metamorphic rocks, it is not easy to demonstrate its occurrence because of extensive retrograde reaction and reequilibration of mineral assemglages during exhumation. We report here geochemical and petrological evidence for partial melting of Triassic UHP metamorphic rocks in the Dabie-Sulu orogenic belt, China. Breakdown of phengitic muscovite during the initial exhumation is considered to be responsible for the melting, resulting in observed variations in lithochemistry.

Two continuous core segments of about 3 m length from the Chinese Continental Scientific Drilling (CCSD) main hole in the Sulu orogen show large variations in the abundance of such elements as SiO2, LREE and LILE at the contact between high-T/UHP eclogite and granitic gneiss. This provides insight into melt-induced element mobility between different slab components. The presence of partial melts is corroborated by petrographic observations: (1) occurrence of biotite + plagioclase coronas around phengite in some samples of eclogite and gneiss, indicating melt generation by phengite breakdown; (2) aggregate of granitic minerals such as quartz, feldspar and biotite in some gneisses, suggesting the presence of hydrous granitic melt; (3) occurrence of felsic vein in some eclogites and gneisses, which may represent melt channelway.

Some low-T/UHP granitic gneiss in the Dabie orogen exhibits extremely low contents of FeO + MgO + TiO2 (1.04 to 2.08 wt%), high SiO2 contents of 75.33 to 78.23 wt%, and high total alkali (Na2O + K2O) contents (7.52 to 8.92 wt%). They are comparable with compositions predicted from partial melting of felsic rocks by experimental studies. Petrographic observations also provide evidence for the presence of partial melts: (1) breakdown of phengitic muscovite to biotite plus melt quartz, and (2) felsic veins of fine-grain minerals occurs locally between coarse-grain minerals. The local accumulation of felsic minerals suggests microscale transport of granitic melts relative to the host rocks. Nevertheless, the partial melts did not escape from the host gneiss, resulting in a kind of metatexite migmatites.

Hierarchically organized aragonite rods and implication for

biomineralization G.-T. ZHOU

1*, Q.-Z. YAO2, J. NI

1 AND G. JIN

2

1CAS Kay Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology, Hefei 230026, P. R. China (*correspondence: gtzhou@ustc.edu.cn)

2School of Chemistry and Materials, University of Science and Technology, Hefei 230026, P. R. China

Highly oriented aragonite tablets have been found in the

nacre layers of molluscan shell and mother of pearl. Several theories have been advanced to explain the biofabrication of this architecture, including (1) crystallization within preformed organic matrix compartments, (2) episodic secretion and subsequent crystallization, layer by layer, of interlamellar organic sheets and mineral crystals, (3) termination of crystal growth by poisoning or heteroepitaxial capping, followed by heteroepitaxial nucleation of the next crystal layer, and (4) the mineral bridge model that explained the formation of aragonite tablets in a nacre layer. Our experiments show that in the absence of any bio- or organic- macromolecules highly organized aragonite rods can be formed over a broad range of pH values at the temperatures of 95 to 70 °C. FESEM results reveal that the mesoscale aragonite rods are not only assembled with aragonite microrods by end-to-end, and side-to-side, but also partially fused one another, forming flat faceted surfaces, i.e. mesocrystal structure. Similar assembly process also occurs for the mineral strontianite of aragonite group and the room-temperature precipitated aragonite, revealing a general self-assembly process occurring. The driving force controlling the self-assembly process may originate from the inherent anisotropic dipole-dipole interactions between the assembled units. Such dipole interaction may generally occur in biomineralization of nacre layers in molluscan shell and mother of pearl, and orchestrate aragonite nanocrystals in an aragonite tablet to coherently orient and array, further leading to the common crystallographic a, b, c orientations of the aragonite tablets in the same nacreous column. Therefore, our experimental results may offer an improved insight into biomineralization mechanisms. It appears that the biological genetic and crystallochemical factors may synergistically operate in biomineralization.

Goldschmidt Conference Abstracts 2008 A1100

Organic geochemistry of deep carbonate rocks in the Tarim Basin

S.X. ZHOU1∗, Z.X. SONG

1,2 AND X.L. JIA

1,2 1Key Laboratory of Gas Geochemistry, Geology and

Geophysics Institute, CAS, Lanzhou, 730000 (*correspondence: sxzhou@lzb.ac.cn)

2Graduate University of CAS, Beijing, 1000049 (szhou0606@163.com, jxl200132923@126.com)

Tarim Basin cores of a deep Cambrian carbonate rocks

from depth of 4000 to 7124 m in the Tacan 1 well were collected, and their molecular and carbon isotopic compositions of individual hydrocarbons in free organic matter and inclusion organic matter were investigated. Some commonly applied biomarker thermal maturity parameters show different change trend at high level thermal maturity. Ts/Tm for C27 hopanes and 20S/20S+20R for C29 steranes in free organic matter still can be used to estimate the maturity of source-rock extracts at vitrinite reflectance (Ro) values of 1.0�1.3%, while tricyclics/hopanes ratio is an effective maturity parameter from 1.0 to 2.26%Ro, but C29 steranes ��/��+�� cannot be applied to indicate maturity stage because of a reversal trend above 1.1%Ro. Although there are higher temperatures at depth in this well, many biomarker thermal maturity parameters do not reach their equilibrium values due to overpressure retardation.

