Middle Devonian Binggou granites from the eastern Kunlun orogen,are characterized by relatively high silicon(SiO2 =71.85%-72.77%),total alkali(K2 O+Na2 O=8.39-8.58),aluminum(A/CNK=0.93-1.03),FeOt /MgO(6.247.86)and 104 Ga/Al values(3.04-3.60),high LREE,obvious negative Eu anomalies,and notable enrichment of HFSE(Zr,Ga,Y,Hf,etc.),strong depletion of Ba,Sr,P and Ti relative to the primitive mantle,similar to the geochemical features of A-type granites.The LA-ICP-MS Zircon U-Pb analyses yield a weighted mean 206Pb/238 U age of 391±3Ma(MSWD=2.36),considered to be the formation age of the Binggou granites.With a comprehensive consideration on many different indexes,such as whole rock Sr-Nd isotopes,geochemistry,experimental petrology and so on,we conclude that the Binggou granites formed by partial melting of crust materials(meta-greywacke)on the conditions of low pressure and high temperature at the stage of postorogenic stretch.The Binggou granites are younger than the other Paleozoic A-type granites reported in the eastern Kunlun orogen,suggesting the ending proto-tethys and the beginning paleo-tethys.
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