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Oskarshamn site investigation
40Ar/39Ar dating of fracture minerals
Henrik Drake, Earth Sciences Centre, Göteborg University
Laurence Page, Department of Geology, Lund University
Eva-Lena Tullborg, Terralogica AB
January 2007
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ISSN 1651-4416
SKB P-07-27
Oskarshamn site investigation
40Ar/39Ar dating of fracture minerals
Henrik Drake, Earth Sciences Centre, Göteborg University
Laurence Page, Department of Geology, Lund University
Eva-Lena Tullborg, Terralogica AB
January 2007
Keywords: Simpevarp, Laxemar, Äspö, fracture minerals, Geochronology, Adularia, Illite, Muscovite, Apophyllite, Hornblende.
This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the authors and do not necessarily coincide with those of the client.
A pdf version of this document can be downloaded from www.skb.se
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Abstract
This report presents the results obtained from geochronological studies of fracture minerals from the Laxemar and Simpevarp subareas and Äspö. Thirteen drill core samples of K-bearing minerals (adularia, muscovite, apophyllite, illite and hornblende) from both open and sealed fractures have been dated with the 40Ar/�9Ar method. The samples are from drill cores from the cored boreholes KA1755A (Äspö), KSH01A and KSH0�A+B (Simpevarp) and KLX02, KLX0�, KLX06 and KLX08 (Laxemar).
Fracture minerals have been selected to provide absolute geochronological constraints of the relative sequence of fracture mineralizations obtained by e.g. cross-cutting relations and stable isotope analyses /Drake and Tullborg 2004, 2005, 2006ab, 2007/. The sequence consists of seven generations of which generation 1 and 6 have been dated in the present study. Furthermore, greisen-like fillings (thought to be coeval with generation � and 4) and muscovite in altered wall rock (related to generation � and 4) have also been dated in the present study.
The analyses yielded plateau ages for ten samples. Seven samples yielded reasonable ages (adu-laria and muscovite) in accordance with interpretations from cross-cutting relations, chemistry and isotope studies /Drake and Tullborg 2004, 2005, 2006ab, 2007/, while two samples yielded younger ages than expected (adularia and muscovite). Four samples did not yield plateau ages or gave insignificant ages (illite, apophyllite and hornblende).
Reliable ages were obtained for generation � and 4 (wall rock muscovite; 1,417 ± � Ma) and for the greisen related fracture fillings in KLX06 (1,42� ± � Ma, 1,424 ± 2 Ma and 1,424 ± 2 Ma) which shows that these fracture fillings as well as the major part of the red-staining of the wall rock in the area are related to the intrusion of the Götemar granite (and probably also Uthammar granite).
The Palaeozoic generation (6) of fracture fillings was also successfully dated by obtained ages of 401, 426 and 44�–448 Ma, which is in accordance with earlier datings of this generation in the Götemar granite /Sundblad et al. 2004/. This generation is related in time with the Caledonian orogeny and the development of its foreland basin.
Ductile shear zones in the area are thought to predate the intrusions at Götemar and Uthammar (~ 1,440–1,450 Ma). The age obtained for muscovite in a mylonite of generation 1 (1,406 Ma) is, thus, younger that the presumed mylonite formation. The obtained age is thought to represent either re-activation of the mylonites (and formation of muscovite) during the intrusions of the Götemar and Uthammar granites or resetting of the Ar-system in the muscovite due to thermal affect during the emplacement of these intrusions. A K-feldspar of generation � gave a Sveconorwegian age (989 Ma) which is younger than expected. It can either be a generation � K-feldspar that has been reset during the Sveconorwegian orogeny or that the K-feldspar actually was formed during Svegonorwegian reactivation.
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Sammanfattning
I denna rapport presenteras resultat från geokronologiska studier av sprickmineral från borrkärnor från Oskarshamns platsundersökning. Tretton borrkärneprover med kaliummineral (adular, muskovit, illit, apofyllit och hornblände), från både öppna och läkta sprickor, har daterats med hjälp av 40Ar/�9Ar-metoden. Proverna är från borrkärnorna KA1755A (Äspö), KSH01A och KSH0�A+B (Simpevarp) samt KLX02, KLX0�, KLX06 och KLX08 (Laxemar).
Sprickmineral har valts ut för att ge absolut geokronologisk data till den relativa sekvensen av sprickmineraliseringar som är baserad på bl.a. klippande relationer och stabila isotoper /Drake and Tullborg 2004, 2005, 2006ab, 2007/. Sekvensen består av sju olika sprickmineralgeneratio-ner varav generation 1 och 6 har daterats i denna studie. Greisen-liknande fyllningar (troligen likåldriga med generation � and 4) och muskovit från sidoberget relaterad till generation � and 4 har också daterats i denna studie.
Analyserna gav platå-åldrar för tio prover. Sju prover gav förväntade åldrar (adular och muskovit) medan två prover gav lägre åldrar än förväntat (adular och muskovit). Fyra prover gav inga platå-åldrar eller irrelevanta åldrar. De förväntade åldrarna överrensstämmer med tidigare tolkningar baserade på klippande relationer, kemi och isotopstudier etc. /Drake and Tullborg 2004, 2005, 2006ab, 2007/.
Tillförlitliga åldrar gavs för generation � och 4 (muskovit i omvandlat sidoberg; 1 417 ± � Ma) och för de greisenliknande sprickorna i KLX06 (1 42� ± � Ma, 1 424 ± 2 Ma och 1 424 ± 2 Ma), vilket visar att dessa sprickor och även huvuddelen av den utbredda rödfärgningen runt sprickor i området är relaterade till Götemargranitens (och troligen även Uthammargranitens) intrusion.
Den Palaeoziska generationen (6) gav också tillförlitliga åldrar på 401, 426 och 44�–448 Ma, vilket stämmer överrens med tidigare dateringar av denna generation i Götemargraniten /Sundblad et al. 2004/. Tidsmässigt är denna generation relaterad till den Kaledoniska orogenesen och troligen också utvecklingen av en förlandsbassäng.
Myloniterna i området tros vara äldre än inrusionerna av Götemar- och Uthammargraniterna (~ 1 440–1 450 Ma). Åldern av muskovit från en mylonit tillhörande generation 1 (1 406 Ma) antas därför inte representera mylonitbildningen. Istället tros denna ålder representera en reaktivering av myloniterna (och bildning av muskovit) i samband med intrusionerna av Götemar- och Uthammargraniterna eller att Ar-systemet i den daterade muskoviten nollställts i samband med dessa intrusioner. En kalifältspat som tros tillhöra generation � gav en svekonorvegisk ålder (989 Ma). Denna ålder är yngre än förväntat och kan antingen bero på att kalifältspaten tillhör generation � och har nollställts i samband med den svekonorvegiska orogenesen eller att kalifältspaten är svekonorvegisk.
