秦祁昆结合部三叠纪岩浆岩岩石学特征及其构造环境

Petrological Characteristics of Triassic Magmatic Rocks from the Conjunction of Qinling,Qilian and Kunlun Orogens and Their Tectonic Environment

秦祁昆结合部发育了大量三叠纪岩浆岩，主要沿青海南山断裂、瓦洪山断裂和多禾茂断裂周边分布，总体呈NW—SE向展布。岩石类型复杂多样，包括火山岩和侵入岩。火山岩主要以玄武岩、安山岩、英安岩、流纹岩和火山角砾岩为主；侵入岩主要为辉长岩、闪长岩、花岗闪长岩、花岗岩、石英斑岩等。同位素年代学研究表明：秦祁昆结合部三叠纪岩浆活动主要集中在早一中三叠世和晚三叠世；233～253Ma代表早一中三叠世岩浆活动，205～225Ma代表晚三叠世岩浆活动。空间上，岩浆活动呈现出由NW向SE逐渐年轻化的趋势。岩石组合及岩石地球化学特征表明：秦祁昆结合部旱一中三叠世岩浆岩形成于古特提斯洋由南向北俯冲的大陆边缘弧环境下，而晚三叠世可能已经逐渐进入后碰撞阶段。

Triassic magmatic rocks widely develop in the conjunction of Qinling, Qilian and Kunlun orogens along Nanshan fault, Wahongshan fault and Duohemao fault in Qinghai with a NW-SE-trending. The types of rocks are complicated and various, including volcanic and intrusive rocks. Volcanic rocks consist of basalt, andesite, dacite, rhyolite and volcanic breccias; intrusive rocks consist of gabbro, diorite, granodiorite, granite and quartz porphyry, etc. Isotopic chronology research reveals that the forming ages of these Triassic igneous rocks are mostly concentrated in Early-Middle Triassic （233-253 Ma） and Late Triassic （205-225 Ma）, and gradually decreased from NW to SE. Geochemistry characteristics and rock assemblages suggest that the Early Middle Triassic magmatic rocks in the conjunction of Qinling, Qilian and Kunlun orogens are formed in continental margin arc setting by the northern subduction of Palaeo-Tethys ocean; however, the Late Triassic magmatic rocks are formed in post collisional stage.