The provenance of Late Ediacaran and Early Ordovician ... · 1. (A) Map showing the localities where the North Gondwana terranes are preserved in North America, Europe and North Africa

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Precambrian Research 192– 195 (2012) 166– 189

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Precambrian Research

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he provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in theouthwest Central Iberian Zone: Constraints from detrital zircon data onorthern Gondwana margin evolution during the late Neoproterozoic

.F. Pereiraa,∗, U. Linnemannb, M. Hofmannb, M. Chichorroc, A.R. Solád, J. Medinae, J.B. Silva f

IDL, Departamento de Geociências, ECT, Universidade de Évora, Apartado 94, 7001-554 Évora, PortugalSenckenberg Naturhistorische Sammlungen Dresden, GermanyCICEGe, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, PortugalLNEG, Unidade de Geologia e Cartografia Geológica, PortugalDepartamento de Geociências, Universidade de Aveiro, PortugalIDL, Departamento de Geologia, FCUL, Portugal

r t i c l e i n f o

rticle history:eceived 7 February 2011eceived in revised form 14 October 2011ccepted 28 October 2011vailable online xxx

eywords:rovenance analysisorthern Gondwana marginvalonian–Cadomian magmatic arcentral-Iberian Zoneest African

mazonian cratons

a b s t r a c t

U–Pb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovi-cian (Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of thesouthwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passivemargin transition. The LA-ICP-MS U–Pb data set (375 detrital zircons with 90–110% concordant ages) isdominated by Neoproterozoic ages (75% for the greywakes and 60% for the quartzites), among which themain age cluster (more significant for Beiras Group greywackes) is Cryogenian (c.840–750 Ma), while afew Mesoproterozoic and Tonian ages are also present (percentages <8%). These two features, and thepredominance of Cryogenian ages over Ediacaran ages, distinguish the Beiras Group greywackes (SWCIZ) from the time-equivalent Serie Negra (Ossa-Morena Zone – OMZ), with which they are in inferredcontact. The age spectra of the Beiras Group greywackes also reveal three major episodes of zircon crys-tallisation in the source area during the Neoproterozoic that are probably associated with a long-livedsystem of magmatism that developed either along or in the vicinity of the northern Gondwana marginat: (1) c. 850–700 Ma – Pan-African suture (not well represented in OMZ); (2) c. 700–635 Ma – earlyCadomian arc; and (3) c. 635–545 Ma – late Cadomian arc. Comparison of Neoproterozoic ages and thoseof the Paleoproterozoic (c. 2–1.8 Ga) and Archean (mainly Neoarchean – 2.8–2.6 Ga, but also older) in theBeiras Group greywackes with U–Pb ages of Cadomian correlatives shows that: (1) SW CIZ, OMZ, Saxo-Thuringian Zone, North Armorican Cadomian Belt and Anti-Atlas) evolved together during the formationof back-arc basins on the northern Gondwana active margin and (2) all recorded synorogenic basins thatwere filled during the Ediacaran by detritus resulting from erosion of the West African craton, the Pan-African suture and a long-lived Cadomian magmatic arc. Differences in detrital zircon age populations inthe greywackes of the Beiras Group (SW CIZ Cadomian basement) and the Serie Negra (OMZ Cadomian
basement) are also observed in their respective overlying Early Ordovician quartzites. Since both theseSW Iberia Cadomian basements evolved together along the active margin of Gondwana (but sufficientlyseparated to account for the differences in their detrital zircon content), this continuation of differingzircon populations into the Early Ordovician suggests that the inferred contact presently juxtaposingthe Beiras Group and the Serie Negra is not pre-Early Ordovician and so is unlikely to demonstrate aCadomian suture.
. Introduction

The basement rocks of Western and Central Europe wereormed during the final stages of Gondwana assembly in the late

∗ Corresponding author.E-mail address: [email protected] (M.F. Pereira).

301-9268/$ – see front matter © 2011 Published by Elsevier B.V.oi:10.1016/j.precamres.2011.10.019

© 2011 Published by Elsevier B.V.

Neoproterozoic (Murphy and Nance, 1991; Linnemann et al., 2004)(Figs. 1A and 2). In this context, Iberia occupies a critical role inenabling an understanding of the evolution of a Late Ediacaranactive margin in North Gondwana and the subsequent transition
to a passive margin in Cambrian–Ordovician times (Murphy et al.,2006a,b; Linnemann et al., 2008; Nance et al., 2008, 2010). Over thelast two decades, advances in our knowledge of stratigraphy, defor-mation, geochemistry, isotope chemistry and geochronology have
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M.F. Pereira et al. / Precambrian Research 192– 195 (2012) 166– 189 167

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ig. 1. (A) Map showing the localities where the North Gondwana terranes are preshowing location of the late Neoproterozoic rocks. (C) Simplified geological map, cr–Pb analyses, from the SW CIZ late Neoproterozoic and Early Ordovician record.

een constrained by linkages between peri-Gondwanan arc cor-elatives of North America, Europe and North Africa with the aimf deciphering their paleogeographic positions relative to potentialedimentary provenances (Murphy et al., 1996, 2002, 2004; Ugidost al., 1997, 2003; Fernández-Suarez et al., 2002; Nance et al., 2002,008; Linnemann et al., 2004, 2008; Gutierrez-Alonso et al., 2003;ereira et al., 2006, 2008a; Abati et al., 2010) (Fig. 2).

In Iberia, the late Neoproterozoic record is exposed in differ-nt tectono-stratigraphic zones (Julivert et al., 1974; Franke, 1989),rom North to South (Fig. 1B): the Cantabrian Zone (CZ), the Weststurian Leonese Zone (WALZ), the Central Iberian Zone (CIZ) and

he Ossa-Morena Zone (OMZ). The mostly extensive exposures ofate Ediacaran age that occur in the WALZ, CIZ and in the OMZ
nd are dominated by sedimentary rocks and with relatively minorgneous rocks (Fernández-Suarez et al., 2000; Eguíluz et al., 2000;utierrez-Alonso et al., 2003; Rodriguez-Alonso et al., 2004; Pereirat al., 2006, 2008b).
in North America, Europe and North Africa. (B) Simplified geological map of Iberiaction and stratigraphic column of the Penacova syncline. Sample locations used for

Iberia’s geographic paleoposition during the late Neoprotero-zoic is generally indicated by the presence or absence of Meso-proterozoic (c. 1 Ga) detrital zircon ages found in Late Ediacaransedimentary rocks. Neoproterozoic sedimentary rocks in NW Iberia(WALZ) show a significant percentage (11–37%) of Mesoprotero-zoic detrital zircon ages suggesting a paleoposition close to theAmazonian craton and Avalonian correlatives (Fernández-Suarezet al., 2000, 2002; Gutierrez-Alonso et al., 2003). On the other hand,the lack or insignificant percentage of Mesoproterozoic ages inSW Iberia (OMZ) provides evidence for a peri-West African cratonpaleoposition near to Cadomian correlatives (Fernández-Suarezet al., 2002; Gutierrez-Alonso et al., 2003; Pereira et al., 2008a;Linnemann et al., 2008). However the Neoproterozoic location of
Iberia is still controversial, and recently Diez Fernandez et al. (2010)proposed an alternative hypothesis suggesting Iberia was locatedto the north of the West African craton close to the Trans-Saharabelt, where there are potential sources of Mesoproterozoic ages.

168 M.F. Pereira et al. / Precambrian Research 192– 195 (2012) 166– 189

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This paper presents new U–Pb LA-ICP-MS geochronologyf detrital zircons from Ediacaran greywackes and Ordovicianuartzites of a key stratigraphic succession in the southwest of theIZ (Penacova, Portugal) close to the CIZ-OMZ transition (Fig. 1B and). Our findings show the predominance of Neoproterozoic ages60–77%), providing important information about older zircon-orming events (in particular, Ediacaran and Cryogenian) that helpo characterise potential sedimentary provenances. Taking as oureference U–Pb zircon ages published for different areas of Northondwana over the last twenty years, we discuss potential sed-

mentary sources for the Iberia Ediacaran basement that maynclude (Nance et al., 2008 and references therein): (1) North AfricaWest African craton and Trans-Sahara belt), (2) South AmericaAmazonian craton and Trans-Brasiliano belt), and (3) Neoprotero-oic peri-Gondwanan arc terranes of North America and EuropeAvalonia and Ganderia located in proximity to the Amazonianraton or Cadomia linked to the West African craton) (Fig. 2).

In addition, a comparison is also made with available U–Pbeochronological data from Late Ediacaran and Early Ordovicianedimentary rocks of SW Iberia, NW Iberia, Cadomia and thenti-Atlas in order to: (1) decipher the paleoposition of Iberialong the northern Gondwana margin, in the context of thevalonian–Cadomian and/or Pan-African orogenies; (2) test possi-
le connections between European and North African correlatives;nd (3) provide additional insights into northern Gondwana mar-in assembly and breakup during late Neoproterozoic and earlyaleozoic times.
tinent at c. 570–560 Ma with possible paleoposition of Iberia.

2. Geological setting

The CIZ is a major subdivision of Iberia (Julivert et al., 1974)that extends from the boundary with the WALZ (NW Iberia) to SWin the CIZ-OMZ transition. In the CIZ-OMZ transition, Early Ordovi-cian rocks with a paleogeographic affinity to the CIZ unconformablyoverlie the OMZ Cadomian basement (Série Negra; Pereira et al.,2006; Linnemann et al., 2008; Solá et al., 2008) (Fig. 1B). The CIZincludes Early Ordovician quartzites that unconformably overlieEdiacaran and Cambrian rocks of the Schist–Greywacke Complex(Carrington da Costa, 1950; Schermerhorn, 1955; Sousa, 1982)also called “Supergrupo Durico-Beirão” (Silva et al., 1987–1989;Sousa and Sequeira, 1987–1989; Sequeira and Sousa, 1991). TheSchist–Greywacke Complex includes the Beiras and Douro Groups,which consist of Neoproterozoic to early Cambrian sedimentaryrocks (Medina et al., 1998). The early Ordovician quartzites thatdirectly overlie the Beiras Group occur in NW–SE-trending limbsof Variscan kilometre-scale folds on the Geological Map of Portugal(1992, 2010).

The Penacova ridge located in the SE extremity of the Buc acomountain range is a 130–140◦ trending syncline with a steeply(70–80◦) dipping axial plane (Fig. 1C). Cambrian rocks are notpresent in the Penacova stratigraphy that includes from the base
to the top: (1) the Beiras Group with greywackes and slates(Late Ediacaran; Medina et al., 1998); (2) the Sarnelhas Formation(Late Cambrian–Early Ordovician transition; “Grauwackes rougesinférieures”; Delgado, 1908; “Grauvaques vermelhos inferiores”;

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arrington da Costa, 1950) including arkosic quartzites; and (3) thermorican Quartzite Formation (Early Ordovician; Oliveira et al.,992).

The Beiras Group slates and greywackes (SW CIZ Cadomianasement) were tilted before the deposition of the arkosic bedsf the Sarnelhas Formation. In the northern limb of the Pena-ova syncline (Fig. 1C), steeply NNE-dipping overturned beds oflates and greywackes of the Beiras Group are overlain by steeplyW-dipping beds of Ordovician quartzites, slates and metacon-lomerates, defining a major angular unconformity at the basef the Ordovician sequence. In Penacova, the sedimentologicaleatures of the Beiras Group suggest a siliciclastic platformal depo-itional environment characterised by sand bars influenced bytorm events (Medina et al., 1998). The steeply NEE-dipping andverturned Beira Group succession is characterised by alternat-ng metre- and centimetre-scale beds of medium- to fine-grainedandstones, and banded silty to clayey sedimentary rocks withnterbedded conglomerates. The section of the Beiras Group exam-ned includes, from the base to the top (Medina, 1996; Fig. 1C):1) thick beds of coarse- to medium-grained sandstones witharallel bedding and low-angle cross-bedding, separated by mud-upported conglomerates (with centimetre-scale rounded pebblesf quartz, clasts of volcanic and sedimentary rocks, includingounded pebbles of black cherts); (2) interbedded thin layers ofne-grained sandstone with silt mudstones showing wavy and

enticular lamination, and ripples; (3) coarse- to medium-grainedreywackes, sandstones with parallel bedding and low-angle cross-edding, also showing channel geometries and including fragmentsf mudstones and trace fossils from the Late Ediacaran (Vidalt al., 1994; Pereira et al., 2008b); (4) interbedded fine-grainedandstones and grey-black mudstones with hummocky structures,ipples and wavy lamination; and (5) grey-black mudstones withew intercalations of sandstones. The early Paleozoic sequence thatnconformably overlies the Beiras Group sedimentary rocks con-ists of basal Late Cambrian–Early Ordovician arkosic quartzitesnd slates with intercalations of conglomerates (Sarnelhas Forma-ion). The Sarnelhas arkosic quartzites show parallel lamination,ross-bedding, channel geometries and ripples. The Sarnelhas For-ation is overlain by the Armorican Quartzite Formation (Earlyrdovician) which includes massive beds of quartzites and thin

ayers of slates. The early Paleozoic sequence is characteristic ofhallow marine siliciclastic platform sedimentation. The angularnconformity with Early Ordovician rocks lying directly over tilteddiacaran strata developed as result of a major crustal extension inhe Cambrian–Ordovician (Pereira et al., 2008b).

The Ediacaran and Ordovician sedimentary rocks wereeformed under low-grade metamorphic conditions (Variscaneformation). The Late Ediacaran succession exhibits a 135–145◦

rending crenulation cleavage superposed to tight to open closedolds with gently E-plunging axis, and 110–120◦ trending and NNE-ipping (62–66◦) spaced or penetrative rough to slaty cleavage,hereas the Ordovician sequence shows closed to open folds with

ently plunging fold axes and 135–145◦ trending spaced fracturedleavage or slaty cleavage.

. U–Pb LA-ICP-MS geochronology

.1. Samples and methods

Four samples were collected for this geochronology study (coor-
inates datum WGS84 in Tables 1–4): PNC 1 and PNC 2 representwo greywackes from the Beiras Group, PNC 3 is an arkosic quartziterom the Sarnelhas Formation, and PNC 4 is a quartzite from thermorican Quartzite Formation. Lens and CL-imaging of zircons
rch 192– 195 (2012) 166– 189 169

are presented in Figs. 3 and 4 and the results obtained from U–Pbgeochronology in Figs. 5–8 and Tables 1–4.

Zircon grains were extracted, then mounted in epoxyresin with zircon standards SL13 (U = 238 ppm) and TEMORA(206Pb*/238U = 0.06683). The polished mounts were photographedand then two of them (samples PNC 2 and PNC 3) were imaged bySEM cathodoluminescence (CL) to document the internal growthzoning of the grains. Zircon grains were then analysed for U, Th, andPb isotopes by LA-ICP-MS (Laser Ablation with Inductively CoupledPlasma Mass Spectrometry) at the Museum für Mineralogie undGeologie (Senckenberg Naturhistorische Sammlungen Dresden),using a Thermo-Scientific Element 2 XR sector field ICP-MS coupledto a New Wave UP-193 Excimer Laser System. A teardrop-shaped,low-volume laser cell was used to enable sequential sampling ofheterogeneous grains (e.g. growth zones) during time-resolveddata acquisition. Each analysis consisted of 15 s background acqui-sition followed by 35 s data acquisition, using laser-spot sizes of15–35 �m. A common-Pb correction based on the interference-and background-corrected 204Pb signal and a model Pb composi-tion (Stacey and Kramers, 1975) was carried out where necessary.The criterion for correction was whether the corrected 207Pb/206Pblay outside the internal error of measured ratios. Time-resolved sig-nals of the LA-ICP-MS were checked in order to detect disturbancescaused by cracks or mineral inclusions. In such cases, analyseswere excluded from age calculations. Raw data was corrected forbackground signals, common Pb, laser-induced elemental frac-tionation, instrumental mass discrimination, and time-dependentelemental fractionation of Pb/Th and Pb/U using an Excel® spread-sheet program developed by Axel Gerdes (Institute of Geosciences,Johann Wolfgang Goethe-University Frankfurt, Frankfurt am Main,Germany). Reported uncertainties were propagated by quadraticaddition of the external reproducibility obtained from the standardzircon GJ-1 (∼0.6% and 0.5–1% for the 207Pb/206Pb and 206Pb/238U,respectively) during individual analytical sessions and the within-run precision of each analysis. Analyses with a concordance in therange 90–110% were used for concordia and probability densitydistribution plots. A total of 415 analyses were carried out on foursamples, while 9% (40 analyses) revealed >10% discordance andwere discarded. Discordance may originate from Pb loss, additionof common Pb or ablation of different domains within the zircon.Concordia diagrams (2� error ellipses), concordia ages (95% confi-dence level) and probability plots were produced using Isoplot/Ex2.49 (Ludwig, 2001). The 207Pb/206Pb age was taken for interpre-tation for all zircons >1.0 Ga, and the 206Pb/238U ages for youngergrains. For further details on analytical protocol and data processingsee Frei and Gerdes (2009).

3.2. Results

3.2.1. Ediacaran greywackes of the Beiras Group (PNC 1 and PNC2)

The zircon population of sample PNC 1 is dominated by medium-sized grains (90–120 �m; 70%) but also includes larger grains(180–200 �m; 30%). Most zircons are translucent and pinkish, anda few are brown and purple. Some grains have mineral inclusions.The zircons show a wide variety of forms ranging from subhedralto euhedral stubby grains with pyramidal or multi-pyramidal ter-minations, subhedral to euhedral elongated prisms and stronglyrounded crystals with no visible crystalline faces.

The zircon ages obtained (Fig. 5 and Tables 1 and 2) are quitesimilar in both samples, with slight differences for the percent-ages of pre-Cryogenian ages (Fig. 7). For sample PNC 1, 110 targets
were analysed, with 110 spots showing 90–110% concordance.The main group of ages is Neoproterozoic (74%, 914–550 Ma). Theremaining zircons are older, with the following distribution: Meso-proterozoic (4%, c. 1.2–1.0 Ga) Paleoproterozoic (14%; c. 2.3–1.7 Ga)

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Table 1Sample PNC 1 – greywacke (Beiras Group; 40◦18′16′′N; 8◦13′43′′W). 117 grains measured, 110 are concordant in the range of 90–110%, only concordant grains are shown in the table. 206Pb/238U age (2�-error), 207Pb/206Pb age(2�-error), degree of concordance.

Number 207Pba (cps) Ub (ppm) Pbb (ppm) Thb/U 206Pbc/204Pb 206Pbc/238U 2� (%) 207Pbc/235U 2� (%) 207Pbc/206Pb 2� (%) rhod 206Pb/238U 2� (Ma) 207Pb/235U 2� (Ma) 207Pb/206Pb 2� (Ma) conc (%)

a2 129,259 860 83 0.28 705 0.0942 2.1 0.776 2.4 0.0597 1.2 0.88 581 12 583 11 593 25 98a3 40,516 351 41 0.62 2228 0.1072 2.1 0.921 2.6 0.0623 1.5 0.81 656 13 663 13 686 32 96a4 11,240 88 10 0.54 2716 0.1049 2.0 0.901 2.8 0.0623 2.0 0.72 643 13 653 14 685 42 94a5 3154 34 3 0.31 595 0.0911 2.8 0.747 24.9 0.0594 24.7 0.11 562 15 566 114 583 537 96a6 17,567 184 19 0.13 2285 0.1072 2.7 0.919 3.8 0.0622 2.7 0.70 656 17 662 19 681 58 96a7 41,106 122 30 0.68 8405 0.2186 1.9 2.476 2.1 0.0822 0.9 0.90 1274 22 1265 15 1249 18 102a8 493,574 122 112 0.60 161,069 0.7090 2.1 29.355 3.3 0.3003 2.5 0.63 3455 56 3465 33 3472 39 100a9 482,514 167 129 0.47 9640 0.6469 3.5 23.240 4.1 0.2606 2.1 0.86 3216 90 3237 41 3250 33 99a10 27,466 239 28 0.82 2307 0.1035 2.0 0.883 3.6 0.0619 3.0 0.56 635 12 643 17 670 63 95a11 18,874 135 17 0.62 2915 0.1141 2.1 0.982 6.8 0.0624 6.5 0.31 697 14 695 35 689 138 101a13 234,265 249 107 0.43 30,629 0.3943 1.9 7.251 2.0 0.1334 0.7 0.94 2143 35 2143 18 2143 12 100a14 161,295 155 62 0.06 64,153 0.4032 2.1 7.454 2.3 0.1341 0.9 0.91 2184 39 2168 21 2152 16 101a15 13,680 122 13 0.57 22,761 0.0961 2.4 0.800 3.1 0.0604 2.0 0.77 591 13 597 14 617 42 96a16 96,452 123 50 0.79 3459 0.3464 2.0 5.812 2.2 0.1217 0.9 0.91 1917 33 1948 19 1981 16 97a17 6632 60 8 0.56 1146 0.1166 2.3 1.010 3.5 0.0628 2.6 0.66 711 16 709 18 701 56 101a20 14,631 123 16 0.86 3017 0.1110 2.1 0.953 2.9 0.0623 2.0 0.72 679 13 680 15 683 43 99a21 27,362 294 31 0.53 731 0.1049 2.0 0.885 3.8 0.0612 3.2 0.53 643 12 644 18 646 69 99a22 9163 86 10 0.84 1206 0.1022 2.2 0.869 2.9 0.0616 1.9 0.75 628 13 635 14 662 41 95a24 15,377 122 17 1.01 1870 0.1232 2.3 1.092 4.5 0.0643 3.8 0.52 749 16 750 24 752 81 100a25 23,011 105 20 0.44 2289 0.1923 1.9 2.057 2.4 0.0776 1.4 0.80 1134 20 1135 16 1136 28 100a26 9277 84 11 0.57 2055 0.1191 2.3 1.058 3.3 0.0644 2.4 0.69 726 16 733 18 755 51 96a27 32,902 305 30 1.03 241 0.0927 3.3 0.751 6.1 0.0588 5.1 0.54 571 18 569 27 559 112 102a28 16,882 114 14 0.05 10,674 0.1314 2.1 1.216 2.5 0.0671 1.4 0.82 796 16 808 14 842 30 94a29 29,753 189 30 1.73 536 0.1306 2.7 1.186 8.2 0.0658 7.7 0.33 791 20 794 46 802 161 99a30 23,966 188 27 0.80 926 0.1317 2.4 1.200 5.7 0.0661 5.2 0.42 797 18 801 32 810 108 98a31 5953 59 6 0.28 6510 0.1027 2.0 0.859 3.1 0.0607 2.3 0.67 630 12 630 14 628 49 100a32 3424 29 5 1.46 540 0.1225 3.0 1.087 6.4 0.0643 5.7 0.46 745 21 747 34 753 120 99a33 8195 106 11 0.41 661 0.1030 2.0 0.875 4.3 0.0616 3.8 0.46 632 12 639 21 662 81 96a36 37,395 75 29 0.87 2129 0.3329 1.9 5.574 2.3 0.1214 1.3 0.82 1852 30 1912 20 1977 23 94a37 56,120 75 32 1.61 4007 0.3423 1.8 6.043 2.5 0.1280 1.7 0.74 1898 30 1982 22 2071 29 92a38 3595 36 4 0.49 795 0.1108 1.9 0.944 3.8 0.0618 3.3 0.51 678 12 675 19 667 70 102a39 1386 17 2 0.33 383 0.1242 3.2 1.086 5.6 0.0634 4.6 0.57 755 23 747 30 722 98 105a40 15,926 157 18 0.77 2824 0.1030 1.9 0.869 4.0 0.0612 3.5 0.49 632 12 635 19 648 74 98a41 16,089 91 12 0.54 1681 0.1275 2.6 1.144 13.7 0.0651 13.5 0.19 774 19 774 77 776 284 100a42 42,844 42 19 1.19 7285 0.3481 2.5 6.069 2.9 0.1264 1.4 0.86 1926 41 1986 25 2049 25 94a43 14,263 106 11 0.39 8055 0.0987 2.1 0.832 2.5 0.0611 1.3 0.85 607 12 614 12 642 29 95a44 84,857 39 23 0.85 2821 0.4914 3.0 11.233 3.1 0.1658 1.0 0.95 2577 64 2543 30 2516 16 102a46 1797 11 2 0.94 1620 0.1168 2.7 1.019 7.4 0.0633 6.9 0.36 712 18 713 39 718 147 99a47 8488 44 5 0.33 2655 0.1177 2.5 1.032 4.1 0.0636 3.3 0.60 717 17 720 21 729 70 98a48 61,322 239 34 0.07 87,210 0.1519 1.8 1.479 2.2 0.0706 1.3 0.81 912 15 922 14 946 27 96a49 20,800 130 16 0.80 2563 0.1115 1.8 0.966 2.6 0.0628 1.9 0.70 681 12 686 13 702 40 97a51 6032 37 5 0.62 320 0.1242 1.9 1.119 4.4 0.0653 4.0 0.44 755 14 762 24 786 84 96a52 16,107 73 9 0.52 2504 0.1173 1.8 1.024 2.4 0.0633 1.6 0.75 715 12 716 13 719 34 99a53 61,141 272 30 0.49 349 0.1044 2.1 0.885 4.5 0.0615 4.0 0.46 640 13 644 22 655 87 98a54 36,466 146 13 0.04 521 0.0945 1.8 0.784 9.0 0.0601 8.8 0.20 582 10 588 41 607 191 96a55 13,989 3 3 3.41 7574 0.5241 1.8 13.374 20.1 0.1851 20.0 0.09 2716 39 2706 210 2699 331 101a57 20,948 6 4 1.80 1336 0.4913 2.1 11.584 2.6 0.1710 1.6 0.79 2576 44 2571 25 2568 27 100a58 6914 22 3 0.39 8050 0.1160 1.9 1.001 3.0 0.0626 2.3 0.63 707 13 705 15 696 50 102a59 227,567 64 34 0.63 7281 0.4673 2.2 10.949 2.7 0.1700 1.5 0.82 2472 45 2519 25 2557 26 97a60 17,250 72 7 0.44 853 0.0909 2.2 0.737 5.1 0.0588 4.6 0.43 561 12 561 22 561 100 100a61 38,915 20 9 1.19 4251 0.3634 2.2 5.931 2.6 0.1184 1.3 0.86 1998 38 1966 23 1932 24 103a62 13,174 25 5 0.99 6624 0.1773 2.0 1.820 2.5 0.0744 1.5 0.81 1052 20 1053 16 1053 29 100a63 12,784 36 5 0.80 1237 0.1233 2.7 1.111 4.7 0.0653 3.8 0.59 750 19 759 25 785 79 96a64 13,399 10 4 0.65 2064 0.3591 2.8 5.947 4.1 0.1201 2.9 0.69 1978 48 1968 36 1958 52 101a65 8239 18 3 2.48 526 0.1316 2.1 1.203 15.5 0.0663 15.4 0.13 797 16 802 90 816 321 98a66 2561 7 1 1.36 642 0.1380 2.0 1.272 4.5 0.0669 4.0 0.45 833 16 833 26 834 83 1002a-2 13,514 70 11 1.98 2798 0.1260 1.9 1.121 2.3 0.0645 1.3 0.83 765 14 763 13 759 28 101

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Table 1 (Continued)