There are obviously different molecular compositions between two existing states in deep carbonate rocks. Free organic matter contain more hydrocarbons and richer in tricyclic trepanes compared with inclusion organic matter at the same samples, and n-alkanes in free organic matter has unimodal distribution than bimodal characteristic in the inclusion organic matter, Pr/Ph and C29 steranes 20S/20S+20R parameters in free organic matter are higher than inclusion organic matter. However, n-alkanes and isoalkanes of the same carbon number have similar carbon isotopic values between two different existence states at the same sample; this maybe suggests that organic matter of two existence states have a similar source, whereas their molecular composition differences are probably due to various thermal maturity and catalysis during late geological processes.

This work was supported partly by the Chinese National

Major Fundamental Research Developing Project (2006CB202305) and the Important Direction Projects of Knowledge Innovation, the Chinese Academy of Sciences (KZCX3-SW-147) and the Chinese National Natural Science Foundation (40572088).

Multitypes of ore-forming fluid systems in the Mesozoic polymetallic

middle and lower reaches of the Yangtze River area

mineralization belt, china T.F. ZHOU

1*, F. YUAN1, Y. FAN

1, D. COOKE2 AND

G. ZHAO3

1School of Resources and Environment Engineering, Hefei University of Technology, P.R. China (*correspondence: tfzhou@hfut.edu.cn)

2CODES, ARC Centre of Excellence in Ore Deposits, University of Tasmania, Australia

3Department of Earth Sciences, University of Hong Kong

There are many types of Cu-Fe-Au-Pb-Zn-U mineralizations in Middle and Lower Reaches of the Yangtze River Area mineralization belt, China. Five types of Mesozoic ore-forming fluid systems are recognized which include: (1) skarn-porphyry-stratabound Cu-Fe-Au system which relate to the high potassium calc-alkaline dioritic intrusions and formed between 145-137Ma [1] mostly in the fault uplift areas like Tongling and Jiurui areas; (2) Porphyritic or IOCG Fe system relate to shoshonitic sub-volcanic rocks and formed between 135-127Ma in fault basins such as the Ningwu and Luzong areas; (3) hydrothermal Cu-Pb-Zn-Ag and U-Au systems related to alkaline/Atype granitic intrusions formed during 129-123Ma mainly developed in the volcanic basins; (4) HS alunite-Cu-Au(?) system related shoshonitic volcanic rocks formed between 133-130Ma mostly in the Luzong volcanic basins; and (5) Epithermal Tl-Au system related to Ordovician exhalative deposition and the late Cretaceous (131Ma) hydrothermal activity in the out zone of this belt [2].

These ore-forming systems were formed in a complex Mesozoic inland continental geodynamic backgrounds confined by the North China Block, the South China Block and properly the paleo-Pacific plate in which the crust-mantle interaction had played an important role.

This research was sponsored by the National Key Basic

Science Research Project of China (2007CB411405), China NSFC project (40772057), SRFDP (20050359013) and the CODES scientific research project, UTAS, Australia. [1] Zhou et al. (2006) Ore Geology Reviews 29, 307-324. [2] Zhou et al. (2005) Mineralogy and Petrology 85, 243-251.

Goldschmidt Conference Abstracts 2008 A1101

Late Mesozoic volcanism across E. Mongolia and Great Xing’an Range, NE China: Geochemical constraint on the post-collisional

extension X.-H. ZHOU

1*, J.-F YING1, L.-C. ZHANG

1, S.A. WILDE2,

J. BADAMGARAV3 AND O.TOMURTOGOO

3 1Institute of Geology and Geophysics, Chinese Academy of

Sciences, Beijing 100029, China (*correspondence: xhzhou@mail.igcas.ac.cn)

2Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia

3Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, Ulaanbaatar, 210351, Mongolia

Late Mesozoic volcanic rocks are extensively distributed

in the eastern section of Central Asia Orogenic Belt and constitutes major part of Great Xing’an Range in NE China, as well as in eastern Mongolia and adjacent to the border of Russia. These volcanic rocks show a wide range in compositions from basaltic andesite, trachyandesite and trachydacite to rhyolite. The majority of volcanic rocks exhibit high-K calc-alkaline affinity with the subordinate showing shoshonitic features. They are characterized with low MgO contents, LILE, LREE enrichment and HFSE depletion. They have depleted to weakely enriched Sr-Nd isotopic compositions. All these geochemical features are similar to the Cenozoic volcanics in Basin and Range province of west United States. Elemental and isotopic variations suggest that fractional crystallization with the predominant removal of olivine and orthopyroxene play an important role in the formation of the SiO2-rich volcanics. Most of the basic and intermediate volcanic rocks are generated from an enriched lithospheric mantle which was metasomatized by fluids released from subducted slabs during the closure of the Paleo-Asian and Mongol-Okhotsk oceans. The generation of such widely distributed volcanic rocks was caused by the decompressional partial melting of enriched lithospheric mantle in an extensional regime, which was resulted from the gravitational collapse and upwelling of asthenosphere after the final closure of the Mongol-Okhotsk oceans from late Jurassic to Cretaceous.

Early Cretaceous Comei large igneous province in SE Tibet:

Whole-rock Sr-Nd and zircon Hf isotopic constraints on mantle source

characteristics D.-C. ZHU

1, X.-X. MO1, Z.-D. ZHAO

1, Y. NIU2 AND

S.-L. CHUNG3

1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China (dchengzhu@163.com)

2Department of Earth Sciences, Durham University, Durham DH1 3LE, UK (Yaoling.Niu@durham.ac.uk)

3Department of Geosciences, National Taiwan University, Taipei 106, Taiwan (sunlin@ntu.edu.tw)

The Early Cretaceous Comei large igneous province

(CLIP) aged from ca. 145 to 128 Ma with peak activity at ca. 32 Ma was recently identified in SE Tibet [1]. The CLIP is dominated by dismembered mafic lava flows, sills and dikes, with subordinate ultramafic and silicic rocks. The mafic rocks in the CLIP can be subdivided into the high-Ti and the low-Ti groups in terms of TiO2 and P2O5. Twelve SHRIMP zircon U-Pb age dates indicate that the high-Ti group is persisted from ca. 145 Ma to 128 Ma, and the tholeiitic magmatism is occurred at 132 Ma, and continued to 128 Ma [1]. The Sr-Nd isotopic compositions of 17 uncontaminated high-Ti group and 6 ultramafic samples [(87Sr/86Sr)i = 0.70398 ~ 0.70596, (143Nd/144Nd)i = 0.512502 ~ 0.512647, εNd(i) = + 0.67 ~ + 3.81] are interpreted to represent the isotopic signature of the Comei plume head. This isotopic composition overlaps those of basalts produced by the Kerguelen plume (e.g. the Rajmahal Group I, the Bunbury Casuarina, the Oligocene and upper Miocene Kerguelen plume materials, and the proposed Cretaceous Kerguelen “plume head” [2]). Weighted mean εHf(t) values of zircons from two dated high-Ti group samples are close to those of the Bunbury Casuarina and the Cretaceous Kerguelen “plume head” [2]. The prolonged alkaline magmatism of the CLIP favors plume head incubation beneath an originally thick lithosphere, as many flood-basalt provinces of the world would have [3]. We propose that the relative wide range of the proposed Sr-Nd isotopic compositions of Comei plume head would be ascribed to the relative long incubation of the Comei plume head beneath thick Eastern Gondwana lithosphere at the transition from the Late Jurassic to the Early Cretaceous time. [1] Zhu et al. (2008) submitted. [2] Ingle et al. (2004) Chem. Geol. 209, 83-106. [3] Sheth and Chandrasekharam (1997) Phys. Earth Planet. Interior 104, 371-376.

Goldschmidt Conference Abstracts 2008 A1102

Selenium isotope variations in weathering zones of Se-rich

carbonaceous rocks at Yutangba, China

J.-M. ZHU1,2, T. M. JOHNSON

2* AND S.K. CLARK2

1Institute of Geochemistry, Chinese Academy of Scicences, Guiyang 550002, China (zhujianming@vip.gyig.ac.cn)

2Department of Geology, University of Illinois, 245 NHB, MC-102, Urbana, IL 61801, USA (*correspondence: tmjohnsn@uiuc.edu, skclark@uiuc.edu)

Extremely selenium-rich carbonaceous chert and

carbonaceous shale occur in the Permian Maokou Fm. of Yutangba, 81km SE of Enshi city, China. Rock and soil can exceed 1000 mg/kg Se, and human and livestock Se poisoning has been reported. Selenium isotope variations in weathering zones of Se-rich carbonaceous rocks were investigated to determine the mechanism of Se enrichment. Mass-dependent fractionation of Se isotopes is caused mainly by reduction of Se oxyanions and thus serves as an indicator these reactions. 82Se/76Se ratios were measured by double spike MC-ICP-MS, with 0.20 per mil precision. δ82/76Se in fresh carbonaceous shale and chert, with 185 ±76 mg/kg Se(n=12), fell within a narrow range, from -0.03 to 1.38‰, (vs. SRM3149) with an average of 0.71±0.49 ‰. Drill core samples from >50m depth, averaging 108 ±54 mg/kg Se (n=25), also have a narrow range of δ82/76Se, from -2.54 to +1.74 per mil with a mean of 0.08±0.98 ‰. In contrast, outcrop samples from a horizontal transect across the nearly vertical, partially weathered beds exposed in a shallow quarry are extremely Se- rich (106-26054mg/kg Se with a mean of 2774 mg/kg; n=45), show very wide Se isotope variation, from -13.19 to +11.37 per mil. This indicates most of the Se has undergone at least one cycle of oxidation, transport, re-reduction, and precipitation in these organic-rich rocks. The pattern of isotopic variation predicted by a simplified model of the system is heavy isotope depletion in zones that Se-rich infiltrating waters encounter early in their downward migration, and heavy isotope enrichment in less accessible zones that receive Se after it has been partially reduced. The observed pattern fits this model, though the fracture-dominated system is complex and other factors may be involved. The mechanism of Se enrichment appears to be repeated oxidative mobilization and reductive re-precipitation, with Se trapped within a redox front that migrated downward along near-vertical bedding planes as the land surface lowered.

This project was supported by NSF of China (Grant No.

40573050)

LA-ICP-MS single particle zircon U-Pb dating and metallogenetic tectonic

setting of Jingduicheng large-scale porphyritic molybdenum deposit in

East Qinling, P.R. China L.M. ZHU, G.W. ZHANG, B. GUO AND B. LEE

The State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, 710069, P.R. China (*correspondence: zhulaimin@nwu.edu.cn)

Introduction

A precise U-Pb dating based on single particle zircon laser probe dating technology (LA-ICP-MS) and petrologic and ore geochemical study have been applied to ore-bearing porphyry of Jinduicheng large-scale porphyritic molybdenum deposit in East Qinling.

Discussion and Result

The weighted average age by Single Particle zircon U-Pb dating of the porphyry is 140.95±0.45Ma, which is consist with the lower limit molybdenite Re-Os model age dated by the former researchers [1]. This indicates that the period of mineralization was almost simultaneous with the diagenesis or slightly later. These two events were involved in the same system of J-K, which was tally with the geodynamical event of extend happened in the period of tectonic system conversion in about 140Ma at east China [2, 3]. The pluton-forming and the molybdenum mineralization took place in the extrusion-extension transforming stage in J-K, and the corresponding tectonic setting was the intracontinental orogenic and extention process after collision and orogenesis of Yangz plate and Northern China plate [2].