5
Contents
1 Introduction 7
2 Objectiveandscope 9
3 Equipment 11�.1 Description of equipment/interpretation tools 11
4 Execution 1�4.1 Selection of samples 1�4.2 Preparations 1�4.� Execution of field work 1�4.4 Analyses and interpretations 1�4.5 Nonconformities 14
5 Results 155.1 Sample KA1755A: 211.70–211.75 m (muscovite) 155.2 Sample KSH01A: 256.90–257.10 m (adularia) 155.� Sample KSH0�B: 14.97–15.�2(I) m (adularia) 175.4 Sample KSH0�A: 181.9�–181.98 m (adularia) 185.5 Sample KSH0�A: 186.52–186.62 m (illite) 205.6 Sample KSH0�A: 86�.66–86�.84 m (adularia) 215.7 Sample KLX02: 676.82–677.00 m (apophyllite) 2�5.8 Sample KLX0�: 722.72–722.96 m (muscovite) 255.9 Sample KLX0�: 970.04–970.07 m (apophyllite) 275.10 Sample KLX06: 5�5.10–5�5.26 m (muscovite) 295.11 Sample KLX06: 565.22–565.�8 m (muscovite) �05.12 Sample KLX06: 595.08–595.18 m (muscovite) �15.1� Sample KLX08: 9��.15–9��.�0 m (hornblende) �2
6 Summaryanddiscussions �5
7 Acknowledgements �7
8 References �9
Appendix1 40Ar/�9Ar-data 41
7
1 Introduction
This document reports 40Ar/�9Ar dating results from fracture minerals. Samples are from the Laxemar and Simpevarp subareas and Äspö. The work was carried out in accordance with activity plan AP PS 400-06-158. In Table 1-1 controlling documents for performing this activity are listed. Both activity plan and method descriptions are SKB’s internal controlling documents.
A relative, geochronological sequence of fracture minerals based on e.g. cross-cutting relations in about 200 drill core samples from more than 10 different cored boreholes has been established. This sequence comprises seven generations and is common for the Simpevarp and Laxemar sub-areas and Äspö. Detailed descriptions of the fracture mineralogy and the sequences and paragenesis have earlier been reported; Simpevarp subarea /Drake and Tullborg 2004, 2006a/, Laxemar subarea /Drake and Tullborg 2005, 2007/ and Äspö /Drake and Tullborg 2005/. Stable isotope analyses on calcite, pyrite, barite and gypsum and geochemical analyses have further contributed to the subdivision into different fracture mineral generations. The fracture mineral generations grade from relatively high temperature (greenschist facies) to low temperature (zeolite facies down to ambient temperatures). They are summarized in Table 1-2 (modified from/Drake and Tullborg 2007/).40Ar/�9Ar dating has been performed on samples from generation 1, �, 5 and 6 and on muscovite in the red-stained wall rock adjacent to a fracture filled with minerals of generation � and 4. Three samples of coarse-grained muscovite in greisen-like fractures (thought to be coeval with genera-tion �) from KLX06 have also been dated. Each sample is found in Table 1-�.
Table1‑1.Controllingdocumentsfortheperformanceoftheactivity.
Activityplan Number VersionGeokronologisk undersökning av sprickmineral AP PS 400-06-158 1.0
Methoddescriptions Number VersionSprickmineralogi SKB MD 144.000 1.0
Åldersdateringar av mineral och bergarter SKB MD 132.002
Table1‑2.Schematicfracturefilling‑sequencefromSimpevarp/Laxemar/Äspö.Themostabundantmineralsineachgenerationareinboldletters.Mineralsinbracketsareonlyfoundoccasionally.
1. Quartz‑andepidote‑richmylonite, including muscovite, titanite, Fe-Mg-chlorite, albite, (apatite, calcite and K-feldspar)
2. Cataclasitea. Early green coloured; epidote-rich, with quartz,Fe‑Mg‑chlorite, (titanite, K-feldspar, and albite)b. Late red-brown colour; K‑feldspar,chlorite,quartz,hematite, albite, (and illite)3. Euhedral quartz,epidote,Fe‑Mgchlorite,calcite, pyrite, fluorite, muscovite, (K-feldspar and
hornblende)4. Prehnite, (fluorite) 5.a. Calcite, (fluorite and hematite)b. Darkred/brownfilling‑Adularia,Mg‑chlorite,hematite; sometimes cataclastic.c. Calcite,adularia,laumontite,Mg‑chlorite,quartz,illite,hematite, (ML-clay – chlorite/illite,
albite and apatite)6. Calcite,adularia,Fe‑chlorite,hematite,fluorite,quartz,pyrite,barite,gypsum,corrensite
(and other types of mixed-layer clay), harmotome, REE-carbonate, galena, apophyllite, illite, chalcopyrite, sphalerite, U-silicate, Cu(Zn,Ni,Sn,Fe)-rich minerals, apatite, laumontite (Ti-oxide, Mg-chlorite and albite)
7. Calcite, pyrite, Fe-oxyhydroxide (near surface)
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The original results are stored in the primary data base (SICADA) and are traceable by the activity plan number 400-06-158.
Table1‑3.
Sample Datedmineral Generation Report
KA1755A: 211.70–211.75 m Muscovite 1 /Drake and Tullborg 2005/KSH01A: 256.90–257.10 m Adularia 6 /Drake and Tullborg 2004/
KSH03B: 14.97–15.32(I) m Adularia 6 /Drake and Tullborg 2006a/KSH03A: 181.93–181.98 m Adularia 6 /Drake and Tullborg 2006a/KSH03A: 186.52–186.62 m Illite 5 or 6 /Drake and Tullborg 2006a/KSH03A: 863.66–863.84 m Adularia 3 or later /Drake and Tullborg 2006a/KLX02: 676.82–677.00 m Apophyllite 6 /Drake and Tullborg 2005/KLX03: 722.72–722.96 m Muscovite 3 or 4 (wall rock) /Drake and Tullborg 2007/KLX03: 970.04–970.07 m Apophyllite 6 /Drake and Tullborg 2007/KLX06: 535.10–535.26 m Muscovite Greisen fractures /Drake and Tullborg 2007/KLX06: 565.22–565.38 m Muscovite Greisen fractures /Drake and Tullborg 2007/KLX06: 595.08–595.18 m Muscovite Greisen fractures /Drake and Tullborg 2007/KLX08: 933.15–933.30 m Hornblende 3 /Drake and Tullborg 2007/
Figure 1‑1. General overview of the Simpevarp site investigation area, with cored and percussion drill holes shown. Drill hole KA1755A is not shown (it is from the tunnel at Äspö).
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2 Objectiveandscope
The objective is to provide absolute geochronological constraints for the relative sequence of fracture generations that has been established in the Simpevarp area /Drake and Tullborg 2004, 2005, 2006a, 2007/ and thereby contribute to the interpretation of the geological evolution of the area.
