Evidence from detrital zircons for recycling of Mesoproterozoic and Neoproterozoic crust recorded in Paleozoic and Mesozoic sandstones of southern Libya

The geodynamic history of the Precambrian basement in central North Africa as well as the age and provenance of its sedimentary cover sequence are still poorly constrained. Here we present first detrital zircon ages (obtained by LA-SF-ICP–MS and SHRIMP) from Paleozoic and Mesozoic sandstones of the eastern Murzuq Basin, southern Libya, which unconformably overlie the Saharan Metacraton. Establishing the age and provenance of these sandstones has important implications for our understanding of the evolution of northern Gondwana during the Paleozoic, especially for reconstructions of paleo-source areas and transport paths.

Detrital zircons from the sandstones show mainly early Paleozoic to Neoarchean ages with four main age populations, at 2750–2500 Ma (8%), 2200–1750 Ma (16%), 1060–920 Ma (18%), and 720–530 Ma (39%). About 13% of all concordant grains yield ages of 1600–1000 Ma. In addition, there are 9 zircon grains (0.7% of all concordant grains) with ages of 3600–2800 Ma. The presence of a high number of ca. 1 Ga zircons is enigmatic and their origin is controversial. Besides direct sourcing from ca. 1 Ga igneous rocks in eastern Chad and ca. 1 Ga igneous rocks along the southeastern margins of the Congo and Tanzania cratons, recycling of Neoproterozoic sediments containing ca. 1 Ga zircons is another alternative hypothesis to explain the presence of ca. 1 Ga zircons in the Paleozoic sedimentary sequence of central North Africa. The ubiquitous occurrence of ca. 1 Ga zircons in Paleozoic sediments of southern Libya provides insights into the correlation and paleotectonic arrangement of Gondwana-derived terranes, present, for example, in the eastern Mediterranean and in southwestern Europe. Current paleotectonic models of dextral terrane transport along the northern Gondwana margin during the early Paleozoic may need to be revised.