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Geochemistry and Petrogenesis of Quartz Diorite in Tagong Area of Northwest Sichuan

LAI Shao-cong;ZHAO Shao-wei;State Key Laboratory of Continental Dynamics,Northwest University;Department of Geology,Northwest University;  
Tagong area of Northwest Sichuan is located in the east of Qinghai-Tibet Plateau,and belongs to the southeast margin of Songpan-Ganzi orogenic belt.The quartz diorites in Tagong area form in Early Cretaceous with K-Ar isotopic ages of 134-136 Ma,and emplace into Late Triassic strata.Mass fractions of SiO2 are 61.37%-62.25%,A/CNK values are 0.93-0.95,mass fractions of total alkali are 5.46%-5.77%,Rittmann indexes are 1.62-1.74,so that the samples belong to subalkaline metaperaluminous high-K calc-alkaline series quartz diorites.The rocks have relative high Mg#values with the isotopic geochemical characteristics of high contents of Sr and low contents of Nd.N(87 Sr)/N(86 Sr)is 0.712 589-0.713 009 with the initial N(87 Sr)/N(86Sr)of 0.709 503-0.709 878,N(143 Nd)/N(144 Nd)is 0.512 135-0.512 196 with negativeεNd(t)of-8.6--7.5;Nd and Hf model ages are 1.33-1.41 Ga and 1.13-1.37 Ga,respectively.The quartz diorites belong to undifferentiationⅠ-type granitoids with late-to post-collision caused by partial melting of ancient lower crust mafic materials at the continental margin-intercontinental orogenic setting in Northwest Sichuan.
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