This report presents the data obtained from 40Ar/�9Ar dating but no detailed interpretation of the geological evolution is reported.
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3 Equipment
3.1 Descriptionofequipment/interpretationtools• Rock saw
• Swing mill
• Tweezers
• Digital camera
• Petrographic Microscope (Leica DMRXP)
• Binocular microscope (Leica MZ12)
• Digital microscope camera (Leica DFC 280)
• Scanning electron microscope (HITACHI S-�400N)
• EDS-detector (INCADryCool)
All the equipment described above is property of the Earth Sciences Centre, Göteborg University, Sweden. For the geochronological analyses the following equipment was used:
• Micromass 5400 mass spectrometer (Lund University, Sweden)
• New Wave Research 50W CO2 laser facility (Lund University, Sweden)
1�
4 Execution
4.1 SelectionofsamplesThe selection of samples for dating is a delicate issue. Pure minerals that can be found in paragenesis are difficult to sample. Instead several minerals, sometimes from several generations found in the same fracture are the common case. Before the selection of samples for geochronological analyses, thin sections and fracture surface samples were examined using binocular microscope, petrographic microscope and scanning electron microscope (SEM-EDS) in order to identify suitable fracture minerals. The samples finally selected belonged to drill cores from KA17755A, KSH01A, KSH0�A+B, KLX02, KLX0�, KLX06 and KLX08.
4.2 PreparationsFrom sealed fractures, the fracture filling was separated from the wall rock using a rock saw and then crushed manually with a hammer or the fracture filling was removed from the sample with a knife. The fragments were put in a swing mill for a few seconds to obtain small grains made up of individual mineral phases. The mineral was then handpicked with tweezers under a binocular microscope.
Apophyllite crystals were handpicked from the fracture surface under a binocular microscope.
4.3 ExecutionoffieldworkSamples have been selected from drill cores from the cored boreholes KLX02, KA17755A, KSH01A, KSH0�A+B, KLX0�, KLX06 and KLX08 during the sampling for the detailed fracture mineralogy studies (activities AP PS 400-0�-045, AP PS 400-05-05� and AP PS 400-05-074).
4.4 AnalysesandinterpretationsThe samples selected for 40Ar/�9Ar geochronology were irradiated together with the 28.�4 TCR sanidine standard (28.�4 Ma recalculated following /Renne et al. 1998/, for �5 hours at the NRG-Petten HFR RODEO facility in the Netherlands. J-Values were calculated with a precision of 0.25%.
The 40Ar/�9Ar geochronology laboratory at Lund University contains a Micromass 5400 mass spectrometer with a Faraday and an electron multiplier. A metal extraction line, which contains two SAES C50-ST101 Zr-Al getters and a cold finger cooled to ca –155°C by a Polycold P100 cryogenic refrigeration unit, is also present. One or two grains of adularia were loaded into a copper planchette that consists of several � mm holes. Samples were step-heated using a defocused 50W CO2 laser. Sample clean-up time that made use of the two hot Zr-Al SAES getters and a cold finger with a Polycold refrigeration unit was five minutes. The laser was rastered over the samples to provide even-heating of all grains. The entire analytical process is automated and runs on a Macintosh-steered OS 10.2 with software modified specifically for the laboratory at Lund University. The software was originally developed at the Berkeley geochronology Centre (Al Deino). 18 Time zero regressions were fitted to data collected from 10 scans over the mass range of 40 to �6. Peak heights and backgrounds were corrected for mass discrimination, isotopic decay and interfering nucleogenic Ca-, K-, and Cl-derived
14
isotopes. Isotopic production values for the cadmium-lined position in the Petten reactor are �6Ar/�7Ar(Ca) = 0.000270, �9Ar/�7Ar(Ca) = 0.000699, and 40Ar/�9Ar(K) = 0.0018�. 40Ar blanks were calculated before every new sample and after every three sample steps. 40Ar blanks were between 6.0–�×10–16. Blank values for masses �9–�6 were all less than 7×10–18. Blank values were subtracted for all incremental steps from the sample signal. The laboratory was able to produce very good incremental gas splits, using a combination of increasing time at the same laser output, followed by increasing laser output. Age plateaus were determined using the criteria of /Dalrymple and Lanphere 1971/, which specify the presence of at least three contiguous incremental heating steps with statistically indistinguishable ages and constituting greater than 50% of the total �9Ar released during the experiment.
4.5 NonconformitiesThree of the samples did not yield plateau ages and one sample gave a very unrealistic age (too young).
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5 Results
5.1 SampleKA1755A:211.70–211.75m(muscovite)The sample consists of mylonite (generation 1) from the Äspö Shear Zone (ZSMNE005A). Minerals present are muscovite, quartz, epidote, K-feldspar, albite and some titanite. The mylonite is cut by a fracture filled with calcite, fluorite and hematite.
The plateau age of muscovite defined on the 40Ar/�9Ar step-heating spectrum is 1 406 ± � Ma (Figure 5-2). This age is however younger than expected. The mylonites in the area are commonly thought to be older than the granite intrusions at Götemar (1,452 +11/–9 Ma, /Åhäll 2001/) and Uthammar (1,441 +5/–� Ma, /Åhäll 2001/) nearby /Nisca 1987, Talbot and Riad 1988/. The age obtained for the muscovite from drill core KA1755A may thus represent re-activation of the mylonite and formation of muscovite at the time of the intrusion of these granites. However, it is more likely that the muscovite existed before the intrusions of the granites and that the obtained age represents heating of the muscovite above its Ar-blocking temperature (~ �50°C) in connection with the intrusions of the Götemar and Uthammar granites.
5.2 SampleKSH01A:256.90–257.10m(adularia)The adularia is found in sealed fractures (generation 6) together with calcite, Mg-rich chlorite, Fe-rich chlorite, pyrite etc. These fractures cut through brown-coloured cataclasite, which is composed of adularia, Mg-rich chlorite and hematite.
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 425.8±1.7 Ma (Figure 5-5). The age is interpreted as the crystallization age of the adularia.
Figure 5‑1. KA1755A: 211.70–211.75 m. Mylonite (generation 1), cut by a fracture filled with calcite (white), fluorite and hematite.
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Figure 5‑2. 40Ar/39Ar muscovite step-heating spectrum for sample KA1755A: 211.70–211.75 m.
Figure 5‑3. Sample KSH01A: 256.90–257.10 m. Sealed fractures (generation 6), filled with calcite, adularia, Mg-chlorite, Fe-chlorite and pyrite etc. are cutting through brown-coloured cataclasite.
Figure 5‑4. Sample KSH01A: 256.90–257.10 m. Back-scattered SEM-image of adularia and Fe-rich chlorite (Fe-chl).
