journal of african earth sciences (wadi damran; named wadi darman by jurák (1978)) areas of the...

Journal of African Earth Sciences 79 (2013) 74–97

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Journal of African Earth Sciences

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U–Pb LA-ICP-MS detrital zircon ages from the Cambrian of Al Qarqaf Arch,central-western Libya: Provenance of the West Gondwanan sand seaat the dawn of the early Palaeozoic

Muftah Mahmud Altumi a, Olaf Elicki b,⇑, Ulf Linnemann c, Mandy Hofmann c,Anja Sagawe c, Andreas Gärtner c

a Libyan Petroleum Institute, Gergarsh Road, 6431 Tripoli, Libyab Freiberg University, Geological Institute, Bernhard-von-Cotta Street 2, 09599 Freiberg, Germanyc Senckenberg Natural History Collections Dresden, Museum of Mineralogy and Geology, GeoPlasmaLab, Königsbrücker Landstraße 159, 01109 Dresden, Germany

a r t i c l e i n f o

Article history:Received 4 April 2012Received in revised form 3 November 2012Accepted 5 November 2012Available online 29 November 2012

Keywords:Hasawnah FormationLibyaGeochronologyCambrianGondwanaSaharan Metacraton

1464-343X/$ - see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.jafrearsci.2012.11.007

⇑ Corresponding author. Tel.: +49 (0)3731 39 2435E-mail addresses: [email protected] (O. Elic

a b s t r a c t

Detrital zircons from various stratigraphic levels of the sandstone-dominated Cambrian Hasawnah For-mation of the Al Qarqaf Arch type area (central-western Libya, Saharan Metacraton area) were geochro-nologically investigated for the first time by LA-ICP-MS techniques for U, Th, and Pb isotopes. Of 720analyzed grains, 329 were concordant. Of the total, about 60% of the U–Pb zircon ages are Neoproterozoicand earliest Cambrian and cluster at c. 700–680, 670–650, 615–610, 590, 570–560, and c. 540–525 Ma.These zircon populations are interpreted as detrital material derived from the Pan-African and possiblyto a smaller proportion from the Cadomian orogen situated marginal to northwestern Gondwana. Afew slightly older Neoproterozoic ages (c. 950–750 Ma) point to rifting events related to the dispersalof the Rodinia supercontinent. A minority of zircons became formed during the configuration of Rodiniaand cluster around the Mesoproterozoic–Neoproterozoic boundary (1039 ± 11, 1006 ± 12 and993 ± 13 Ma). Further, some early Mesoproterozoic zircon ages had been found (1592 ± 39 and1475 ± 20 Ma). The potential source area for the Mesoproterozoic zircons is interpreted to have beenfar distant from the Al Qarqaf Arch, probably concealed within the Arabian–Nubian Shield or situatedin Chad, or in the Congo and Tanzania cratons. There is still no evidence for the existence of massive Mes-oproterozoic crust in the Saharan Metacraton area. A considerable proportion (28%) of zircons representsPalaeoproterozoic populations at c. 2.4–2.3 Ga, and c. 2.2–1.6 Ga. Less than 5% of all zircons are Archaeanin age (c. 3.4–3.25 Ga, c. 2.95–2.7 Ga, c. 2.6–2.5 Ga). A potential source area for Palaeoproterozoic andArchaean zircon grains is the West African Craton and the western part of the Saharan Metacraton.The best candidates for the main source region for the sandstones of the Hasawnah Formation in theAl Qarqaf Arch type area are the Neoproterozoic–early Cambrian orogens of the Pan-African cycle inthe Trans-Saharan Belt (Pharussian and Dahomeyean belts) and of the peri-Gondwanan terranes (Cado-mia). This conclusion is in accordance with published data from the Hoggar (Tassilis, Algeria) and fromsouthwestern (eastern Murzuq Basin) and southeastern Libya (Al Kufrah Basin). In comparison to thestrong input of Neoproterozoic zircon grains, input from the Palaeoproterozoic and Archaean sourcesof the cratonic basement (Saharan Metacraton and West African craton) is relatively limited. The exactsource of the exotic Mesoproterozoic zircons remains problematic. The presented data lead to the conclusion that the centre of early Palaeozoic thermal subsidence in central-northern Africa has to be located inthe region of the Saharan Metacraton. The distinct unconformity at the base of the Cambrian HasawnahFormation indicates major uplift and considerable denudation in the latest Neoproterozoic to early Cam-brian time interval. Because of the conspicuous maturity of the Hasawnah Formation siliciclastic depos-its, a coeval intense chemical weathering under warm to humid climatic conditions in low to moderatesouthern latitudes and the formation of a Gondwanan peneplain is indicated.

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; fax: +49 (0)3731 39 12435.ki), [email protected] (U. Linnemann).

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M.M. Altumi et al. / Journal of African Earth Sciences 79 (2013) 74–97 75

1. Introduction

The late Proterozoic to early Phanerozoic represents a period offundamental reorganization of geological processes and of sedi-mentological, palaeogeographic, structural, climatic and evolution-ary settings. One focus of these dramatic changes in Earth history isin the origination and early evolution of the northern margin of theGondwana palaeosupercontinent. With the aim of developing acomprehensive model for the dynamic evolution of the northernGondwanan margin in the Ediacaran to early Palaeozoic, investiga-tions have been significantly intensified during the last decade.Whereas data from northwestern Africa, the Near East, westernand central Europe and the Sinai Peninsula and Israel have alreadybeen published, data from central-northern Africa is limited.Hence, there is a significant knowledge gap to be filled in orderto create a consistent reconstruction of the entire palaeogeograph-ic region.

In extensive areas of northern Africa the Precambrian igneousand/or metamorphosed basement is nonconformably covered bya Cambrian–Ordovician sandstone blanket (Beuf et al., 1971;Tawadros, 2001, 2012; Hallett, 2002; Squire et al., 2006; Linne-mann et al., 2011). This phenomenon is also known from othertime-equivalent regions of the world (e.g. Middle East and NorthAmerica: Powell, 1989; Sharland et al., 2001; Khalifa et al., 2006;Shinaq and Elicki, 2007; Hagadorn, 2011). Such regions offer anexcellent opportunity to study such fundamental geological pro-cesses as tectonic evolution, depositional history, erosion andtransportation from source areas, palaeoclimate, and structuringof early life systems of this time window. In some regions thereis also some economic aspect where included sediments, as in Li-bya, are significant elements of source rock or reservoir architec-ture or if they denote important aquifers (Binsariti and Saeed,2000; Hallett, 2002; Craig et al., 2008, 2009).

This paper is stratigraphically and regionally focussed on such asedimentary cover: the Cambrian Hasawnah Formation of the AlQarqaf Arch area of central-western Libya. The first detailed geo-logical investigation of the area was undertaken early in the secondhalf of the last century (Massa and Collomb, 1960; Collomb, 1962;Hecht et al., 1963; Goudarzi, 1970; Jurák, 1978) for mapping andexploration of natural resources. A second, important increase inknowledge has been published since the 1980s and has continueduntil recent time mainly due to oil exploration activities in Palae-ozoic basins in the region (Salem and Busrewil, 1980; Salem andBelaid, 1991; Salem et al., 1991a,b,c, 2003, 2008a,b,c; Klitzschand Thorweihe, 1999; Sola and Worsley, 2000; Tawadros, 2001;Hallett, 2002; Salem and Oun, 2003; Salem and El-Hawat, 2008).

Despite excellent outcrop, geochronological investigation of theCambrian succession in Libya has been neglected and recent dataare practically unavailable until recently with very rare exceptions(see below). However, such information together with sedimento-logical data is greatly needed for the reconstruction of the dynamicevolution in the aftermath of the Pan-African Orogeny of this partof Gondwana, and for correlation of this region to other areas of thepalaeocontinent.

The aim of the present paper is to present the first geochrono-logical data from detrital zircons of various lithostratigraphic levelswithin the Hasawnah Formation from the northern, central andsouthern Jebel Hasawnah mountain range of the Al Qarqaf Archand to draw conclusions as to the Precambrian to Cambrian evolu-tion of the palaeogeographic region. These geochronological datashould contribute to filling the gap in available stratigraphic infor-mation from this mainly non-marine and non-fossiliferous Cam-brian succession. Furthermore, the data provide a sound basis forassessment of the tectonomagmatic evolution of the Precambrianbasement of the Saharan Metacraton and adjacent areas.

2. Geological setting

The Neoproterozoic to earliest Palaeozoic structural evolutionof northeastern Africa is mainly characterized by two tectonicphases following the breakup of the late Precambrian superconti-nents Rodinia and Pannotia: the Pan-African amalgamation andthe ‘‘Infracambrian’’ extension (Craig et al., 2008; Johnson et al.,2011). During the first of these intervals a few palaeooceans hadbeen closed, among which the Trans-Saharan Ocean was mostimportant with respect to present southern Libya (Schandelmeierand Wipfler, 1999).

In Libya, early Palaeozoic rocks are mainly exposed at the mar-gins of large intracratonic basins in the central-western to south-western region of the country (Ghadamis Basin, Murzuq Basin),in the southeast (Al Kufrah Basin), and in the Tibesti Mountainsin the south (Al Festawi, 2001; Tawadros, 2001). One of the mostimportant outcrop areas is in the Jebel Hasawnah (also called JebelFezzan or Jebel Al Qarqaf) of the Al Qarqaf Arch (AQA; Fig. 1), aprominent southwest-trending uplift structure in Libya, mainlyformed by Caledonian and Hercynian movements (Al Festawi,2001). The amplitude of the uplift is about 6000 m (up to 800 melevation at present surface) in the AQA area relative to the base-ment level in the northern Ghadamis Basin area where this levelis about 5200 m below surface (Hallett, 2002). Following Al Fasa-twi et al. (2003), the AQA was a topographic high already in lateCambrian to early Ordovician time. Tectonic activity during theMesozoic and Cenozoic modified the region to various extents.The last tectonic uplift of significant amplitude was during the Al-pine phase of deformation and is indicated by apatite fission trackdata (Craig et al., 2008). The AQA largely separates the GhadamisBasin in the northwest from the Murzuq Basin in the south(Fig. 1) and represents the northernmost basement outcrop ofthe so-called Saharan Metacraton (Abdelsalam et al., 2002; EastSaharan Craton sensu Bertrand and Caby, 1978) in this part of Afri-ca (Conant and Goudarzi, 1967; Tawadros, 2001).

Palaeogeographically, the study area was situated at the wes-tern margin of the Gondwana palaeocontinent, which was in lowto moderate southern latitudes at the beginning of the Cambrianand migrated southward during Cambrian and Ordovician time(e.g. Scotese, 2009; Torsvik and Cocks, 2009).

The first geochronological data for basement granitoids fromvarious regions of the AQA were published by Schürmann (1974),who presented ages of 640–549 Ma (Rb/Sr) and 541–491 Ma (K/Ar) for muscovite granites. These are consistent with additionaldata (K/Ar ages of 554–520 Ma) later reported by Jurák (1978).These results indicate widespread igneous activity in the area atthat time (Fullagar, 1980). Oun and Busrewil (1987) investigatedsome of the granitic basement from the Wadi Badran area of south-ern Jebel Hasawnah and came to the conclusion that the geochem-istry of these rocks suggests an S-type nature for the granites,probably due to a ‘‘within-plate tectonic environment’’. Later on,Oun and Daly (1980) analyzed basement granites from the south-ern (Wadi Badran; named Wadi Taráb by Jurák (1978)) and north-ern (Wadi Damran; named Wadi Darman by Jurák (1978)) areas ofthe Jebel Hasawnah, determining a late Pan-African age (c.519 ± 34 Ma, Rb/Sr whole rock ages) and, in contrast to the formerauthors, an anorogenic A-type origin of the granites due to crustalextension incorporating some early Pan-African roof metasedi-mentary rocks.

Subsequent sediments nonconformably overlie the Pan-Africangranitic basement and were generated due to local erosion of thiselevated bedrock. They are represented by localized thin, unfossil-iferous sandstone packages (Mourizidie Formation) deposited in‘‘Infra-Cambrian’’ time within local palaeo-lows (Bellini and Massa,1980; Hallett, 2002; Benshati et al., 2009). To a much broader

Fig. 1. Geological map of Libya. (A) Overview map of major geological regions of Libya. (B) Enlarged detailed geological map of Al Qarqaf Arch (AQA) study area; numbersindicate colours for stratigraphic units (1 – Cambrian, 2 – Ordovician, 3 – Silurian, 4 – Lower Devonian, 5 – Middle and Upper Devonian, 6 – Lower Carboniferous, 7 – MiddleCretaceous, 8 – Upper Cretaceous, 9 – Palaeogene and Neogene, 10 – Cenozoic volcanic rocks); modified after Craig et al. (2008). (C) Satellite image of AQA corresponding toimage B, with location of sampled sections (compare Fig. 2) in Jebel Hasawnah outcrop area (modified after Google Earth). (For interpretation of the references to colour inthis figure, the reader is referred to the web version of this article.).

76 M.M. Altumi et al. / Journal of African Earth Sciences 79 (2013) 74–97

extent, the basement is nonconformably covered by a siliciclasticCambro-Ordovician succession, the Qarqaf Group (Burollet, 1960;Oun and Daly, 1980; see Fig. 2). Although Klitzsch (1981) dis-claimed this grouping because of unconformities between the in-cluded formations, the use of this term remains somewhatcommon. The lowest portion of the Qarqaf Group is representedby the Hasawnah Formation, the subject of this paper.

