川西北羊拱海花岗岩体的地球化学特征及成因探讨

GEOCHEMICAL CHARACTERISTICS AND DISCUSSION ON PETROGENESIS OF YANGGONGHAI GRANITE BODY IN NORTHWESTERN SICHUAN

位于松潘甘孜褶皱带东部三角区内的羊拱海岩体主要是由中心相酸性的二长花岗岩向边缘相中酸性的花岗闪长岩的过渡。通过对该花岗岩体的常量元素、微量元素及稀土元素地球化学特征的研究可知,羊拱海花岗岩属于高钾钙碱性、弱过铝—过铝质岩石系列,Rb、Th、K等富集,Ti、Ba、Nb、Sr、P明显亏损,表现为较平坦的具有较弱Eu亏损的稀土配分模式;岩体具有I型与S型花岗岩过度类型的特点,是在印支晚期区域上大规模的陆—陆碰撞造山环境中形成的。

Yanggonghai granite body, located in triangle region of the eastern Songpan-Ganzi folded zone, which mainly transformed from acid monzogranite in central phase to intermediate-acid granodiotite in marginal phase. Researching on the geochemical characteristics of major elements, trace elements and rare earth elements, we concluded that Yanggonghai granite body, whose Rb, Th and K are enrichment but Ti, Ba, Nb, Sr and P obviously depletion, was attribute to high K calc-alkaline and weakly peraluminous to peraluminous rock seties, with Eu had a relatively weak negative anomaly in REE distribution pattern. This granite body had many features between I-type granite and S-type granite, and it was formed in the environment of a large-scale continent-continent collision in late Indosinian.