南秦岭佛坪麻粒岩的矿物学和地球化学特征及其构造意义  

Mineralogical and geochemical characteristics of Foping granulites in South Qinling and their tectonic implications

作　　者：刘东星[1] 刘养杰[1] 

机构地区：[1]西北大学地质学系,西安710069

出　　处：《世界地质》2016年第2期441-449,共9页World Geology

基　　金：西北大学国家基础学科人才培养基地"地质学创新基金"(XDCX2010-01)

摘　　要：采用电子探针、红外光谱和全岩化学分析方法,对佛坪麻粒岩开展了系统的矿物学和地球化学研究。研究结果表明本区麻粒岩以酸性岩为主,主要组成矿物为长石、石英、石榴子石、紫苏辉石及少量的黑云母和钙质角闪石。岩石富集轻稀土和大离子亲石元素,亏损高场强元素,具有强烈的Nb、Ta负异常,表明源岩在成因上与洋壳的俯冲消减作用有关。结合区域地质和测年资料,我们认为佛坪麻粒岩源岩的形成与勉略古洋壳向南秦岭地块之下的俯冲有关,是中—晚三叠世南秦岭与扬子地块的陆-陆碰撞所导致的麻粒岩相变质作用的产物。The Foping granulites are located in the South Qinling Orogenic Belt. The origin of these rocks plays an important role in understanding the tectonic interaction between the Qinling Orogen and the Yangtze Block during Mesozoic time. This work carried out systematic mineralogical and geochemical investigations on the Foping granulites by employing electron probe,infra-red spectrum,and whole-rock chemical analytical methods. The results indicate that the granulites are primarily felsic in composition and composed mainly of plagioclase,quartz,almandine,pyrope,hypersthene,and minor biotite and calcic amphibole. The granulites are characterized by enrichment in light rare earth elements and large ion lithophile elements,and depletion in high field-strength element,with significant negative anomalies of Nb and Ta. These features are indicative of subduction-related geochemical signature. In combination with geological and radiometric age data,this study suggests that the formation of the protoliths of the Foping granulites was associated with the northward subduction of the Mianlue oceanic lithosphere beneath the South Qinling Block. In the Middle-Late Triassic,the continent-continent collision between the South Qinling and the Yangtze blocks resulted in the granulite-facies metamorphism that led to the formation of the Foping granulites.

关 键 词：佛坪 南秦岭 麻粒岩 碰撞造山 矿物学特征 

分 类 号：P588.34[天文地球—岩石学] P595[天文地球—地质学]