Insights into crust formation and recycling in North Africa from combined U-Pb, Lu-Hf and O isotope data of detrital zircons from Devonian sandstone of southern Libya

Abstract

Combined U-Pb, Lu-Hf and O isotope data of detrital zircons from the Devonian sandstone of southern Libya provide important new boundary parameters for reconstruction of palaeosource areas and sediment transport and may lead to novel approaches to test current plate tectonic models, with important implications for our understanding of the evolution of northern Gondwana (in present-day coordinates) during the Palaeozoic. Detrital zircon U-Pb ages from Devonian sandstone of the eastern margin of the Murzuq Basin show four main age populations: 2.7-2.5 Ga (13%), 2.1-1.9 Ga (10%), 1.1-0.9 Ga (25%) and 0.7-0.5 Ga (46%). The ubiquitous occurrence of c. 1.0 Ga detrital zircons is characteristic of the Saharan Metacraton sedimentary cover sequence and provides new insights into palaeogeographic reconstructions of Gondwanaderived terranes in the Eastern Mediterranean and SW Europe. The Lu-Hf isotope data suggest that zircons crystallized within a narrow time interval from magmas with heterogeneous Hf isotope compositions. These magmas were derived by melting of pre-existing rocks, rather than being juvenile. The calculated Hf model ages range from 3.7 Ga to 1.3 Ga, with a major population between 2.8 Ga and 1.9 Ga, indicating prominent recycling of Archaean and Palaeoproterozoic crust.