2a-3 44,507 13 11 1.29 1185 0.6398 1.7 18.852 1.8 0.2137 0.6 0.95 3188 44 3034 18 2934 10 1092a-4 7224 42 6 1.40 1425 0.1243 1.9 1.117 3.4 0.0652 2.8 0.55 755 13 762 18 780 59 972a-6 11,701 80 10 0.41 2574 0.1197 2.0 1.048 2.7 0.0635 1.8 0.74 729 14 728 14 726 38 1002a-7 13,399 94 11 0.30 8604 0.1134 1.8 0.975 2.4 0.0624 1.6 0.75 692 12 691 12 687 34 1012a-8 9005 56 7 0.49 1406 0.1249 1.8 1.113 2.5 0.0646 1.7 0.74 759 13 760 13 762 35 1002a-9 4853 45 6 1.80 1158 0.1117 1.8 0.993 12.1 0.0645 11.9 0.15 683 11 700 63 757 252 902a-10 145,541 37 31 0.65 55,306 0.6941 2.0 25.207 2.2 0.2634 0.9 0.92 3398 54 3316 22 3267 14 1042a-11 54,493 89 31 0.22 1385 0.3471 2.8 5.664 3.1 0.1184 1.2 0.92 1921 47 1926 27 1932 22 992a-13 95,457 34 20 0.49 5131 0.5111 3.0 13.070 4.3 0.1855 3.0 0.71 2662 66 2685 41 2702 49 982a-15 10,457 58 7 0.24 2206 0.1166 2.8 1.027 6.4 0.0639 5.7 0.45 711 19 718 33 738 121 962a-16 14,458 75 10 0.38 1464 0.1289 2.3 1.160 4.0 0.0652 3.2 0.59 782 17 782 22 782 68 1002a-17 42,283 13 8 0.69 6197 0.4849 3.0 12.173 3.5 0.1821 1.8 0.86 2548 64 2618 34 2672 30 952a-18 25,551 187 20 0.56 3809 0.1025 1.7 0.850 2.8 0.0601 2.3 0.61 629 10 625 13 608 49 1032a-19 55,382 376 47 0.85 9382 0.1105 2.2 0.946 3.2 0.0621 2.4 0.68 676 14 676 16 677 50 1002a-20 15,518 113 13 0.77 2039 0.1081 1.9 0.902 5.5 0.0605 5.1 0.35 662 12 653 27 622 110 1062a-21 146,937 251 70 0.14 47,523 0.2816 2.0 4.025 2.2 0.1036 0.9 0.91 1600 28 1639 18 1690 17 952a-24 11,766 102 10 0.52 19,902 0.0896 1.8 0.730 2.1 0.0591 1.1 0.86 553 10 557 9 572 24 972a-25 7862 61 7 0.95 7481 0.1089 1.7 0.923 2.7 0.0615 2.1 0.64 666 11 664 13 655 45 1022a-26 22,076 125 20 1.44 21,292 0.1270 1.7 1.155 1.9 0.0659 0.9 0.88 771 12 779 10 805 19 962a-27 6531 61 6 0.50 2762 0.0937 2.0 0.767 3.5 0.0594 2.9 0.57 578 11 578 16 580 64 1002a-28 8133 78 7 0.52 2818 0.0910 2.0 0.739 2.8 0.0589 1.9 0.72 561 11 562 12 563 42 1002a-29 12,968 118 12 0.63 7096 0.0965 1.9 0.796 2.9 0.0598 2.2 0.66 594 11 594 13 596 48 1002a-30 15,967 166 19 0.48 1875 0.1119 1.7 0.961 2.6 0.0623 2.0 0.64 684 11 684 13 683 43 1002a-31 14,254 68 11 0.50 4649 0.1523 1.9 1.461 2.4 0.0696 1.6 0.77 914 16 914 15 916 32 1002a-32 14,010 103 13 1.03 3672 0.1080 1.8 0.920 2.5 0.0618 1.8 0.71 661 11 662 12 668 38 992a-33 90,219 93 43 0.84 27,187 0.4059 2.0 7.577 2.3 0.1354 1.1 0.88 2196 37 2182 21 2169 19 1012a-35 56,372 57 24 0.49 19,813 0.3811 1.8 7.035 2.1 0.1339 1.1 0.86 2082 32 2116 19 2149 19 972a-36 8946 78 11 1.89 7633 0.1063 2.1 0.889 3.1 0.0607 2.3 0.67 651 13 646 15 627 50 1042a-37 21,889 201 20 0.51 36,952 0.0961 1.9 0.786 2.3 0.0593 1.3 0.83 591 11 589 10 578 27 1022a-38 24,200 187 26 1.20 5333 0.1056 1.9 0.911 2.4 0.0625 1.5 0.79 647 12 657 12 692 32 942a-39 144,968 159 55 0.20 19,526 0.3405 1.9 5.563 2.1 0.1185 0.9 0.91 1889 31 1910 18 1933 16 982a-40 45,555 356 33 0.46 667 0.0890 1.7 0.719 4.2 0.0586 3.9 0.40 550 9 550 18 552 85 1002a-41 17,118 112 13 0.55 6836 0.1123 1.7 0.958 2.5 0.0619 1.9 0.67 686 11 682 13 671 40 1022a-42 36,147 21 11 0.78 4338 0.4440 1.7 8.752 2.3 0.1430 1.6 0.71 2368 33 2312 22 2263 28 1052a-44 3424 20 2 0.45 2250 0.1067 2.6 0.908 4.1 0.0617 3.2 0.63 654 16 656 20 664 68 982a-46 13,483 61 7 0.70 4308 0.1123 2.1 0.965 2.7 0.0624 1.7 0.77 686 14 686 14 686 37 1002a-47 4261 21 3 1.03 6967 0.1087 1.8 0.917 3.3 0.0611 2.8 0.55 665 12 661 16 644 60 1032a-48 5927 26 3 0.57 1027 0.1355 1.8 1.241 4.2 0.0664 3.8 0.42 819 14 820 24 820 79 1002a-49 3914 14 2 1.43 6329 0.1048 2.2 0.891 3.9 0.0617 3.3 0.56 642 13 647 19 664 70 972a-50 11,282 41 5 0.81 17,840 0.1150 2.2 1.003 3.2 0.0632 2.2 0.71 702 15 705 16 716 47 982a-51 10,269 51 6 0.44 970 0.1131 2.3 0.988 8.2 0.0633 7.9 0.28 691 15 697 42 719 168 962a-52 9926 23 4 0.55 2177 0.1498 2.0 1.429 2.8 0.0692 1.9 0.74 900 17 901 17 905 39 992a-53 14,211 52 6 0.48 11,156 0.1102 2.2 0.936 3.1 0.0616 2.2 0.72 674 14 671 15 659 47 1022a-54 101,436 58 23 0.48 5151 0.3713 2.6 6.344 2.9 0.1239 1.4 0.88 2035 45 2025 26 2014 24 1012a-55 21,415 82 8 0.44 6112 0.0982 1.9 0.813 2.5 0.0601 1.7 0.75 604 11 604 12 605 36 1002a-57 13,728 50 5 0.25 5336 0.1025 2.0 0.861 2.9 0.0609 2.0 0.70 629 12 631 14 635 44 992a-58 14,031 43 5 0.79 4111 0.1091 1.7 0.936 2.1 0.0622 1.3 0.80 667 11 671 10 681 27 982a-59 14,643 45 5 0.51 4101 0.1123 2.0 0.966 2.9 0.0624 2.1 0.68 686 13 687 15 688 45 1002a-60 7446 23 2 0.53 2198 0.1035 1.9 0.878 2.6 0.0616 1.8 0.74 635 12 640 12 659 38 962a-61 5944 18 2 0.78 1367 0.1104 2.2 0.948 4.5 0.0623 3.9 0.50 675 14 677 22 685 83 992a-62 4140 6 1 0.63 5618 0.1745 2.5 1.777 5.3 0.0738 4.7 0.47 1037 24 1037 35 1037 95 1002a-64 3139 8 1 0.97 498 0.1169 2.2 1.013 5.5 0.0628 5.0 0.40 713 15 710 28 703 107 1012a-65 3192 9 1 0.46 415 0.1250 2.1 1.123 3.1 0.0652 2.3 0.67 759 15 765 17 780 48 97

a Within-run background-corrected mean 207Pb signal in counts per second.b U and Pb content and Th/U ratio were calculated relative to GJ-1 and are accurate to approximately 10%.c Corrected for background, mass bias, laser induced U–Pb fractionation and common Pb (if detectable, see analytical method) using Stacey and Kramers (1975) model Pb composition. 207Pb/235U calculated using

207Pb/206Pb/(238U/206Pb × 1/137.88). Errors are propagated by quadratic addition of within-run errors (1SE) and the reproducibility of GJ-1 (1SD).d Rho is the error correlation defined as err206Pb/238U/err207Pb/235U.

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Table 2Sample PNC 2 – greywacke (Beiras Group; 40◦18′16′′N; 8◦13′43′′W). 118 grains measured, 102 are concordant in the range of 90–110%, only concordant grains are shown in the table 206Pb/238U age (2�-error), 207Pb/206Pb age(2�-error), degree of concordance.

Number 207Pba (cps) Ub (ppm) Pbb (ppm) Thb U 206Pbc/204Pb 206Pbc/238U 2� (%) 207Pbc/235U 2� (%) 207Pbc/206Pb 2� (%) rhod 206Pb/238U 2� (Ma) 207Pb/235U 2� (Ma) 207Pb/206Pb 2� (Ma) conc (%)

a2 26,233 164 17 0.46 477 0.0983 2.5 0.818 5.1 0.0604 4.5 0.48 604 14 607 24 617 97 98a3 11,576 63 10 1.22 1672 0.1328 2.5 1.215 13.4 0.0663 13.2 0.19 804 19 807 78 817 276 98a4 29,813 17 11 1.99 1114 0.4938 2.4 11.487 3.2 0.1687 2.1 0.75 2587 51 2564 30 2545 35 102a9 11,602 73 11 0.38 15,344 0.1522 2.0 1.416 2.4 0.0675 1.3 0.84 913 17 896 14 853 27 107a10 57,750 333 44 0.38 2535 0.1321 2.0 1.206 2.6 0.0662 1.6 0.77 800 15 803 14 813 34 98a13 36,217 237 23 0.14 562 0.1004 1.8 0.836 3.0 0.0604 2.4 0.60 617 11 617 14 616 52 100a14 16,029 111 13 0.54 24,823 0.1185 2.8 1.043 4.3 0.0638 3.3 0.65 722 19 726 22 736 69 98a15 2746 12 3 2.29 917 0.1742 1.9 1.778 5.0 0.0740 4.6 0.39 1035 18 1037 33 1042 93 99a16 25,289 33 13 0.71 1186 0.3591 2.4 6.024 2.8 0.1217 1.5 0.84 1978 40 1979 25 1981 27 100a17 15,591 140 13 0.38 2385 0.0937 2.5 0.769 13.9 0.0595 13.7 0.18 578 14 579 63 584 297 99a18 12,511 95 16 0.68 261 0.1663 2.0 1.688 2.4 0.0736 1.3 0.84 992 19 1004 15 1030 26 96a19 10,266 73 10 0.45 1167 0.1301 2.3 1.182 3.1 0.0659 2.1 0.74 788 17 792 17 804 43 98a20 14,724 84 10 0.35 1398 0.1169 2.8 1.021 6.2 0.0634 5.5 0.45 713 19 715 32 721 118 99a21 14,724 84 10 0.34 1618 0.1220 2.6 1.092 5.8 0.0649 5.2 0.44 742 18 750 31 771 109 96a22 14,144 56 10 0.70 373 0.1583 2.9 1.578 12.3 0.0723 11.9 0.24 947 26 962 79 994 243 95a24 8816 72 9 0.65 1949 0.1110 2.5 0.950 3.8 0.0621 2.9 0.65 679 16 678 19 676 62 100a25 13,046 45 10 0.64 979 0.1883 2.4 2.004 5.8 0.0772 5.3 0.41 1112 24 1117 40 1126 105 99a26 24,083 169 24 1.13 1804 0.1226 2.1 1.089 3.0 0.0644 2.1 0.70 746 15 748 16 754 45 99a27 42,844 328 40 0.52 623 0.1174 2.3 1.038 3.5 0.0641 2.7 0.65 716 15 723 18 744 56 96a28 39,513 73 27 0.72 329 0.3146 3.3 4.562 4.8 0.1052 3.5 0.68 1763 50 1742 41 1718 65 103a29 10,854 46 17 0.28 358 0.3599 2.0 4.760 15.3 0.0959 15.2 0.13 1982 33 1778 138 1546 286 128a30 47,610 170 32 0.19 765 0.1795 1.9 1.899 6.5 0.0767 6.2 0.30 1064 19 1081 44 1114 123 96a31 1611 13 2 2.54 2581 0.1102 3.0 0.938 6.9 0.0617 6.2 0.44 674 19 672 34 664 132 102a32 74,621 58 28 0.42 41 0.3173 3.7 5.068 23.5 0.1159 23.3 0.16 1776 58 1831 222 1893 418 94a35 8440 40 9 1.32 1014 0.1911 2.0 2.038 6.8 0.0773 6.5 0.30 1128 21 1128 47 1129 129 100a36 6415 53 9 0.80 460 0.1655 2.0 1.646 3.1 0.0722 2.5 0.62 987 18 988 20 990 50 100a37 20,341 129 18 0.67 1817 0.1329 2.2 1.221 3.3 0.0666 2.4 0.67 804 17 810 18 827 51 97a38 3958 53 7 0.87 356 0.1295 1.9 1.172 8.6 0.0656 8.4 0.22 785 14 788 48 795 176 99a39 21,619 101 14 0.57 264 0.1240 2.1 1.105 7.4 0.0646 7.1 0.28 754 15 756 40 762 149 99a40 24,344 80 12 0.57 253 0.1288 2.4 1.159 11.8 0.0653 11.6 0.20 781 18 781 66 782 243 100a43 12,243 51 10 0.71 2218 0.1956 1.9 2.126 3.3 0.0788 2.7 0.58 1152 20 1157 23 1167 53 99a44 93,499 48 25 0.33 483 0.4659 2.4 10.601 2.7 0.1650 1.3 0.88 2466 49 2489 26 2508 22 98a46 31,889 14 7 1.04 45 0.3148 2.4 4.545 24.3 0.1047 24.2 0.10 1764 37 1739 225 1709 445 103a48 6287 38 6 0.42 276 0.1548 2.3 1.575 8.5 0.0738 8.2 0.27 928 20 960 54 1036 166 90a49 4402 8 2 1.03 242 0.1696 2.1 1.747 16.5 0.0747 16.4 0.13 1010 20 1026 113 1060 329 95a50 67,607 43 19 0.85 2228 0.3633 3.9 6.377 4.4 0.1273 2.1 0.88 1998 67 2029 39 2061 37 97a51 44,850 96 15 0.46 167 0.1292 2.7 1.208 9.8 0.0678 9.4 0.28 783 20 804 56 863 195 91a52 36,472 185 20 0.44 3551 0.1077 2.0 0.913 2.8 0.0615 2.0 0.72 659 13 659 14 656 42 100a53 29,700 115 16 0.67 1086 0.1303 1.9 1.195 3.6 0.0665 3.1 0.51 790 14 798 20 822 65 96a54 34,013 121 17 0.75 818 0.1365 2.0 1.228 3.1 0.0653 2.4 0.64 825 16 813 18 783 50 105a57 45,734 23 11 0.61 1382 0.4276 2.0 8.295 2.5 0.1407 1.5 0.80 2295 39 2264 23 2236 26 103a58 53,971 68 12 0.09 488 0.1566 2.0 1.521 13.0 0.0704 12.9 0.15 938 17 939 83 941 264 100a59 37,698 33 7 0.51 84 0.1401 1.8 1.254 9.4 0.0649 9.2 0.20 845 15 825 54 771 193 110a60 3253 13 2 0.13 485 0.1236 2.9 1.100 4.2 0.0645 3.1 0.68 751 20 753 23 759 65 99a61 3451 12 2 1.92 527 0.1300 2.3 1.153 4.6 0.0643 4.0 0.51 788 17 778 25 752 84 105a63 42,808 14 8 0.40 1604 0.5276 3.3 12.546 3.5 0.1725 1.3 0.93 2731 73 2646 33 2582 21 106a65 14,094 27 4 0.83 584 0.1344 3.1 1.243 7.7 0.0671 7.1 0.40 813 23 820 44 840 147 97a66 2826 7 1 1.11 227 0.1326 2.7 1.209 14.0 0.0661 13.7 0.19 803 21 805 81 811 287 992a-2 20,373 84 11 0.45 277 0.1209 3.4 1.098 10.9 0.0659 10.3 0.31 736 24 752 59 803 216 922a-4 2697 21 3 1.60 4448 0.1040 3.2 0.870 5.9 0.0607 5.0 0.53 638 19 636 28 628 108 1022a-5 15,211 104 16 1.88 1381 0.1174 2.2 1.013 3.7 0.0626 2.9 0.61 715 15 711 19 696 62 1032a-6 7553 59 7 1.34 679 0.0989 2.3 0.842 3.6 0.0618 2.7 0.64 608 13 620 17 666 59 912a-7 13,898 14 7 1.81 2338 0.4039 2.4 6.906 3.0 0.1240 1.8 0.79 2187 44 2099 27 2015 33 109

