摘要
西秦岭天水地区早中生代草川铺岩体内发育一套似斑状花岗岩，岩体主要由寄主似斑状二长花岗岩及闪长质微粒包体组成。sHRIMP锆石U—Pb定年结果显示，寄主岩体的侵位年龄为（210．9±1．7）Ma，平均标准权重偏差（MSWD）为1．74，属于早中生代花岗岩体。岩石地球化学研究表明：寄主岩体属于高钾钙碱性系列，具准铝质特征，A／cNK值为0．99～1.07；稀土元素总质量分数为（128．13～196．56）×10^-6，轻、重稀土元素质量分数比值为8．20～9．47，岩体富集轻稀土元素，微量元素特征表现为高场强元素贫化，但元素Ta、Nb明显亏损。岩相学、地球化学和年代学特征表明，早中生代草川铺岩体与南秦岭糜署岭岩体具有相似的岩相学特征和近一致的结晶年龄，并且二者的稀土、微量元素特征相似。因此，早中生代草川铺岩体和糜署岭岩体是同一套岩浆活动的产物，前者虽然构造位置处于北秦岭造山带内，但其物质来源于南秦岭造山带，表明南秦岭造山带和北秦岭造山带在晚三叠世之前已经碰撞。由于早中生代草川铺岩体具高钾钙碱性埃达克岩地球化学特征，所以其是南秦岭造山带向北秦岭造山带俯冲熔融的产物。
Abstract. Porphyaceous granitoid, which develops in Early Mesozoic Caochuanpu intrusion in Tianshui area of West Qinling, is mainly composed of host porphyaceous monzogranite and diorite microgranular enclave. SHRIMP zircon U-Pb dating shows that the emplacement age of host rock is （210.9±1.7）Ma with the mean standard weighted deviation （MSWD） of 1.74, so that the rock belongs to Early Mesozoic granitoid. Lithogeochemistry characteristics show that host rocks are high-K calc-alkaline series and metaluminous, and the values of A/CNK are 0.99- 1.07; total mass fractions of rare earth elements are （128.13-196.56） X 10-8 , the ratios of mass fractions of light and heavy rare earth elements are 8.20-9.47, so that the intrusions are rich in light rare earth element, high field strength elements are poor, and Ta and Nb are depleted. The petrology, geochemistry and geochronology show that the petrology, conformity, trace elementand rare earth element characteristics of Early Mesozoic Caochuanpu intrusion are the same as that of Mishuling intrusion in South Qinling. Consequently, Caochuanpu and Mishuling intrusions are the products of the same magmatic activity. Tectonic setting of Caochuanpu intrusion is North Qinling orogenic belt, but the material source is South Qinling orogenic belt, so that the collision between North Qinling and South Qinting orogenic belts happens before Late Triassic. Because Early Mesozoic Caochuanpu intrusion has the characteristics of high-K calc- alkaline adakitic rock, it is the product of subduetion and melting from South Qinling to North Qinling.
出处
《地球科学与环境学报》
CAS
2015年第2期11-20,共10页
Journal of Earth Sciences and Environment
基金
中国地质调查局地质大调查项目(1212011120100
1212011120099)
