秦岭造山带晚三叠世花岗岩体侵位深度及其构造意义

Emplacement depth of the late Triassic granite in the Qinling orogenic belt and its tectonic significance

秦岭造山带广泛分布的晚三叠世花岗岩是华南板块和华北板块碰撞形成的典型产物,是造山带转入区域伸展构造体制的标志。目前关于秦岭造山带的研究主要集中在地球化学和年代学方面,而有关花岗岩侵位的温压等物理化学条件研究则相对较少。本文通过角闪石全铝压力计和角闪石-斜长石温度计计算,获得其温压数据。结果显示,糜署岭、老君山、秦岭梁、东江口岩体的侵位深度分别为11.4、7.3、8.3、8.5 km,对应于地壳中上部。糜署岭岩体主要为花岗闪长岩,侵位深度大于其余岩体(二长花岗岩),而且岩体的侵位深度主要和岩性有关。利用侵位深度和已发表的热年代学数据,对这些岩体侵位后的剥蚀速率进行估算,结果表明T_(3)-J_(2)的平均剥蚀速率约为140 m/Ma,说明燕山运动和印亚碰撞对秦岭造山带花岗岩的剥蚀贡献不大。

The late Triassic granites widely distributed in the Qinling orogenic belt are typical products of the collision between the North China and South China plates,indicating that the orogenic belt had turned into a regional extensional tectonic system at that time.Previous researches on the Qinling orogenic belt mainly focus on fields of geochemistry and chronology of granites,with only relatively limited researches on the physical conditions such as temperature and pressure of the granite emplacement.In this paper,the temperature and pressure data have been obtained by using the Al-inhornblende-thermometer and amphibole-plagioclase thermometer.The results show that the emplacement depths of the Mishuling,Laojunshan,Qinlingliang and Dongjiangkou granite bodies are 11.4,7.3,8.3 and 8.5 km respectively,corresponding to the middle-upper part of the crust.The Mishuling intrusive body mainly consists of granodiorite,and its emplacement depth is larger than those of other intrusive bodies(monzogranite).It is considered that the emplacement depths of intrusive bodies are mainly related to their lithological features.Based on the emplacement depths and published thermochronological data of intrusive bodies,the denudation rates of these intrusive bodies have been estimated.The average denudation rate of T_(3)-J_(2) intrusive bodies is about 140 m/Ma,indicating that the Yanshanian movement and the Indo-Asian collision had limitedly influenced the denudation of granites in the Qinling orogenic belt.