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5.3 SampleKSH03B:14.97–15.32(I)m(adularia)Sealed fracture mainly filled with adularia and subordinate calcite and hematite.
The plateau ages defined on the 40Ar/�9Ar step-heating spectrums are 44�.� ± 1.2 Ma (Split 1, Figure 5-8) and 448.0 ± 1.2 Ma (Split 2, Figure 5-9). The age span of 44�–448 Ma is interpreted as the crystallization age of the adularia. This age span is consistent with the “warm brine” origin of co-precipitated calcite, revealed by stable isotope analysis (C and O). These fluids were interpreted to have formed during the Palaeozoic /Drake and Tullborg 2006a/.
Figure 5‑5. 40Ar/39Ar adularia step-heating spectrum for sample KSH01A: 256.90–257.10 m.
Figure 5‑6. Sealed fracture filled with adularia, calcite and hematite.
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5.4 SampleKSH03A:181.93–181.98m(adularia)The sample consists of sealed fractures of several generations. The first generation is cataclasite (generation 2) which is cut by calcite-filled fractures (generation �). The latest formed fractures are filled with adularia (generation 6) and laumontite. It is difficult to discern in thin-section if adularia and laumontite are coeval. There exist fragments of calcite within the adularia filling. This calcite has stable isotope ratios which are similar to generation �–4 calcite.
Figure 5‑7. Back-scattered SEM-image of adularia in the sealed fracture.
Figure 5‑8. 40Ar/39Ar adularia step-heating spectrum for sample KSH03B: 14.97–15.32(I) m. Split 1.
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Figure 5‑9. 40Ar/39Ar adularia step-heating spectrum for sample KSH03B: 14.97–15.32(I) m. Split 2.
Figure 5‑10. Cataclasite (generation 2, red-brown coloured, left) is cut by calcite-filled fractures (generation 3, white colour). The latest formed fractures are filled with adularia (generation 6) and laumontite,(orange colour).
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 400.9 ± 1.1 Ma (Figure 5-12). The plateau age is interpreted as the crystallization age of the adularia and is a maximum age of the laumontite in the same fracture since the laumontite is found in the centre of the adularia-coated fracture.
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5.5 SampleKSH03A:186.52–186.62m(illite)A dark green illite-rich fracture filling is cut by sealed fractures filled with calcite (“warm brine” origin) and small amounts of adularia.
The illite sample did not yield a plateau age. However, the integrated age (488.5±1.1 Ma, Figure 5-14) defined on the 40Ar/�9Ar step-heating spectrum might give a speculative indication of the age of the mineral /cf. p. �6–�7 in McDougall and Harrison 1999/. The integrated age for the illite would be reasonable since it is cut by Palaeozoic calcite of generation 6, a generation that is dated to 400–448 Ma (this report and /Sundblad et al. 2004/).
Figure 5‑11. Photomicrograph of adularia and laumontite (at the right arrow in Figure 5-10 above).
Figure 5‑12. 40Ar/39Ar adularia step-heating spectrum for sample KSH03A: 181.93–181.98 m.
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5.6 SampleKSH03A:863.66–863.84m(adularia)The sample consists of a more than 20 centimetre wide light green mylonite/cataclasite (genera-tion 1 or 2) including wall rock fragments. Two sets of thin (< 1 millimetre) fractures cut the mylonite/cataclasite. The mylonite/cataclasite matrix consists of about 80–90% of fine-grained epidote and the rest is K-feldspar and quartz.
The fractures cutting the mylonite/cataclasite are filled with K-feldspar (probably adularia), quartz and occasionally chlorite. When chlorite, K-feldspar and quartz appear in the same fracture, the chlorite is present in the centre of the fracture whereas the K-feldspar and quartz coat the fracture walls. The chlorite is of Fe-Mg-type (as common in generation � and earlier).
Figure 5‑13. Dark green illite-rich fracture filling cut by sealed fractures filled with calcite and small amounts of adularia.
Figure 5‑14. 40Ar/39Ar illite step-heating spectrum for sample KSH03A: 186.52–186.62 m.
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The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 989 ± 2 Ma (Figure 5-17). The left hand side of the spectrum most likely indicates slow cooling of multi diffusion domain K-feldspars. The plateau age can be interpreted as either crystallization of the K-feldspar or complete resetting of an older K-feldspar during a Sveconorwegian event. This means that it can either be a generation � K-feldspar that has been reset or that the K-feldspar was formed in connection with the Sveconorwegian orogeny (this K-feldspar is classified as a generation � mineral, based on the chemistry of the related chlorite).
Figure 5‑15. K-feldspar (red), quartz and chlorite (black) in fractures that cut through mylonite/cataclasite. Photograph from a sawed piece of the sample.
Figure 5‑16. Microphotograph of adularia and quartz in fractures that cut through mylonite/cataclasite.
2�
5.7 SampleKLX02:676.82–677.00m(apophyllite)Open fracture coated by euhedral apophyllite and barite of generation 6.
The sample yielded plateau ages (two splits, Figures 5-19 and 5-20) but these ages are much lower than expected and this is probably due to the observed decomposition of the apophyllite during the analyses. These ages are thus considered to be insignificant.
Figure 5‑17. 40Ar/39Ar adularia step-heating spectrum for sample KSH03A: 863.66–863.84 m.
Figure 5‑18. Sample KLX02: 676.82–677.00 m.
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Figure 5‑20. 40Ar/39Ar apophyllite step-heating spectrum for sample KLX02: 676.82–677.00 m. Split 2.
Figure 5‑19. 40Ar/39Ar apophyllite step-heating spectrum for sample KLX02: 676.82–677.00 m. Split 1.
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5.8 SampleKLX03:722.72–722.96m(muscovite)The fracture filling is 10–15 mm thick and consists of dominantly Fe-Mg chlorite, quartz and calcite (generation �). The fracture has later been re-activated and a 5 millimetre wide fracture filled with prehnite (generation 4) cuts through the chlorite-quartz-calcite filling.
The wall rock is bleached close to the filled fracture, and more reddish 1–2 centimetres away from the fracture. The colour in these sections depends on the features of the plagioclase altera-tion; 1) in the red coloured part the pseudomorphs after plagioclase consist of albite, K-feldspar, muscovite (sericite) and prehnite. The red colour originates from minute hematite crystals in micro-pores in the secondary minerals in the pseudomorphs after plagioclase. 2) In the bleached parts, the plagioclase pseudomorphs consist of albite, prehnite and euhedral muscovite.
Most biotite is replaced by chlorite. The dated sample consists of muscovite from pseudomorphs after plagioclase in the bleached part of the rock. The bleaching and red-staining of the wall rock are thought to be related to the same event because many fractures filled with minerals of one generation only (often prehnite) show bleached rock close to the fracture and red-stained rock further away from the fracture. The different colours (bleached or red-stained) may depend on distance from the fracture, temperature, or fluid chemistry etc.