Jinduicheng ore-bearing porphyry and deposit geochemical data indicate that the metallogenetic substance origin from deep earth, and was generated by mixing of lower crust and upper mantle. When the molybdenum enriched magma intruding to the upper crust along structure weakness zones, ore-forming fluid generated by magma condensation fraction filling in the cracks and replacing the surround rock, then the deposit was formed.

[1] Li et al. (2005) Mineral Deposits 24(3), 292-301 (in Chinese with English abstract). [2] Zhang et al. (2001) Qinling belt and continental dynamics. Beijing: Science Press, 1-729 (in Chinese) [3] Meng et al. (2000) Tectonophysics 323, 183-196.

Goldschmidt Conference Abstracts 2008 A1103

Transition metal isotope variations in North Pacific deep water

X.K. ZHU1*, J. LI

1, S.H. TANG1 AND H.F. LING

2 1Lab Isotope Geol., MLR, Inst. Geol., CAGS, Beijing, China (*correspondence: xiangkun@cags.net.cn) 2State Key Lab Mineral Deposits, Nanjing Univ, China

(hfling@public1.ptt.js.cn)

Fe-Mn crust has been proved to provide excellent records of isotope composition of dissolved metals such as Fe, Cu and Zn in deep seawater. Three crusts collected from central North Pacific have been selected for this study. These crusts have been subjected to detailed investigation in terms of radiogenic isotopes, and their ages have been constrained using multiple approaches extending to ca. 80Ma (Ling et al. 2005). The sub-samples were obtained by micro-milling, and Fe, Cu and Zn isotope measurements were performed using a Nu Plasma HR MC-ICPMS after chemical purification. The results are expressed in ε units which are deviations in parts per 104 from the same isotope ratios of the reference materials IRMM-14, NBS976, Lyon-Zn, respectively.

All three crusts show consistent variations in Fe isotope compositions, an overall range from 0.9 to -12 in ε57/54Fe units. In more detail, the Fe isotope compositions of the crusts start with ca.-5 ε57Fe units at the surfaces, broadly increase to maxima at ca. 50Ma, then decrease sharply to minima at ca. 70Ma. Furthermore, the ε57Fe values obtained from all three crusts are negatively correlated with 206/204Pb and 208/204Pb ratios.

In contrast, Cu and Zn isotopes obtained from three crusts are show much smaller variations, and somehow decoupled with the Fe and Pb isotopes.

These results illustrate for the first time that the evolution of Fe, Cu and Zn isotope compositions in North Pacific seawater back to latest Cretaceous. In general, the main Fe sources for open oceans are terrestrial aerosols and MOR hydrothermal plumes. The crust studied is far away from MOR, and there is no evidence of MOR hydrothermal contribution in terms of Pb- and Nd-isotopes. The main turning point in the trend of Fe isotope variation occurs at ca. 50Ma, which is broadly coincident with the switchover of terrestrial inputs from North America to Asia (Ling et al. 2005). The strong linkage between Fe- and Pb-isotope compositions strongly suggests that Fe isotope variation in North Pacific deep water is related with global climate change through source inputs.

The decoupling of Cu and Zn isotopes with Fe isotopes in the studied crusts implies different mechanism is required for the explanation of Cu and Zn isotope variations.

Groundwater modeling in Zhalute county, Inner Mongolia,

China with the help of ERT used to build the hydrogeology conceptual

model XIAOBIN ZHU, J. WU AND Y. XIA

Department of Earth Sciences, Nanjing University, Nanjing, P.R. China (zxb@nju.edu.cn)

The industrialization and the rapid economic growth in

Zhalute, a county located in the east of Inner Mongolia, China with a total area of 17,193 km2, attributed to the survey and the exploitation of abundant natural resources, such as coal, rare earths, silica, Kaolin and so on in this area recently. The average annual precipitation and evaporation is about 387.0mm and 1137.6mm respectively. It’s not an area with enough water resources. Therefore, the water resources should be used effectively and reasonably with the development of economics. The precondition of reasonable using is that we should know the quantity of water resources. So the evaluation of groundwater resources, an important supply source in this area, is of great significance to the sustainable development. The landform in Zhalute county includes mountain, which is the north part of this county and plain, which is the south part and the population is large. Groundwater resources are evaluated for the plain area with a total area of 2900 km2 using GMS and the method of water balance. The study area is very large while the basic geology and hydrogeology datum are not sufficient. For the limited data, the Electrical Resistivity Tomography (ERT), a geophysical method, is used when we build the hydrogeology conceptual model, which is the base of simulation. 163 cross-sections are surveyed by ERT. The length of each cross-section is 300m. The space structure of the aquifers is constructed combining these cross-sections and the data of boreholes.

The simulation results show that the quantity of groundwater resources is almost the same with that got by the method of water balance. The average pumping, recharge of precipitation, recharge of rivers, recharge of irrigation, evaporation, boundary recharge and boundary discharge is 0.35×108m3/a, 1.3×108m3/a, 0.096×108m3/a, 0.12×108m3/a, 1.05×108m3/a, 0.078×108m3/a and 0.22×108m3/a respectively. The total exploitable groundwater is 2.38×108m3/a. The results give some advices to the exploitation of groundwater and provide evidence to the reasonable deployment of water resouces in the future. It’s benefit to the healthy and the sustainable development of economics in this area.

