Geochemistry and petrogenesis of the I and A type composite granite masses in the coastal area of Zhejiang and Fujian province.
浙闽沿海地区I型-A型复合花岗岩体的地球化学及成因

The geological and geochemical characteristics of the I and A type composite granites along the coastal area of Zhejiang and Fujian province have been studied systematically by citing the three typical rock masses of Gushan Kuiqi, Qingtian and Putuoshan Taohuadao as instances. Investigation resuits have shown that the features of major elements, trace elements and rare earth elements between the I type and A type granites are quite different. Compared with the I type granites, the A type granites are generally rich in sillicon, alkali, poor in calcium, magnesium, aluminum, and have higher Rb/Sr, Rb/Ba,Ga/Al, and lower LREE/HREE ratios and display obviously negative europium anomaly. Nd Sr isotopic compositions between them also show some differences although both of them have similar features to that of the magma derived from partial melting of crustal mantle mixing materials. These differences above are caused both by differentiation and by involvement of mantle derived magma, but only one of them plays the leading role in the formation of the I and A type composite granites. By analysing their occurring tectonic setting comprehensively and considering the fact that the geochemical variation tendency in different I and A type composite granite is different, this paper concludes that the I and A type composite granites in the studied area are products affected jointly by regional tectonic stress, deep faults, involvement of mantle derived magma and differentiation of primary magma.