The Hasawnah Formation was defined by Massa and Collomb(1960) and outcrops widely in the Jebel Hasawnah type region.As well, beyond this type area the formation is proven both at sur-face and in the subsurface, with a broad extent in western, centraland eastern Libya (Tawadros, 2001, 2012; Hallett, 2002). Accordingto Hallett (2002), the Hasawnah Formation extends also into Egypt,Algeria and Chad, where it is identified under different names(Craig et al., 2008). However, regional correlation is somewhatproblematic due to the lack of age-diagnostic fossils or other thanlithostratigraphic data. For the same reason, it is also unclear

whether a stratigraphically complete section exists in the type areaat all. No formal type section has been designated until today, sothat the formation is rather inadequately defined.

The thickness of the Hasawnah Formation is reported to be 250–300 m for the AQA area, but, may be up to 1000 m in the subsurfaceof the Ghadamis Basin, 1150 m in the Al Kufrah Basin and 1700 m incentral Libya (Klitzsch, 1970; Deunff and Massa, 1975; Hallett,2002). Sedimentology and lithofacies of the formation in the AQAare poorly known. The formation overlies the Precambrian base-ment with distinct erosional contact and in the AQA region it showsa tripartite subdivision (Cepek, 1980): the basal part of the lowerunit is characterized by the occurrence of a distinctive basal con-glomeritic portion (total thickness up to 14 m) consisting of severallayers differing in pebble diameter and proportion of sandy matrixand with a slight fining-upward tendency (Jurák, 1978; Cepek,1980; personal observations). The pebbles are several centimetersin diameter and predominantly of well rounded quartz. This

Fig. 2. Lithostratigraphy of Hasawnah Formation in AQA area with indication of stratigraphic span of sampled sections (Da2 – Wadi Damran-2, X – unnamed wadi ‘‘X’’, A1 –Wadi Al Abd-1, Ba1 – Wadi Badran-1, Ba2 – Wadi Badran-2) and position and names of sampled horizons (yellow rectangles). Generalized lithologic log redrawn andmodified after Cepek (1980). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)


conglomeratic lithology grades upward into mainly medium-grained, high-angle cross-bedded sandstone showing fining-up-ward sets with truncated tops. The thickness of the complete lowerunit of the Hasawnah Formation in the AQA is about 100 m. The

unit is interpreted as fluviodeltaic with some intertidal influencetoward the top (Cepek, 1980; Hallett, 2002; personal observations).The middle unit (about 70 m thick) is petrographically similar, butdiffers from the unit below in its greater diversity of sedimentary

Table 1Settings for the instruments used in the geochronological Laboratory (GeoPlasmaLabDresden) of the Senckenberg Natural Hostory Collections Dresden (Excimer Laser,New Wave, UP 193) and (ICP-MS, Thermo Fisher, Element 2 XR).

ICP-MS Finnigan Element 2 XR

Forward power 1390 WGas flow rate 15.0 l min�1 (plasma)

1.07 l min�1 (aux)Scan mode E-scanScanned masses 202, 204, 206, 207,

208, 232, 235, 238Mass resolution 300Dead time 18 nsOxide UO+/U+ <1%Dwell time 4 msSettling time 61 ms/amuNumber of scans 1500Background 15 sAblation time 30 sIntegration time 1.4 s (=25 scans)

Laser system UP193 New Wave193 nm, excimer

Nominal spot diameter 25–35 lm (unknowns)35 lm (standard)

Carrier gas 0.25 l min�1 He1.1 l min�1 Ar

Laser settings 10 Hz, 55% LPDrill speed (DS)/Raster scan speed RSS) �0.5 lm/s (DS)Cell volume c. 3 cm3

Sensitivity 6 � 106 counts/pg U


structures (cross-bedding, planar lamination, convolute bedding,ripples), by the intercalation of fine-grained sandstone and silt-stone, and by the first, scarce occurrences of thin trace fossil hori-zons, dominated by Skolithos, arthropod and simple traces(personal observations). The environmental conditions for thismiddle unit are interpreted as transitional from marine intertidalto subtidal by Cepek (1980). The upper unit of the Hasawnah Forma-tion is about 80 m thick in the AQA and again consists of petro-graphically similar sandstone. It differs from the middle unit by adistinct decrease in silty intercalations and change in the characterof sedimentary structures (massive sandstone, sand bars with com-plex internal structures, trough cross-bedding, synsedimentarychaotic deformation), together indicating a dominantly subtidaldepositional environment (Cepek, 1980).

Although the general trend of lithofacies change within theHasawnah Formation suggests a transition from fluvial/deltaic(lower unit) to tidally influenced (middle unit) to rather offshore(upper unit) deposition, the inventory of sedimentary structuresis somewhat ambiguous and does not permit more detailed con-clusions with regard to depositional environment (Cepek, 1980).

Stratigraphically, the Hasawnah Formation is interpreted asCambrian in age. Although the available fossil content (nonspecifictrace fossils) is not age diagnostic, the lithostratigraphic position ofthe formation beneath the immediately overlaying TremadocianAsh Shabiyat Formation (e.g. Collomb, 1962; Hecht et al., 1963;Bellini and Massa, 1980; Davidson et al., 2000; Tawadros, 2001;Hallett, 2002), together with the suggested correlation with sub-surface strata of the Ghadamis Basin and Sirt Basin containing mid-dle to late Cambrian palynomorphs (corresponding to Cambrianseries 3 and Furongian; Tawadros, 2001; Vecoli et al., 2003), andwith the equivalent Sidi Toui Formation of Tunisia (with a rich pal-ynomorph flora: Tawadros, 2012), makes such a conclusion rea-sonable. Recently, some geochronological zircon data fromsandstones of the Cambrian–Ordovician boundary interval havebeen published for a few samples from the Dor el Gussa area (east-ern margin of the Murzuq Basin, approximately 350 km southeastof the Jebel Hasawnah; Meinhold et al., 2011): about two thirds ofall investigated zircons yield Neoproterozoic dates with a majorityin the range 720–530 Ma (maximum at 620–600 Ma).

The upper boundary of the Hasawnah Formation with the AshShabiyat Formation is represented by an angular unconformity inthe western AQA, but is transitional in the Ghat area (Tawadros,2012). The succeeding Ordovician portion of the Qarqaf Group con-tains four formations: the early Ordovician marine Ash Shabiyat(=Achebyat) Formation, middle Ordovician shallow-marine to del-taic Hawaz (=Haouaz) Formation, middle to late Ordovician marineand ?subglacial Melaz Shoqran (=Melez Chograne) Formation, andlate Ordovician proglacial fluvial to marginal marine Mamuniyat(=Memouniat) Formation (Fig. 2). The bundling of these formationswithin the Qarqaf Group is not fully accepted by all authors be-cause of the observation of unconformities between them (Kli-tzsch, 1981). For more detailed description of the Ordovicianportion of the Qarqaf Group see Tawadros (2001, 2012) and litera-ture cited therein.

3. Methods and samples

Detrital zircon grains of six sandstone samples were investi-gated in the present study. Zircon concentrates were separatedfrom 1 to 2 kg of each sample using standard methods at the Geo-logical Institute of Freiberg University, Germany. Final selection ofthe zircon grains for U–Pb dating was achieved by hand-pickingunder a binocular microscope. Zircon grains of all sizes and mor-phological types were selected, mounted in resin blocks and pol-ished to half their thickness. Zircons were analyzed for U, Th andPb isotopes by LA-ICP-MS techniques at the Museum of Mineralogy

and Geology (GeoPlasma Lab, Senckenberg Natural History Collec-tions, Dresden) using a Thermo-Scientific Element 2 XR sector fieldICP-MS coupled to a New Wave UP-193 Excimer Laser System.Instrument settings for the Laser and the ICP-MS are given inTable 1. A teardrop-shaped, low-volume laser cell constructed byBen Jähne (Dresden) and Axel Gerdes (Frankfurt am Main) wasused to enable sequential sampling of heterogeneous grains (e.g.growth zones) during time-resolved data acquisition. Each analysisconsisted of approximately 15 s background acquisition followedby 30 s data acquisition, using a laser spot size of 25 lm and35 lm respectively. A common-Pb correction based on the inter-ference- and background-corrected 204Pb signal and a model Pbcomposition (Stacey and Kramers, 1975) was carried out if neces-sary. The necessity of the correction is judged on whether the cor-rected 207Pb/206Pb ratio lies outside the internal errors of themeasured ratios. Discordant analyses were interpreted with care.Raw data were corrected for background signal, common Pb,laser-induced elemental fractionation, instrumental mass discrim-ination, and time-dependant elemental fractionation of Pb/Th andPb/U using an Excel� spreadsheet program developed by Axel Ger-des (Institute of Geosciences, Johann-Wolfgang-Goethe UniversityFrankfurt, Frankfurt am Main, Germany). Reported uncertaintieswere propagated by quadratic addition of the external reproduc-ibility obtained from the standard zircon GJ-1 (�0.6% and 0.5–1%for 207Pb/206Pb and 206Pb/238U respectively) during individual ana-lytical sessions and the within-run precision of each analysis. Con-cordia diagrams (2r error ellipses) and concordia dates (95%confidence level) were produced using Isoplot/Ex 2.49 (Ludwig,2001), and frequency and relative probability plots using AgeDis-play (Sircombe, 2004). The 207Pb/206Pb date was taken for interpre-tation for all zircons >1.0 Ga, and the 206Pb/238U dates for youngergrains. Analyses were carried out using the procedures of Gerdesand Zeh (2006) and Frei and Gerdes (2009). For further details onanalytical protocol and data processing, see those references.

The uncertainty in the degree of concordance of Precambrian–Palaeozoic grains dated by the LA-ICP-MS method is relativelylarge and results obtained from just a single analysis have to be


interpreted with care. A typical uncertainty of 2–3% (2r) in207Pb/206Pb for a late Neoproterozoic grain (e.g. 560 Ma) relatesto an absolute error in the 207Pb/206Pb age of 45–65 Ma. Such a re-

Table 2U–Th–Pb data of detrital zircon grains from sample X1-1 (61 of 120 measured grains whicsandstone, lower part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf Arch, Libya, co

Number 207Pba

(cps)Ub

(ppm)Pbb

(ppm)Th/

Ub

206Pb/204Pbc

206Pb/238Uc

2r(%)

207Pb/235Uc

2r(%)

2a61 10787 90 8 0.60 18342 0.0839 2.2 0.67 3.2a53 18614 192 16 0.64 31549 0.0845 3.2 0.67 3.72a2 15307 354 33 0.73 9363 0.0850 2.2 0.69 2.62a17 7527 170 15 0.46 12828 0.0851 2.3 0.68 3.2a43 8584 134 12 0.43 14608 0.0860 2.6 0.69 3.1a41 9097 135 12 0.45 2497 0.0863 2.6 0.70 5.7a50 11778 130 12 0.63 20004 0.0863 2.6 0.69 3.4a16 32388 738 157 0.52 14765 0.0863 2.5 0.69 2.82a29 7202 167 15 0.34 5148 0.0866 2.2 0.69 3.42a27 7213 166 15 0.35 12225 0.0867 2.2 0.70 3.4a19 66401 1355 206 0.26 16273 0.0869 2.5 0.69 2.72a60 4575 36 4 0.88 7588 0.0875 2.3 0.72 3.5a49 8381 93 8 0.75 7409 0.0878 2.8 0.71 3.62a32 6155 140 13 0.35 10475 0.0881 2.3 0.71 3.32a63 19695 198 18 0.75 4946 0.0880 3.1 0.72 3.62a52 2986 30 3 1.16 5035 0.0882 3.1 0.71 5.2a4 16323 234 23 0.64 510 0.0887 2.7 0.72 4.2a40 16889 298 28 0.44 28361 0.0892 2.5 0.72 2.92a59 23511 215 19 0.29 35724 0.0893 4.0 0.71 4.32a44 5568 82 8 0.79 9346 0.0898 2.0 0.73 3.8a3 13632 280 26 0.35 23321 0.0909 2.5 0.72 2.9a29 536 16 1 0.69 904 0.0909 4.4 0.74 8.2a42 15020 252 23 0.61 25007 0.0909 2.6 0.74 3.02a42 13799 180 17 0.68 2848 0.0912 2.4 0.74 6.7a35 4027 87 8 0.53 2555 0.0914 3.1 0.74 7.82a24 12879 310 29 0.55 21727 0.0928 2.0 0.76 2.92a46 17942 260 29 1.23 30391 0.0931 2.0 0.75 2.62a5 11489 222 21 0.31 19517 0.0941 2.0 0.76 2.7a18 11410 225 30 1.93 6547 0.0944 2.8 0.77 3.6a58 7429 59 6 0.61 12343 0.0954 3.0 0.78 4.02a4 7025 137 13 0.44 7094 0.0955 2.1 0.77 2.92a9 10332 204 20 0.34 8860 0.0964 2.1 0.79 3.1a37 9792 184 18 0.61 15814 0.0971 2.9 0.82 3.32a14 9448 187 18 0.28 15745 0.0982 2.2 0.81 3.0a63 5445 31 3 0.69 8899 0.0988 2.7 0.82 3.3a13 10353 190 28 2.14 17335 0.1000 2.6 0.81 3.32a37 12371 239 25 0.59 20273 0.1004 2.0 0.84 2.92a16 5228 102 11 0.48 8756 0.1014 2.0 0.83 3.0a54 5999 27 3 0.29 1937 0.1022 6.0 0.85 15.42a3 6286 118 12 0.53 10437 0.1021 2.3 0.84 3.12a18 9718 190 19 0.25 15925 0.1021 2.0 0.85 3.32a65 12933 77 8 0.25 20488 0.1029 2.4 0.88 2.9a17 9355 159 18 0.57 15262 0.1045 2.6 0.87 3.3a48 17751 172 22 0.97 28830 0.1059 2.6 0.89 3.0a11 10382 165 20 0.90 16907 0.1061 2.7 0.89 3.32a7 13270 234 27 0.60 5862 0.1087 2.1 0.93 2.82a11 3777 59 8 0.93 6025 0.1096 2.2 0.93 3.9a51 24578 137 22 0.33 13324 0.1575 3.1 1.51 3.42a33 20024 99 31 0.49 2970 0.2818 2.3 4.05 3.0a57 73290 131 40 0.72 16183 0.2965 5.0 4.41 5.22a25 45952 173 61 0.77 14167 0.3233 2.2 4.99 2.82a10 57178 154 56 0.58 49693 0.3242 2.2 5.09 2.6a20 104333 248 95 1.68 895 0.3322 2.9 5.83 3.2a27 54992 115 45 0.57 41482 0.3492 2.4 6.30 2.6a5 50538 113 45 0.64 9268 0.3497 2.5 6.11 2.8a30 1591 6 2 1.03 1368 0.3541 4.1 5.60 5.9a15 51974 120 51 0.93 27499 0.3545 3.1 6.05 3.2a21 56016 123 56 0.72 43153 0.4064 2.7 7.18 2.92a57 24310 14 9 1.21 3124 0.5033 2.6 12.43 3.72a15 273959 148 138 1.39 86227 0.6730 2.3 26.33 2.4

