秦岭–祁连结合部位早古生代晚期岩浆事件及其对构造演化的启示

The conjunction area of the Qinling and Qilian orogenic belt was overlapped by different tectonic systems. The potassic granites are ideal geological records of the related geological events. Therefore, in this study, we will investigate the newly identified Xiongshangou potassic granites and Xianping potassic granites in the northern margin of West Qinling, Tailu potassic granites in the conjunction area of Qinling and Qilian orogenic belts, and Nantouhe potassic granites and Pandaoshi potassic granites in the east section of North Qilian. On basis of detailed field survey, we plan to do research on geochemistry and single mineral chronology, combined with petrology, mineralogy and Sr-Nd-Pb-Hf isotope composition for the potassic granites, trying to confirm the formation age and petrogenesis of the these plutons. At the same time, we want to make sure of the thermal evolution, nature and source characteristics of the magma. In addition, we plan to clarify the genetic relationships between the potassic granites and the Early Paleozoic intermediate-acid granitoids in the conjunction area of the Qinling and Qilian orogenic belts and its adjacent areas. Based on the above studies, we’ll discuss the Early Paleozoic dynamic process, post-collisional uplift and tectonic transition of the Qinling and Qilian orogenic belts. Therefore, this study provides new evidence on Early Paleozoic crust accretion and reformation in the conjunction area of the Qinling and Qilian orogenic belts.

秦岭–祁连结合部构造位置特殊，是不同构造体系的叠加和过渡区，而该区钾质花岗岩类恰恰记录了相应的地质事件。因此，本研究拟以申请者新识别出的西秦岭北缘熊山沟岩体和仙坪岩体、秦岭–祁连结合部位太禄岩体及北祁连东段南头河岩体和盘道石岩体等五个钾质花岗岩体为研究对象，在野外调查的基础上，以地球化学及单矿物年代学为主要研究手段，结合岩石学、矿物学及同位素地球化学等方法进行系统论证其岩石成因，查明钾质花岗岩的形成时代，搭建精细的早古生代后碰撞阶段成岩及构造年代学格架，同时厘定岩浆热演化过程、岩浆性质及源区特征。另外，对比研究钾质花岗岩与早古生代中酸性花岗岩之间的成因联系，进而探讨秦岭造山带和祁连造山带早古生代构造演化的动力学过程，以及与早古生代造山期后的隆升构造过程和体制转换关系，从而为深入研究秦岭–祁连结合部位早古生代陆壳增生与改造提供新证据。

本项目瞄准秦祁结合部位钾质花岗岩与原特提斯洋俯冲增生演化相关的科学问题，对西秦岭北缘、秦祁结合部位及北祁连东段五个钾质花岗岩体岩石组合、构造属性和形成时代进行详细研究，搭建精细的早古生代后碰撞阶段成岩及构造年代学格架，对比研究钾质花岗岩的成因联系，基本实现了项目预定目标，取得如下重要认识和进展：（1）详细厘定和建立了秦祁结合部位早古生代钾质花岗岩的分布和岩石类型，主体岩性为二长花岗岩和正长花岗岩，搭建了该区花岗岩的构造格架。（2）秦祁结合部位早泥盆世出露有A型花岗岩和高分异I型花岗岩，其中北祁连南投河A1型花岗岩形成时代为395.4Ma；北祁连盘道石A型花岗岩形成时代为407.4Ma；秦祁结合部位太禄A1型花岗岩形成时代为406.6~416.7Ma；北秦岭仙坪高分异后碰撞I型花岗岩形成时代为410.7Ma。早泥盆世的花岗岩总体形成于造山后地壳伸展阶段，是下地壳长英质物质部分熔融的产物。（3）中晚志留世二长花岗岩和正长花岗岩为后碰撞花岗岩类，以北秦岭熊山沟后碰撞I型花岗岩为代表，其形成时代为424.4~425.4Ma。以上成果对于探索原特提斯构造域秦岭和祁连早古生代造山带的形成演化以及构造过程，揭示秦祁结合部位早古生代构造演化的动力学过程，以及与早古生代造山期后的隆升构造过程和体制转换关系。