Goldschmidt Conference Abstracts 2008 A1104

Garnet amphibolite found in Baikouquan ophiolitic mélange:

A clue to a HP metamorphic belt in Junggar, Xinjiang

YONGFENG ZHU* AND BO CHEN

School of Earth and Space Science, Peking University, Beijing 100871, China (*correspondence: yf305@126.com)

Several huge ophiolite mélanges occur in western Junggar

[1-2]. Our studying Baikouquan ophiolite mélange locates close to Keramay city (Xinjiang, NW China). The mafic rocks in this ophiolite mélange were demonstrated to be come from the upper mantle from depth of ~94km [2]. Spinel lherzolite in Baikouquan- Baijiangtan ophiolite mélange was exhumated from deep mantle together with the subducted crust materials.

Here we report the first discovery of garnet amphibolite in the Baikouquan ophiolite mélange. The discovered garnet amphibolite, coexisting with amphibolite and greenschist, mainly consists of amphibole and zoisite + Na-rich plagioclase assemblage with minor amounts of garnet, ilmenite, albite, epidote, chlorite, titanite, augite, rutile, apatite, and quartz. Garnet usually contains abundant apatite, rutile, and zircon inclusions. Petrographic observations provided in this paper demonstrate that the mineral assemblage formed during the early metamorphic stage (probably in eclogite phase) is garnet – clinopyroxene (possibly from omphacite) – rutile – apatite – zircon. This discovery indicates that eclogite was formed during the subduction, and means that Baikouquan ophiolite mélange together with this reported garnet amphibolite as well as the Tangbale blueschist in western Junggar represent a HP metamorphic belt similar as ion other regions of central Asia [4-6]. [1] Xu X et al. (2006) Geology in China 33, 470-475. [2] Zhu YF & Xu X (2007) Acta Petrologica Sinica 23, 1075-1086. [3] Zhang LF et al. (2002) Am. Miner. 87, 861-866. [4] Zhu YF & Ogasawara Y (2002) Intern. Geol. Rev. 44, 831-836. [5] Zhu YF & Ogasawara Y (2002) Geology 30, 947-950. [6] Zhu YF (2003) Lithos 68, 115-119. [7] Zhu YF & Xu X (2006) Acta Petrologica Sinica 22, 2833-2842.

Influence of historical land use on the distributions of soil trace elements in

Maricopa County, AZ X. ZHUO

1*, P. PRAPAIPONG2 AND E.L. SHOCK

1,2 1Department of Chemistry and Biochemistry 2School of Earth and Space Exploration, Arizona State

University, Tempe, AZ, 85287, USA (*correspondence: xiaoding.zhuo@asu.edu)

The distribution of trace elements in urban areas depends

on geologic background, human inputs, and the subtleties of changes in land use over time. In the arid southwestern US, urbanization occurs on land that was previously used for agriculture, as well as land that was, until recently, pristine desert. In this study, surface soil samples (top 10 cm) collected at 200 locations across Maricopa County, Arizona, were analyzed by ICP-MS. Results for Pb, Cd, Ag and Cu show strong correlations with urbanization, while Ni, V, U and Sr may reflect changes in background geology. Arsenic data may reveal the long-term effects of irrigation with As-rich water from the Verde River. When comparing As and Fe, older agricultural sites differ more from desert sites than newer sites, suggesting a shift in the source of As with time. Data for Pb were regressed against historical traffic data collected and distilled for each sampling location through GIS analysis. There is a somewhat stronger correlation between soil Pb distribution patterns and traffic data from 1972 than with traffic data from 2004, suggesting an origin from recent human history. Patterns for other metals that suggest urban influences (Ag, Cd, Cu) may include point source contributions.

Goldschmidt Conference Abstracts 2008 A1105

The application of concentration gradient of zonality coefficient for indicator elements as a criterion in

mining geochemistry MANSOUR ZIAII

Shahrood University of Technology (mziaii@shahroodut.ac.ir) The concentration gradient of indicator elements (g) in a

geochemical field was calculated based on the variations in the indicator elements relative to survey interval of successive samples. The calculated g value for indicator elements and their zonality coefficient (gc) in lithogeochemical anomalies were used to devise a new approach for separating non-economic mineralization from economical anomalies.

Modeling in geochemical exploration by use of gc has four advantages over the other exploration approaches: (1) It presents a simplistic quantitative model for lithogeochemical explorations in order to distinguish between supra-ore halos from sup-ore ones. (2) It introduces a special approach to enhance weak geochemical halos and to extend their size. (3) It reduces the interfering effect of the background content in calculating geochemical anomalies. (4) It is quantitative method used to distinguish between blind mineralization from zone dispersed mineralization. The usefulness of this model is demonstrated by a small detailed lithogeochemical survey for porphyry copper-molybdenum deposits in NW Iran. gc was found to be the most useful quantitative model for exploration of the Sungun porphyry copper deposit. Cu and Mo contents of rocks and soils can detect the border zone of such a target of copper mineralization away from the center of mineralization (geochemical field). gc ratios in surface can distinguish the BM from ZDM with Cu and Mo.

Geochemical and mineralogical pattern recognition and modeling

with a Bayesian approach to migmatitic–hydrothermal tin deposits

M. ZIAII*, A. ABEDI AND M. ZIAEI

Faculty of Mining and Geophysics, Shahrood University of Technology, Shahrood, Iran (*correspondence: mziaii@shahroodut.ac.ir)

Most primary tin mineralization in the world has a

magmatic–hydrothermal origin and is associated with granitic intrusive rocks. The geochemistry of trace elements has been widely used to develop models of metallogensis and mineral exploration for various types of hydrothermal ore deposits. Tourmaline compositions have long been used as a useful exploration guide in several types of economically important ore deposits. The Bayesian approach is an effective method of identifying the probability of mineralogical and geochemical type (MGT) mineralization of trace elements in tourmaline ore mineralization. Monomineralic samples have been identified using a computer-based Bayes’ method and exploration geochemical techniques of tin deposits for MGT. In order to employ the method, a data bank was used consisting of the results of analyzing more than 500 monomineralic samples collected from the main migmatitic–hydrothermal tin deposits in a territory of CIS. The Bayes approach applied to geochemical data, such as posteriori probabilities and discriminant analysis, provide numerical and graphical means through which the relationships between the trace elements and samples can be studied. The method used here, along with GIS, to find MGT that can be used as geochemical indicators of regions with tin mineralization.