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 tc Corrected for background, mass bias, laser induced U–Pb fractionation and common

composition. 207Pb/235U calculated using 207Pb/206Pb/(238U/206Pb � 1/137.88). Errors areof GJ-1 (2SD).

d Rho is the error correlation defined as err206Pb/238U/err207Pb/235U.

sult gives space for interpretation of concordance or slight discor-dance. The latter could be caused by episodic lead loss,fractionation, or infiltration of Pb isotopes by a fluid or via micro-

h are concordant in the range of 90–110%) (unnamed Wadi ‘‘X’’ section X1, Cambrian,ordinates: 28�23051.200N, 13�55043.400E).

207Pb/206Pbc

2r(%)

Rhod 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

0.0580 2.3 0.69 520 11 522 13 531 51 980.0577 2.0 0.85 523 16 522 15 520 44 1000.0589 1.4 0.84 526 11 533 11 562 32 940.0579 2.2 0.72 526 12 527 13 528 49 1000.0580 1.8 0.81 532 13 532 13 531 40 1000.0585 5.1 0.46 533 14 536 24 547 111 970.0581 2.1 0.77 534 13 534 14 535 46 1000.0579 1.3 0.89 534 13 532 12 527 28 1010.0582 2.6 0.65 535 11 536 14 537 57 1000.0582 2.5 0.66 536 11 536 14 538 56 1000.0577 1.0 0.93 537 13 534 11 520 21 1030.0593 2.7 0.65 541 12 548 15 578 58 940.0586 2.2 0.80 542 15 545 15 554 47 980.0582 2.5 0.67 544 12 543 14 537 54 1010.0596 1.7 0.87 544 16 552 15 588 38 920.0586 4.2 0.59 545 16 546 22 551 92 990.0592 3.2 0.65 548 14 553 18 575 69 950.0588 1.5 0.86 551 13 552 13 560 32 980.0578 1.7 0.92 551 21 546 18 523 37 1050.0587 3.2 0.54 554 11 555 16 558 70 990.0577 1.5 0.85 561 13 552 12 519 33 1080.0589 6.9 0.54 561 24 561 36 562 150 1000.0594 1.5 0.87 561 14 565 13 581 32 970.0588 6.3 0.36 562 13 562 30 560 137 1000.0589 7.2 0.39 564 17 563 34 563 157 1000.0591 2.2 0.66 572 11 572 13 571 48 1000.0585 1.7 0.75 574 11 569 11 550 37 1040.0583 1.8 0.74 580 11 572 12 541 40 1070.0592 2.3 0.77 582 16 580 16 575 50 1010.0594 2.7 0.75 587 17 586 18 582 58 1010.0588 2.0 0.71 588 12 582 13 561 45 1050.0596 2.3 0.69 593 12 593 14 591 49 1000.0612 1.6 0.88 597 16 607 15 645 34 930.0595 2.0 0.75 604 13 600 13 585 42 1030.0604 2.0 0.80 607 15 610 15 618 43 980.0590 2.0 0.80 614 15 605 15 568 44 1080.0605 2.1 0.69 617 12 618 13 620 45 1000.0590 2.2 0.67 623 12 611 14 568 49 1100.0602 14.1 0.39 627 36 624 74 611 306 1030.0597 2.1 0.73 627 14 619 14 592 46 1060.0605 2.6 0.60 627 12 625 16 621 57 1010.0624 1.5 0.84 631 15 643 14 686 33 920.0605 2.1 0.77 641 16 636 16 620 46 1030.0608 1.5 0.86 649 16 645 14 631 32 1030.0605 2.0 0.81 650 17 644 16 622 42 1040.0619 1.8 0.75 665 13 667 14 672 39 990.0616 3.2 0.58 671 14 668 19 661 68 1020.0696 1.4 0.91 943 27 935 21 917 30 1030.1043 1.8 0.79 1600 33 1645 24 1702 34 940.1078 1.2 0.97 1674 75 1714 44 1763 23 950.1119 1.7 0.79 1806 35 1817 24 1830 31 990.1139 1.4 0.85 1810 35 1835 22 1863 24 970.1273 1.4 0.90 1849 46 1951 28 2060 25 900.1309 0.9 0.94 1931 41 2019 23 2110 16 910.1268 1.2 0.91 1933 42 1992 24 2054 20 940.1148 4.3 0.68 1954 69 1916 53 1876 78 1040.1238 0.9 0.96 1956 52 1984 28 2012 15 970.1281 1.1 0.93 2198 50 2134 26 2073 19 1060.1791 2.5 0.73 2628 57 2638 35 2645 42 990.2838 0.9 0.93 3317 59 3359 24 3384 14 98

o approximately 10%.Pb (if detectable, see analytical method) using Stacey and Kramers (1975) model Pbpropagated by quadratic addition of within-run errors (2SE) and the reproducibility


cracks. Thus, zircons showing a degree of concordance in the rangeof 90–110% in this paper are classified as concordant because of theoverlap of the error ellipse with the concordia (e.g. Frei and Gerdes,2009; Jeffries et al., 2003; Linnemann et al., 2007, 2011). Th/U ra-tios were obtained from the LA-ICP-MS measurements of investi-gated zircon grains. U and Pb content and Th/U ratio werecalculated relative to the GJ-1 zircon standard and are accurateto approximately 10%.

Table 3U–Th–Pb data of detrital zircon grains from sample Ba2-10 (54 of 120 measured grains wCambrian, sandstone, lower part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf Arc

Number 207Pba

(cps)Ub

(ppm)Pbb

(ppm)Th/Ub

206Pb/204Pbc

206Pb/238Uc

2r(%)

207Pb/235Uc

2r(%)

a44 19912 203 20 0.76 8051 0.0848 1.1 0.678 2.7a29 14202 190 17 0.56 24146 0.0850 1.6 0.678 2.2a54 18455 133 12 0.48 2943 0.0850 1.5 0.682 3.63a30 28234 665 59 0.41 564 0.0864 4.2 0.700 6.7a64 16934 80 7 0.56 5014 0.0878 2.1 0.708 4.63a13 13041 191 18 0.79 1326 0.0885 3.8 0.718 8.33a26 12722 212 21 0.83 21697 0.0902 3.2 0.727 3.8a11 5476 67 7 1.02 1232 0.0916 1.2 0.744 3.13a28 14820 230 22 0.35 24608 0.0915 3.1 0.757 3.4a3 5356 59 7 1.53 2258 0.0925 2.6 0.759 5.1a12 21091 255 22 0.05 35330 0.0946 1.0 0.766 1.7a8 17253 190 18 0.31 28253 0.0953 1.4 0.791 2.33a15 15140 228 22 0.47 24553 0.0963 3.2 0.814 3.73a52 15512 129 13 0.85 1929 0.0969 3.0 0.814 3.9a39 17243 167 17 0.54 1624 0.0977 1.2 0.814 4.62a11 12052 174 18 0.52 19923 0.0982 4.0 0.812 5.0a4 22209 234 24 0.46 14304 0.1001 1.2 0.837 1.63a64 12573 67 7 0.71 1113 0.1003 3.4 0.863 3.93a49 3616 32 4 1.33 5981 0.1005 3.0 0.834 5.1a21 15559 196 21 0.58 16805 0.1015 1.5 0.848 3.13a42 12398 139 15 0.52 7284 0.1023 3.2 0.865 3.9a36 63446 1063 110 0.12 237 0.1025 1.1 0.850 5.0a43 11671 137 15 0.62 2043 0.1033 1.1 0.871 4.33a22 18631 229 28 1.23 3318 0.1041 3.4 0.881 5.03a40 8929 107 12 0.66 9198 0.1060 3.3 0.901 4.03a5 20993 289 33 0.74 629 0.1094 3.3 0.935 5.3a31 2133 23 3 0.53 3339 0.1096 1.6 0.953 6.8a16 2828 32 4 0.86 4487 0.1101 1.4 0.942 3.33a6 9222 138 16 0.68 14762 0.1105 3.4 0.946 5.03a18 9659 130 16 0.75 15310 0.1106 3.5 0.960 4.13a62 4939 26 3 0.57 1213 0.1138 3.1 1.013 3.73a11 5900 65 8 0.76 4142 0.1147 3.1 0.991 3.7a28 14812 191 24 1.28 1026 0.1151 1.6 0.995 3.7a20 4051 46 6 0.76 6257 0.1154 1.7 1.014 4.8a55 29805 183 22 0.80 725 0.1178 1.2 1.043 15.9a17 14165 126 17 0.83 21885 0.1194 1.3 1.049 2.4a38 15010 126 16 0.26 22451 0.1280 1.2 1.163 1.93a55 10935 52 8 1.29 2619 0.1284 3.0 1.153 3.5a46 27795 187 27 0.82 1907 0.1293 1.4 1.165 2.22a8 46912 431 65 0.71 1216 0.1429 4.3 1.345 5.2a35 30593 274 40 0.63 3265 0.1477 1.4 1.399 2.7a48 21540 198 32 0.79 865 0.1665 1.4 1.667 4.9a9 33367 175 32 0.68 2326 0.1688 1.3 1.703 2.2a7 34118 167 33 0.79 46253 0.1750 1.2 1.752 1.5a30 31012 237 61 0.20 11490 0.2629 1.0 3.349 1.53a8 75663 207 76 1.34 5817 0.3088 3.1 4.981 3.2a22 25153 52 20 1.19 4557 0.3149 1.4 4.663 2.0a58 22040 21 8 1.01 5714 0.3190 1.7 4.884 2.6a65 87049 50 20 0.60 19582 0.3632 1.3 6.407 1.6a60 43130 32 14 1.33 2838 0.3634 1.2 6.176 2.1a47 132646 206 84 0.57 1330 0.3846 1.6 6.638 1.93a14 108304 208 88 1.20 3181 0.4052 3.0 8.683 3.53a51 105574 54 33 1.09 13796 0.4983 3.2 12.018 3.43a65 352387 98 55 0.33 20003 0.5245 3.3 14.561 3.4a52 256981 190 150 1.08 1397 0.6822 1.5 23.346 2.3

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 tc Corrected for background, mass bias, laser induced U–Pb fractionation and common

composition. 207Pb/235U calculated using 207Pb/206Pb/(238U/206Pb � 1/137.88). Errors areof GJ-1 (2SD).


Sampling for zircon dating was done by two of the authors(M.M.A. and O.E.) in the course of measuring transitional sectionsfrom granitic basement to overlaying Hasawnah Formation. Six sam-ples for geochronological analysis were taken from different strati-graphic levels (distance above the conglomeratic base of theformation) from various geographic areas in the northern, centraland southern Jebel Hasawnah mountain range (Figs. 1 and 2). Allsix samples are from the Hasawnah Formation (Cambrian) of the

hich are concordant in the range of 90–110%) (Wadi Badran, section Wadi Badran 2,h, Libya, coordinates: 28�11025.300N, 13�58031.100E).

