北秦岭含柯石英斜长角闪岩的发现及其地质意义  

Identification of coesite-bearing amphibolite in the North Qinling and its geological significance

作　　者：宫相宽[1] 陈丹玲[1] 任云飞[1] 刘良[1] 高胜[1] 杨士杰[1] 

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,西安710069

出　　处：《科学通报》2016年第12期1365-1378,共14页Chinese Science Bulletin

基　　金：国家重点基础研究发展计划(2015CB856103);国家自然科学基金(41472053,41430209,41421002);长江学者和创新团队发展计划(IRT1281)资助

摘　　要：详细的激光拉曼光谱分析，在陕西丹凤县城东北部的秦岭岩群斜长角闪岩锆石中发现柯石英、绿辉石、石榴子石和金红石等多种矿物包裹体．柯石英具有典型的524cm叫主峰以及270和151cm^-1次峰的拉曼光谱组合，绿辉石显示680cm^-1拉曼特征峰．柯石英、石榴子石和绿辉石显微包裹体的发现证明，丹凤斜长角闪岩应该是退变的超高压榴辉岩，变质的峰期压力〉2．8GPa．利用LA—ICP—MS锆石原位U-Pb定年方法，结合锆石CL图像特征、显徽包裹体分布和微量元素组成，得到丹凤含柯石英斜长角闪岩的峰期变质时代N496．9±2．5Ma，并同时得到451．7±4和425．8±3．3Ma两期叠加变质事件年龄．丹凤斜长角闪岩锆石包裹体中柯石英的发现以及年代学研究结果与前人在郐区斜长角闪岩锆石包裹体中微粒金刚石的发现和490．4±5．8Ma峰期变质年龄的获得，以及秦岭岩群已有榴辉岩和超高压长英质片麻岩普遍获得的～500Ma的峰期变质以及-450和～420Ma的后期构造事件叠加完全一致，表明北秦岭构造带的秦岭岩群在～500Ma的早古生代确实经历过超高压变质作用，存在巨量陆壳物质的深俯冲．The Qinling orogen lying in between the North and South China blocks is a key for understanding the tectonic framework of China continent. Tectonically, the Qinling orogen is divided into the North Qinling Tectonic Belt （NQTB） and the South Qinling Tectonic Belt （SQTB） by the Shangdan Fault Zone. With discoveries and study of the continental subduction ultrahigh pressure （UHP） metamorphic belt in the Dabie-Sulu and the North Qaidam-Altyn orogens in east and west China, respectively, a frequently-asked question is whether or not the Qinling orogen which belongs to the same orogenic system with the Dabie-Sulu orogen in central China has experienced the similar continental subduction and what timing of the subduction is. In fact, several UHP metamorphic outcrops such as the diamond-bearing eclogite and muscovite quartz schist in the Guanpo area, quartz-feldspathic UHP rocks in the Songshugou area and diamond-bering amphibolite in the Qingyouhe area have been reported lately in the Qinling group of the NQTB. However, these UHP findings have not been widely accepted with serious attention. The reason for this situation can be attributed to absence of convincing interpretation for the mineral exsolution structure and the UHP index minerals other than diamond especialy often-seen coesite in the orogens containing the UHP metamorphic bodies in the world. In this study, we present our newly-identified mineral inclusions of coesite, omphacite, garnet and rutile by laser Raman analysis in an amphibolite sample outcropped in the Qinling Group, northeast Danfeng county, Shaanxi Province. The Qinling Group, as the oldest geological unit of the NQTB is mainly composed of gneisses, schists and marbles. The HP-UHP eclogites, garnet-amphibolites and amphibolites found in the field all occur as lenses within paragneiss or schist. The coesite is characterized by Raman spectra at 524 cm^-1 with weak peaks at 270 and 151cm^-1, the omphacite shows typical Raman spectra at 680 cm^-1, and garnet at 910 cm^-1. The identificat

关 键 词：秦岭岩群 柯石英 斜长角闪岩 锆石U-PB定年 微量元素 

分 类 号：P588.125[天文地球—岩石学]