Amphibolites from makran accretionary complex record Permian-Triassic Neo-Tethyan evolution

Abstract

ABSTRACT Zircon U-Pb-Hf isotopes, integrated with bulk-rock major, trace element, and isotopic compositions of amphibolites from the Makran ophiolitic mélange complex (OMC), carry implications on the evolution of the Neo-Tethys Ocean. Field and petrographical-geochemical data confirm these amphibolites as products of the metamorphism of a mafic protolith. Zircons from the amphibolites have U-Pb ages of Late Early Permian (273 Ma) to Late Triassic (210 Ma), and their εHf(t) values vary from +6.32 to +15.4. The Makran amphibolites are geochemically similar to transitional- or enriched-MORBs. The 143Nd/144Nd(t) ratios for amphibolites range from 0.51260 to 0.512551, and 87Sr/86Sr(t) from 0.704433 to 0.706244. The Pb-isotope composition of these rocks is radiogenic, ranging from 15.61-15.64 for 207Pb/204Pb(t), 18.98-19.21 for 206Pb/204Pb(t) and 38.88-39.36 for 208Pb/204Pb(t). The isotopic and geochemical signatures of these rocks suggest that they were most likely formed during continental rifting and originated from a relatively enriched mantle source. This is also attested by their high zircon Ce/Ce* ratios. We interpret these amphibolites related to the Permian-Triassic plumes that triggered Gondwana rifting to open the Neo-Tethyan Ocean before metamorphosed, fragmented, and accreted into the Makran accretionary complex probably during Early to Late Cretaceous time.