207Pb/206Pbc

2r(%)

Rhod 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

0.0580 2.5 0.42 525 6 526 11 528 54 990.0579 1.5 0.73 526 8 526 9 525 33 1000.0582 3.2 0.41 526 7 528 15 536 71 980.0588 5.3 0.62 534 21 539 29 559 115 960.0585 4.0 0.47 542 11 544 19 549 88 990.0589 7.4 0.46 547 20 550 36 562 161 970.0584 2.0 0.85 557 17 555 16 546 44 1020.0589 2.9 0.38 565 6 565 14 565 63 1000.0599 1.4 0.91 565 17 572 15 602 31 940.0595 4.4 0.50 571 14 573 23 584 97 980.0588 1.4 0.59 583 6 578 8 558 31 1040.0602 1.7 0.64 587 8 592 10 610 37 960.0614 2.0 0.85 593 18 605 17 652 43 910.0610 2.5 0.78 596 17 605 18 639 53 930.0605 4.5 0.25 601 7 605 21 620 96 970.0600 3.0 0.81 604 23 604 23 603 64 1000.0607 1.1 0.72 615 7 617 8 628 24 980.0624 1.8 0.88 616 20 632 18 687 39 900.0602 4.1 0.59 617 18 616 24 611 88 1010.0606 2.7 0.49 623 9 624 14 625 58 1000.0613 2.2 0.82 628 19 633 19 650 48 970.0601 4.9 0.22 629 7 625 24 609 105 1030.0612 4.2 0.26 634 7 636 21 645 90 980.0614 3.7 0.67 638 20 642 24 654 79 980.0617 2.3 0.82 650 20 653 19 662 48 980.0620 4.1 0.62 669 21 670 26 673 89 990.0631 6.6 0.24 670 10 680 34 711 141 940.0621 2.9 0.42 673 9 674 16 677 63 990.0621 3.6 0.68 675 22 676 25 679 78 1000.0629 2.2 0.85 676 23 683 21 706 46 960.0645 2.0 0.84 695 20 710 19 759 42 920.0627 2.1 0.83 700 21 699 19 697 44 1000.0627 3.4 0.44 702 11 701 19 699 71 1000.0637 4.5 0.36 704 11 711 25 733 95 960.0642 15.8 0.07 718 8 725 86 748 335 960.0637 2.0 0.53 727 9 729 12 733 42 990.0659 1.5 0.63 777 9 783 11 802 32 970.0651 1.9 0.85 779 22 779 19 778 40 1000.0654 1.7 0.65 784 11 784 12 786 36 1000.0683 2.9 0.83 861 35 865 31 877 60 980.0687 2.3 0.53 888 12 888 16 890 48 1000.0726 4.6 0.30 993 13 996 31 1003 94 990.0732 1.8 0.58 1006 12 1010 14 1018 36 990.0726 0.9 0.81 1039 11 1028 10 1003 18 1040.0924 1.1 0.70 1505 14 1493 12 1475 20 1020.1170 1.0 0.95 1735 47 1816 28 1910 19 910.1074 1.4 0.70 1765 21 1761 17 1756 26 1000.1110 2.0 0.66 1785 27 1800 22 1817 36 980.1279 0.9 0.82 1997 23 2033 14 2070 17 960.1232 1.7 0.57 1998 20 2001 18 2004 30 1000.1252 1.0 0.85 2098 29 2064 17 2031 17 1030.1554 1.7 0.86 2193 56 2305 32 2406 29 910.1749 1.0 0.96 2606 70 2606 32 2605 17 1000.2013 0.8 0.97 2718 74 2787 33 2837 14 960.2482 1.8 0.64 3353 38 3241 23 3173 28 106



Qarqaf Group in the AQA area. Sample names, locations, coordinates,lithology and stratigraphic levels are as follows (see also Fig. 2):

Sample no.: DA2-3.Location: Wadi Damran (28�31054.400N, 13�57024.900E).Lithology: medium- to fine-grained sandstone with thin coarse-grained intercalations, showing small-scale low-angle cross-bedding.Stratigraphic level: middle portion of lower unit of HasawnahFormation (38 m above base).Sample no.: X1-1.Location: unnamed wadi ‘‘X’’ (28�23051.200N, 13�55043.400E).Lithology: stratified mixture of (1) detritus of the deeplyweathered granitic basement, and (2) medium- to coarse-grained conglomerate to conglomeratic sandstone which

Table 4U–Th–Pb data of detrital zircon grains from sample Ba1-3 (46 of 120 measured grains whichCambrian, sandstone, lower part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf Arch, L

Number 207Pba

(cps)Ub

(ppm)Pbb

(ppm)Th/Ub 206Pb/

204Pbc

206Pb/238Uc

2r(%)

207Pb/235Uc

2r(%)

2

2

a55 26169 177 16 0.50 27604 0.0863 1.8 0.70 2.5 02a24 188895 2611 216 0.03 62549 0.0894 1.8 0.72 2.1 0a30 5498 79 8 0.67 9369 0.0905 2.7 0.73 3.8 0a9 11809 150 13 0.27 20040 0.0909 2.9 0.74 3.6 0a52 17205 107 9 0.11 28908 0.0922 2.3 0.76 2.9 0a66 9566 44 4 0.41 11113 0.0927 1.8 0.76 2.9 02a41 21363 223 21 0.31 10837 0.0929 2.0 0.76 2.7 02a65 13915 58 5 0.32 9912 0.0930 1.5 0.76 2.2 02a53 10922 69 7 0.44 18460 0.0948 1.6 0.78 2.4 0a40 2717 30 3 0.43 4119 0.0958 2.0 0.79 4.4 02a28 15985 206 20 0.23 15290 0.0963 1.3 0.79 2.3 02a50 17842 158 16 0.49 30047 0.0966 1.8 0.80 3.6 02a64 3544 15 2 0.80 807 0.0968 3.6 0.80 7.5 02a43 18313 171 17 0.47 30665 0.0973 1.8 0.80 2.5 02a61 15584 83 8 0.33 26215 0.0977 1.9 0.81 2.5 02a33 14826 208 20 0.18 24910 0.0980 1.9 0.81 3.2 0a37 18494 245 23 0.24 12819 0.0984 1.5 0.82 2.1 0a60 9764 49 5 0.44 15936 0.1002 3.5 0.85 4.8 02a55 12594 64 7 0.60 3489 0.1029 1.8 0.86 2.6 0a21 2184 25 3 0.96 2652 0.1051 1.9 0.89 4.8 0a53 8155 48 7 1.22 13283 0.1070 2.1 0.91 4.0 0a65 2639 11 1 1.07 4292 0.1072 2.0 0.91 4.0 0a16 4637 52 6 0.38 7691 0.1076 1.7 0.90 4.7 02a8 14939 161 21 0.87 24188 0.1101 1.9 0.94 2.4 0a50 2493 15 2 1.16 4039 0.1106 2.1 0.94 4.9 02a20 15623 161 22 0.96 24743 0.1164 1.7 1.02 2.3 02a10 29107 203 32 0.49 9759 0.1484 2.0 1.41 2.3 02a18 2301 15 3 0.68 3352 0.1501 2.0 1.43 4.9 02a44 28307 120 23 0.84 39604 0.1651 1.5 1.63 2.0 0a61 82050 71 24 0.46 72696 0.3066 3.4 4.76 3.9 0a44 39546 57 21 0.76 13047 0.3229 1.8 5.01 2.0 02a17 79388 155 62 1.05 66410 0.3312 1.5 5.48 2.0 0a36 32688 68 27 1.16 3891 0.3315 2.2 5.21 2.5 02a26 91568 175 70 0.73 78985 0.3431 1.4 5.51 1.7 02a27 9176 17 8 1.49 7874 0.3441 1.3 5.56 2.6 02a21 58497 85 42 1.59 45406 0.3620 1.4 6.46 1.7 02a9 169807 237 101 0.43 10978 0.3915 1.5 7.02 2.1 0a6 79302 117 51 0.42 55030 0.4014 2.0 7.45 3.1 0a38 157105 230 101 0.49 125462 0.4060 1.5 7.01 1.7 0a5 33741 38 19 0.71 15994 0.4384 1.8 8.36 2.1 02a63 123415 40 23 0.83 76559 0.4806 1.7 10.73 1.9 0a49 288120 156 83 0.36 170584 0.4863 1.7 11.32 2.3 02a31 249640 232 125 0.29 41252 0.4876 3.3 11.57 3.5 02a15 121176 91 54 0.76 19192 0.5009 1.5 12.66 1.8 0a11 557938 337 203 0.25 130229 0.5407 1.6 16.71 1.6 02a52 38730 11 9 1.43 18563 0.5733 1.7 16.58 2.3 0

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 apc Corrected for background, mass bias, laser induced U–Pb fractionation and common Pb (

composition. 207Pb/235U calculated using 207Pb/206Pb/(238U/206Pb � 1/137.88). Errors are propof GJ-1 (2SD).


pebbles are 1–10 cm in size and almost exclusively representedby plutonic quartz.Stratigraphic level: lowermost Hasawnah Formation (1.5 mabove base).Sample no.: A1-3.Location: Wadi Al Abd (28�13039.900N, 13�53058.400E).Lithology: coarse-grained sandstone with thin, medium- to fine-grained intercalations showing small-scale low-angle cross-bedding.Stratigraphic level: lower portion of lower unit of Hasawnah For-mation (20 m above base).Sample no.: Ba1-3.Location: Wadi Badran (28�11052.600N, 13�57003.600E).Lithology: medium-grained sandstone showing high-angletrough cross-bedding.

are concordant in the range of 90–110%) (Wadi Badran, section Wadi Badran 1,ibya, coordinates: 28�11052.600N, 13�57003.600E).

07Pb/06Pbc

2r(%)

Rhod 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

.0588 1.8 0.71 533 9 539 10 561 38 95

.0586 1.1 0.86 552 10 552 9 552 24 100

.0587 2.7 0.71 558 15 558 17 557 59 100

.0588 2.2 0.80 561 16 561 16 561 47 100

.0594 1.7 0.80 568 13 571 13 582 37 98

.0592 2.2 0.65 571 10 572 13 573 47 100

.0592 1.8 0.75 572 11 573 12 574 39 100

.0592 1.6 0.70 573 8 573 10 574 34 100

.0595 1.8 0.66 584 9 584 11 584 39 100

.0597 3.9 0.46 590 11 590 20 593 84 99

.0594 1.9 0.56 593 7 590 10 580 42 102

.0597 3.2 0.50 595 10 594 16 593 68 100

.0597 6.6 0.48 596 21 595 35 592 143 101

.0599 1.7 0.72 599 10 599 11 600 37 100

.0599 1.6 0.76 601 11 600 11 599 35 100

.0598 2.5 0.61 603 11 601 15 596 55 101

.0601 1.4 0.72 605 9 606 9 608 31 100

.0614 3.2 0.74 616 21 624 23 652 69 94

.0607 1.9 0.68 631 11 631 12 630 41 100

.0611 4.5 0.39 644 12 644 23 644 96 100

.0615 3.4 0.54 656 13 656 19 657 72 100

.0617 3.4 0.50 656 12 658 19 665 73 99

.0605 4.3 0.37 659 11 650 23 621 93 106

.0621 1.5 0.78 673 12 674 12 676 33 100

.0619 4.5 0.42 676 13 675 25 670 95 101

.0634 1.6 0.72 710 11 713 12 722 34 98

.0688 1.2 0.87 892 17 892 14 893 24 100

.0689 4.5 0.41 902 17 900 30 897 92 101

.0718 1.2 0.78 985 14 983 12 980 25 100

.1125 1.8 0.88 1724 52 1777 33 1840 33 94

.1125 0.9 0.90 1804 29 1821 17 1841 16 98

.1200 1.3 0.75 1844 24 1898 17 1956 23 94

.1141 1.2 0.87 1846 35 1855 21 1865 22 99

.1165 1.0 0.80 1902 22 1902 15 1903 18 100

.1171 2.2 0.50 1906 21 1909 22 1913 40 100

.1294 1.0 0.81 1992 24 2040 15 2090 18 95

.1301 1.5 0.71 2130 27 2114 19 2099 26 101

.1346 2.3 0.66 2175 38 2167 28 2158 40 101

.1253 0.9 0.87 2197 28 2113 16 2033 15 108

.1383 1.2 0.83 2344 35 2271 19 2206 21 106

.1619 1.0 0.87 2530 36 2500 18 2476 16 102

.1689 1.4 0.77 2555 36 2550 21 2547 24 100

.1720 1.1 0.95 2560 70 2570 33 2577 18 99

.1833 1.1 0.81 2617 31 2655 17 2683 18 98

.2241 0.4 0.97 2786 36 2918 16 3010 6 93

.2098 1.5 0.74 2922 40 2911 22 2904 25 101

proximately 10%.if detectable, see analytical method) using Stacey and Kramers (1975) model Pbagated by quadratic addition of within-run errors (2SE) and the reproducibility

Table 5U–Th–Pb data of detrital zircon grains from sample A1-3 (61 of 120 measured grains which are concordant in the range of 90–110%) (Wadi Al Abd, section Wadi Al Abd 1,Cambrian, sandstone, lower part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf Arch, Libya, coordinates: 28�13039.900N, 13�53058.400E).

