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Geochronological and Geochemical Characteristics of Early Mesozoic Caochuanpu Granitoids in Tianshui Area of West Qinling and Their Geological Significance
Author(s): 
Pages: 11-20
Year: Issue:  2
Journal: Journal of Earch Sciences and Environment

Keyword:  granitoidgeochronologyEarly MesozoiczirconU-Pb datinggeochemistryWest Qinling;
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)×10-6,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 Qinling orogenic belts happens before Late Triassic.Because Early Mesozoic Caochuanpu intrusion has the characteristics of high-K calcalkaline adakitic rock,it is the product of subduction and melting from South Qinling to North Qinling.
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