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Table 2 (Continued)

Number 207Pba (cps) Ub (ppm) Pbb (ppm) Thb U 206Pbc/204Pb 206Pbc/238U 2� (%) 207Pbc/235U 2� (%) 207Pbc/206Pb 2� (%) rhod 206Pb/238U 2� (Ma) 207Pb/235U 2� (Ma) 207Pb/206Pb 2� (Ma) conc (%)

2a-8 10,803 84 9 0.36 3799 0.1097 2.6 0.954 9.4 0.0631 9.0 0.28 671 17 680 48 712 191 942a-9 20,450 185 16 0.14 6326 0.0912 2.3 0.747 2.7 0.0594 1.5 0.83 563 12 567 12 582 33 972a-10 39,461 322 34 0.63 1898 0.0991 2.4 0.839 2.8 0.0615 1.3 0.88 609 14 619 13 655 28 932a-11 14,641 101 12 0.89 1353 0.1023 2.1 0.858 5.0 0.0608 4.6 0.43 628 13 629 24 632 98 992a-13 60,766 74 31 0.96 18,723 0.3551 2.2 5.741 2.5 0.1173 1.1 0.90 1959 38 1938 22 1915 20 1022a-14 43,978 358 37 0.44 2248 0.1000 2.4 0.834 2.8 0.0605 1.4 0.86 614 14 616 13 622 30 992a-15 31,027 240 28 0.73 29,135 0.1062 2.3 0.894 2.7 0.0611 1.6 0.82 650 14 649 13 643 34 1012a-16 16,946 105 14 0.70 2261 0.1275 2.3 1.165 3.5 0.0662 2.6 0.65 774 16 784 19 814 55 952a-17 24,525 153 20 0.58 1659 0.1198 2.3 1.028 4.9 0.0622 4.3 0.47 729 16 718 25 682 92 1072a-18 14,260 120 13 0.54 7441 0.1004 2.4 0.833 3.2 0.0601 2.0 0.77 617 14 615 15 609 44 1012a-19 17,658 124 14 0.76 7466 0.1027 2.7 0.890 3.4 0.0629 1.9 0.82 630 16 646 16 704 41 902a-20 31,090 290 31 0.93 3616 0.0949 2.1 0.771 3.1 0.0589 2.2 0.69 584 12 580 14 565 49 1032a-21 42,256 280 34 0.44 2170 0.1167 2.7 0.993 3.4 0.0617 2.1 0.78 712 18 700 18 665 46 1072a-22 30,424 248 27 0.52 6326 0.1057 2.4 0.891 2.8 0.0611 1.5 0.86 648 15 647 14 644 31 1012a-24 10,705 70 8 1.22 901 0.0952 3.5 0.792 8.3 0.0603 7.5 0.42 586 20 592 38 616 163 952a-25 18,340 112 17 1.17 2239 0.1317 2.6 1.209 3.1 0.0666 1.8 0.82 798 19 805 18 825 37 972a-26 24,690 214 23 0.72 18,373 0.0983 2.4 0.810 2.8 0.0598 1.4 0.87 605 14 603 13 595 29 1022a-27 18,189 173 18 0.41 1067 0.1062 2.6 0.894 4.5 0.0611 3.6 0.59 650 16 649 22 643 78 1012a-28 41,209 306 34 0.65 1148 0.1029 2.6 0.855 4.2 0.0603 3.2 0.63 631 16 627 20 614 70 1032a-29 29,098 179 25 1.13 865 0.1160 2.7 1.022 4.1 0.0639 3.0 0.67 707 18 715 21 738 64 962a-30 11,807 90 15 2.38 18,828 0.1186 2.4 1.032 3.5 0.0631 2.4 0.71 723 17 720 18 711 52 1022a-31 17,960 20 9 1.09 1973 0.3850 2.5 6.373 3.2 0.1201 2.0 0.78 2100 44 2029 28 1957 35 1072a-33 3569 28 4 0.62 725 0.1202 2.6 1.068 4.6 0.0644 3.8 0.57 732 18 738 24 756 79 972a-35 54,493 338 42 1.22 478 0.1033 3.6 0.852 4.4 0.0598 2.6 0.82 634 22 626 21 597 55 1062a-36 60,582 70 31 0.81 1030 0.3779 2.4 6.202 2.8 0.1190 1.4 0.86 2066 43 2005 25 1942 26 1062a-38 13,732 117 12 0.59 4489 0.0983 2.5 0.823 2.9 0.0607 1.4 0.87 605 15 610 13 628 31 962a-39 13,078 95 10 0.28 4377 0.1141 2.4 0.962 3.1 0.0611 2.0 0.77 697 16 684 16 643 43 1082a-40 38,319 204 27 1.06 1071 0.1093 2.8 0.936 4.6 0.0621 3.6 0.61 669 18 671 23 677 77 992a-41 220,472 52 44 0.64 6151 0.7178 2.1 27.511 2.1 0.2780 0.3 0.99 3488 57 3402 21 3352 5 1042a-42 21,959 158 23 1.12 794 0.1333 2.6 1.193 4.2 0.0650 3.4 0.61 806 20 798 24 773 71 1042a-43 12,561 73 7 0.26 7834 0.0948 4.4 0.787 5.8 0.0602 3.8 0.76 584 25 590 26 612 82 952a-44 4223 22 3 2.05 884 0.1113 2.5 0.979 4.0 0.0638 3.1 0.63 680 16 693 20 735 66 932a-46 102,619 38 25 0.80 15,122 0.5598 2.4 13.966 2.6 0.1809 1.1 0.91 2866 56 2747 25 2662 18 1082a-47 44,839 155 22 0.44 7473 0.1369 2.6 1.260 2.9 0.0667 1.2 0.91 827 21 828 17 829 26 1002a-48 20,656 55 10 1.13 1615 0.1742 2.5 1.783 3.7 0.0742 2.8 0.66 1035 24 1039 25 1047 57 992a-49 20,981 92 13 2.23 3363 0.1069 2.4 0.921 3.8 0.0625 3.0 0.63 655 15 663 19 691 63 952a-50 12,577 38 5 0.94 1593 0.1281 2.4 1.190 8.4 0.0673 8.0 0.29 777 18 796 47 849 167 922a-51 21,473 64 9 0.87 3029 0.1304 2.6 1.214 3.8 0.0675 2.8 0.67 790 19 807 21 853 59 932a-52 26,640 89 11 0.98 1307 0.1073 2.2 0.922 4.1 0.0623 3.5 0.53 657 14 663 20 684 75 962a-53 47,974 126 18 0.69 4889 0.1348 2.3 1.220 2.7 0.0656 1.3 0.87 815 18 810 15 795 27 1032a-55 24,130 31 7 1.61 160 0.1561 2.5 1.530 7.5 0.0711 7.1 0.33 935 22 943 47 961 145 972a-58 31,473 101 10 0.59 41,683 0.0925 2.2 0.752 3.0 0.0589 2.1 0.73 570 12 569 13 564 46 1012a-60 25,000 92 9 0.54 5666 0.0952 2.3 0.784 2.9 0.0598 1.7 0.81 586 13 588 13 596 36 982a-61 10,750 34 4 0.49 2030 0.1071 2.4 0.934 3.8 0.0633 2.9 0.64 656 15 670 19 717 62 912a-62 17,958 48 5 0.45 6055 0.1116 2.4 0.946 2.9 0.0615 1.5 0.85 682 16 676 14 655 32 1042a-63 17,117 55 5 0.40 5620 0.0946 2.3 0.781 2.7 0.0599 1.5 0.83 582 13 586 12 599 33 972a-64 15,558 50 6 0.53 1072 0.1107 2.4 0.973 3.9 0.0638 3.1 0.61 677 15 690 20 734 66 922a-65 47,431 99 14 0.09 10,231 0.1435 2.4 1.304 3.8 0.0659 2.9 0.63 865 19 847 22 803 61 1082a-66 29,840 73 9 0.89 2641 0.1056 2.7 0.879 4.1 0.0604 3.1 0.66 647 17 641 20 618 67 105



174M

.F. Pereira

et al.

/ Precam

brian R

esearch 192– 195 (2012) 166– 189

Table 3Sample PNC 3 – arkosic quartzite (Sarnelhas Formation; 40◦17′15′′N; 8◦15′38′′W). 120 grains measured, 113 are concordant in the range of 90–110%, only concordant grains are shown in the table. 206Pb/238U age (2�-error),207Pb/206Pb age (2�-error), degree of concordance.


a3 27,402 80 10 0.46 243 0.1127 2.5 0.966 11.3 0.0621 11.0 0.22 689 16 686 58 679 235 101a4 125,510 102 46 1.37 14,623 0.3713 1.5 6.061 1.6 0.1184 0.6 0.93 2035 27 1985 14 1932 11 105a5 7572 42 5 0.56 1591 0.1077 1.6 0.917 2.5 0.0618 2.0 0.62 659 10 661 12 666 43 99a6 21,381 111 13 0.65 6806 0.1089 1.7 0.938 2.3 0.0625 1.6 0.72 666 11 672 11 691 34 96a7 20,333 93 12 0.54 17,022 0.1228 2.1 1.064 2.8 0.0629 1.9 0.73 747 15 736 15 704 41 106a8 27,163 209 25 0.95 1059 0.0793 1.5 0.619 4.8 0.0566 4.6 0.32 492 7 489 19 478 101 103a9 8865 63 6 0.68 1354 0.0876 1.7 0.709 2.4 0.0587 1.6 0.73 541 9 544 10 556 35 97a10 12,143 78 10 1.48 19,318 0.0994 1.6 0.828 2.0 0.0604 1.2 0.79 611 9 612 9 618 26 99a13 9696 58 6 0.86 1602 0.0987 1.8 0.824 2.6 0.0605 1.9 0.70 607 10 610 12 623 40 97a14 2720 17 2 0.40 987 0.0985 1.8 0.826 4.1 0.0608 3.7 0.45 606 11 611 19 632 79 96a15 5182 28 4 1.46 1556 0.1128 1.5 0.963 3.7 0.0619 3.4 0.40 689 10 685 19 671 73 103a16 22,567 120 13 0.88 36,575 0.0940 1.6 0.768 1.9 0.0593 1.2 0.80 579 9 579 9 578 25 100a17 39,532 269 26 0.55 3295 0.0935 1.7 0.763 2.3 0.0592 1.6 0.73 576 9 576 10 576 34 100a18 40,310 299 26 0.49 2623 0.0861 1.5 0.692 2.1 0.0583 1.5 0.71 532 8 534 9 541 32 98a19 42,654 295 28 0.47 8457 0.0925 1.5 0.736 2.2 0.0578 1.6 0.70 570 8 560 10 521 35 109a20 8565 61 6 0.88 3143 0.0906 1.5 0.727 2.4 0.0582 1.9 0.60 559 8 555 10 539 42 104a21 15,623 126 12 0.17 565 0.0972 2.0 0.827 3.9 0.0617 3.3 0.51 598 11 612 18 665 71 90a22 134,033 65 37 0.85 9096 0.4723 1.5 11.010 2.0 0.1691 1.4 0.73 2494 30 2524 19 2548 23 98a24 46,536 349 38 1.20 3300 0.0932 2.2 0.755 2.4 0.0588 0.9 0.92 574 12 571 10 559 21 103a25 10,826 88 7 0.58 18,086 0.0823 1.3 0.653 3.0 0.0575 2.7 0.44 510 7 510 12 510 59 100a26 29,680 219 26 1.34 48,241 0.0991 1.5 0.808 2.0 0.0592 1.4 0.71 609 8 601 9 573 31 106a27 9759 106 8 0.20 780 0.0808 1.7 0.632 3.3 0.0567 2.8 0.51 501 8 498 13 482 62 104a28 9388 81 9 2.40 6518 0.0787 2.0 0.619 2.9 0.0570 2.0 0.71 489 10 489 11 493 45 99a29 27,736 220 20 0.51 20,183 0.0863 1.7 0.693 2.5 0.0582 1.9 0.67 534 9 535 11 538 41 99a30 37,727 378 31 0.35 18,820 0.0828 1.5 0.654 1.6 0.0573 0.7 0.91 513 7 511 7 505 15 102a31 36,877 321 29 0.43 7259 0.0877 1.6 0.709 2.7 0.0586 2.2 0.59 542 8 544 11 552 47 98a33 18,072 144 16 1.24 16,321 0.0946 1.7 0.768 2.2 0.0589 1.3 0.80 583 10 579 10 564 28 103a35 154,060 212 75 0.69 46,951 0.3217 1.7 4.966 1.9 0.1119 0.8 0.90 1798 27 1813 16 1831 15 98a36 15,515 125 15 1.48 7770 0.0946 1.9 0.763 2.7 0.0585 2.0 0.68 583 10 576 12 549 43 106a37 129,056 72 40 0.85 14,323 0.4761 1.8 11.134 2.0 0.1696 0.8 0.92 2510 37 2534 18 2554 13 98a38 8301 48 6 1.00 12,516 0.1210 1.6 1.064 2.5 0.0638 2.0 0.61 736 11 736 13 734 42 100a39 46,477 57 22 1.23 43,321 0.3109 1.7 4.417 2.2 0.1030 1.4 0.76 1745 25 1716 18 1680 26 104a40 12,345 87 8 0.33 3182 0.0880 1.5 0.711 2.5 0.0586 1.9 0.62 544 8 545 11 551 42 99a41 15,830 105 11 1.02 25,276 0.0937 1.9 0.778 3.5 0.0602 2.9 0.55 577 10 584 16 611 63 95a42 18,350 122 10 0.39 4373 0.0845 1.6 0.674 2.7 0.0578 2.1 0.62 523 8 523 11 523 46 100a43 15,567 16 9 3.60 2930 0.3089 2.3 4.601 3.2 0.1080 2.3 0.71 1735 35 1750 27 1767 41 98a44 3293 16 2 0.83 781 0.1062 2.3 0.882 4.9 0.0602 4.3 0.47 651 14 642 24 612 93 106a46 3771 19 2 0.05 800 0.1111 1.7 0.955 5.2 0.0623 4.9 0.33 679 11 681 26 686 105 99a47 18,749 86 10 1.11 6935 0.1035 1.5 0.859 2.1 0.0602 1.4 0.73 635 9 630 10 612 31 104a48 7125 32 3 0.69 11,513 0.0983 2.1 0.804 3.5 0.0593 2.8 0.59 604 12 599 16 578 61 104a49 88,981 30 17 0.53 10,999 0.5078 1.8 11.732 2.6 0.1676 1.9 0.69 2647 39 2583 24 2534 31 104a50 24,791 144 12 0.71 2728 0.0784 2.0 0.622 3.3 0.0575 2.6 0.61 486 9 491 13 512 58 95a51 8331 38 4 0.85 10,312 0.0907 1.7 0.747 2.5 0.0598 1.8 0.70 560 9 567 11 595 39 94a52 8160 34 3 0.42 6656 0.0954 1.5 0.771 2.8 0.0586 2.4 0.54 587 9 580 13 554 52 106a53 9135 43 3 0.25 1678 0.0810 1.6 0.647 2.3 0.0579 1.6 0.71 502 8 506 9 527 35 95a54 12,233 57 5 0.40 20,159 0.0903 1.8 0.725 2.4 0.0582 1.6 0.74 557 9 554 10 539 35 103a55 6383 27 2 0.48 1470 0.0844 1.8 0.672 3.4 0.0578 3.0 0.51 522 9 522 14 522 65 100a57 6861 31 3 0.47 1512 0.0867 1.5 0.694 2.7 0.0581 2.2 0.56 536 8 535 11 533 49 101a58 52,649 20 10 0.87 26,291 0.4018 1.9 7.205 2.3 0.1300 1.4 0.80 2177 35 2137 21 2099 24 104a59 45,090 17 8 0.74 4860 0.3902 2.2 7.192 2.6 0.1337 1.4 0.85 2124 40 2136 23 2147 24 99a60 87,247 38 15 0.85 5487 0.3614 4.1 5.777 4.2 0.1159 1.2 0.96 1989 70 1943 37 1895 21 105a61 10,893 48 4 0.24 17,173 0.0780 3.2 0.612 4.0 0.0569 2.4 0.80 484 15 485 15 488 52 99a62 21,808 64 6 0.39 35,607 0.0999 1.6 0.811 2.1 0.0588 1.4 0.75 614 9 603 10 561 30 109a63 17,243 57 6 0.46 12,828 0.0951 1.7 0.768 2.1 0.0586 1.3 0.80 585 9 578 9 551 28 106a64 13,769 31 3 0.57 720 0.0895 1.9 0.740 6.6 0.0599 6.3 0.29 553 10 562 29 600 136 92a65 38,131 9 5 1.30 5508 0.4572 1.7 9.779 2.2 0.1551 1.4 0.77 2427 34 2414 20 2403 23 101a66 10,167 35 3 0.37 16,551 0.0944 1.5 0.769 2.0 0.0590 1.3 0.74 582 8 579 9 569 29 102