Number 207Pb(cps)

Ua

(ppm)Pba

(ppm)Th/

Uc

206Pb/204Pb

206Pb/238Ud

2r(%)

207Pb/235Ud

2r(%)

207Pb/206Pbd

2r(%)

Rho 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

a15 10805 238 23 0.74 6882 0.0892 2.0 0.72 3.0 0.0584 2.2 0.68 551 11 550 13 546 48 101a39 4492 90 9 1.00 2082 0.0896 2.6 0.72 5.5 0.0583 4.8 0.48 553 14 551 24 542 105 1022a6 3313 59 7 1.85 5602 0.0900 1.0 0.73 3.1 0.0587 2.9 0.31 556 5 556 13 555 64 1002a5 6245 110 12 1.16 10548 0.0903 1.2 0.73 2.5 0.0587 2.2 0.48 557 7 557 11 557 49 100a48 11162 136 12 0.42 18440 0.0911 1.7 0.74 3.1 0.0587 2.6 0.54 562 9 561 14 556 58 1012a42 6978 105 10 0.53 4310 0.0910 1.0 0.74 2.5 0.0587 2.3 0.39 562 5 560 11 554 50 101a26 13428 297 30 0.68 11628 0.0912 2.1 0.74 3.9 0.0588 3.3 0.54 563 12 562 17 559 72 101a19 10699 155 21 2.67 194 0.0926 3.6 0.76 6.1 0.0594 5.0 0.58 571 20 573 27 581 108 98a11 7448 155 20 2.25 12136 0.0930 1.7 0.76 2.9 0.0595 2.4 0.57 573 9 576 13 587 51 982a10 5094 87 9 0.77 8472 0.0931 1.4 0.76 4.5 0.0594 4.3 0.32 574 8 575 20 580 93 992a31 7067 127 16 1.40 11748 0.0959 1.6 0.79 2.6 0.0597 2.0 0.63 590 9 591 12 592 44 1002a14 16601 289 30 0.78 27480 0.0960 0.7 0.80 2.1 0.0600 1.9 0.35 591 4 594 9 605 42 98a36 9713 232 32 2.38 2979 0.0972 1.9 0.80 4.1 0.0598 3.6 0.46 598 11 598 19 598 78 100a42 162 3 0 1.14 261 0.0973 4.0 0.81 16.6 0.0603 16.1 0.24 598 23 602 78 616 347 97a51 7383 74 9 1.68 4515 0.0972 1.9 0.80 3.7 0.0594 3.2 0.51 598 11 595 17 583 69 1032a55 5799 46 5 1.18 2382 0.0971 1.4 0.80 2.9 0.0598 2.5 0.48 598 8 597 13 595 55 100a61 15554 90 10 1.11 1030 0.0973 2.4 0.80 8.3 0.0598 7.9 0.29 599 14 598 38 598 171 100a30 17381 350 42 1.20 19099 0.0985 2.1 0.82 3.0 0.0603 2.2 0.69 606 12 608 14 615 47 982a44 9889 133 16 1.51 1300 0.0988 1.3 0.84 3.4 0.0619 3.2 0.37 607 7 621 16 670 68 912a4 6590 110 12 0.84 1489 0.0992 1.5 0.82 2.7 0.0601 2.3 0.56 610 9 609 13 608 49 100a28 19101 395 43 0.70 3858 0.1001 1.9 0.83 2.5 0.0603 1.6 0.77 615 11 615 12 615 34 100a55 31775 117 16 1.36 165 0.1000 3.0 0.83 8.9 0.0604 8.4 0.34 615 18 615 42 617 181 1002a39 6888 109 12 0.65 11317 0.1003 1.7 0.83 3.3 0.0603 2.8 0.53 616 10 616 15 615 61 1002a8 7853 131 14 0.77 9952 0.1005 1.0 0.84 2.2 0.0603 1.9 0.47 618 6 617 10 614 42 101a65 6183 34 4 0.91 10026 0.1008 2.0 0.83 3.1 0.0597 2.4 0.64 619 12 614 14 592 51 105a32 10456 225 25 0.82 16894 0.1010 2.0 0.84 3.3 0.0603 2.6 0.60 620 12 619 15 613 57 1012a3 14049 229 27 1.17 2153 0.1021 1.4 0.86 3.6 0.0610 3.4 0.39 627 8 629 17 639 72 982a32 20447 363 45 1.18 3331 0.1027 1.1 0.86 1.9 0.0607 1.5 0.59 630 7 630 9 628 33 100a54 8198 64 7 0.87 13122 0.1031 1.7 0.86 3.0 0.0606 2.5 0.55 632 10 631 14 625 54 101a35 4570 94 13 1.87 3869 0.1032 1.6 0.87 3.3 0.0609 2.9 0.50 633 10 634 16 636 61 1002a35 2133 39 5 1.29 3459 0.1038 1.6 0.87 4.9 0.0611 4.7 0.33 637 10 638 24 642 100 992a60 5525 38 5 1.11 1763 0.1039 1.7 0.88 3.6 0.0611 3.2 0.46 637 10 639 17 644 69 992a29 8774 150 19 1.06 5933 0.1059 0.8 0.90 2.1 0.0613 2.0 0.37 649 5 649 10 651 42 1002a65 13884 76 11 1.88 4565 0.1062 0.7 0.92 1.7 0.0628 1.5 0.42 651 4 662 8 702 32 93a59 31722 104 15 0.98 312 0.1107 3.2 0.95 4.8 0.0623 3.6 0.66 677 21 679 24 685 77 99a10 9755 148 18 0.87 1816 0.1118 2.0 0.96 3.3 0.0626 2.6 0.61 683 13 686 17 695 56 98a18 8919 155 20 0.95 14058 0.1137 1.8 0.96 2.5 0.0615 1.7 0.72 694 12 685 12 657 36 1062a21 9814 162 23 2.04 1554 0.1152 1.6 1.00 13.4 0.0629 13.3 0.12 703 11 704 70 705 282 100a64 13834 63 9 1.02 3169 0.1297 2.2 1.19 2.9 0.0665 1.9 0.76 786 16 796 16 823 39 96a66 20230 57 9 1.01 615 0.1370 2.8 1.27 5.1 0.0671 4.3 0.55 827 22 831 30 841 90 98a53 25010 112 19 0.74 2469 0.1608 1.8 1.62 2.2 0.0728 1.3 0.80 961 16 976 14 1010 27 952a43 12000 34 12 1.44 4241 0.2813 1.2 3.81 2.4 0.0983 2.1 0.50 1598 17 1595 20 1592 39 100a29 89326 349 127 1.21 7282 0.2942 2.1 4.09 2.6 0.1009 1.5 0.81 1662 31 1653 22 1641 29 1012a48 36144 75 25 0.81 1803 0.2971 1.1 4.49 2.3 0.1096 2.1 0.45 1677 16 1729 19 1792 38 942a57 44923 57 20 0.63 39193 0.3026 2.6 4.74 3.1 0.1136 1.7 0.85 1704 40 1774 27 1857 30 92a21 25120 90 34 1.12 12577 0.3167 1.7 4.55 2.1 0.1042 1.2 0.82 1774 27 1740 18 1701 22 104a14 34340 101 38 0.90 29940 0.3262 1.8 5.00 2.1 0.1112 1.1 0.86 1820 29 1820 18 1819 19 1002a33 45902 149 54 0.68 40633 0.3264 1.0 5.03 1.7 0.1118 1.3 0.61 1821 17 1825 15 1829 24 100a4 105612 313 124 1.11 91839 0.3288 1.8 5.05 2.1 0.1113 1.1 0.86 1832 29 1827 18 1821 20 1012a27 37014 109 41 0.76 32255 0.3307 1.3 5.19 1.7 0.1138 1.1 0.75 1842 21 1851 15 1860 21 992a11 85699 232 89 0.96 2817 0.3409 1.1 5.44 1.5 0.1158 1.1 0.70 1891 17 1891 13 1892 19 1002a61 35729 36 14 0.91 2609 0.3436 1.1 5.55 1.7 0.1171 1.4 0.61 1904 17 1908 15 1913 24 1002a22 18628 47 19 0.87 15745 0.3472 1.1 5.60 1.8 0.1170 1.5 0.59 1921 18 1916 16 1911 26 101a40 21897 65 26 1.32 18918 0.3480 1.7 5.39 2.3 0.1124 1.5 0.74 1925 28 1883 20 1838 28 105a3 20806 58 24 0.92 17480 0.3536 1.8 5.63 2.7 0.1154 2.0 0.67 1952 31 1920 24 1886 36 103a7 14565 38 17 1.53 4756 0.3611 1.9 5.64 2.9 0.1133 2.2 0.65 1987 32 1923 25 1853 40 1072a36 46301 136 62 1.39 39908 0.3623 1.5 5.74 1.8 0.1150 0.9 0.85 1993 26 1938 15 1879 17 106a44 24505 57 23 0.80 20859 0.3802 1.9 6.02 2.7 0.1147 1.9 0.71 2077 34 1978 23 1876 34 111a5 27939 48 25 1.03 17942 0.4430 1.6 9.23 2.3 0.1510 1.7 0.70 2364 32 2361 21 2358 28 100a24 150896 225 164 2.00 14378 0.4984 2.5 11.75 2.8 0.1710 1.3 0.89 2607 53 2585 26 2567 22 1022a7 118693 126 74 0.72 20527 0.5015 1.4 12.32 1.7 0.1782 0.9 0.84 2620 30 2629 16 2636 15 99a25 184423 124 118 1.49 65773 0.6798 1.7 25.47 1.9 0.2717 0.7 0.92 3344 45 3326 18 3316 11 101

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 (2SE) and the reproducibilityof GJ-1 (2SD).



Table 6U–Th–Pb data of detrital zircon grains from sample DA2-3 (61 of 120 measured grains which are concordant in the range of 90–110%) (Wadi Damran, section Wadi Damran 2,Cambrian, sandstone, lower part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf Arch, Libya, coordinates: 28�31054.400N, 13�57024.900E).

Number 207Pba

(cps)Ub

(ppm)Pbb

(ppm)Th/

Ub

206Pb/204Pbc

206Pb/238Uc

2r(%)

207Pb/235Uc

2r(%)

207Pb/206Pbc

2r(%)