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 1,417 ± � Ma (Figure 5-2�). It is interpreted as the crystallization age of the muscovite. This is also thought to be the age of the fracture minerals of generations � and 4 (epidote, chlorite, quartz, calcite, prehnite). The assumption that generations � and 4 are of essentially the same age is based on that both genera-tions fill fractures bordered by red-stained wall rock and, furthermore, the two generations show identical stable and Sr isotope results for calcites /Drake and Tullborg 2006a, 2007/. The obtained age of these fillings indicate that they are related to the intrusions (or post-magmatic fluid circulation) of the Götemar and Uthammar granites as shown by e.g. ages of muscovite in greisen-like fractures closer to the Götemar granite (see Section 5.9, 5.10, 5.11). The age of the muscovite also indicate that the major part of the extensive red-staining of the rocks in the area, studied by /Eliasson 199�, Drake and Tullborg 2006cd/, is related to these intrusions and/or related post-magmatic circulation.
Figure 5‑21. Photograph of the drill core showing a fracture sealed with calcite, quartz and chlorite and subsequently prehnite. The red-stained wall rock is bleached close to the fracture, due to a high amount of muscovite in the altered plagioclase.
26
Figure 5‑22. Photomicrograph of an altered plagioclase crystal with muscovite crystals in it.
Figure 5‑23. 40Ar/39Ar muscovite step-heating spectrum for sample KLX03: 722.72–722.96 m.
27
5.9 SampleKLX03:970.04–970.07m(apophyllite)The sample consists of an open fracture coated by euhedral apophyllite of generation 6. Small amounts of calcite and barite are also present. The sample did not yield a plateau age.
Figure 5‑24. Photograph of the fracture surface covered with apophyllite.
Figure 5‑25. Back-scattered SEM-image of apophyllite on the fracture surface. Scale marker is ~ 200 µm.
28
Figure 5‑26. 40Ar/39Ar apophyllite step-heating spectrum for sample KLX03: 970.04–970.07 m. Split 1.
Figure 5‑27. 40Ar/39Ar apophyllite step-heating spectrum for sample KLX03: 970.04–970.07 m. Split 2.
29
5.10 SampleKLX06:535.10–535.26m(muscovite)Sealed fracture (2–� cm wide) coated by coarse-grained muscovite and filled with coarse-grained pyrite and small amounts of calcite. Diffuse contact to the wall rock, which is strongly sericitized.
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 1,424 ± 2 Ma (Figure 5-29). It is interpreted as the crystallization age of the muscovite. This age shows that these fillings are related to the intrusion (and/or post-magmatic circulation) of the Götemar granite. The somewhat lower age (minimum ~ 20 Ma) for the muscovite than for the intrusion of the Götemar granite (1,452 +11/–9 Ma, /Åhäll 2001/) might be due to formation of muscovite related to post-magmatic circulation and that the closure temperature for Ar is quite low in muscovite (~ �50°C).
Figure 5‑28. Photograph of the drill core showing a fracture sealed with muscovite, pyrite, quartz and calcite (not visible in the photograph).
Figure 5‑29. 40Ar/39Ar muscovite step-heating spectrum for sample KLX06: 535.10–535.26 m.
�0
5.11 SampleKLX06:565.22–565.38m(muscovite)Sealed fracture (about 10 cm wide), filled with coarse-grained quartz, muscovite and fluorite. Diffuse contact to the wall rock, which is strongly sericitized.
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 1,42� ± � Ma (Figure 5-�1). It is interpreted as the crystallization age of the muscovite. This age shows that these fillings are related to the intrusion (and/or post-magmatic circulation) of the Götemar granite. The somewhat lower age (minimum ~ 20 Ma) for the muscovite than for the intrusion of the Götemar granite (1,452 +11/–9 Ma, /Åhäll 2001/) might be due to formation of muscovite related to post-magmatic circulation and that the closure temperature for Ar is quite low in muscovite (~ �50°C).
Figure 5‑30. Photograph of the drill core showing a fracture sealed with muscovite, quartz and fluorite.
Figure 5‑31. 40Ar/39Ar muscovite step-heating spectrum for sample KLX06: 565.22–565.38 m.
�1
5.12 SampleKLX06:595.08–595.18m(muscovite)Sealed fracture (about 2–� cm wide), bordering to a presently open fracture. The wall rock is strongly sericitized.
Quartz, muscovite and fluorite are coarse-grained and the dominating minerals in this sample. Muscovite is coating the fracture and quartz is found in the centre of the fracture. Other minerals (e.g. topaz, Ti-oxide, chalcopyrite, barite, Fe-oxide, Fe-Mg chlorite, sphalerite, sylvite, halite, native gold, and albite) are found in small amounts.
The plateau age defined on the 40Ar/�9Ar step-heating spectrum is 1,424 ± 2 Ma (Figure 5-��). It is interpreted as the crystallization age of the muscovite. This age shows that these fillings are related to the intrusion (and/or post-magmatic circulation) of the Götemar granite. The somewhat lower age (minimum ~ 20 Ma) for the muscovite than for the intrusion of the Götemar granite (1,452 +11/–9 Ma, /Åhäll 2001/) might be due to formation of muscovite related to post-magmatic circulation and that the closure temperature for Ar is quite low in muscovite (~ �50°C).
Figure 5‑32. Photograph of the drill core showing a fracture sealed with mainly muscovite, quartz and fluorite.
Figure 5‑33. 40Ar/39Ar muscovite step-heating spectrum for sample KLX06: 595.08–595.18 m.
�2
5.13 SampleKLX08:933.15–933.30m(hornblende)The sample shows sealed fractures boarded by red-stained wall rock. Minerals in the fractures are hornblende (most abundant), calcite, titanite (occasionally euhedral), K-feldspar, Fe-Mg chlorite, (magnetite, pyrite, albite and epidote). These minerals are thought to be of generation �. The sample did not yield a plateau age.
Figure 5‑34. Photograph of the drill core showing fractures sealed with mainly hornblende, calcite, K-feldspar and chlorite.
Figure 5‑35. Back-scattered SEM-image of hornblende (“Hbl”) and calcite (darker than hornblende) in a sealed fracture.
��
Figure 5‑36. 40Ar/39Ar hornblende step-heating spectrum for sample KLX08: 933.15–933.30 m.
�5
6 Summaryanddiscussions
The analyses yielded plateau ages for ten samples (Table 6-1). Seven samples yielded ages (adularia and muscovite) in accordance with interpretations from cross-cutting relations, chemistry and isotope studies /Drake and Tullborg 2004, 2005, 2006a,b, 2007/ while two samples yielded younger ages than expected (adularia and muscovite). Four samples did not yield plateau ages or gave insignificant ages (illite, apophyllite and hornblende). Ages were obtained for generation �, 4 and 6 (Table 6-2). The ages for generation � and 4 are also valid for some fillings from generation 5 based on similar wall rock alteration features and stable isotopes. This also provides age constraints for the extensive red-staining of the wall rock in the area.
