Navot Morag

Detrital zircon Hf isotopic composition indicates long-distance transport of North Gondwana Cambrian–Ordovician sandstones

A voluminous Cambrian–Ordovician sequence of quartz-rich sandstones was deposited in northern Gondwana following its assembly by a series of Neoproterozoic–Cambrian orogenic events. Paleocurrent markers indicate that the sediments were carried from Gondwana hinterland toward the supercontinent margins in the north (present coordinates). Derivation from Neoproterozoic terranes is evident from the ubiquity of detrital zircons with Neoproterozoic U-Pb ages, but the exact provenance of these siliciclastic deposits remains unclear. Herein we present new Hf isotopic data from U-Pb dated detrital zircons of the Cambrian–Ordovician sandstone that tops the juvenile Neoproterozoic basement of the Arabian-Nubian Shield in Israel and Jordan. It is remarkable that the detrital zircon Hf isotopic signal is in marked contrast to the Nd and Hf isotopic signature of the underlying basement. A preponderance (61%) of the Neoproterozoic-aged detrital zircons from the Cambrian–Ordovician sandstones yielded negative e Hf(t) values incompatible with a juvenile source. Therefore, most of the detrital zircons were derived from distant terranes comprising pre-Neoproterozoic crust reworked during the assembly of Gondwana, rather than from the adjacent Arabian-Nubian Shield. Because our sampling sites are situated at the northern tip of the Arabian-Nubian Shield, sand must have been transported several thousand kilometers before deposition. This finding also implies that the Arabian-Nubian Shield and other Neoproterozoic orogens of northeast Africa were completely worn down by the onset of Cambrian deposition and that vast areas in the northern part of Gondwana were low lying at that time.