Rhod 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

a64 4932 30 3 1.17 5516 0.0829 2.5 0.659 3.6 0.0576 2.6 0.69 514 12 514 15 515 57 100a65 2716 18 2 0.61 4288 0.0841 2.5 0.671 4.8 0.0578 4.1 0.53 521 13 521 20 523 90 1002a24 7616 157 14 0.50 8079 0.0863 2.7 0.691 4.2 0.0581 3.2 0.66 534 14 534 17 532 69 1002a25 24573 469 41 0.34 8212 0.0870 2.5 0.712 2.7 0.0593 1.2 0.90 538 13 546 12 579 26 932a37 10622 223 21 0.47 17712 0.0890 2.8 0.719 3.2 0.0585 1.6 0.86 550 15 550 14 550 35 100a24 3589 69 6 0.00 2117 0.0906 1.9 0.729 3.8 0.0584 3.3 0.49 559 10 556 17 544 73 1032a43 9363 135 17 1.82 15561 0.0912 2.6 0.739 3.0 0.0588 1.5 0.86 563 14 562 13 558 34 1012a49 7413 79 8 0.69 4470 0.0921 2.6 0.748 3.9 0.0589 2.9 0.67 568 14 567 17 564 63 1012a18 16797 292 28 0.34 1523 0.0923 3.0 0.758 8.3 0.0595 7.8 0.36 569 16 573 37 586 168 972a15 4992 95 10 0.75 2280 0.0927 2.6 0.754 3.4 0.0590 2.2 0.76 571 14 570 15 566 48 1012a27 3451 70 7 0.46 5730 0.0927 2.7 0.753 4.3 0.0589 3.3 0.63 572 15 570 19 564 73 101a15 31172 615 59 0.56 12073 0.0934 1.7 0.752 2.5 0.0584 1.7 0.71 575 10 570 11 546 38 1052a4 7717 129 13 0.65 425 0.0939 2.7 0.776 4.7 0.0600 3.8 0.58 578 15 583 21 603 83 962a7 24645 449 43 0.40 5178 0.0938 2.4 0.781 2.8 0.0604 1.5 0.86 578 13 586 13 617 31 942a53 4945 43 5 1.40 8150 0.0949 3.2 0.775 4.0 0.0593 2.4 0.81 584 18 583 18 578 51 1012a17 7886 124 14 1.18 6071 0.0982 2.9 0.814 3.9 0.0601 2.6 0.75 604 17 604 18 606 56 100a12 18033 347 32 0.05 29379 0.0989 1.4 0.761 2.8 0.0558 2.4 0.50 608 8 574 12 444 54 1372a62 13313 86 9 0.43 10359 0.0990 2.9 0.801 3.3 0.0587 1.4 0.90 608 17 597 15 556 31 1092a51 3994 36 4 0.89 1724 0.0994 3.0 0.825 4.4 0.0602 3.2 0.68 611 17 611 20 609 69 100a17 5763 100 10 0.35 3294 0.0997 1.8 0.824 8.9 0.0600 8.7 0.20 612 10 611 42 603 189 1022a44 12666 161 18 0.90 6888 0.0999 2.4 0.830 3.1 0.0602 1.9 0.79 614 14 613 14 612 41 1002a38 9445 160 23 1.84 6207 0.1044 2.6 0.878 3.2 0.0610 1.9 0.80 640 16 640 15 640 41 1002a28 14083 231 26 0.56 779 0.1060 4.2 0.906 8.7 0.0620 7.7 0.48 650 26 655 43 674 164 962a10 14017 219 26 0.84 22276 0.1077 2.5 0.913 2.9 0.0615 1.5 0.86 660 16 659 14 655 31 1012a21 853 17 2 1.48 1278 0.1082 2.9 0.921 9.7 0.0618 9.2 0.30 662 18 663 48 665 197 992a48 33296 278 31 0.37 51225 0.1088 2.6 0.952 3.1 0.0635 1.6 0.85 666 17 679 15 724 34 922a52 17808 243 26 0.28 2503 0.1107 4.8 0.943 5.8 0.0618 3.4 0.82 677 31 674 29 667 72 1012a33 2283 40 6 1.64 3550 0.1117 2.7 0.944 4.2 0.0613 3.3 0.62 682 17 675 21 650 71 1052a32 6554 185 23 0.94 1229 0.1136 2.5 0.959 3.2 0.0612 2.1 0.76 694 16 683 16 647 45 1072a59 2662 17 2 0.71 4181 0.1229 3.7 1.076 5.2 0.0635 3.6 0.72 747 26 741 27 725 76 1032a31 2289 27 4 1.00 3352 0.1378 2.8 1.269 5.4 0.0668 4.6 0.52 832 22 832 31 832 96 100a42 167677 509 143 0.19 11762 0.2836 1.6 3.968 1.8 0.1015 1.0 0.85 1610 22 1628 15 1651 18 98a26 36166 118 40 0.97 31942 0.2884 2.0 4.086 2.5 0.1027 1.5 0.81 1634 29 1652 20 1674 27 98a2 106308 319 100 0.33 23151 0.2999 1.6 4.613 1.8 0.1116 0.8 0.90 1691 24 1752 15 1825 14 93a13 146654 157 76 0.60 115 0.3054 2.5 4.365 3.6 0.1037 2.6 0.70 1718 38 1706 30 1691 47 102a5 8891 24 10 1.68 3348 0.3133 1.7 4.579 2.9 0.1060 2.3 0.59 1757 26 1745 24 1732 43 101a8 284078 736 253 0.59 18745 0.3133 1.4 4.741 1.6 0.1098 0.6 0.91 1757 22 1775 13 1796 12 98a49 25322 42 16 1.09 22042 0.3155 2.0 4.550 2.2 0.1046 1.1 0.88 1768 31 1740 19 1707 20 104a25 10106 31 15 2.63 8888 0.3256 1.5 4.636 2.4 0.1033 1.9 0.61 1817 24 1756 21 1684 36 108a20 78424 184 69 0.73 56595 0.3306 1.5 5.742 1.7 0.1260 0.9 0.87 1841 24 1938 15 2042 15 90a43 36334 73 28 0.93 9491 0.3305 1.3 4.840 2.0 0.1062 1.5 0.64 1841 21 1792 17 1736 28 1062a35 7374 31 15 2.40 6911 0.3326 2.5 4.786 4.0 0.1044 3.1 0.62 1851 40 1782 34 1703 58 1092a64 92942 97 34 0.50 31410 0.3326 3.2 5.258 3.3 0.1147 0.9 0.96 1851 51 1862 28 1874 16 99a47 19301 33 16 1.97 5813 0.3358 1.7 4.952 2.3 0.1069 1.6 0.73 1867 28 1811 20 1748 30 1072a16 63571 177 74 1.30 6055 0.3359 3.0 5.284 3.2 0.1141 1.2 0.93 1867 49 1866 28 1865 21 1002a47 64044 108 43 1.03 54817 0.3374 2.6 5.309 2.8 0.1141 1.0 0.93 1874 43 1870 24 1866 18 1002a3 27983 74 29 0.91 23943 0.3410 2.4 5.366 2.7 0.1141 1.2 0.89 1891 40 1879 24 1866 22 101a58 47137 43 18 0.98 4551 0.3476 1.4 5.413 1.9 0.1129 1.2 0.78 1923 24 1887 16 1847 21 1042a26 38527 93 44 1.56 20208 0.3612 2.6 6.056 2.9 0.1216 1.2 0.91 1988 45 1984 25 1980 22 100a31 20421 50 27 2.54 16605 0.3636 1.6 5.606 2.2 0.1118 1.5 0.73 1999 28 1917 19 1829 28 109a9 58380 122 49 0.49 43236 0.3646 1.3 6.174 1.6 0.1228 0.9 0.81 2004 22 2001 14 1997 17 100a30 69441 201 82 0.74 54639 0.3687 1.3 5.876 1.5 0.1156 0.6 0.91 2023 23 1958 13 1889 11 107a6 144906 331 130 0.41 114719 0.3717 1.4 5.889 1.6 0.1149 0.8 0.87 2038 24 1960 14 1878 14 1082a13 138786 308 129 0.63 107518 0.3738 2.6 6.513 2.7 0.1264 0.8 0.95 2047 45 2048 24 2048 14 1002a40 44412 86 41 1.28 7542 0.3797 2.7 6.634 3.0 0.1267 1.3 0.90 2075 48 2064 27 2053 23 1012a30 171690 397 156 0.17 58024 0.3890 2.4 6.644 2.5 0.1239 0.9 0.94 2118 43 2065 23 2013 15 105a29 175854 278 140 0.85 1030 0.4274 2.1 8.492 2.4 0.1441 1.3 0.85 2294 40 2285 23 2277 23 101a22 252566 410 197 0.61 41130 0.4292 1.3 8.945 1.5 0.1512 0.7 0.87 2302 25 2332 14 2359 13 98a35 147476 372 176 0.42 11857 0.4484 1.6 10.083 4.2 0.1631 3.9 0.37 2388 31 2442 40 2488 66 96a16 108799 192 104 0.80 16170 0.4743 2.3 10.743 2.6 0.1643 1.2 0.89 2502 48 2501 24 2500 20 100a4 45678 54 27 0.24 25590 0.4776 1.6 10.698 2.1 0.1624 1.4 0.77 2517 34 2497 20 2481 23 101a14 199958 217 117 0.20 79545 0.5062 1.4 12.871 1.6 0.1844 0.8 0.87 2640 30 2670 15 2693 13 98a33 591176 648 509 0.84 34296 0.6653 1.4 20.891 1.9 0.2278 1.2 0.76 3288 37 3134 19 3036 20 108

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 (2SE) and the reproducibilityof GJ-1 (2SD).



TabU–TCam

N

a23aa3333a3aaa2aaa3a3333a3aa3aaaa33a2a3a3aa2a

a

b

c

comof G

d


Stratigraphic level: basal portion of lower unit of Hasawnah For-mation (7 m above base).Sample no.: Ba2-10.Location: Wadi Badran (28�11025.300N, 13�58031.100E).Lithology: fine-grained sandstone showing low-angle herring-bone cross-bedding.Stratigraphic level: basal portion of lower unit of Hasawnah For-mation (4.5 m above base).Sample no.: Ba2-14.Location: Wadi Badran (28�11025.300N, 13�58031.100E).Lithology: centimeter-scale alternation of (1) coarse-grainedand (2) medium- to fine-grained sandstone, showing unidirec-tional trough cross-bedding.Stratigraphic level: middle portion of middle unit of HasawnahFormation (136 m above base).

le 7h–Pb data of detrital zircon grains from sample Ba2-14 (45 of 120 measured grains wbrian, sandstone, middle part of the Hasawnah Formation, Qarqaf Group, Al Qarqaf A

umber 207Pba

(cps)Ub

(ppm)Pbb

(ppm)Th/

Ub

206Pb/204Pbc

206Pb/238Uc

2r(%)

207Pb/235Uc

2r(%)

24 27632 298 29 0.44 397 0.0888 2.6 0.72 6.5a11 4631 88 8 0.39 7808 0.0889 4.1 0.73 4.9a50 16673 145 14 0.78 2314 0.0897 3.4 0.74 4.718 7165 106 12 1.33 12059 0.0900 2.6 0.73 3.735 13916 128 16 1.04 437 0.0901 2.6 0.73 6.9a26 14212 293 27 0.41 4350 0.0908 4.1 0.75 4.5a14 14511 222 25 1.04 10216 0.0909 3.4 0.75 3.8a24 4658 77 8 0.94 4148 0.0916 3.3 0.76 4.9a52 2599 19 2 1.59 4319 0.0930 3.4 0.77 5.348 10633 110 11 0.44 10328 0.0934 2.6 0.76 3.6a3 8770 121 20 3.30 14553 0.0935 3.2 0.78 3.86 7148 90 9 0.59 11859 0.0964 2.6 0.80 3.436 9734 167 17 0.69 5793 0.0966 2.6 0.81 4.023 17447 250 23 0.05 17443 0.0981 2.4 0.82 2.7a3 16585 300 32 0.52 24191 0.0985 4.0 0.81 4.35 62280 287 39 0.93 107 0.0994 2.6 0.83 7.642 20400 237 26 0.73 33461 0.1003 2.6 0.84 3.053 8687 56 6 0.52 2070 0.1004 2.8 0.84 5.4a39 4388 53 7 1.48 7148 0.1008 3.4 0.85 4.617 7764 98 15 2.27 12579 0.1027 2.5 0.87 3.2a44 54492 497 49 0.13 2195 0.1032 3.2 1.07 11.2a9 15090 230 27 0.80 24268 0.1054 3.3 0.90 3.6a8 10187 159 18 0.76 1403 0.1059 3.3 0.91 5.2a49 19477 174 20 0.42 4300 0.1126 3.2 0.98 4.139 40960 705 78 0.25 682 0.1130 2.9 0.99 4.6a30 3049 43 5 0.88 4795 0.1131 3.3 0.99 4.926 18038 208 25 0.43 6593 0.1146 2.5 0.99 4.040 19301 72 22 0.56 14135 0.2923 2.8 4.12 3.3a37 108081 374 126 0.51 262 0.2962 3.9 4.26 5.151 48044 61 21 1.04 2852 0.2995 4.8 4.41 5.154 23121 35 12 0.61 8112 0.3000 2.7 4.63 3.647 63671 133 45 0.63 7789 0.3115 2.8 4.66 2.949 4480 4 2 1.19 3994 0.3126 4.4 4.65 5.9a22 17308 40 16 0.93 3032 0.3367 3.3 5.42 3.8a53 22641 21 8 0.68 2575 0.3407 3.3 5.66 3.928 35315 79 32 0.76 27591 0.3423 2.8 5.52 3.5a10 110879 356 132 0.49 9463 0.3444 4.2 5.40 4.341 64733 118 49 0.86 55442 0.3553 2.4 5.69 3.0a33 181042 301 124 0.22 1850 0.3726 3.6 6.57 3.88 239357 674 269 0.37 4329 0.3867 2.5 7.57 2.6a21 55076 111 54 0.90 481 0.4029 3.4 7.92 5.852 56533 43 21 0.73 38338 0.4278 2.6 8.64 2.937 156116 157 89 0.48 87789 0.4967 2.7 12.09 3.0a5 105559 109 80 1.63 458 0.5779 4.2 16.19 4.525 10011 2 3 0.23 24 0.5803 2.5 18.76 24.5

Within-run background-corrected mean 207Pb signal in counts per second.U and Pb content and Th/U ratio were calculated relative to GJ-1 and are accurate tCorrected for background, mass bias, laser induced U–Pb fractionation and commonposition. 207Pb/235U calculated using 207Pb/206Pb/(238U/206Pb � 1/137.88). Errors areJ-1 (2SD).Rho is the error correlation defined as err206Pb/238U/err207Pb/235U.

4. Results

The U–Th–Pb data of all investigated detrital zircons are pre-sented in Tables 2–7. A total 120 detrital zircon grains were ana-lyzed in each sample. We discuss in that paper only zircons,which are concordant in the range of 90–110%. In sample X1-1 (Ta-ble 2), 61 grains are concordant (Fig. 3). The youngest concordantgrain yields a date of 520 ± 11 Ma; the oldest zircon yields a dateof 3384 ± 14 Ma. Two grains in this sample are Archaean in age(3384 ± 14 Ma, 2645 ± 42 Ma) (Table 2, Fig. 3). Some 17% of allgrains are Palaeoproterozoic, ranging from 2073 ± 19 Ma to1702 ± 34 Ma. No Mesoproterozoic zircons were detected. Themajority, 60% of all grains, are Neoproterozoic and range from943 ± 27 Ma to 544 ± 12 Ma. Around 20% of all zircon grains yield

hich are concordant in the range of 90–110%) (Wadi Badran, section Wadi Badran 2,rch, Libya, coordinates: 28�11025.300N, 13�58031.100E).