The Yunlong deposit is one of the important tin deposits in Yunnan province of south China. It occurs mainly as cassiterite–quartz–tourmaline ore veins that are hosted in a suite of highly metamorphosed rocks that are migmatitic rocks. Generally, two models have been proposed for the Yunlong tin deposit. The genesis of the ore deposit has been hotly debated and various models have been proposed including granite-related magmatic–hydrothermal and migmatitic–hydrothermal origins (Jiang S. et al. 2004).

The results of analyzing 20 monomineralic samples of tourmaline from the Yunlong tin deposit, show a multi-MGT anomaly of superposition which is a combination of two MGT: (1) tin-cassiterite-silicate type (65 %), (2) tourmaline-metamorphic type (16 %). Mineralogical and geochemical maps (MGM) can be drawn based on results of MGT anomalies in a GIS environment. These maps can replace traditional metallogenic maps. To conclude, this method: (1) identifies tourmaline as the mineral that can be selected from both tin ores and non-ores, (2) provides an efficient modeling tool for metallogenic mapping, and (3) leads to the automation of tin mining in the mine-scale.

Goldschmidt Conference Abstracts 2008 A1106

Tracing the source of oxygen during pyrite oxidation with ∆17OSO4

K. ZIEGLER1*, M.L. COLEMAN

2 AND

EDWARD D. YOUNG1,3

1Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095, USA (*correspondence: kziegler@ess.ucla.edu)

2Jet Propulsion Lab, Pasadena, CA 91109, USA 1,3Department of Earth and Space Sciences, UCLA, Los

Angeles, CA 90095, USA

We show how the three isotopes of oxygen (∆17O=δ17O-0.528*δ18O) can be used to trace the sources of oxygen in sulfate produced during sulfide oxidation, an important biogeochemical process on Earth’s surface and possibly also on Mars [1].

δ18OSO4 signatures are determined both by the δ18O value of the reactants (O2 vs. H2O), and by the isotopic fractionation factors associated with the reaction mechanisms. Two studies [2, 3] have recently attempted to use δ18OSO4 values to quantify the different oxygen contributions to sulfate. When tracing oxidation using 18O/16O alone, the relative contributions of fractionation mechanisms and reactant δ18O values are difficult to deconvolve; a two-isotope approach is not sufficient to identify sources of oxygen uniquely in this process.

We are investigating the use of ∆17O as a quantitative and qualitative tracer for processes and oxygen sources involved in sulfate production. We conducted controlled abiotic and biotic (A. ferrooxidans) laboratory experiments, in which the use of water spiked to obtain an extreme ∆17O value has allowed us to clearly distinguish and quantify the processes and sources of sulfate-oxygen.

Results show that during the initial phase of microbial pyrite oxidation, 80-90% of the oxygen derives from air. After the microbes’ exponential growth stage, ∆17OSO4 values indicate a switch to water as the dominant source of oxygen (>95%). A biotic fractionation factor ε18O(SO4-H2O) of +9.86‰ is deduced, and extrapolation of the biotic ε18O(SO4-O2) value gives a span of –28.64 to –34.44‰. An abiotic ε18O(SO4-H2O)

value of +8.75‰ is inferred from a S-oxidation experiment with 100% air-oxygen followed by precipitation as BaSO4 in spiked water.

∆17OSO4 signatures specify the source of oxygen, and possibly reveal biotic processes. Our results hold promise for using ∆17O as a tracer in natural as well as experimental systems. [1] Brunner & Coleman (2005) LPSC XXXVI, abstr. 1932. [2] Balci et al. (2007) GCA 71, 3796-3811. [3] Pisapia et al. (2007) GCA 71, 2474-2490.

The El Salvador Cu Deposit, Chile: Insight from a decade of Re-Os data

A. ZIMMERMAN1; H. STEIN

1,2 AND Y. WATANABE

3 1AIRIE Program, Colorado State University

(aaron.zimmerman@colostate.edu) 2Geological Survey of Norway, 7491 Trondheim 3Institute for Geo-Resources and Environment, AIST Higashi

1-1-1, Tsukuba, Japan

Sulfide samples from the El Salvador Cu porphyry deposit, Indio Muerto area, Chile, have been analyzed over the past decade using improving Re-Os techniques. New molybdenite ages suggest a slightly older bias to the early ages, due to issues with either the Os spike or Os standard, or more likely sample-spike isotopic equilibration using alkaline fusion. Nonetheless, the entire data suite suggests formation of a major Cu deposit over a short time period of ~0.5 m.y.

Molybdenite sample DD-1140-20 is used to compare the accuracy and reproduciblity of incrementally improved Re-Os procedures. As previously reported [1], an age of 42.2 ± 0.2 Ma was determined using single 185Re and 190Os spikes with alkaline fusion equilibration. Subsequent new separate replicates using single 185Re and 190Os spikes and an aqua regia-Carius tube digestion resulted in ages of 41.2 ± 0.2 and 41.3 ± 0.2 Ma. Given the disparity in ages, two more new separate replicates utilizing mixed 185Re-188Os-190Os spike and aqua regia-Carius tube digestion gave 41.2 ± 0.2 and 41.3 ± 0.3 Ma, confirming the prior aqua regia digestions. Additional samples from the deposit also fell within the range of 41.6 to 41.0 Ma, verifying the Carius tube results.