The mylonites in the area are thought to predate the intrusions of the Götemar and Uthammar granites (~ 1,440–1,450 Ma). The age obtained for muscovite (1,406 Ma) in a mylonite of generation 1 is, thus, not thought to represent the age of the mylonite formation. Instead, the obtained age is thought to represent either re-activation of the mylonites (and formation of muscovite) during the intrusions of the Götemar and Uthammar granites or resetting of the Ar-system in the dated muscovite due to thermal heating of the country rocks during these intrusions. A generation � K-feldspar gave a Sveconorwegian age (989 Ma) which is younger than expected. It can either be a generation � K-feldspar that has been reset in connection with the Sveconorwegian orogeny or that the K-feldspar was formed during Sveconorwegian reactivation.
Reliable ages were obtained for generation � and 4 and for the greisen related fractures in KLX06, which shows that these fracture fillings are related to the intrusion of the Götemar granite (and probably also Uthammar granite). It is also indicated that mylonites were re-activated at this event.
The Palaeozoic generation (6) was also adequately dated (401, 426 and 44�–448 Ma for adularia), which is in accordance with earlier datings of this generation in the Götemar granite /Sundblad et al. 2004/. This generation is related in time to the Caledonian orogeny and probably also to its migrating foreland basin.
The results from this study indicate that the bedrock in the area has not been heated to tempera-tures higher than the blocking temperature for muscovite (~ �50°C) since about 1,400 Ma.
Table6‑1.
Sample Mineral Result(Ma)Split1
Result(Ma)Split2
Generation/DrakeandTullborg2007/
KA1755A: 211.70–211.75 m Muscovite 1,406 ± 3 1KSH01A: 256.90–257.10 m Adularia 425.8 ± 1.7 6
KSH03B: 14.97–15.32(I) m Adularia 443.3 ± 1.2 448.0 ± 1.2 6KSH03A: 181.93–181.98 m Adularia 400.9 ± 1.1 6KSH03A: 186.52–186.62 m Illite No plateau 5 or 6KSH03A: 863.66–863.84 m Adularia 989 ± 2 3 or laterKLX02: 676.82–677.00 m Apophyllite No significant age No significant age 6KLX03: 722.72–722.96 m Muscovite 1,417 ± 3 3 or 4 (wall rock)KLX03: 970.04–970.07 m Apophyllite No plateau No plateau 6KLX06: 535.10–535.26 m Muscovite 1,424 ± 2 Greisen fracturesKLX06: 565.22–565.38 m Muscovite 1,423 ± 3 Greisen fracturesKLX06: 595.08–595.18 m Muscovite 1,424 ± 2 Greisen fracturesKLX08: 933.15–933.30 m Hornblende No plateau 3
�6
Table6‑2.Schematicfracturefilling‑sequencefromSimpevarp/Laxemar/Äspöwithagesfromthisreport.Themostabundantmineralsineachgenerationareinboldletters.Mineralsinbracketsareonlyfoundoccasionally.
1. Quartz‑andepidote‑richmylonite, including muscovite, titanite, Fe-Mg-chlorite, albite, (apatite, calcite and K-feldspar) } > 1.45 Ga. Re-activated during
intrusion of the Götemar granite
2. Cataclasite } Probably older than 1.45 Gaa. Early green coloured; epidote-rich, with quartz,
Fe‑Mg‑chlorite, (titanite, K-feldspar, and albite)b. Late red-brown colour; K‑feldspar,chlorite, quartz,
hematite, albite, (and illite)3. Euhedral quartz,epidote,Fe‑Mgchlorite,
calcite, pyrite, fluorite, muscovite, (K-feldspar and hornblende) } Probably ~ 1.424–1.417 Ga,
related to the intrusion of the Götemar granite
4. Prehnite,(fluorite) 5. }a. Calcite, (fluorite and hematite) ~ 1.424–0.44 Ga, some fillings
(e.g. earliest formed laumontite) is related to the intrusion of the Götemar granite. Some may be Sveconorwegian and some later (possibly Paleozoic)
b. Darkred/brownfilling–Adularia,Mg‑chlorite,hematite; sometimes cataclastic.
c. Calcite,adularia,laumontite,Mg‑chlorite,quartz,illite,hematite, (ML-clay – chlorite/illite, albite and apatite)
6. Calcite,adularia,Fe‑chlorite,hematite,fluorite,quartz,pyrite,barite,gypsum,corrensite (and other types of mixed-layer clay), harmotome, REE-carbonate, galena, apophyllite, illite, chalcopyrite, sphalerite, U-silicate, Cu(Zn,Ni,Sn,Fe)-rich minerals, apatite, laumontite (Ti-oxide, Mg-chlorite and albite)
} ~ 0.44–0.40 Ga (Paleozoic)
7. Calcite, pyrite, Fe-oxyhydroxide (near surface) } ~ 0.40 Ga and later, possibly recent
�7
7 Acknowledgements
SKB is thanked for funding. Sven Åke Larson and Carl-Henric Wahlgren are thanked for providing useful comments. Björn Sandström and Tobias Hermansson are thanked for construc-tive discussions.
�9
8 References
DalrympleGB,LanphereMA, 1971. 40Ar/49Ar technique of K-Ar dating: a comparison with the conventional technique., Earth and Planetary Science Letters, 12, p �00-�08.
DrakeH,TullborgE-L,2004.Oskarshamn site investigation. Fracture mineralogy and wall rock alteration, results from drill core KSH01A+B. SKB-P-04-250. 120 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2005. Oskarshamn site investigation.Fracture mineralogy and wall rock alteration, results from drill cores KAS04, KA1755A and KLX02. SKB-P-05-174. 69 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2006a. Oskarshamn site investigation. Fracture mineralogy, Results from drill core KSH0�A+B. SKB P-06-0�. 65 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2006b. Oskarshamn site investigation. Fracture mineralogy of the Götemar granite, Results from drill cores KKR01, KKR02 and KKR0�. SKB P-06-04. 61 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2006c. Oskarshamn site investigation. Mineralogical, chemical and redox features of red-staining adjacent to fractures, Results from drill cores KSH01A+B and KSH0�A+B. SKB P-06-01. 115 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2006d. Oskarshamn site investigation. Mineralogical, chemical and redox features of red-staining adjacent to fractures, Results from drill core KLX04. SKB P-06-02. 105 pp. Svensk Kärnbränslehantering AB.