207Pb/206Pbc

2r(%)

rhod 206Pb/238U

2r(Ma)

207Pb/235U

2r(Ma)

207Pb/206Pb

2r(Ma)

Conc.%

0.0589 6.0 0.40 549 14 551 28 563 130 980.0592 2.7 0.83 549 22 554 21 575 60 960.0595 3.3 0.72 554 18 560 20 587 71 940.0590 2.7 0.70 555 14 558 16 567 59 980.0589 6.4 0.38 556 14 558 30 564 140 990.0597 1.8 0.92 560 22 567 20 594 39 940.0597 1.8 0.88 561 18 567 17 593 39 950.0598 3.6 0.68 565 18 571 21 598 77 940.0600 4.1 0.64 573 18 579 24 603 88 950.0594 2.6 0.71 575 14 577 16 582 55 990.0602 2.1 0.84 576 18 583 17 610 45 940.0599 2.3 0.75 593 15 595 16 600 49 990.0605 3.1 0.65 594 15 600 18 622 66 960.0603 1.3 0.88 604 14 606 13 615 28 980.0597 1.5 0.93 605 23 603 20 594 33 1020.0606 7.1 0.34 611 15 614 36 625 153 980.0605 1.5 0.86 616 15 618 14 623 33 990.0607 4.6 0.52 617 17 619 25 628 100 980.0613 3.0 0.75 619 20 626 21 651 65 950.0612 2.0 0.78 630 15 633 15 645 44 980.0751 10.8 0.28 633 19 738 61 1071 216 590.0620 1.6 0.89 646 20 653 18 676 35 960.0622 4.1 0.63 649 20 656 26 682 87 950.0632 2.6 0.77 688 21 694 21 716 56 960.0635 3.6 0.62 690 19 699 23 726 76 950.0634 3.7 0.66 690 21 697 25 720 78 960.0629 3.2 0.62 699 17 700 21 704 67 990.1022 1.9 0.83 1653 40 1658 28 1665 35 990.1043 3.3 0.76 1672 57 1685 43 1701 61 980.1068 1.7 0.94 1689 71 1714 43 1745 32 970.1118 2.4 0.74 1691 40 1754 31 1829 44 920.1085 1.0 0.94 1748 42 1760 25 1774 19 990.1078 3.9 0.75 1754 68 1758 51 1763 72 990.1168 1.8 0.88 1871 54 1889 33 1908 32 980.1204 2.2 0.83 1890 54 1925 35 1962 39 960.1169 2.0 0.81 1898 47 1903 30 1910 36 990.1137 1.1 0.97 1908 69 1885 38 1859 20 1030.1161 1.9 0.79 1960 41 1930 27 1898 33 1030.1279 0.9 0.97 2042 64 2055 34 2069 16 990.1419 0.5 0.98 2108 46 2181 23 2250 8 940.1426 4.6 0.59 2183 64 2222 53 2259 80 970.1465 1.2 0.91 2296 50 2301 26 2306 21 1000.1765 1.1 0.93 2600 59 2611 28 2621 18 990.2032 1.7 0.93 2940 99 2888 44 2852 28 1030.2345 24.3 0.10 2950 60 3030 268 3083 388 96


Fig. 3. U–Pb dates of detrital zircon grains from sample X1-1 (sandstone, Hasawnah Formation, Cambrian, unnamed wadi ‘‘X’’, AQA). (A) Concordia diagram. (B–C) Combinedbinned frequency and probability density distribution plots of detrital zircon grains. (B) 3500–400 Ma. (C) 1000–400 Ma.


early Cambrian dates ranging from 542 ± 15 Ma to 520 ± 11 Ma(Table 2, Fig. 3). The probability plot shows distinct peaks at c.660, 625, 560 and 533 Ma (Fig. 3). To characterize the maximum

age of sedimentation, a concordia date of 523 ± 7 Ma was calcu-lated from the three youngest concordant zircons of sample X1-1(Fig. 4).

Fig. 4. U–Pb age (concordia age) of three youngest detrital zircon grains fromsample X1-1 (sandstone, Hasawnah Formation, Cambrian, unnamed wadi ‘‘X’’,AQA). Cambrian in wadi ‘‘X’’ must be 523 ± 7 Ma or younger.


Among the zircons of sample Ba2-10 (Table 3), 54 grains wentconcordant (Table 3, Fig. 5). The youngest concordant grain yieldsa date of 525 ± 6 Ma; the oldest zircon yields a date of3173 ± 28 Ma. Three grains are Archaean in age (3173 ± 28 Ma,2827 ± 14 Ma, 2605 ± 17 Ma). Some 13% of grains are Palaeoprote-rozoic, in the range 2406 ± 29 Ma to 1910 ± 19 Ma. Three Mesopro-terozoic zircons were detected in the sample (1018 ± 36 Ma,1003 ± 94 Ma, 1003 ± 18 Ma). Around 70% of all zircons in the sam-ple are Neoproterozoic, in the range 888 ± 12 Ma to 547 ± 20 Ma(Table 3, Fig. 5). Five grains yield early Cambrian dates(542 ± 11 Ma to 525 ± 6 Ma). The probability plot is dominatedby peaks at c. 670, 630, 525, and 560 Ma (Fig. 5).

From the zircons of sample Ba1-3, 46 grains were concordant(Table 4, Fig. 6). The youngest and only Cambrian zircon grainyields a date of 533 ± 9 Ma. The oldest zircon is one of five Archae-an grains with a date of 2904 ± 25 Ma. The other four Archaeandates of zircons from sample Ba1-3 are 3010 ± 6 Ma,2683 ± 18 Ma, 2577 ± 18 Ma and 2547 ± 24 Ma. A remarkable pro-portion of 25% Palaeoproterozoic grains occurs in the sample. Suchdates range from 2476 ± 16 Ma to 1840 ± 33 Ma. No Mesoprotero-zoic zircons are present. Around 62% of all zircons in sample Ba1-3are Neoproterozoic, in the range from 985 ± 14 Ma to 552 ± 10 Ma(Fig. 6, Table 4). The probability plot shows distinct peaks at c. 660,590, 570, and 560 Ma (Fig. 6).

In sample A1-3, 61 grains are concordant (Table 5, Fig. 7) andthe youngest zircon grain yields a date of 551 ± 11 Ma; the old-est zircon yields a date of 3316 ± 11 Ma. Two more Archaeangrains are also present (2636 ± 15 Ma, 2567 ± 22 Ma). A greaterproportion of Palaeoproterozoic zircons (27%) is in the range2358 ± 28 Ma to 1641 ± 29 Ma. Around 67% of all zircons in thissample are Neoproterozoic, in the range 961 ± 16 Ma to551 ± 11 Ma. No Cambrian zircons are present. The probabilityplot shows distinct peaks at c. 650, 630, 615, 590, and 560 Ma(Fig. 7).

From sample DA2-3, 63 grains are classified as concordant(Table 6, Fig. 8). The youngest grain yields a date of 514 ± 12 Ma.Only two zircons yield an Archaean age (3036 ± 20 Ma,2693 ± 13 Ma). The majority of all zircon dates (44%) fall withinthe Palaeoproterozoic, in the range 2500 ± 20 Ma to 1610 ±22 Ma. No Mesoproterozoic grains were detected. The second-largest population is represented by Neoproterozoic zircons(42%), in the range 832 ± 22 Ma to 550 ± 15 Ma. Four Cambrian zir-cons are present (538 ± 13 Ma, 534 ± 14 Ma, 521 ± 13 Ma,

514 ± 12 Ma). The probability plot shows three major peaks, at c.660, 610, and 570 Ma.

Among the zircons of sample Ba2–14, grains are concordant(Table 7, Fig. 9) and the youngest grain yields a date of549 ± 14 Ma. The oldest zircon is Archaean (2950 ± 60 Ma). Twoadditional Archaean zircons yield dates of 2621 ± 18 Ma and2852 ± 28 Ma. A large proportion (33%) of Palaeoproterozoic grainsare present in the sample; dates are in the range 2306 ± 21 Ma to1665 ± 35 Ma. No Mesoproterozoic grains were found. Some 60%of all zircons in the sample are Neoproterozoic, in the range699 ± 17 Ma to 549 ± 14 Ma. Cambrian zircons are not presentamong the analyzed grains. The probability plot shows distinctpeaks at c. 680, 615, and 560 Ma.

5. Discussion

In the present study, U–Pb dates from detrital zircons providemuch information concerning the geotectonic history of sourceareas and timing of geotectonic events in the AQA region. From720 analyzed zircons, 329 grains were concordant and providegood constraints on Precambrian and Cambrian orogenic eventsin the source areas. Within the geological context of the AQA, silic-iclastic rocks of the Hasawnah Formation denote the basal portionof an early Palaeozoic sequence overstepping the basement of theSaharan Metacraton (Abdelsalam et al., 2002). In the central part ofthe AQA, the basement of the metacraton crops out in a number oflocalities as deeply weathered granitoids. Hitherto, radiometricdates were few, yet already pointed to Neoproterozoic to earlyCambrian intrusion ages: 640–549 Ma (Rb/Sr; Schürmann, 1974),541–491 Ma (K/Ar; Schürmann, 1974), 554–520 Ma (K/Ar; Jurák,1978).

Because Cambrian strata of the Hasawnah Formation overlie thedeeply eroded granitoids nonconformably, strong uplift coupledwith deep erosion and weathering processes during latest Neopro-terozoic and early Cambrian time is indicated. High-maturity sanddeposits like the Hasawnah Formation imply intervals of intensechemical weathering and cleaning by streaming water at this time(e.g., Linnemann et al., 2000, 2011; Dott, 2003; Avigad et al., 2005).This palaeogeographic area of Gondwana drifted into lower lati-tudes during the lower and middle Cambrian (McKerrow et al.,1992; McKerrow and Cocks, 1995), where a warm to humid cli-mate is suggested. Volcanism during late Neoproterozoic and earlyCambrian time created an unusually corrosive atmosphere withvery high atmospheric pCO2 that forced an extreme chemicalweathering of the largely vegetation-free landscape under warmto humid climatic conditions (Avigad et al., 2005). Intense erosionand denudation of Pan-African orogens and cratonic basement ledto prevalent peneplanation. Cambrian–Ordovician rifting andwidespread thermal subsidence at the margins of Gondwana cre-ated shallow marine shelves where masses of the high-maturitysands accumulated. The assumed aggressive weathering mightalso have had a great impact on the radiation of organisms, be-cause abundant nutrients would have been transported into theoceans by giant drainage systems in late Neoproterozoic–Cambriantime (Brasier, 1992; Tucker, 1992; Campbell et al., 2008; Squireet al., 2006).

Due to the absence of body fossils, a biostratigraphic age is notavailable for the Hasawnah Formation. However, our zircon datasupport the onset of Cambrian sedimentation already in the Terre-neuvian (earliest Cambrian). Stratigraphically, sample X1-1 is ouroldest sample from the five sections (Fig. 2). The youngest popula-tion of detrital zircons from that sample indicates a maximum ageof sedimentation for Cambrian strata in the AQA area. A concordiaage of 523 ± 7 Ma from the three youngest zircon grains was calcu-lated (Fig. 4). Despite the large error, that age is good enough to

Fig. 5. U–Pb dates of detrital zircon grains from sample Ba2-10 (sandstone, Hasawnah Formation, Cambrian, section Ba2 = Wadi Badran-2, AQA). (A) Concordia diagram.(B–C) Combined binned frequency and probability density distribution plots of detrital zircon grains. (B) 3500–400 Ma. (C) 1100–400 Ma.


pinpoint the onset of Cambrian deposition in the AQA within theTerreneuvian (542–521 Ma) or slightly younger. Thus, during thefirst 10–12 Ma of the Cambrian period there is no evidence for

deposition of sediments in the AQA. In the AQA the formation ofthe Gondwanan peneplain (Avigad et al., 2005) and earlyPalaeozoic subsidence commenced in the early Cambrian (present

Fig. 6. U–Pb dates of detrital zircon grains from sample B1-3 (sandstone, Hasawnah Formation, Cambrian, section Ba1 = Wadi Badran-1, AQA). (A) Concordia diagram. (B–C)Combined binned frequency and probability density distribution plots of detrital zircon grains. (B) 3000–500 Ma. (C) 1100–500 Ma.


study). On the contrary, related subsidence processes in the Tassilisarea south of the Hoggar (Algerian Sahara) did not begin before thelatest Cambrian to early Ordovician (Linnemann et al., 2011). This

means that the centre of early Palaeozoic thermal subsidence incentral-northern Africa must have been situated farther east, inthe area of the Saharan Metacraton.

Fig. 7. U–Pb dates of detrital zircon grains from sample A1-3 (sandstone, Hasawnah Formstion, Cambrian, section A1 = Wadi Al Abd-1, AQA). (A) Concordia diagram. (B–C)Combined binned frequency and probability density distribution plots of detrital zircon grains. (B) 3500–400 Ma. (C) 1000–400 Ma.


The overwhelming majority (56.53%) of detrital zircon U–Pbdates from all six investigated samples fall within the Neoprotero-zoic (Fig. 10). Peaks in the probability plots (Figs. 3–9) cluster at c.

700–680, 670–650, 615–610, 590, 570 and 560 Ma. For northwest-ern Gondwana such dates are indicative of Pan-African and Cado-mian orogenic events (see discussion in Linnemann et al., 2011

Fig. 8. U–Pb dates of detrital zircon grains from sample DA2-3 (sandstone, Hasawnah Formation, Cambrian, section Da2 = Wadi Damran-2, AQA). (A) Concordia diagram. (B–C) Combined binned frequency and probability density distribution plots of detrital zircon grains. (B) 3500–400 Ma. (C) 900–400 Ma.


and references therein). A few Neoproterozoic dates scatter aroundc. 950–750 Ma, which might be related to rifting and drifting dur-ing dispersal of the Rodinia palaeosupercontinent (e.g. Linnemann

et al., 2011). The clusters of Neoprotereozoic zircon populations arelargely identical with those from the Cambro-Ordovician sand-stones of the Tassilis area of the Algerian Sahara (see Figs. 11 and

Fig. 9. U–Pb dates of detrital zircon grains from sample Ba2-14 (sandstone, Hasawnah Formation, Cambrian, section Ba2 = Wadi Badran-2, AQA). (A) Concordia diagram. (B–C) Combined binned frequency and probability density distribution plots of detrital zircon grains. (B) 3200–400 Ma. (C) 1000–400 Ma.


