DistributionandtransferofCoandNiduringslabsubduction:Acase studyofSouthwestTianshan.

During the slab subduction,the basic oceanic crust,underlying serpentinized lithospheric mantle and sediments covering the subducted oceanic crust will under go slab dehydration and sediment melting at different depthsinturn.The melts/fluidsreleased from subductingslabs could carry some element stometasoma tizethemantlewedge,which might returnt o the crust duringarc magmatism.Mean while,migration and exchange of chemical compositions between different components occurred,and eventually travelled into deep mantle,result inginmantleheter ogeneity and deep crust.mantle interaction.This paper reports new data of major elements and contents of Cu,Co and Ni of mineral sinser pent inite,pyroxenite,greens chist,blues chist and eclogite in the typical HP. UHP metamorphic belt from the South west Tianshan,China.The results show that except for high Cu contents(1.26 x 10(-6)similar to 76.9x 10(-6))of diopside in pyroxe nite,other silicate minerals have low Cu contents of 1.0 x 10(-6) similar to 10.0 x 10(-6);while Co and Ni show significant variation samong different rocks and different minerals.The contents of Co and Ni are 22.6 x10(-6)similar to 49.6x10(-6) and 482 x 10(-6)similar to 1097 x 10(-6) inserpentine,6.0 x 10(-6)similar to 66.2 x 10(-6) and 21.6 x 10(-6)similar to 506 x 10(-6) inomphacite,20.8 x 10(-6)similar to 289 x 10(-6) and 69.5 x 10(-6)similar to 351 x 10(-6) indiopside,9.0 x 10(-6)similar to 94.3 x 10(-6) and 75.5 x 10(-6) similar to 495 x10(-6) inglaucophane,respectively. Garnetgrains are presentingreens chist,blues chist and eclogite,respectively.Their Co and Ni contents are inranges of 1.2 x 10(-6)similar to 134 x 10(-6) and 7.7 x 10(-6)similar to 26.9 x 10(-6),respectively.Incomparison,garnet in both blues chist and eclogitehashigher Co and Ni contentsthaningreenschist.Profile analyses demonstratethatthe Co contentingarnet of blues chist and eclogitein creases significantly from coretorim, while Ni contentisrelativelyinvariable.ThedistributioncharacteristicsofCu,Co and Ni in these mineral sreveal that theme tamorphicgradechanges from greenschisttoe clogite with the in creases of the subductiondepthoftheslab,Cuinsilicate mineralsrarelychanges,while their Co and Ni contentsdisplayanincreasingtrend,which may berelated to the involvement of serpentiniteandpyroxenite, and moremobilebehavior of Co than Ni duringmelt.fluidactivities. The distribution and transfer characteristics of the three elements indicate that the Cu contribution of the subduction plateto Cu.richdeposits for medin subduction zones may mainly come from sulfidesratherthansilicateminerals,and the melting of the silicatemineralsintheresidualslabmay contribute Ni and Cotomagmatic Cu.Ni sulfide deposits for medatpost.subductionstages.Combined with there ductivecharacteristics of subductionmelts/fluidsrevealed from HP.UHP etamorphicbeltintheSouth west Tianshan,the above in ferencesprovideimportant constraints for explaining the discovery of Paleozoicporphyrycopperdeposits in the southernmargin of the Central Asian OrogenicBelt, especially the discovery of reducedporphyrycopperdeposits,as well as the temporal and spatialdistribution and metallogenic characteristics of magmatic Cu.Ni sulfide deposits