U–Pb LA-ICP-MS detrital zircon ages from the Cambrian of Al Qarqaf Arch, central-western Libya: Provenance of the West Gondwanan sand sea at 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, Libya b Freiberg University, Geological Institute, Bernhard-von-Cotta Street 2, 09599 Freiberg, Germany c Senckenberg Natural History Collections Dresden, Museum of Mineralogy and Geology, GeoPlasmaLab, Königsbrücker Landstraße 159, 01109 Dresden, Germany article info Article history: Received 4 April 2012 Received in revised form 3 November 2012 Accepted 5 November 2012 Available online 29 November 2012 Keywords: Hasawnah Formation Libya Geochronology Cambrian Gondwana Saharan Metacraton abstract 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 720 analyzed grains, 329 were concordant. Of the total, about 60% of the U–Pb zircon ages are Neoproterozoic and 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 possibly to a smaller proportion from the Cadomian orogen situated marginal to northwestern Gondwana. A few slightly older Neoproterozoic ages (c. 950–750 Ma) point to rifting events related to the dispersal of the Rodinia supercontinent. A minority of zircons became formed during the configuration of Rodinia and cluster around the Mesoproterozoic–Neoproterozoic boundary (1039 ± 11, 1006 ± 12 and 993 ± 13 Ma). Further, some early Mesoproterozoic zircon ages had been found (1592 ± 39 and 1475 ± 20 Ma). The potential source area for the Mesoproterozoic zircons is interpreted to have been far distant from the Al Qarqaf Arch, probably concealed within the Arabian–Nubian Shield or situated in 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 represents Palaeoproterozoic populations at c. 2.4–2.3 Ga, and c. 2.2–1.6 Ga. Less than 5% of all zircons are Archaean in 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 and Archaean 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 the Al Qarqaf Arch type area are the Neoproterozoic–early Cambrian orogens of the Pan-African cycle in the 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 from southwestern (eastern Murzuq Basin) and southeastern Libya (Al Kufrah Basin). In comparison to the strong input of Neoproterozoic zircon grains, input from the Palaeoproterozoic and Archaean sources of the cratonic basement (Saharan Metacraton and West African craton) is relatively limited. The exact source of the exotic Mesoproterozoic zircons remains problematic. The presented data lead to the conclus ion that the centre of early Palaeozoic thermal subsidence in central-northern Africa has to be located in the region of the Saharan Metacraton. The distinct unconformity at the base of the Cambrian Hasawnah Formation 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 moderate southern latitudes and the formation of a Gondwanan peneplain is indicated. Ó 2012 Elsevier Ltd. All rights reserved. 1464-343X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jafrearsci.2012.11.007 ⇑ Corresponding author. Tel.: +49 (0)3731 39 2435; fax: +49 (0)3731 39 12435. E-mail addresses: elicki@geo.tu-freiberg.de (O. Elicki), ulf.linnemann@senckenberg.de (U. Linnemann). Journal of African Earth Sciences 79 (2013) 74–97 Contents lists available at SciVerse ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci