川西北羊拱海及邻区花岗岩体微量元素地球化学特征

Trace Element Geochemical Characteristics of the Granite Bodies in Yanggonghai and its Neighboring Area in Northwestern Sichuan

位于松潘-甘孜造山带内的羊拱海及邻区岩体主要为印支期-燕山期花岗闪长岩、二长花岗岩等。通过对羊拱海、达盖寨及二道桥花岗岩体微量元素及稀土元素地球化学特征的研究可知,岩体表现为较平滑的具有较弱Eu负异常或无Eu异常的向右陡倾的稀土配分模式曲线,且从微量元素比值K/Rb、Rb/Sr等均反映出羊拱海及邻区岩体具有同熔型花岗岩的特点。由此推测,岩体的形成于同碰撞的造山环境,属于同构造期侵入岩。是印支晚期发生大规模的造山运动,形成断裂、褶皱构造,在造山带内地壳加厚,由于深部剪切热使下地壳产生局部熔融产生同熔岩浆上侵定位形成花岗岩体。

Granite bodies in Yanggonghai and its neighboring area, located in Songpan-Ganzi folded zone, mainly are granodiorite, monzogranite etc. According the triangle region of the eastern to the research on the geochemical characteristics of trace elements, rare earth elements and trace element ratio like K/Rb and Rb/Sr, it is found that all of the yanggonghai,Dagaizhai and Erdaoqiao granite bodies, with Eu weak negative anomaly or no anomaly in REE distribution patterns, are syntectic granites. These bodies were formed in the syn-collisional orogenic environment, and attribute to syn-structure intrusive rocks. In late Indosinian, with a large-scale continent-continent collision, fractures and fold structures were formed, the earth crust thickened, shear heat under the deep crust made lower crust partial melt, and the syntectic magma up-emplaced through the fractures and then formed granite bodies.