北秦岭漂池岩体的源区特征及其形成的构造环境

THE SOURCE AND TECTONIC SETTING OF THE PIAOCHI BATHOLITH IN THE NORTH QINLING

北秦岭漂池花岗质岩基为早古生代岩浆活动的产物,岩石类型主要为二云母花岗岩。通过主要元素、微量元素及Nd,Sr,O同位素特征的分析,其成因类型为S型花岗岩,成岩物质来自壳源碎屑物。研究表明,秦岭群片麻岩类是形成漂池岩体的主要源岩。结合区域地质背景分析,岩体并不形成于板块碰撞环境,而形成于北秦岭早古生代活动大陆边缘,受板块俯冲作用的动力学影响所诱发的陆缘地壳物质熔融的产物。因此,漂池岩体形成的构造类型是活动陆缘的S型花岗岩,它作为一个新的构造类型应在今后关于花岗岩板块构造环境分类中单独划出。

The Piaochi granitic batholith in the North Qinling, which formed in the Early Paleozoic, is composed mainly of two-mica granites. Systematic geochemical studies show that the two-mica granites are typical S-type granites, derived from crustal clastic sediments. Their formation had a genetic link with Qinling Group gneisses. According to the regional tectonic setting, the Piaochi batholith was not formed in continent-continent collision environment, but formed on the Early Paleozoic North Qinling active continental margin. It resulted from fusion of continental-margin crustal material induced by the dynamics of plate subduction. Thus, the rocks of the Piaochi plu-ton should belong to the S-type granites of active continental margin. It is a new tectonic type of granitoids, and should be defined independently in the classification of plate-tectonic setting for granitoid formation.