Zircon U-Pb-Hf isotopes, bulk-rock geochemistry and Sr-Nd-Pb isotopes from late Neoproterozoic basement in the Mahneshan area, NW Iran: Implications for Ediacaran active continental margin along the northern Gondwana and constraints on the late Oligocene crustal anatexis

摘要

The Mahneshan granite intrusions and granodiorite-gneiss bodies in northwest Iran are part of the Takab magmatic -metamorphic complex, which includes numerous Precambrian continental crust that are now embedded in the Alpine-Himalayan orogenic system. The Mahneshan magmatic assemblage comprises of late Ediacaran-Cambrian gneiss and granites (531-576 Ma) and late Oligocene biotite (25.41 +/- 0.4 Ma) granite intrusion. The late Oligocene granite has intruded into the Neoproterozoic sequences in this area. The bulk-rock geochemistry shows that the Ediacaran-Cambrian granitoids and gneisses are calc-alkaline and preserve arc-related signatures. The zircon Hf and bulk rock Sr-Nd-Pb isotopic data suggest that the Ediacaran-Cambrian granitoid plutons were generated via partial melting of continental crust. The late Oligocene granite is formed by the anatexis of Neoproterozoic igneous rocks due to crustal thickening.