M.F.

Pereira et

al. /

Precambrian

Research

192– 195 (2012) 166– 189175

Table 3 (Continued)


2a-2 94,760 111 40 0.25 14,458 0.3487 1.7 6.103 2.1 0.1270 1.2 0.81 1928 29 1991 19 2056 22 942a-3 41,944 24 17 2.15 2826 0.4779 1.5 12.009 2.1 0.1822 1.5 0.72 2518 32 2605 20 2673 25 942a-4 154,031 86 48 0.77 9376 0.4685 1.3 11.579 1.8 0.1793 1.2 0.75 2477 28 2571 17 2646 20 942a-5 5540 41 5 1.13 9124 0.1070 1.7 0.891 3.2 0.0604 2.8 0.51 655 10 647 16 617 60 1062a-6 40,334 385 39 0.55 8110 0.0956 1.0 0.809 1.9 0.0613 1.6 0.56 589 6 602 9 651 33 902a-7 22,653 204 16 0.24 2483 0.0822 1.5 0.654 3.1 0.0577 2.7 0.47 509 7 511 13 517 60 992a-9 33,436 231 24 0.36 2601 0.0991 1.2 0.806 3.0 0.0590 2.8 0.39 609 7 600 14 567 61 1072a-10 167,180 77 48 0.61 83,472 0.5295 1.6 14.568 2.2 0.1995 1.5 0.73 2739 35 2787 21 2822 24 972a-11 29,927 331 27 0.48 23,731 0.0789 0.9 0.619 1.4 0.0569 1.1 0.64 490 4 489 6 489 24 1002a-13 3991 33 4 1.23 4853 0.1031 1.8 0.870 3.5 0.0612 3.0 0.51 633 11 636 17 646 64 982a-14 14,409 126 12 0.36 2940 0.0939 1.2 0.757 5.2 0.0585 5.0 0.24 578 7 573 23 549 109 1052a-15 21,139 44 11 1.49 233 0.1693 1.3 1.771 8.4 0.0759 8.3 0.15 1008 12 1035 56 1092 167 922a-16 18,024 163 16 0.40 29,941 0.0986 1.2 0.813 1.9 0.0598 1.5 0.62 606 7 604 9 597 32 1022a-17 35,310 289 38 1.23 10,184 0.1080 1.1 0.910 1.7 0.0611 1.3 0.62 661 7 657 8 643 29 1032a-18 28,145 247 24 0.24 15,719 0.1022 1.1 0.857 1.8 0.0608 1.4 0.60 627 6 628 8 632 31 992a-19 27,934 197 21 0.45 20,288 0.1040 2.0 0.889 2.7 0.0620 1.9 0.72 638 12 646 13 675 40 952a-20 22,061 196 22 0.66 35,940 0.1050 1.0 0.882 2.2 0.0609 2.0 0.44 644 6 642 11 637 42 1012a-21 158,960 165 68 0.32 91,201 0.3915 1.5 6.918 1.8 0.1282 1.0 0.84 2130 28 2101 16 2073 18 1032a-22 23,555 222 21 0.44 39,634 0.0929 1.1 0.758 1.7 0.0592 1.3 0.65 573 6 573 7 573 28 1002a-24 26,969 308 33 1.06 20,339 0.0798 1.2 0.635 1.6 0.0577 1.1 0.72 495 6 499 6 520 25 952a-25 9387 86 9 0.41 10,034 0.0968 1.1 0.798 2.2 0.0598 1.9 0.51 596 6 596 10 596 42 1002a-26 21,283 237 23 0.50 2159 0.0940 1.0 0.775 1.8 0.0598 1.5 0.54 579 5 582 8 595 33 972a-27 23,127 220 21 0.32 29,947 0.0976 1.4 0.811 1.8 0.0603 1.1 0.79 600 8 603 8 614 23 982a-28 154,291 155 70 0.61 52,052 0.4112 1.3 7.627 1.7 0.1345 1.1 0.78 2220 25 2188 15 2158 19 1032a-29 16,333 150 14 0.17 8855 0.0960 1.0 0.789 2.1 0.0596 1.8 0.49 591 6 591 9 590 40 1002a-30 12,429 137 15 0.85 3906 0.0971 1.5 0.798 2.5 0.0596 2.0 0.61 598 9 596 11 589 43 1012a-31 5740 27 5 1.07 7401 0.1512 1.7 1.473 3.0 0.0707 2.5 0.56 908 14 919 18 948 51 962a-32 22,055 234 21 0.36 7778 0.0894 0.9 0.724 1.8 0.0587 1.5 0.53 552 5 553 8 557 33 992a-33 14,161 94 12 0.93 3643 0.1140 2.0 0.990 5.5 0.0630 5.2 0.35 696 13 699 28 708 110 982a-35 1774 19 2 0.43 2903 0.0981 1.4 0.832 6.4 0.0615 6.2 0.23 603 8 615 30 657 133 922a-36 3720 29 4 1.43 2191 0.1192 1.9 1.033 4.1 0.0628 3.7 0.46 726 13 720 22 702 78 1032a-37 27,709 182 24 0.34 43,086 0.1318 1.3 1.165 2.0 0.0641 1.5 0.64 798 10 784 11 745 33 1072a-38 9566 87 8 0.34 16,226 0.0971 1.1 0.785 2.5 0.0586 2.3 0.43 597 6 588 11 553 50 1082a-39 18,269 135 16 0.82 18,111 0.1085 1.4 0.916 2.1 0.0612 1.6 0.66 664 9 660 10 647 34 1032a-40 6019 46 6 0.80 824 0.1215 1.5 1.094 2.7 0.0653 2.2 0.55 739 10 750 14 784 47 942a-41 5309 33 4 0.48 8537 0.1075 2.6 0.916 3.9 0.0618 2.9 0.67 658 16 660 19 667 62 992a-42 13,720 86 10 0.63 12,157 0.1076 1.2 0.915 2.1 0.0616 1.8 0.55 659 7 660 10 661 38 1002a-43 114,694 149 56 1.30 524 0.3026 2.9 4.648 3.2 0.1114 1.4 0.90 1704 44 1758 27 1823 26 942a-44 68,730 79 28 1.00 3313 0.3012 1.3 4.816 1.5 0.1159 0.8 0.86 1697 19 1788 13 1895 14 902a-46 247,560 181 72 0.38 138,853 0.3784 1.7 6.533 2.0 0.1252 1.1 0.85 2069 31 2050 18 2032 19 1022a-47 13,530 79 8 0.39 22,958 0.0969 1.2 0.783 2.5 0.0586 2.2 0.48 596 7 587 11 551 49 1082a-48 16,179 67 9 0.83 24,591 0.1239 1.6 1.112 2.8 0.0651 2.4 0.55 753 11 759 15 776 50 972a-49 6205 31 4 0.75 5171 0.1040 1.6 0.853 3.2 0.0595 2.8 0.48 638 9 626 15 585 61 1092a-50 45,009 201 24 0.74 73,911 0.1097 1.3 0.917 1.8 0.0606 1.2 0.73 671 8 661 9 625 27 1072a-51 25,355 121 12 0.45 11,790 0.0975 1.0 0.804 1.8 0.0598 1.5 0.58 600 6 599 8 597 32 1012a-52 39,320 173 18 0.43 62,175 0.0996 1.3 0.847 2.1 0.0617 1.6 0.62 612 7 623 10 663 35 922a-53 12,232 46 5 0.34 19,528 0.1114 1.4 0.955 2.5 0.0622 2.0 0.58 681 9 681 12 680 43 1002a-54 10,568 42 5 1.10 3669 0.1042 1.5 0.862 2.7 0.0600 2.3 0.54 639 9 631 13 604 49 1062a-57 188,894 90 38 0.50 38,939 0.3900 1.6 6.743 1.8 0.1254 0.9 0.87 2123 29 2078 16 2035 16 1042a-58 29,607 17 7 1.53 1300 0.3302 1.7 5.424 2.5 0.1192 1.8 0.70 1839 28 1889 21 1944 32 952a-59 67,619 36 14 0.63 57,912 0.3528 1.3 5.652 1.8 0.1162 1.2 0.72 1948 21 1924 15 1899 22 1032a-60 255,719 181 64 0.54 16,348 0.3327 1.6 5.629 4.8 0.1227 4.5 0.34 1851 26 1921 42 1996 80 932a-61 77,781 32 14 0.74 19,395 0.3932 1.6 7.009 1.9 0.1293 1.0 0.85 2138 29 2113 17 2088 17 1022a-62 10,777 38 4 0.58 18,195 0.0927 1.3 0.752 2.5 0.0589 2.1 0.54 572 7 570 11 562 45 1022a-64 21,623 80 7 0.66 9279 0.0773 20.0 0.610 20.1 0.0572 1.7 1.00 480 93 483 80 499 37 962a-66 17,198 50 5 0.64 28,548 0.0977 1.1 0.808 1.7 0.0599 1.2 0.67 601 6 601 8 601 27 100



176M

.F. Pereira

et al.

/ Precam

brian R

esearch 192– 195 (2012) 166– 189

Table 4Sample PNC 4 – quartzite (Armorican Quartzite Formation – Penacova; 40◦17′03′′N; 8◦15′50′′W). 60 grains measured, 50 are concordant in the range of 90–110%, only concordant grains are shown in the table. 206Pb/238U age(2�-error), 207Pb/206Pb age (2�-error), degree of concordance.

Number 207Pba (cps) Ub (ppm) Pbb (ppm) Thb /U 206Pbc/204Pb 206Pbc/238U 2� (%) 207Pbc/235U 2� (%) 207Pbc/206Pb 2� (%) rhod 206Pb/238U 2� (Ma) 207Pb/235U 2� (Ma) 207Pb/206Pb 2� (Ma) conc (%)