DrakeH,TullborgE-L,2007. Oskarshamn site investigation. Fracture mineralogy, Results from drill cores KLX0�, KLX04, KLX06, KLX07A, KLX08 and KLX10A. Oskarshamn site investigations. SKB P-06-XX. pp. Svensk Kärnbränslehantering AB (in press).
EliassonT,1993. Mineralogy, geochemistry and petrophysics of red coloured granite adjacent to fractures. SKB TR-9�-06. 68 pp. Svensk Kärnbränslehantering AB.
McDougallI,HarrisonMT,1999. Geochronology and Thermochronology by the 40Ar/�9Ar Method, Second edition. Oxford University Press. Oxford, 269 pp.
NiscaDH,1987. Aerogeophysical interpretation: bedrock and tectonic analysis. SKB PR-25-87-04. pp. Svensk Kärnbränslehantering AB.
RennePR,SwisherCC,DeinoAL,KarnerDB,OwenaTL,DePaoloDJ, 1998. Intercalibration of standards, absolute ages and uncertainties in 40Ar/49Ar dating., Chemical Geology, 145, p. 117–152.
SundbladK,AlmE,HuhmaH,VaasjokiM,SollienDB, 2004. Early Devonian tectonic and hydrothermal activity in the Fennoscandian Shield; evidence from calcite-fluorite-galena mineralization, In: Mertanen S (ed), Extended abstracts, 5th Nordic Paleomagnetic workshop. -Supercontinents, remagnetizations and geomagnetic modelling., Geological Survey of Finland, p 67–71.
TalbotC,RiadL,1988. Natural fractures in the Simpevarp area. PR-25-87-0�. 28 pp. Svensk Kärnbränslehantering AB.
ÅhällK-I,2001. Åldersbestämning av svårdaterade bergarter i sydöstra Sverige. SKB R-01-60. 28 pp. Svensk Kärnbränslehantering AB.
41
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1.15
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1.82
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1619
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0.02
267
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21.
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92.
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316
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031.
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2.74
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3.94
114
1.58
501
1619
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2.76
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296
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432.
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2.85
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197
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81.
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0.0
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11.
811
2.68
361
1.55
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2.4
100
99.9
1,42
3.42
773
1.07
836
Inte
g. A
ge =
1,42
33
(•) P
late
au A
ge =
95.4
1,42
42
4�
KLX
03:9
70,R
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Apo
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lite
Run
IDPw
r/T°C
Ca/
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Ar(
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40* A
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Ar
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Cum
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40A
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ge(M
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Age
1620
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2.4
3.90
791
0.00
0688
78.2
1.67
648
2.61
29E
+13
24.7
24.7
97.4
31.9
5642
0.37
226
1620
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2.7
3.98
817
0.00
0578
95.1
2.35
636
5.11
56E
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48.3
7399
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540.
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116
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94.
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80.
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21.
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63.
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23.
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392.
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216
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662.
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323
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098
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210.
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Age
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03:9
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Run
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r/T°C
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1620
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35.
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34.
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140.
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810.
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22.
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310
097
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Age
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1621
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080.
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241.
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32.
610
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1.24
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1621
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1510
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1621
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1.09
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216
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6.01
334
0.97
906
1621
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0.07
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142.
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711.
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100
956.
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7.8
66.0
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227
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1.22
768
0.99
099
1621
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4.8
0.04
062
0.00
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0.8
66.6
6445
9.65
18E
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1.7
28.8
99.7
968.
5537
81.
2668
316
21-0
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0.05
516
0.00
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1.5
66.4
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1.10
49E
+13
230
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5.98
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1.34
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466
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132
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7.50
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862.
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751.
3637
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535
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6.72
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397
1621
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0.03
294
0.00
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1.7
66.8
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1.08
64E
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237
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0.63
776
0.92
927
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60.
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90.
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351.
467
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831.
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33.
140
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3.40
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0.85
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1621
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0.04
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0.8
68.4
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34.
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291.
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Age
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52
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late
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989
2
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03:1
86,R
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0001
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Run
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1622
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1.8
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278
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5.79
320.
4254
216
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0.06
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297.
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560.
324
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062.
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2.6
0.05
924
0.00
1363
0.6
30.4
5401
5.70
49E
+13
1220
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7.19
925
0.49
524
1622
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2.8
0.05
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0.7
31.2
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181.
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328.
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562.
531
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84.
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310
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3.90
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91.
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0.52
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4.4
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3.7
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5.6
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128
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561.
4758
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33.
180
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9.86
654
0.63
476
1622
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6.5
0.26
485
0.00
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8.1
28.1
326
2.18
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34.
685
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3.17
761
0.52
659
1622
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90.
1647
0.00
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5.7
27.4
8569
2.76
22E
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90.9
99.6
463.
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90.
4936
616
22-0
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820.
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5312
26.5
8513
4.31
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39.
110
099
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0.13
682
0.42
814
Inte
g. A
ge =
488.
51.
1
KSH
01:2
57,R
unID
#16
40‑0
1(J
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0001
2):
Ksp
arR
unID
Pwr/T
°CC
a/K
36A
r/39A
r%
36A
r(C
a)40
* Ar/39
Ar
Mol
39A
r%
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pC
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Ar*
Age
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1640
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2.2
0.06
037
0.00
1292
0.6
22.2
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1.03
98E
+14
15.8
15.8
98.3
383.
2405
10.
7191
316
40-0
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60.
0330
30.
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061.
123
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026.
9765
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310
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4.15
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4212
1640
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•3.4
0.01
737
0.00
0125
1.9
25.0
1283
1.98
6E+1
430
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6.42
101
1.00
814
1640
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•3.8
0.02
504
0.00
0136
2.5
25.0
2787
1.40
77E
+14
21.4
77.9
99.8
426.
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51.
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90.
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791.
824
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631.
1383
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2.98
338
1.63
328
1640
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70.
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60.
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090.
525
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43.
1496
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34.
810
099
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8.05
266
1.01
212
Inte
g. A
ge =
417.
31.
3(•
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teau
Age
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.842
5.8
1.7
46
KLX
03:7
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unID
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41‑0
1(J
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66±
0.0
0001
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c/Se
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Run
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1641
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3755
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0.91
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1.41
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317.
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3.65
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1.9
0.16
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1.8
110.
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19.
1525
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29.
211
99.7
1,40
2.51
874
1.45
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327
0.00
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0.9
111.
8937
32.
1621
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321
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416.
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61.
167
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0.04
095
0.00
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1.6
112.
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14.
1838
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342
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99.9
1,41
7.52
769
0.90
363
1641
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2.5
0.04
188
0.00
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27.9
110.
3354
91.
0421
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310
.585
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402.
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1.42
537
1641
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2.7
0.16
215
0.00
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2.8
110.
4524
46.
0325
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26.
191
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403.
8283
72.
3446
916
41-0
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90.
1465
70.
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872.