12, and Linnemann et al., 2011). The only difference to the Tassilisarea is in the occurrence of three zircons within the AQA formedaround the Mesoproterozoic–Neoproterozoic boundary at c. 1 Ga.

Dates are somewhat scattered, with clusters at 1039 ± 11,1006 ± 12 and 993 ± 13 Ma (Fig. 10, Tables 2–7). Only two furtherMesoproterozoic zircons, dated at 1592 ± 39 Ma and

Fig. 10. Tectonomagmatic and orogenic events combined with binned frequencyplots of all 329 U–Pb dates of analyzed zircon grains showing degree of concordancein range 90–110%.


1475 ± 20 Ma (Figs. 10 and 11, Tables 2–7), were found. Taken as awhole, among all the 329 zircon dates from the six investigatedsamples, only four are clearly Mesoproterozoic and the single zir-con with a date of 993 ± 13 Ma overlaps the Mesoproterozoic–Neo-proterozoic boundary only in the error ellipse. Hence, in theCambrian, a potential source area of Mesoproterozoic zircon grainsseems to have been situated far distant from the AQA. A similaroccurrence pattern of Mesoproterozoic zircons was recently re-ported by Meinhold et al. (2011) from Cambrian strata of the east-ern flank of the Murzuq Basin, about 350 km to the southeast. Inthat study the authors report that about 20 of 202 measured

zircons from the Hasawnah Formation sandstones yielded Meso-proterozoic dates, among which the majority clusters around1 Ga. It seems that the eastern Murzuq Basin area investigated byMeinhold et al. (2011) was located closer to a source area thatwas largely composed of Mesoproterozoic crust. Because the pro-portion of Mesoproterozoic zircon grains is greater in the sampleof these authors compared to that of the AQA (a phenomenon alsoobserved in Ordovician to Carboniferous sedimentary rocks inves-tigated in the same study), such a geological unit must have beenlocated much farther to the east. A potential source area could beconcealed within the Arabian–Nubian Shield (e.g. Kolodner et al.,2006) or situated in Chad, or much more distant, at the southeast-ern margins of the Congo and Tanzania cratons (Le Heron et al.,2009; Meinhold et al., 2011). Conversely, there is no evidence forthe existence of massive Mesoproterozoic crust in the SaharanMetacraton area (see also discussion in Linnemann et al., 2011).

The second-largest fraction of zircon dates in the present sam-ple set is represented by Palaeoproterozoic zircon populations, de-rived from one or more cratonic basement units generated bymagmatic events at c. 2.4–2.3 Ga and 2.2–1.6 Ga (Figs. 10 and11). In addition, there are a number of Archaean zircons whichscatter around c. 3.4–3.25 Ga, 2.97–2.95 Ga and 2.6–2.5 Ga (Figs. 10and 11). Most of these seem to be derived from the West AfricanCraton or a related cratonic source. The West African Craton wasstabilized by orogenic events in the Archaean (Leonian, Liberian)and the Palaeoproterozoic (Eburnean). There, phases of major crus-tal growth occurred between 3.6 and 3.05 Ga (Kröner et al., 2001;Potrel et al., 1996, 1998), 3.0–2.7 Ga (Guerrot et al., 1989; Key et al.,2008) and 2.4–1.9 Ga (Abouchami et al., 1990; Boher et al., 1992;Rocci et al., 1991; Zhao et al., 2002a,b; Linnemann et al., 2011).Therefore, West Africa is clearly a potential source for most ofthe Palaeoproterozoic and Archaean zircons that cluster around3.4–1.9 Ga.

Palaeoproterozoic zircon populations in the range c. 1.85–1.6 Ga seem to be representative for the western part of the Saha-ran Metacraton. Such dates are also reported by Abdelsalam et al.(2002) and Meinhold et al. (2011). Among the zircons in the pres-ent samples, grains of this age dominate among the Palaoprotero-zoic zircon populations. Palaeoproterozoic zircons derived fromthe West African Craton are less common (Fig. 11). However, in zir-con populations from Cambrian–Ordovician sandstone in the Tass-ilis area south of the Hoggar (Algerian Sahara), the opposite is thecase (Linnemann et al., 2011; see Fig. 11). In this more westerlyarea, zircons yielding dates of c. 2.2–1.9 Ga dominate the Palaeo-proterozoic zircon populations. Such zircons seem to be a goodindicator for the proximity of the West African source. Southeastof the AQA, in the Murzuq Basin, the zircon population in the range1.85–1.6 Ga dominates slightly among Palaeoproterozoic grains(Meinhold et al., 2011). Much further to the east and southeast,in the eastern Al Kufrah Basin, no zircon population of this agerange has been found (Le Heron et al., 2009). Hence, in the Cam-brian of the AQA and eastern Murzuq Basin, zircon populationsof such an age range were most probably derived from a localsource. Thus, these zircon dates seem to be a good tracer of asource in the western part of the Saharan Metacraton and indicatea phase of major crustal growth in that area. For the Al Kufrah Ba-sin it is important to note, that the study of Le Heron et al. (2009)includes only zircons of one single sample from a Neoproterozoicsandstone. No information about zircon ages from Palaeozoic sili-ciclastics is available. Therefore our conclusions from the AQAand the eastern Murzuq Basin concerning Palaeoproterozoic zirconpopulations should be used with care in view of the Al KufrahBasin.

In summary, it can be stated that the dominant source area forCambrian sandstones of the Hasawnah Formation in the AQA wasNeoproterozoic crust of Pan-African basement. A good candidate is

Fig. 11. Binned frequency plots of 329 U–Pb dates of analyzed zircon grains from Cambrian of AQA (present study) in comparison to 630 U–Pb dates from Cambro-Ordovicianof Tassilis area south of Hoggar in Algerian Sahara (data from Linnemann et al., 2011).


the Pan-African orogen in the Trans-Saharan Belt (Pharussian andDahomeyean belts, Fig. 13). It is relatively close to the AQA, andthe cluster of zircon populations is very similar to the ones of theHasawnah Formation (Linnemann et al., 2011). Further, only fewMesoproterozoic zircon ages are known from there (Drost et al.,2010). Other Pan-African belts to the east and south (East Africanand Oubangouide belts, Fig. 13) and the Arabian–Nubian Shieldcontain a significant Mesoproterozoic zircon population (Avigadet al., 2003). Therefore, we prefer an interpretation with dominantsediment source in the Trans-Saharan belt. Another partial sourcearea for the Cambrian sandstones of the Hasawnah Formationcould be represented by the Cadomian orogen of peri-Gondwana,which was formed at the margin of northwest Gondwana duringLate Neoproterozoic to Early Cambrian times (Linnemann et al.,2007) and which show zircon populations similar to the Pan-Afri-can one of the Trans-Saharan Belt (Linnemann et al., 2011).

A similar data set like for the AQA (presented in this paper) isreported from the Cambrian–Ordovician of the Tassilis (Hoggar)to the west of the AQA (Linnemann et al., 2011; Fig. 11), as wellas from southeastern equivalents in the eastern Murzuq Basin area(Meinhold et al., 2011). However, no Neoproterozoic zirconsrelated to Pan-African basement are reported from the Al KufrahBasin farther to the southeast (Le Heron et al., 2009). The latter,however, is to handle with care, because the zircon data came formonly one Neoproterozoic sample. Nevertheless, out data setstrongly supports the interpretation, that the prevailing sedimentsource area for the Hasawnah Formation sandstones must havebeen situated to the west. The source rock area must have beencomposed by Pan-African rocks and belong most probably to theTrans-Saharan Belt (Fig. 13). We cannot exclude an input fromperi-Gondwanan terranes (Cadomian orogenic belt, see above).The few Mesoproterozoic zircons in our investigated samples indi-

Fig. 12. Detrital zircon date distributions of the six analyzed Cambrian sandstone samples of AQA (present study) in comparison to Baltica, Amazonia, West Africa and otheradjacent parts of Gondwana (data compilation from Drost et al., 2010; Linnemann et al., 2004, 2011 and references therein).


cate only modest input from a distant source to the east-southeast.The majority of Palaeoproterozoic zircons in the range 1.85–1.6 Gamost probably came from a local source in the Saharan Metacraton.A smaller proportion of Palaeoproterozoic zircon grains (1.9–2.2 Ga) and most of the Archaean zircons seem to be derived fromthe West African Craton or alternatively, from a portion of thePan-African basement which has recycled older crust of the WestAfrican Craton.

6. Conclusions

A total of 720 detrital zircons from the Cambrian Hasawnah For-mation of the Al Qarqaf Arch (AQA) area (central-western Libya)has been analyzed. Among these, 329 grains were concordant inthe range of 90–110%. Some 60% of the determined U–Pb datesof all samples are Neoproterozoic. Peaks cluster at c. 700–680,670–650, 615–610, 590, 570–560 Ma, and c. 540–525 Ma. Suchdates are characteristic of Pan-African and Cadomian orogenicevents in the northwestern Gondwana palaeogeographic region.A few zircons yielded older Neoproterozoic ages around 950–750 Ma and point to rifting and drifting processes related to Rodi-nia dispersal.

Only three zircons became formed around the Mesoproterozo-ic–Neoproterozoic boundary, yielding U–Pb dates of1039 ± 11 Ma, 1006 ± 12 Ma and 993 ± 13 Ma. Two further Meso-proterozoic zircons show ages of 1592 ± 39 Ma and 1475 ± 20 Ma.Their potential source area seems to have been situated far distantfrom the AQA. The eastern Murzuq Basin region, from where somegeochronological data have already been published (Meinhold

et al., 2011), was closer to a Mesoproterozoic source area, whichmust have been located much farther to the east and could be con-cealed within the Arabian–Nubian Shield or situated in Chad, orthe Congo and Tanzania cratons. There is no evidence of the exis-tence of massive Mesoproterozoic crust in the Saharan Metacratonarea.

The second-largest fraction of investigated zircons is repre-sented by Palaeoproterozoic populations with ages of c. 2.4–2.3 Ga and 2.2–1.6 Ga. There are also a number of Archaean zircons(c. 3.4–3.25 Ga, 2.95–2.7 Ga, 2.6–2.5 Ga) seemingly derived fromthe West African Craton or a related cratonic source. West Africais the potential source for most of the Palaeoproterozoic and Ar-chean zircons with ages of 3.4–1.9 Ga, whereas Palaeoproterozoiczircons of c. 1.85–1.6 Ga seem to be representative of the westernpart of the Saharan Metacraton. These zircon populations from theCambrian of the AQA and eastern Murzuq Basin most probably de-rived from a local source. Thus, these zircon ages c. 1.85–1.6 Ga)indicate a phase of significant crustal growth in the western partof the Saharan Metacraton and seems to be represent a very goodtracer of this source area.

The unconformity between basement and Hasawnah Formationsandstone indicates strong uplift and deep erosion during the lat-est Neoproterozoic and early Cambrian (c. 550–530 Ma) in ourinvestigated area. The high maturity of the sandstones impliesintervals of coeval intense chemical weathering under warm to hu-mid climatic conditions. These processes resulted in denudationand peneplain formation before the deposition of the HasawnahFormation.

Because related subsidence in the Tassilis (Algerian Sahara) didnot begin before the latest Cambrian to early Ordovician (Linne-

Fig. 13. Sources of Cambrian sandstones of AQA (black arrows) in framework of orogenic provinces of Africa. Constituent continental terranes shown in Gondwanaconfiguration (compiled by U. Linnemann from maps of Bahlburg et al., 2009; Begg et al., 2009; Linnemann et al., 2007, 2011 and references therein). (For colour version ofthis figure, the reader is referred to the web version of this article.)


mann et al., 2011), the centre of early Palaeozoic thermal subsi-dence in central-northern Africa must have been located farthereast (Saharan Metacraton).

The main source area of the Hasawnah Formation Cambriansandstones of the AQA was Neoproterozoic crust of the Pan-Africanbasement of the Trans-Saharan Belt, in accordance with data fromthe area of the Tassilis in the Algerian Sahara (Hoggar, west of theAQA; Linnemann et al., 2011), the eastern Murzuq Basin (Meinholdet al., 2011) and the much more southeasterly located Al KufrahBasin (Le Heron et al., 2009). A very limited input is indicated fromthe far distant east-southeast (Mesoproterozoic dates), as well assome influence from a local source (Saharan Metacraton; Palaeo-proterozoic zircons). Some relationship is suggested with the WestAfrican Craton by some Palaeoproterozoic and Archaean zircondates, although, e.g. a polyphase recycling of zircon grains from an-other area could be theoretically possible.

Acknowledgements

The authors greatly acknowledge the Deutsche Forschungs-gemeinschaft (DFG) and the Libyan Petroleum Institute (Tripoli, Li-bya) for support of fieldwork in Libya. Many thanks go to Adel M.Abdada (Tripoli, Libya) for important help during fieldwork andfor logistic support, and to Dr. Michael Magnus (Freiberg Univer-sity, Germany) for discussion on heavy-mineral microscopy andpreparation. The authors are grateful to Dr. Peter Kruse (Adelaide,Australia) for helpful remarks and linguistic assistance. The workreported here is embedded in the DFG research project of O.E.no. EL 144/19: ‘‘The start of the Phanerozoic at the northern edge

of the East Saharan Craton (Libya): stratigraphy, facies, and pro-cess-correlation along the W-Gondwanan shelf’’.

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