Zircons in serpentinite can not only provide chronological information,but also constrain the genesis of serpentinite and regional tectonic evolution process.Longyasongduo serpentinite in Tangjia-Sumdo Paleo-Tethys suture zone was studied by means of zircon U-Pb dating,whole-rock geochemistry,and zircon Hf isotope in this paper.The results show that Longyasongduo serpentinites have high MgO,TFeO and Mg#values but low Al2O3 and TiO2 contents.The chondrite-normalized REE patterns display a gentle U-type.The primitive mantle-normalized spider diagrams exhibit enrichment in U,Ta and depletion in Th,Nb,Zr and Hf.Zircon U-Pb dating of Longyasongduo serpentinite yielded ages of(230.3±2.3)Ma,with εHf(t)values of +13.4 to +16.0.Through chronological and geochemical studies,we argue that the protolith of Longyasongduo serpentinite is the residual of partially melted spinel lherzolite in the mantle wedge.Longyasongduo serpentinite was metasomatized by supercritical fluid generated by subduction of Sumdo Paleo-Tethys oceanic crust to form metasomatic zircon,which may also be metasomatized by aqueous solutions,resulting in enrichment of fluid-mobile elements.Based on previous studies,we infer that the Sumdo Paleo-Tethys Ocean was still in a northward subduction setting in the Late Triassic.
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