910
6.66
049
2.33
94E
+12
2.4
93.9
99.8
1,37
0.02
229
8.74
8916
41-0
1I3.
20.
3346
30.
0011
154.
110
5.71
808
6.02
71E
+12
6.1
100
99.7
1,36
1.52
129
1.54
079
Inte
g. A
ge =
1,40
73
(•) P
late
au A
ge =
641,
417
3
KLX
06:5
65,R
unID
#16
43‑0
1(J
=0
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66±
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Age
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ge
1643
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0.00
744
0.00
6624
011
2.60
289
4.94
18E
+13
40.1
40.1
98.3
1,42
2.72
231.
4361
816
43-0
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0095
50.
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950.
211
2.70
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4.18
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+13
33.9
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423.
6325
71.
5243
416
43-0
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30.
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620.
211
2.53
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2.38
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319
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1212
81.
3063
716
43-0
1E•3
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2885
60.
0063
680.
611
3.18
417
9.50
24E
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0.8
94.2
98.4
1,42
7.79
573
8.91
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1643
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0.07
208
0.00
1424
0.7
112.
3833
77.
1995
E+1
25.
810
099
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420.
8026
91.
9867
4In
teg.
Age
=1,
423
3(•
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teau
Age
=10
01,
423
3
47
KLX
08:9
33,R
unID
#16
42‑0
1(J
=0
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66±
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0001
2):
Hor
nble
nde
Run
IDPw
r/T°C
Ca/
K36
Ar/39
Ar
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Ar(
Ca)
40* A
r/39A
rM
ol39
Ar
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tep
Cum
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40A
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a)±
Age
1642
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1.5
1.89
616
1.20
3062
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440.
0608
6.85
89E
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0.1
0.1
87.3
5,94
6.68
225
7.73
308
1642
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1.7
1.65
990.
1406
060.
240
4.77
883
2.47
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0.3
0.4
90.7
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3.75
095
3.26
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1642
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1.9
5.82
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0.01
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5.6
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31.
82.
296
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309.
4528
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4710
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131.
5467
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311
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2.5
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3.42
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4.5
11.9
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1,10
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1642
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2.7
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118
97.1
1,22
2.20
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1.60
575
1642
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2.8
8.62
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13.9
106.
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54.
2802
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35.
723
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1,37
0.38
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2.04
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1642
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2.9
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23.7
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33.
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34.
628
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334.
5952
31.
1313
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11.6
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26.7
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34.
9262
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36.
534
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330.
8826
91.
9654
1642
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3.1
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35.7
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9230
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34.
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5744
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572.
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33.
647
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184.
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2840
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53.
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238
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362.
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1.33
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5138
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393.
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4842
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72.
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7536
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4532
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222.
2824
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1.37
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1642
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3.9
2.47
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39.6
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2.31
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1135
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92.
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1.24
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1642
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4.5
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8861
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32.
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243.
2465
1.23
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1642
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4.7
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1227
35.1
93.5
7912
2.14
05E
+13
2.8
80.7
99.7
1,24
8.28
277
0.84
397
1642
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4.9
2.98
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1.53
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+13
282
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244.
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30.
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916
42-0
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12.
5497
40.
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541
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451.
8535
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32.
585
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245.
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30.
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916
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20.
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340
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181.
4748
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32
87.1
99.6
1,27
7.24
975
1.08
6716
42-0
1AA
5.5
3.80
904
0.00
113
46.4
96.8
6355
1.38
15E
+13
1.8
88.9
99.8
1,27
9.62
969
0.99
708
1642
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73.
4384
60.
0009
947
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018.
7607
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21.
290
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273.
5684
91.
3067
916
42-0
1AC
62.
3506
60.
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4338
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241.
044E
+13
1.4
91.5
99.8
1,26
7.35
115
2.98
555
1642
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D7
2.90
097
0.00
1012
39.5
98.0
5727
1.18
22E
+13
1.6
9399
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290.
8891
21.
1355
416
42-0
1AE
104.
750.
0013
8447
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1.12
85.
2486
E+1
37
100
99.8
1,31
9.53
395
1.24
532
Inte
g. A
ge =
1,27
32
48
KLX
02:6
76,R
unID
#16
44‑0
1(J
=0
.010
66±
0.0
0001
2):
Apo
phyl
lite
Run
IDPw
r/T°C
Ca/
K36
Ar/39
Ar
%36
Ar(
Ca)
40*A
r/39A
rM
ol3
9Ar
%S
tep
Cum
.%%
40A
r*A
ge(M
a)±
Age
1644
-01A
1.7
4.53
645
0.00
1316
47.5
2.14
167
4.06
54E
+13
5.5
5.5
91.3
40.7
2427
0.18
916
44-0
1B•1
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2436
80.
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3362
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6157
23.
3421
E+1
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480.
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216
44-0
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91.
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413
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150.
1600
616
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2002
80.
0007
9972
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6357
51.
507E
+14
20.5
85.1
90.7
12.1
8521
0.06
585
1644
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4.17
913
0.00
0799
720.
5416
31.
0989
E+1
414
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089
.110
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460.
0763
8In
teg.
Age
=13
.06
0.09
(•) P
late
au A
ge =
94.5
11.6
0.8
KLX
02:6
76,R
unID
#16
44‑0
2(J
=0
.010
66±
0.0
0001
2):
Apo
phyl
lite
Run
IDPw
r/T°C
Ca/
K36
Ar/39
Ar
%36
Ar(
Ca)
40* A
r/39A
rM
ol39
Ar
%S
tep
Cum
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40A
r*A
ge(M
a)±
Age
1644
-02A
1.7
4.16
591
0.00
1728
33.2
2.41
163
2.78
28E
+13
2.3
2.3
87.6
45.7
931
0.22
786
1644
-02B
•1.9
4.17
821
0.00
0853
67.5
0.95
383
1.61
57E
+14
13.4
15.7
92.1
18.2
5099
0.05
466
1644
-02C
•2.1
4.14
771
0.00
0856
66.7
0.96
908
3.96
92E
+14
32.9
48.6
9218
.541
20.
0426
616
44-0
2D•2
.34.
2192
70.
0009
8559
1.14
318
1.05
4E+1
48.
757
.390
.521
.852
190.
0846
116
44-0
2E•2
.54.
1586
80.
0008
0371
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9632
64.
4412
E+1
436
.894
.193
.418
.430
360.
0439
816
44-0
2F•2
.74.
1927
40.
0005
1411
2.3
1.08
466
1.44
26E
+13
1.2
95.3
101.
720
.739
890.
5079
316
44-0
2G•2
.94.
1470
80.
0006
9881
.81.
1412
35.
729E
+13
4.7
100
96.8
21.8
1507
0.12
4In
teg.
Age
=19
.56
0.08
(•) P
late
au A
ge =
97.7
18.9
1