The disparity between Re-Os ages obtained by alkaline fusion digestion in an open Zr crucible and aqua regia digestion in a sealed Carius tube is likely attributable to incomplete spike-sample isotopic equilibration, spike loss by evaportaion during alkaline fusion, or spike calibrations. Alternatively, the difficulty in producing and quantifying an Os standard may also play a role as the single 190Os spike was calibrated against the so called “B-Standard” whereas the mixed spike was calibrated against a new standard (subseqently used to characterize the Henderson molybdenite Reference Material [2]). Furthermore, Re-Os data from early alkaline fusion analyses of molybdenite sample DD-1104-14 suggested spike loss from evaporation or spike-sample disequilibration when two replicates resulted in ages of 42.0 ± 0.2 and 41.4 ± 0.2 Ma.

[1] Watanabe et al. (1999) GSA Abstracts with Programs 31/7, A-30. [2] Markey et al. (2007) Chem. Geol. 244, 74-87.

Goldschmidt Conference Abstracts 2008 A1107

Wild 2 olivine, low-Ca pyroxene and sulfides

M.E. ZOLENSKY

KT, NASA Johnson Space Center, Houston, TX 77058 USA (michael.e.zolensky@nasa.gov)

Introduction

While the first glimpses of samples returned from Comet Wild 2 by the Stardust spacecraft indicated that its mineralogy was most similar to what has been found in anhydrous chondritic interplanetary dust particles (IDPs) and refractory IDPs [1], there have been recent suggestions that this mineralogy is more similar to what has been observed for meteorites [2], based primarily on the presence of some grains with igneous textures and mineralogies. We compare the observed composition ranges of olivine, pyroxene and Fe-Ni sulfides in Wild 2 grains with those from chondritic IDPs and chondrite meteorites to explore whether these data suggest general affinities to any particular astromaterial. Results

Wild 2 olivine has an extremely wide composition range, Fo4-100, with a peak at Fo99. The composition range displayed by the low-calcium pyroxene is also very extensive, En52-100, with a peak at En95. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with generally less than 2 atom% Ni. While we have not yet observed any direct evidence of water-bearing minerals, the presence of rare Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. In the course of our work we have been reminded that there are still very few good olivine and pyroxene analyses from the Wild 2 samples, especially as regards minor elements. Also, most of the few available analyses of chondrite matrix olivine or pyroxene derive from microprobe analyses of matrix which is generally too fine-grained to support such analyses. Obviously new analyses of olivine and pyroxene IDPs are required, along with minor-element analyses of chondrite matrix, micrometeorite and IDP silicates. At this time it is premature to conclude that Wild 2 is mineralogically more similar to meteorites than IDPs. However, the meteorite Kaidun has some interesting similarities to Wild 2 [3]. [1] Zolensky et al. (2006) Science 314, 1735-1740. [2] Ishii et al. (2008) Science 319, 447-450. [3] Zolensky & Ivanov (2003) Chemie de Erde 63, 185-246.

Uranium-series studies of Holocene basalts from the Hainan Island,

South China H. ZOU

1, K. MCKEEGAN2 AND Q. FAN

3 1Department of Earth and Space Sciences and Institute of

Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095 (hzou@ess.ucla.edu)

2Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 (kdm@ess.ucla.edu)

3Institute of Geology, China Earthquake Administration, Beijing 100029, China (fqc@ies.ac.cn)

Extensive basaltic magmas erupted in the Hainan Island,

south China, with eruption ages ranging from 16 million years to Holocene (8000 years BP). The Holocene basalts in the Hainan Island are located in two volcanoes: Ma’Anling and Leihuling. The Ma’Anling basalts are olivine tholeiites whereas the Leihuling basalts are olivine alkali basalts.

The Holocene basalts from the Hainan Island show LREE-enriched patterns. Their εNd values range from +4.1 to +4.8, 87Sr/86Sr ratios vary from 0.7039 to 0.7042, and 206Pb/204Pb ratios range from 18.63 to 18.71. Their Nd-Sr-Pb isotopic compositions suggest that the basalts from the Hainan Island were derived from a Dupal mantle source with EM2-DMM mixing.

The tholeiites from Ma’Anling display 18-20% 230Th excesses and the alkali basalts from Leihuling Leihuling show 22-32% 230Th excesses. As a test of the U-Th measurement, a 16 Ma basaltic sample from the Hainan Island exhibits U-Th equilibrium with (230Th/238U)=1.003. The pronunced 230Th excesses in the Holocene basalts indicate that the tholeiites from Ma’Anling and the alkali basalts from Leihuling were originated from melting of a mantle source in the garnet stability field (>75 km).

The lithosphere thickness in the Hainan Island is 55 km. The significant 230Th excesses in the Ma’Anling and Leihuling basalts indicate that the Dupal mantle source for the Hainan Basalts is located in a deep asthenospheric mantle. Thus the Uranium series data are not consistent with previous interpretations that the Hainan basalts with Dupal mantle signatures are formed by decompressional melting of a shallow subcontinental lithospheric mantle.

The slightly smaller 230Th excess in the Ma’Anling tholeiites than the Leihuling alkal basalts may indicate (1) that the magma residence time in magma chambers for tholeiites are longer than alkali basalts and/or (2) that the alkali basalts from Leihuling may be generated from a deeper mantle source with higher garnet content than the tholeiites from Ma’Anling.