a2 13,357 76 11 0.64 7763 0.1360 2.6 1.227 2.9 0.0655 1.3 0.90 822 20 813 16 789 27 104a3 5810 32 4 1.11 1533 0.1190 2.5 1.033 4.5 0.0629 3.7 0.57 725 17 720 23 706 78 103a5 9844 56 8 0.59 1180 0.1435 2.8 1.372 5.4 0.0693 4.6 0.51 865 22 877 32 909 95 95a7 6751 62 6 0.30 3855 0.0937 2.3 0.771 3.3 0.0597 2.3 0.71 577 13 580 15 591 51 98a9 15,264 42 8 1.35 4984 0.1650 2.2 1.637 2.8 0.0719 1.8 0.78 985 20 985 18 984 36 100a10 15,885 80 8 0.16 360 0.0959 2.5 0.779 6.1 0.0590 5.6 0.40 590 14 585 28 566 122 104a11 17,896 105 12 0.48 3234 0.1162 2.6 1.012 3.7 0.0632 2.6 0.71 708 17 710 19 714 55 99a13 11,816 48 8 1.89 334 0.1291 2.1 1.207 5.4 0.0678 4.9 0.39 783 16 804 30 863 102 91a14 11,486 105 11 1.23 3005 0.0961 2.5 0.775 3.2 0.0585 2.0 0.78 592 14 583 14 548 44 108a15 9020 71 8 0.43 3563 0.1048 2.7 0.881 3.7 0.0610 2.5 0.74 642 16 642 18 639 53 100a16 86,694 149 37 0.22 10,539 0.2513 2.4 3.199 2.8 0.0923 1.3 0.88 1445 32 1457 22 1474 26 98a17 39,696 238 31 0.63 800 0.1212 2.8 1.049 4.1 0.0628 2.9 0.70 738 20 728 21 700 62 105a18 14,924 116 13 0.42 2540 0.1106 2.2 0.930 3.4 0.0610 2.6 0.65 676 14 668 17 639 55 106a19 11,002 61 10 1.62 1609 0.1253 2.5 1.122 4.0 0.0650 3.1 0.62 761 18 764 22 773 66 98a21 11,437 54 9 0.84 16,662 0.1468 2.4 1.383 3.4 0.0683 2.5 0.70 883 20 882 21 878 51 101a22 9454 45 7 0.62 4779 0.1554 2.6 1.484 3.5 0.0693 2.4 0.73 931 22 924 21 906 49 103a24 12,394 69 9 1.10 465 0.1042 2.3 0.861 8.1 0.0599 7.8 0.29 639 14 631 39 600 169 106a25 20,575 32 13 2.29 451 0.3259 3.8 5.504 5.2 0.1225 3.6 0.73 1819 61 1901 46 1992 63 91a28 22,121 248 24 1.06 1660 0.0872 2.7 0.694 4.7 0.0577 3.9 0.57 539 14 535 20 520 85 104a29 13,325 89 10 0.41 2992 0.1097 3.1 0.951 3.5 0.0629 1.5 0.90 671 20 679 17 704 32 95a30 17,270 155 17 0.41 14,367 0.1067 2.7 0.889 4.4 0.0605 3.5 0.61 653 17 646 21 620 75 105a33 15,396 177 15 0.48 15,101 0.0816 2.4 0.657 3.5 0.0585 2.6 0.68 505 12 513 14 547 56 92a35 26,514 257 25 0.43 7368 0.0970 2.5 0.826 3.1 0.0617 1.8 0.82 597 15 611 14 665 38 90a36 7223 43 6 0.55 10,615 0.1347 3.0 1.279 5.4 0.0689 4.5 0.55 815 23 836 31 895 94 91a37 13,380 106 12 0.79 21,228 0.1022 2.5 0.882 3.3 0.0626 2.1 0.77 627 15 642 16 695 45 90a38 10,288 85 9 0.29 4421 0.1050 2.5 0.870 3.3 0.0601 2.0 0.78 644 16 636 15 607 44 106a39 75,529 45 25 0.68 45,925 0.4821 2.3 10.888 3.4 0.1638 2.5 0.68 2536 49 2514 33 2495 42 102a40 32,432 220 27 0.89 9526 0.1111 2.3 0.936 2.6 0.0611 1.2 0.88 679 15 671 13 644 27 105a41 7558 70 6 0.22 2853 0.0860 2.4 0.688 4.1 0.0581 3.3 0.59 532 12 532 17 532 71 100a42 18,606 70 10 0.26 678 0.1395 2.7 1.262 4.1 0.0656 3.1 0.65 842 21 829 24 794 66 106a43 9182 84 7 0.47 2633 0.0855 2.7 0.688 3.8 0.0584 2.6 0.71 529 14 532 16 544 58 97a44 8569 62 5 0.45 3698 0.0862 2.2 0.696 2.9 0.0585 1.8 0.78 533 12 536 12 549 39 97a46 10,113 8 3 0.07 8276 0.3838 2.1 6.439 3.3 0.1217 2.5 0.64 2094 38 2038 30 1981 45 106a47 5441 39 3 0.82 1277 0.0775 2.6 0.602 4.0 0.0564 3.1 0.63 481 12 479 16 467 69 103a48 5184 26 3 0.99 1953 0.1056 2.6 0.885 3.9 0.0608 2.9 0.67 647 16 644 19 632 63 102a50 6193 36 3 0.27 2338 0.0817 2.7 0.634 12.7 0.0563 12.5 0.21 506 13 499 51 465 276 109a51 5796 26 3 1.46 9177 0.1068 2.5 0.923 4.1 0.0627 3.2 0.61 654 16 664 20 698 69 94a52 2492 11 2 1.38 3805 0.1268 3.1 1.152 6.3 0.0659 5.4 0.50 770 23 778 35 803 113 96a53 151,998 79 34 0.39 18,960 0.4027 2.7 7.345 2.8 0.1323 0.8 0.95 2181 50 2154 25 2129 15 102a54 32,675 159 17 0.86 4171 0.1007 2.3 0.854 3.0 0.0615 1.9 0.78 619 14 627 14 657 40 94a55 29,805 150 14 0.74 2314 0.0862 2.3 0.692 3.3 0.0582 2.4 0.69 533 12 534 14 538 53 99a57 7665 38 4 0.35 1391 0.0964 2.7 0.782 5.5 0.0589 4.8 0.49 593 15 587 25 562 104 106a58 11,911 50 5 0.09 1893 0.0946 2.6 0.790 7.1 0.0606 6.6 0.36 583 14 591 32 624 143 93a59 7503 41 3 0.32 13,017 0.0824 2.3 0.653 2.8 0.0574 1.6 0.82 511 11 510 11 508 35 101a60 17,310 35 6 1.27 464 0.1422 2.8 1.282 12.8 0.0654 12.5 0.22 857 22 838 76 787 261 109a62 13,709 66 6 0.41 3219 0.0869 2.3 0.697 3.2 0.0581 2.1 0.73 537 12 537 13 535 47 100a63 119,173 65 23 0.87 2784 0.3031 2.5 4.753 2.9 0.1137 1.6 0.84 1707 37 1777 25 1860 29 92a64 9894 44 4 0.39 992 0.1004 2.3 0.846 3.9 0.0611 3.1 0.61 617 14 623 18 643 66 96a65 20,535 74 8 0.73 10,216 0.1002 2.5 0.831 2.9 0.0601 1.5 0.86 616 15 614 14 608 33 101a66 18,823 28 6 1.27 25,546 0.1720 2.4 1.740 2.6 0.0733 1.0 0.92 1023 22 1023 17 1023 21 100




F agesA

azcfg6aTa

ig. 3. CL imaging of representative zircons with analytical sites and their resultingnalysis spots and ages are listed in Table 2.

nd Archean (9%; c. 3.5–2.5 Ga) (Figs. 5A and 7). The Neoprotero-oic population is dominated by Cryogenian zircon grains (55%,. 833–632 Ma), followed by Ediacaran (16%, c. 630–550 Ma) andew Tonian (3%, c. 914–900 Ma) ages. Plotted on a probability dia-ram, the Neoproterozoic group shows two main age clusters at c.
86 Ma and c. 637 Ma (Cryogenian), and other less significant peakst c. 763 Ma (Cryogenian), c. 591 Ma and c. 565 Ma (Ediacaran).he youngest zircon provided yields of 549.6 ± 4.4 Ma (Late Edi-caran; 99.5% concordance), the oldest grain providing c. 3.4 Ga
indicated, of sample PNC 2 (Greywacke of the Beiras Group; late Neoproterozoic).

(Paleoarchean). The youngest population average age was esti-mated, using six younger zircon ages, at 560.3 ± 6.6 Ma (LateEdiacaran; 2�, MSWD = 0.87, Probability = 0.35) (Fig. 5A).

In sample PNC 2, zircons are medium-sized (100–150 �m), rang-ing from pink to colourless and from prismatic to rounded. They are
mostly anhedral and euhedral grains are rare. CL imaging showsthat most grains are composite but there are also simple zircons(Fig. 3). Most of the composite grains have cores of variable sizesurrounded by a single thin overgrowth (a-61, 2a-66), but there are


F and tE

ap2zp2ceb

ig. 4. CL imaging of representative zircons with analytical sites with analytical sitesarly Ordovician). Analysis spots and ages are listed in Table 3.

lso cores surrounded by multiple overgrowths (2a-41, a-36). Sim-le zircons are stubby or show concentric oscillatory zoning (2a-52,a-63, 2a-58), with a typical low luminescence (high U content)ones in the centre of the crystal. There are also stubby euhedralrisms, grains with weak concentric growth zoning (2a-20, a-53;
a-61) with a very low luminescence and grains with faint con-entric zoning (a-10, 2a-15). Other types of elongated and narrowuhedral to subhedral prisms (a-40; 2a-27, 2a-24, a-51) show aanded zone in the centre and concentric zoning at the rims.
heir resulting ages indicated, of sample PNC 3 (Quartzite of the Sarnelha Formation;

In sample PNC 2, 118 targets were analysed, with 102 zirconspots showing 90–110% concordance. These findings (Fig. 5B) arequite similar to those with sample PNC 1 with slight differences inpercentages for pre-Neoproterozoic ages and within the age clusterdistribution for the Neoproterozoic population (Fig. 7).

The zircon population of sample PNC 2 shows the following agedistribution: Neoproterozoic (77%, c. 992–563 Ma), Mesoprotero-zoic (8%, c. 1.2–1.0 Ga), Paleoproterozoic (10%, c. 2.2–1.7 Ga), andArchean (5%, c. 3.4–2.5 Ga) (Figs. 5B and 7). Like sample PNC 1, the


F Beirasa show

Ng7T

ig. 5. U–Pb Concordia plots of zircon grains from samples PNC 1 and PNC 2 of the

ll analyses. Concordia plots A2 and B2 showing the Neoproterozoic ages. A3 and B3

eoproterozoic population of sample PNC 2 is dominated by Cryo-enian zircon grains (52%, 845–631 Ma), with two age clusters at c.96 Ma and c. 660 Ma, and another smaller population at c. 723 Ma.onian ages (8%, c. 992–865 Ma) show an age cluster at c. 942 Ma

Group (for locations of the samples see Fig. 1). Concordia plots A1 and B1 showing the ages of the younger zircon populations of the late Neoproterozoic greywackes.

(Figs. 5B, 7 and 8). The Ediacaran population (18%, c. 630–563 Ma)population is characterised by two age clusters at c. 616 Ma and588 Ma. The youngest zircon was dated at 562.5 ± 6.1 Ma (Late Edi-acaran; 96.6% concordance), the oldest at c. 3.4 Ga (Paleoarchean).


Fig. 6. U–Pb Concordia plots of zircon grains from samples PNC 3 and PNC 4 of the Sarnelha and Armorican Quartzite formations respectively (for locations of the samplessee Fig. 1). Concordia plots A1 and B1 showing all analyses. Concordia plots A2 and B2 showing the Neoproterozoic, Cambrian and Ordovician ages. A3 shows the ages of theyounger zircon populations of the Sarnelha Formation quartzite and B3 shows the youngest age yielded by the Armorican quartzite.


F m lateq

Ta

3a

ttdpsnascast5apw

ig. 7. Probability plots and pie diagrams of detrital zircon U–Pb age populations frouartzites (PNC 3 and PNC 4, at the top) of SW CIZ samples analysed in this study.

he youngest population was estimated at 578.5 ± 4.7 Ma (Late Edi-caran; 2�, MSWD = 0.85, Probability = 0.36) (Fig. 5B).

.2.2. Ordovician quartzites of Sarnelhas and Penacova (PNC 3nd PNC 4)

The zircon population of sample PNC 3 is dominated by mediumo large (120–220 �m) grains, ranging from transparent colourlesso translucent pink, and more rarely brown. Two groups can beistinguished: one group with euhedral to subhedral prismatic toyramidal crystal forms, and another group with more rounded andtubby forms. This sample includes more elongated crystals witho visible faces when compared with greywacke samples PNC 1nd PNC 2. CL imaging reveals a wide variety of forms and internaltructures with composite and simple grains (Fig. 4). Composite zir-ons include rounded or irregularly shaped cores (a-62, a-33), thatre typically very small (a-6, a-54, 2a-33). Zoning patterns in thetubby simple grains range from clear (a-52, 2a-66, 2a-18, 2a-42),o weak (2a-16) concentric fine (a-31) oscillatory zoning. Grain a-
7/a-52 is a simple crystal with sector-growth zoning, affected by
high luminescence recrystallisation front. CL imaging also showsrismatic and narrow crystals characterised by thin banded zoningith moderate luminescence contrast (2a-2) truncated by diffuse

Neoproterozoic greywackes (PNC 1 and PNC 2, at the bottom) and Early Ordovician

recrystallisation fronts (2a-11, 2a-24) (Fig. 4). Most of the zirconsfrom sample PNC 4 (95%), a quartzite from the Armorican QuartziteFormation are fine- to medium-grained (80–110 �m). Zircon grainsrange from transparent colourless to translucent and slightly pink.Most are elongated euhedral to subhedral prisms or stubby subhe-dral with smooth crystalline faces.

The zircon ages obtained for PNC 3 and PNC 4 are shown inFig. 6 (Tables 3 and 4). The distribution of age populations foundin the arkosic quartzite of the Sarnelhas Formation (sample PNC3) is different from the two samples of the Beiras Group (samplesPNC 1 and PNC 2). 60% of zircon ages of sample PNC 3 are Neo-proterozoic (out of a population of 120 analysed targets, 113 have90–110% concordance) (Figs. 6–8). The Neoproterozoic populationis dominated by: Ediacaran zircon grains (36%, c. 627–544 Ma)with two main age clusters at c. 609 Ma and 582 Ma, Cryogenian(23%, c. 798–633 Ma) and rare Tonian (1%, c. 908 Ma) ages. Thepre-Neoproterozoic record consists of Paleoproterozoic (17%, c.2.4–1.7 Ga), Archean (5%, c. 2.8–2.5 Ga) and Mesoproterozoic (1%,
only 1 grain, c. 1.1 Ga). Early Paleozoic ages are dominated by Cam-brian ages (14%, c. 542–489 Ma), whereas Ordovician grains arescarce (3%, c. 486–484 Ma). The youngest zircon provided yieldsof 484.2 ± 7.3 Ma (Early Ordovician; 99.2% concordance) and the

182 M.F. Pereira et al. / Precambrian Resea

Fig. 8. Relative age probability plots of U–Pb detrital zircon analyses (in the intervalc. 850–540 Ma) from the late Neoproterozoic (Beiras Group) and Early Ordovician(Sarnelhas and Armorican Quartzite Formation) detrital sedimentary rocks of SWCp

D

oTC

az8(scaNwzoc(aai

4

odooi

IZ (this study). Shaded bar outline for comparison the age ranges of the late Neo-roterozoic sedimentary rocks of the OMZ.

ata from Pereira et al. (2011).

ldest provided c. 2.8 Ga (Neoarchean–Mesoarchean transition).he youngest population age is estimated at 492.3 ± 2.6 Ma (Lateambrian; 2�, MSWD = 3.1, Probability = 0.079) (Fig. 6).

In sample PNC 4, out of a population of 60 analysed targets, group of 50 spots has 90–110% concordance. The Neoprotero-oic population is dominant (66%) with: 36% of Cryogenian (c.42–639 Ma), 20% of Ediacaran (c. 627–577 Ma) and 10% of Tonianc. 985–857 Ma) ages (Figs. 6–8). The population of zircon ageshows two main age clusters in the Ediacaran at c. 596 Ma and. 550 Ma and two other relatively less significant age clusterst c. 652 Ma (Cryogenian) and c. 626 Ma (Ediacaran). The pre-eoproterozoic ages only represent 14% of the population as ahole (10% Paleoproterozoic, c. 2.5–1.9 Ga; and 4% Mesoprotero-

oic, c. 1.5–1.0 Ga). The early Paleozoic population includes 9 grainsf Cambrian age (18%, c. 539–505 Ma) and 1 Ordovician grain (2%,. 481 Ma). The youngest zircon grain dated yields 480.9 ± 5.9 MaEarly Ordovician; 102.9% concordance), the oldest zircon is datedt c. 2.4 Ga (Siderian) and the youngest population age is estimatedt 529.7 ± 4.5 Ma (Early Cambrian; 2�, MSWD = 0.002, Probabil-ty = 0.96) (Fig. 6).

