Granitoid magmatism in the Qinling orogen, central China and its bearing on orogenic evolution

查看全文 作　　者：WANG [1]XiaoXia;WANG [2]Tao;ZHANG [3]ChengLi

机构地区：[1]MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources,Chinese Academy of Geological Sciences;[2]Institute of Geology, Chinese Academy of Geological Sciences;[3]State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University

出　　处：《Science China Earth Sciences》索引2015年第58卷第9期,共16页

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.40872054,41172062 and 41430209);the National Key Basic Science Research Project of China(Grant Nos.2009CB825006 and 2009CB825003);China Geological Survey(Grant Nos.1212010012012,12120113094000,1212011120135 and 1212010811033);Development Project of Innovative Team,Northwest University 摘　　要：The Qinling orogen is a typical composite orogen for understanding multi-stages of magmatism and orogenic processes. Many studies have been carried out on the magmatic rocks in the Qinling orogen but their petrogenesis is still controversial. This paper presents a review of all granitoid rocks based on previous and new studies of geochronology and geochemistry. Four distinct periods of granitoid magmatism, Neoproterozoic(979–711 Ma), Paleozoic(507–400 Ma), Early Mesozoic(250–185 Ma) and Late Mesozoic(160–100 Ma), have been recognized from the Qinling orogen according to zircon U-Pb ages, intrusion associations and deformation, as well as regional geology. The Neoproterozoic granitic rocks consist of three stages at 979–911, 894–815 and 759–711 Ma, respectively, corresponding to strongly deformed S-type, weakly deformed I-type and A-type granitoids. They can be interpreted as magmatic occurrences in syn-collisional, post-collisional and extensional settings, respectively, in response to old continental terranes of the Neoproterozoic tectonomagmatic events in the old continents of China, such as South China and Tarim cratons. Although this continental terrane would be involved in the Phanerozoic Qinling orogeny, the Neoproterozoic magmatic rocks are not the products of the Qinling orogenic processes. The Paleozoic magmatic rocks can be classified into three stages at 507–470, 460–422 and 415–400 Ma, respectively. The first-stage magmatism is temporally associated with ultra-high pressure metamorphism in the North Qinling terrane. These magmatic rocks are interpreted as magmatic occurrences in subductional, syn-collisional and post-collisional settings, respectively. The Early Mesozoic magmatic rocks occur in two stages at 252–185 and 225–200 Ma, respectively. The first-stage granitoids are mainly represented by I-type quartz diorites and granodiorites, and the second stage by granodiorites and monzogranites with the I- to A-type characteristics and some with rapakivi textures. Their emplacement ages and geochemical parameters such as A/CNK, K2O/Na2 O ratios and εNd(t) values do not show any polarity change in perpendicular to subduction/collision zone. Therefore, all these Early Mesozoic granitoids are unlikely the product of continental subduction as some researchers suggested. Instead, they are plausibly related to the subduction of the Mianlue Ocean and the subsequent collision between the South China Craton and the South Qinling terrane. The Late Mesozoic granitoids were emplaced mainly at two stages of 160–130 and 120–100 Ma, and characterized by the evolution from I- to I-A- and A-type granitoids. These characteristics are consistent with the granitoid magmatic evolution from contractional to extensional settings during the Jurassic/Cretaceous in eastern China. Accordingly, the Late Mesozoic granitoid rocks in the Qinling orogen probably have a similar petrogenetic mechanism to those of the huge magmatic belt along the western Pacific margin, i.e., intra-continent magmatism related to a far-field effect of the subduction of Paleo-Pacific plate. 关键词：秦岭造山带花岗质岩石岩浆活动中国东部岩浆演化 A型花岗岩锆石U-Pb年龄地球化学参数

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Granitoid magmatism in the Qinling orogen, central China and its bearing on orogenic evolution

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