Goldschmidt Conference Abstracts 2008 A1108

Geochemical characteristics of REE in the 8# ore-body of Shifengshan copper deposit, Yimen, Yunnan,

China H. ZOU

1, R. HAN1, W. FANG

2 AND M. LIU

3 1Kunming University of Science and Technology, Kunming

650093, P.R.China (zouhaijunlmq@yahoo.com.cn) 2Geological Survey Center for Non-ferrous Mineral

Resources, Beijing 100012, P.R. China 3Architecture Desinning Institute of Yunnan Province

Tested with ICP-MS method, samples include fault tectonites, ore-hosted rocks and ores. Rocks are the purple sandy slate rocks (MP), gray pelitic-tuffaceous dolomite rocks (MG), gray silicified dolomite rocks (DL) and black-blue siliceous-strip dolomite rocks (DM).

Figure 1: REE distribution models.

The REE distribution models include four types:

1) The model of MP and MG rocks, tectonites and ores belongs to high ∑REE - depleted Eu - enriched light REE type; 2) The model of DL and DM rocks shows low ∑REE - strongly depleted Ce - slightly depleted Eu - enriched light REE; 3) The model of tectonites of the NE-trending ore-bearing faults shows low ∑REE-enriched Eu and light REE; 4) The model of very low ∑REE - strongly depleted Ce – enriched Eu and heavy REE means the superposed ore-forming process of biotite monzonite veins. The origin of Cu and REE were from the MP and MG rocks of the diapir; The REE distribution models of tectonites and ores have high similarity (inheritance) with the diapir models. The ore-forming process occured along the contact zones among the diapirs and DL (DM) rocks. The biotite monzonite veins intruded along the NE-trending fault zones, which formed the NE-trending calcite-quartz-chalcopyrite veins in the early-formed ore-bodies. The REE characteristics show the NW-trending faults formed earlier than the NE-trending ones which strongly reformed the MP and MG rocks. The NW-trending faults were the ore-leading structures, the EW-trending faults were the distribution structures, and the NE-trending faults were the distribution and ore-hosted structures.

Granted by the fund for NCET in State University (NCET-

04-917) and the Major Discipline for KUST (2008).

The theoretical basis for ACE, an age calculation engine for

cosmogenic nuclides C. ZWECK* AND M. ZREDA

Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721 (*correspondence: czweck@hwr.arizona.edu)

ACE (formerly known as iCronus) is an integrated

development environment for cosmogenic nuclide dating. By default it can be used for 3He, 10Be, 14C, 21Ne, 26Al and 36Cl samples, but is designed to be flexible enough to include other cosmogenic nuclides. Throughout the development process ACE employs a two stage calibration/dating algorithm so that production rates used to date samples are theoretically consistent with independently dated calibration samples. To account for temporal changes in cosmogenic nuclide production rates, the algorithm explicitly solves the buildup differential equation for inventory evolution at each time step using a temporal finite-difference scheme. By default, changes in production rates due to secular variability in the geomagnetic and atmospheric attenuation of cosmic rays are incorporated, with General Circulation Model reanalysis data used to account for the spatial variability in atmospheric shielding. All components of the calibration/dating algorithm are customizable and the modular design of ACE allows swapping of key theoretical components, so that sensitivities of computed ages to assumptions in experimental design can be assessed. For a range of real and synthetic data we use ACE to show the hierarchy of sensitivity of computed ages to current uncertainties in the theory of cosmogenic nuclide dating. Examples include the choice of atmospheric scaling, muogenic production rates, secular variability in paleoclimatic, and geomagnetic data and calibration datasets, and computations of low-energy neutron intensities.

Goldschmidt Conference Abstracts 2008 A1109

Diagenesis evaluation in sedimentary basins for hydrocarbon exploration

H. ZWINGMANN1, R. GAUPP

2, K. HIGGS3 AND Y. ZHANG

4 1CSIRO Petroleum, PO Box1130, Perth, 6102, Australia

(horst.zwingmann@csiro.au) 2Institute of Geosciences, Friedrich-Schiller-University,

Burgweg 11, 07749 Jena, Germany 3GNS Science, 1 Fairway Drive, Avalon, P.O. Box 30-368,

Lower Hutt, New Zealand 4Youyu Zhang, Research Institute of Petroleum Exploration

and Development (RIPED), Beijing 100083, China

Low temperature isotopic and geochemical studies are important tools in hydrocarbon and mineral exploration. Integration of diagenetic studies with isotopic dating and geochemical tracing tools can constrain timing and pathways of hydrocarbons into reservoirs. Time represents a key value in determining whether hydrocarbons will inhibit further diagenetic reactions, which can significantly affect reservoir quality by increased or diminished porosity preservation. Isotopic age and geochemical tracing data provide information about the origin of hydrocarbons, fluid flow, brittle faulting and mass transfer. Results of combined diagenesis and isotopic studies using tools such as K-Ar, 40Ar-39Ar, Rb-Sr, REE and stable isotope data (O) from areas in Europe (NW German basin), Australia (Copper Eromanga basin), New Zealand (Taranaki basin) and China (Tarim basin) will be presented to demonstrate applications of these tools to unravel geochemical aspects of diagenetic processes. All study areas contain reservoirs with a range of specific high temperature diagenetic illites that significantly reduce reservoir characteristics and allow investigation of diagenetic processes and thermal histories of deeply buried tight gas sandstone reservoirs. Diagenetic regimes are similar in most study areas suggesting trends to evaluate diagenetic patterns. All studies focus on the geochemical record of authigenic illite as the major clay mineral component in these sandstones. The illite displays a wide range of morphologies, modes of occurrence and origins, which can be dated and traced by geochemical tools.