. Significance of U–Pb detrital zircon data

The U–Pb geochronology of the Beiras Group greywackesbtained calibrates the stratigraphic column of SW Iberia whose
epositional age is imprecisely represented on the Geological Mapf Portugal (1992, 2010). The probable maximum depositional agef c. 578–560 Ma for the Beiras Group greywackes matches thenterval of deposition of the Serie Negra in the OMZ (c. 590–545 Ma;
rch 192– 195 (2012) 166– 189

Pereira et al., 2011 and references therein). Our new data sug-gest that deposition in both CIZ and OMZ Ediacaran basins wascoeval with the development of an active margin with volu-minous arc magmatism along the northern Gondwana margin(Avalonian–Cadomian belt; Nance et al., 1991, 2002; Linnemannet al., 2004, 2007, 2008; Pan-African belt; Abati et al., 2010 and ref-erences therein). In over 75% of the Beiras Group greywackes, zirconages are late Neoproterozoic. Cryogenian ages are those most rep-resented (c. 833–631 Ma, 50%), followed by Ediacaran (20%) andTonian (3–8%) ages (Figs. 8 and 9).

Cryogenian ages show a significant concentration in the inter-val c. 680–635 Ma, whereas Ediacaran zircons occur in age clustersin increasing order of abundance at c. 584, 565 and 615–605 Ma.A notable feature that distinguishes the Beiras Group greywackes(SW CIZ) from the Serie Negra greywackes (OMZ) is the higher fre-quency of young Cryogenian ages relative to Ediacaran ages. OlderCryogenian ages (c. 840–750 Ma) are represented both in the BeirasGroup and the Serie Negra greywackes, but are more abundant inthe former (Fig. 8).

The remaining 25% of zircons analysed from Beiras Groupgreywackes are Paleoproterozoic (10%), Archean (5–9%) and Meso-proterozoic (4–8%) in age. The Paleoproterozoic and Archean agesmatch the main zircon-forming events of the West African craton(Liegeois et al., 1991; Hirdes and Davis, 2002; Thieblemont et al.,2004).

In the Ordovician quartzites of SW CIZ, the percentage of Neo-proterozoic ages (60%; Fig. 7) is lower as compared with that ofthe Beiras Group greywackes (74–77%; Fig. 7). Sample PNC 3 (Sar-nelha quartzite) is dominated by Ediacaran ages (c. 627–544 Ma,ca. 35% with two age clusters at c. 582 Ma and c. 544 Ma), followedby Cryogenian ages (23%) and few Tonian (percentages <1%) ages.Mesoproterozoic ages are relatively unrepresented (percentages<1%). The probability plot of the Sarnelhas arkosic quartzite (PNC 3)is very similar to those previously obtained for Ediacaran and Cam-brian sedimentary rocks of the OMZ (Pereira et al., 2008a, 2011;Linnemann et al., 2008) and the Early Ordovician Urra volcaniclasticFormation of the CIZ-OMZ transition (Solá et al., 2008). However,contrary to what the OMZ samples show, the interval of Cryoge-nian ages (c. 798–633 Ma) in sample PNC 3 is well represented andis similar to that found in Beiras Group greywackes (samples PNC1 and 2).

Our data reveal differences between the Neoproterozoic zir-con ages found in the Sarnelhas arkosic quartzites (PNC 3) andthe Armorican quartzite of Penacova (PNC 4). In the Armoricanquartzite of Penacova, Cryogenian ages are dominant and moreabundant than Ediacaran ages (with an age cluster at c. 596 Ma)whereas in the Sarnelhas arkosic quartzite the population of Edi-acaran zircons is larger than the Cryogenian. Sample PNC 4 showsimportant differences as compared with correlative Armoricanquartzites from the CIZ-OMZ transition. Armorican quartzites fromPenacova (see this study) have Tonian (10%) and Mesoprotero-zoic (4%) ages whereas Armorican quartzites from the CIZ-OMZtransition have few Tonian ages and no Mesoproterozoic ages(Linnemann et al., 2008).

The source of the Sarnelhas quartzite (PNC 3) resembles thedistribution of detrital zircon ages from sedimentary rocks of theEdiacaran and Cambrian of the OMZ and also the Urra volcaniclasticFormation and Armorican quartzites from the CIZ-OMZ transitionzone. The Armorican quartzites of Penacova (PNC 4, see this study)have a zircon age distribution that overlaps with that of BeirasGroup greywackes (PNC 1 and PNC 2) and Sarnelha quartzites.

The Ordovician quartzites of SW CIZ (Sarnelhas and Penacova)
comprise 14–18% Cambrian zircons (c. 535–510 Ma) and a fewOrdovician zircons (percentages <3%, c. 488–480 Ma). The early-and mid-Cambrian age range is well characterised in the OMZ, incontrast with the SW CIZ, and represents the onset of rifting along


comp

t2qwdzwtSme

5

B8m

(

Fig. 9. Zircon data from the Beiras Group greywackes (late Neoproterozoic) and

he northern Gondwana margin (Sánchez-García et al., 2003, 2008,010; Chichorro et al., 2008). Composite zircon grains of Ordovicianuartzites have Cambrian (c. 522–513 Ma) overgrowths on coresith Cambrian ages (c. 542 Ma and c. 537 Ma), indicating recyclinguring early Cambrian magmatism. The Early Ordovician detritalircons found in Sarnelhas and Penacova quartzites represent aidespread magmatic event in SW CIZ (Urra volcaniclastic Forma-

ion, c. 490–488 Ma, Solá et al., 2008) and in the NW CIZ (Ollo deapo Formation, Montero et al., 2007) that preceded the passiveargin stage along the southern flank of the Rheic Ocean (Murphy

t al., 2006a,b; Nance et al., 2010).

. Geodynamic implications

The ages of Cryogenian and Ediacaran detrital zircons of theeiras Group greywackes are concentrated in the interval c.40–565 Ma, during which there were two major events of mag-atism in North Gondwana (Fig. 9):

1) The Avalonian–Cadomian arc described in North America,Western-Central Europe and North Africa (Murphy and Nance,1991; Fernández-Suarez et al., 2000; Nance and Murphy, 1994;
Nance et al., 2002, 2008; Nagy et al., 2002; Pereira et al.,2006, 2008a; Linnemann et al., 2008; Abati et al., 2010). TheAvalonian–Cadomian orogeny formed in a convergent marginof Gondwana (with fragmentary evidence of many episodes
arison with a compilation of zircon age distributions of potential provenances.

within the interval c. 760–670 Ma and 610–540 Ma; Nance et al.,2008; Murphy et al., 2008).

(2) Igneous events in North Africa attributable to Pan-Africanorogenic processes (Liégeois et al., 1994; Abdelsalam et al.,2002 and references therein; Samson et al., 2004; D’Lemoset al., 2006; Küster et al., 2008; Abati et al., 2010 and refer-ences therein). After a period dominated by intra-continentalrifting with oceanisation (early Neoproterozoic), tectonic inver-sion of basins has occurred along with the consequentcontinent–continent collisions between cratons to form Gond-wana (Kroner and Stern, 2004; Saalman et al., 2007 andreferences therein). The record of the Pan-African orogeny (lateNeoproterozoic) is well expressed along the Trans-Brasilianoand Trans-Sahara belts connection (c. 790–660 Ma, 650–600 Maand 590–540 Ma; Liégeois et al., 2003; Silva et al., 2005;Cordani et al., 2009). These two Neoproterozoic orogenic pro-cesses (Pan-African and Cadomian; Murphy and Nance, 1991;Nance and Murphy, 1994) are sometimes difficult to distinguishbecause they overlap in time and locally in space where thePan-African belts (interior collisional orogenic sutures of Neo-proterozoic supercontinent assembly) extend through NorthAfrica close to the northern Gondwana margin reaching theAvalonian–Cadomian orogenic belt (in a peripheral position
with respect to the Neoproterozoic supercontinent; Fig. 10).Subduction zones between converging Gondwana blocks prob-ably relocated to the margins of Gondwana after the collisionbetween continents (Murphy and Nance, 1991).


F hases

h up –

t

tIwsaobmuC

ftm5a5pr(s

ig. 10. Schematic models for the (A) Cryogenian and (B) Ediacaran evolutionary pighlight the main source areas for the SW Iberia Cadomian basements (Beiras Groheir detrital zircon content.

Several hypotheses may be considered when looking for poten-ial sources for the Cryogenian and Ediacaran detrital zircons of SWberia and correlatives (Figs. 9 and 11). When comparing our data

ith data from Cadomian correlatives (Fig. 11) we find a number ofimilarities and differences. As mentioned before, there is a notice-ble frequency of Cryogenian ages in the Ediacaran greywackesf the Beiras Group (see this study). In contrast, in the Ediacaranasins of the OMZ (SW Iberia) and the Saxo-Thuringian Zone (Cado-ia), the older Cryogenian ages (c. 850–700 Ma) are significantly

nder-represented as compared with the Ediacaran and youngerryogenian ages (Linnemann et al., 2007, 2008).

The four main phases of late Cryogenian–Ediacaran zircon-orming events attributable to Cadomian magmatism recorded inhe Ediacaran and Cambrian sequences of the OMZ (late Cado-

ian magmatic arc – Fig. 10B – are: c. 635 Ma, 615–605 Ma,90–570 Ma, and 560–550 Ma; Pereira et al., 2011). These eventsre also recorded in the SW CIZ (c. 635 Ma, 615–605 Ma, 584 Ma and65 Ma; see this study). When compared with Cadomia, the main
hase of arc magmatism in the Saxo-Thuringian Zone (Germany) isecorded, as in the OMZ, at c. 610 Ma by Cambrian platformal rocksZwethau Formation) and between c. 590 and 560 Ma by back-arcynorogenic strata (Rothstein Formation and the Weesenstein and
of the northern Gondwana active margin geodynamic evolution. In B-, grey arrowsSW CIZ, and Serie Negra – OMZ) separated sufficiently to justify the differences in

Clanzschwitz Groups) (Linnemann et al., 2007, 2008). The pres-ence of c. 750–560 Ma detrital zircons in the Ediacaran greywackesof the Saxo-Thuringian Zone, interpreted as representing the ero-sion of Pan-African and Avalonian–Cadomian source rocks, can beextended to OMZ and SW CIZ correlatives. However, the back-arcbasin of the Beiras Group (SW CIZ) may have been located closerto source rocks of an early Cadomian magmatic arc and/or of thePan-African suture (Fig. 10A). In turn, the back-arc basins of theSaxo-Thuringian Zone, the North Armorican Cadomian Belt andOMZ may have been located near source rocks of a late Cadomianmagmatic arc (Fig. 10B).

In SW Iberia and in the Saxo-Thuringian Zone, outcrops of Neo-proterozoic rocks with ages older than c. 630 Ma (Fig. 11) areunknown but we cannot exclude the possibility that they mayexist at depth. In contrast, in the North Armorican Cadomian Belt(France) there are outcrops of Cryogenian gneisses (PentevrianComplex; Egal et al., 1996) with c. 755–745 Ma protolith ages(Samson et al., 2005) that are interpreted as being the oldest roots
of the Cadomian arc (Chantraine et al., 1994). These Cryogenianrocks are intruded by Ediacaran granitoids (Jospinet granodioritewith c. 626 Ma; Nagy et al., 2002) and are overlain by the Briove-rian Supergroup strata, interpreted as having been deposited in


Fig. 11. Schematic chart with proposed correlation between peri-Gondwanan correlatives: North Africa, Cadomia, SW Iberia, NW Iberia and Anti-Atlas (see refs. Destombese

M

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aece7FOc1tAopoatNfII1

t al., 1985; Doré, 1994; Hamoumi et al., 1994; Robardet et al., 1994).

odified from Pereira et al. (2006).

adomian back-arc basins (Chantraine et al., 1994), like the Serieegra (Pereira et al., 2006, 2008a) and the Beiras Group (Pereirat al., 2008b; see this study) in SW Iberia (Fig. 11). The Ediacaranreywackes of the Brioverian Supergroup show detrital zirconsith a young population scattered in the interval c. 840–550 Ma

Binic Formation; Fernández-Suarez et al., 2002) which match theesults obtained for Cadomia and SW Iberia. The Brioverian sedi-entary rocks are intruded by Ediacaran granitoids (c. 600 Ma, Portoguer tonalite; c. 576–574 Ma, Fort La Latte and St. Quay quartz

iorites; Nagy et al., 2002).The range of Cryogenian ages of the Beiras Group greywackes is

kin to early Avalonian magmatic activity (c. 763–630 Ma, Nancet al., 2008 and references therein): the oceanic island arc vol-anic rocks of the Burin Group (c. 763 Ma; Newfoundland; Murphyt al., 2008), the early arc phase with the Economy River gneiss (c.34 Ma; Nova Scotia; Doig et al., 1991), the Hawkes Hill Tuff and theurby’s Cove Intrusive Suite (c. 729 Ma and 673 Ma; Newfoundland;’Brien et al., 1996), the Stanner-Hanter and the Malverns Plutonicomplexes (c. 700 Ma and c. 677 Ma; Britain; Tucker and Pharoah,991) and also, the Stirling belt and volcanic arc rocks of Cape Bre-on Island (c. 681–650 Ma; Bevier et al., 1993). The main phase ofvalonian arc magmatism and coeval synorogenic sedimentationccurred at c. 640–570 Ma (Nance et al., 2002). Ganderia is anothereri-Gondwana terrane (Van Staal et al., 2009) whose history partlyverlaps with the magmatic history of Avalonia (Nance et al., 2008nd references therein) in an early phase of arc magmatism ofhe Lingley Suite and the Brookville orthogneiss (c. 625–605 Ma;ew Brunswick; Bevier and Barr, 1990; Currie and McNicoll, 1999)

ollowed by a later phase at c. 578–555 Ma (Roti and Cripplebackntrusive suites, Newfoundland and Bras d’Or plutons, Cape Bretonsland; Dunning and O’Brien, 1989; Barr et al., 1990; Dostal et al.,996; Rogers et al., 2006).

Not excluding the Avalonian magmatic activity of Newfound-land and Nova Scotia and the Cadomian arc preserved in Europe aspotential sources of the Cryogenian detrital zircons of SW Iberia,other (more conservative) alternatives are possible (Fig. 2):

(1) The oldest Cryogenian ages found in Beiras Group greywackesprobably represent detritus deposited along the northernGondwana margin from denudation of North Africa interiorPan-African shields (the Trans-Sahara belt, the Arabian-Nubianshield and the West African craton). The Trans-Sahara beltis characterised by zircon-forming events in the interval c.900–630 Ma: (i) the Sahara metacraton at c. 858 Ma (Dam EtTor gneiss), c. 744 Ma (Jebel Moya granite), c. 741 Ma (south-west Aswan granite), c. 714 Ma (Emzeggar monzogranite),c. 718, 680 and 661 Ma (Nubian Desert granites), c. 643 Ma(Dabaga monzogranite), c. 634 Ma (Aswan granite), c. 626 Ma(Jebel Umm Shagir granite), c. 605–591 Ma (Bayuda Desert andSabaloka granites) and c. 578 Ma (Nakkil granite) (Abdelsalamet al., 2002 and references therein; Küster et al., 2008); (ii)the Tuareg shield at c. 868 Ma (Iskel tonalite), c. 849 Ma (IskelMonzogranite), c. 730–696 Ma (Tilemsi arc and Kidal tonali-ties), c. 651–620 Ma (Iskel granite and Kidal tonalite) and c.587–583 Ma (South Tirek granodiorite, Immezzarene granite)(Caby, 2003 and references therein). The Arabian-Nubian shieldshows episodes of zircon crystallisation at c. 810 Ma (Eritreapre-syn-kinematic diorites and tonalities) and c. 620–585 Ma(Eritrea late- to post-kinematic granites) (Teklay, 2005); islandarc mafic magmatism crystallised at c. 900–740 Ma in western
Eritrea and northern Ethiopia (Teklay, 2005; Avigad et al., 2007).
(2) The Anti-Atlas Supergroup of the West African craton includes:the Tasiriwine ophiolite dated at c. 762 Ma (Samson et al., 2004),considered to be the western extension of the Bou Azzer-El

1 Resea

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86 M.F. Pereira et al. / Precambrian

Graara ophiolite (Pan-African suture; Kroner and Stern, 2004),the synorogenic sedimentary rocks of the Saghro Group withdepositional ages of c. 620–610 Ma and associated with the ero-sion of Neoproterozoic magmatic rocks (c. 640–610 Ma; Abatiet al., 2010). The Saghro Group was later intruded by Ediacarangranitoids ranging from c. 615 Ma to 580 Ma (D’Lemos et al.,2006; Ennih and Liegeois, 2008; Abati et al., 2010 and referencestherein) such as the Bleida granodiorites with c. 579–578 Macrystallisation ages (Inglis et al., 2004). Like the Serie Negra andthe Beiras Group (SW Iberia), the Saghro Group has an impor-tant population of zircons dated at c. 620–580 Ma with a majorpeak at c. 610 Ma, which probably represents the erosion of amagmatic arc located close to the Pan-African suture that isbuilt on the West African craton basement (Abati et al., 2010).

3) Other potential sources for the oldest Cryogenian ages foundin Beiras Group greywackes are the extension of the Pan-African suture in the southern end of the Trans-Sahara belt, inWest Africa, which is connected to the relatively remote Trans-Braziliano belt, in South America (Kroner and Stern, 2004;Basei et al., 2010). These two potential sources are consid-ered again when we discuss the Early Neoproterozoic detritalzircons. Although less abundant, the c. 992–865 Ma record inthe Beiras Group (4–8%) provided additional constraints. TheTonian record is almost absent in the OMZ. Tonian zircon-forming events (c. 900–800 Ma) have been recorded in theArabian-Nubian shield (Stern, 2002) and in the Trans-Brazilianbelt (Pimentel et al., 1999; Saalman et al., 2007), which mayrepresent relatively remote potential source areas with juve-nile magmatism. The Sm–Nd isotopic signatures obtained forthe Beiras Group greywackes suggest an important contribu-tion of source igneous rocks younger than 1.2 Ga and relatedto juvenile magmas (e.g. Tassinari et al., 1996), whereas for theSerie Negra greywackes the source was mainly composed ofolder crustal rocks and with less contribution of juvenile mag-mas (López-Guijarro et al., 2008). The �Ndt values of BeirasGroup greywackes, calculated for 560 Ma (time of depositionobtained in this study based on the results of Tassinari et al.(1996), are moderate negative (−1.6 < �Ndt < −3.6) and theTDM model ages range from 1.32 to 1.24 Ga. The Serie Negragreywackes Sm–Nd isotopic signature have relatively lower�Ndt values (−5.5 < �Ndt < −11.4) and older TDM model ages(1.6< TDM < 1.9 Ga) (López-Guijarro et al., 2008; Solá et al., 2011).This juvenile magmatic source may be represented by the detri-tal zircon with the oldest Cryogenian and Tonian ages fromBeiras Group greywackes.

The oldest zircons analysed from Beiras Group greywackes are,n ascending order of importance, Paleoproterozoic, Archean and

esoproterozoic in age. The highest concentration of Paleoprotero-oic zircon ages occurs in the interval c. 2–1.8 Ga and matches theburnean zircon-forming event of the West African craton (Liegeoist al., 1991; Hirdes and Davis, 2002; Thieblemont et al., 2004),he Orosirian zircon-forming event of the Amazonian craton (Baseit al., 2010 and references therein) as well as Ganderia (Barr et al.,003). These ages also coincide with the interval of ages obtainedrom the 2.2–2 Ga Icartian basement metamorphic rocks of Cado-

ia (North Armorican Cadomian Belt, France; Chantraine et al.,994). The oldest ages of the Beiras Group are mainly Neoarchean2.8–2.6 Ga) but also Meso-Paleoarchean. They indicate recyclingf magmatic rocks formed during: (1) the Siderian (c. 2.35–2.3 Ga)ircon-forming event of the Amazonian craton (Basei et al., 2010nd references therein) and is also reported in Ganderia (Barr
t al., 2003); (2) the Liberian (c. 2.9–2.7 Ga) zircon-forming eventf the West African craton (Potrel et al., 1996; Koulamelan et al.,997; Key et al., 2008); and (3) the Leonian zircon-forming eventc. 3.5–3.0 Ga; Thieblemont et al., 2004 and references therein),
rch 192– 195 (2012) 166– 189

exclusive of the West African craton. The intervals typical for theWest African and Amazonian cratons are not intended to discrimi-nate which of them are the main potential source.

The presence of Mesoproterozoic zircons together with Tonianages in the SW CIZ (not well represented or almost absent in theOMZ) suggest the possibility of sources from outside the WestAfrican craton. In the case of NW Iberia (West-Asturian LeoneseZone) the significant presence in Ediacaran sedimentary rocks ofdetrital zircons with Mesoproterozoic and Tonian ages has beenused to suggest these basins were located adjacent to sourcesof the Amazonian craton (Fernández-Suarez et al., 2002). Despitethe existence of 8% of Mesoproterozoic zircon ages in the BeirasGroup greywackes, this is not a strong argument for consideringthe Amazonian craton as the main potential source. The existenceof a secondary source may have been related to the dispersionof sediments along the continental margin of North Gondwana.The Série Negra greywackes also contain few Mesoproterozoic zir-cons (Linnemann et al., 2008). The Mesoproterozoic detrital zirconsfound in the Beiras Group greywackes may have come from:

(1) A sedimentary source located in a paleoposition external to theWest African craton, which formed close to the Amazonian cra-ton and was displaced by large distances along the northernGondwana active margin.

(2) A sedimentary source located in a paleoposition close to theWest African craton, which formed in the Arabian-Nubianshield and the Sahara Metacraton.

Our findings also indicate that Ordovician quartzites of Penacovawith maximum depositional ages in the interval c. 490–480 Mabelonged to a continental platform (preserved in North Africa,Iberia, Armorica and Bohemia) along the northern Gondwana mar-gin (Robardet, 2002). These deposits are attributed to extensiverifting coeval with the formation of the Rheic Ocean (Gutierrez-Alonso et al., 2003; Murphy et al., 2006a,b; Nance et al., 2010). Themost important result is that, like in the Ediacaran Beiras Groupgreywackes, most of the detrital zircons in the Early Ordovicianquartzites are derived from the erosion of recycled Neoproterozoicmagmatic rocks.

Several differences are apparent when we compare the Ordovi-cian (Armorican) quartzites of NW and SW Iberia. Detrital zirconsof Armorican quartzites of NW Iberia (CZ, WALZ and NW CIZ,Gutierrez-Alonso et al., 2003) are mainly Neoproterozoic (c.950–550 Ma) and Mesoproterozoic (c. 1.3–1.0 Ga) in age, but alsoinclude Paleoproterozoic (c. 2.3–1.8 Ga) and Archean (c. 3.0–2.5 Ga)ages, and do not include ages in the interval c. 2–1.8 Ga (Eburneanorogeny) found in SW Iberia (OMZ-CIZ transition zone, Linnemannet al., 2008; and SW CIZ, see this study), that are typical of theWest African Craton (Fernández-Suarez et al., 2002; Gutierrez-Alonso et al., 2003; Pereira et al., 2008a, 2011; see this study).The contrasting detrital zircon populations of NW and SW Iberiain the Early Ordovician may reflect differences in source areasprobably due to strong crustal extension and the developmentof complex systems of grabens and horsts (Linnemann et al.,2008; Sánchez-García et al., 2010) and/or along margin ter-rane transport in northern Gondwana (Fernández-Suarez et al.,2002). The opening of new wrench-basins with significant rates ofsubsidence and uplift, filled with detritus from denudation ofthe former Neoproterozoic magmatic arc, dominate the northernGondwana passive margin between c. 490 and 540 Ma. The con-trasting detrital zircon populations of NW and SW Iberia in the EarlyOrdovician may reflect differences in source areas probably due to
strong crustal extension and the development of complex systemsof grabens and horsts (Linnemann et al., 2008) and/or along marginterrane transport in northern Gondwana (Fernández-Suarez et al.,2002). The opening of new wrench-basins with significant rates

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6

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1

2

3


f subsidence and uplift, filled with detritus from denudation ofhe former Neoproterozoic magmatic arc, dominate the northernondwana passive margin between c. 490 and 540 Ma.

This study reveals a close relationship between the distribu-ion of detrital zircon ages in the Ediacaran greywackes and thearly Ordovician quartzites of SW CIZ, suggesting that sedimen-ary provenance of extensive areas in continental passive margins

ay persist over time, with slight differences related to input ofoung detrital zircons (Cambrian and Ordovician ages in the exam-le of the northern Gondwana margin). The detrital zircon contentf the Early Ordovician passive margin sedimentary rocks in Iberias strongly dependent on the mineralogy of the older rocks on

hich they are unconformably deposited. Our data suggest thathe detrital zircons of the Armorican quartzites in SW Iberia wereverwhelmingly derived from direct recycling of the Ediacaranreywackes of the Beiras Group (CIZ; see this study) and the Serieegra (OMZ; Linnemann et al., 2008). Other sources were veryinor. In NW Iberia, the striking similarity between the distribu-

ion of detrital zircon ages of the Armorican quartzites and the olderate Ediacaran sedimentary rocks in the Narcea Anticline (WALZ;ernández-Suarez et al., 2002) is consistent with this reasoning.

. Conclusions

When interpreted in conjunction with the findings of previoustudies on the Neoproterozoic evolution of the northern Gondwanaargin, the data yielded by this study indicates that:

. The detrital zircon populations of the Beiras Group greywackes(Ediacaran) point to the existence of three major episodesof zircon crystallisation probably associated with long-livedNeoproterozoic magmatism located near or at the northernGondwana margin at: c. 850–700 Ma – Pan-African suture; c.700–635 Ma – early Cadomian arc; and c. 635–545 Ma – lateCadomian arc.

. The oldest detrital zircon ages (Paleoproterozoic and Archean)recorded in the Beiras Group greywackes detrital zircons indi-cate that the main source of the SW CIZ is derived from the WestAfrican craton. However, the contribution of another or othersecondary source(s) containing Mesoproterozoic and Tonianages needs to be considered. Such possible secondary sourceswere probably derived indirectly from the Amazonian craton,due to drift of sediment along the shore and/or derived from anexternal source displaced by large distances along the northernGondwana active margin.

. The differences found in populations of detrital zircon from theCadomian basement of SW Iberia (Ediacaran greywackes of theBeiras Group-SW CIZ Cadomian basement and the Serie Negra-OMZ Cadomian basement) are also observed when comparingthe populations of detrital zircon from respective overlyingOrdovician quartzites. For the earliest Ordovician siliciclasticrocks of the SW CIZ (Sarnelhas Formation), the main source ofdetritus is probably derived from the OMZ Cadomian basement,as seen for similar aged volcanic–sedimentary rocks of the CIZ-OMZ transition (Urra volcaniclastic Formation; Tremadoc). Thissuggests that the SW CIZ Cadomian basement was not exposed atthat time. The later deposition of thick sequences of sandstones(Armorican Quartzite Formation) along the continental marginGondwana had different sources: Serie Negra itself fed certaincoastal areas (CIZ-OMZ transition) whereas the Beiras Group wasthe source of detritus in other coastal areas (SW CIZ). In the Early
Ordovician, rifting in SW Iberia was characterised by the forma-tion of rift shoulders, tilted blocks and/or horsts and grabenssuch that the Beiras Group was exposed in some places but notin others. As a consequence, the Early Ordovician quartzites of
rch 192– 195 (2012) 166– 189 187

the SW CIZ do not contain a population of detrital zircons derivedfrom a mixture of sources from both SW Iberia Cadomian base-ments. Although the Serie Negra and Beiras Group basins haveevolved together in the active margin of Gondwana, they weresufficiently separated to justify the differences in their detritalzircon content. Therefore the inferred contact that exists todayand juxtaposes the Beiras Group and the Serie Negra cannot bepre-Early Ordovician. Thus there is no apparent reason to believethat the contact between the OMZ and CIZ marks a Cadomiansuture.

4. Our findings strengthen the correlation between SW Iberia,Cadomia and the Anti-Atlas in the context of the evolution ofback-arc basins close to the northern Gondwana active margin.These synorogenic basins were filled during the Ediacaran bydetritus resulting from erosion of the West African craton, thePan-African suture and a long-lived Cadomian magmatic arc.

Acknowledgements

This paper is a contribution to project: GONDWANA-PTDC/CTE-GIX/110426/2009 funded by Fundac ão para a Ciência e Tecnologia,Portugal. An anonymous reviewer, B. Murphy and J. Braidare acknowledged for constructive review which improved themanuscript. Thanks also go to M.W. Lewis (ESE) for revising theEnglish text.

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The provenance of Late Ediacaran and Early Ordovician ... · 1. (A) Map showing the localities where the North Gondwana terranes are preserved in North America, Europe and North Africa