关键词: 松南低凸起, 花岗岩, 年代学, 地球化学, 构造环境, 琼东南盆地

Abstract:  In this paper, the lithofacies, zircon chronology and geochemistry are studied to discuss the petrogenesis and tectonic environment of the Songnan low uplift granite in Qiongdongnan basin, northern of the South China Sea. The results show that the buried hill lithology is mainly granodiorite and monzonitic granite. The zircon UPb dating results of LAICPMS are 228.6 and 243.7 Ma, the age of Triassic magmatic activity. The rock mass belongs to highk calcium alkaline series, with high content of SiO2(54.94%79.71%), moderate alkali (3.53%6.43%), Al2O3 ( 9.82%18.23%), CaO(1.24%9.55%), and MgO(0.37%2.28%). The A/CNK values range from 1.09 to 2.13, which are both aluminum and peraluminous granites. The rocks are generally rich in large ion lithophile elements such as K, Rb and Th, depleted of high field strength elements such as Ta, Nb, Ti, with moderate to weak negative Eu anomalies (δEu= 0.50~0.85). The petrological and geochemical characteristics show that the granodiorite is aluminum Itype granite, and the monzogranite is peraluminous Stype granite, which were formed by partial melting of sediments in the crust. The comprehensive analysis suggests that the granite has the characteristics of postcollisional granite, formed in extensional tectonic environment, and is related to the reverse extension after collision of South China and Indosinian blocks.

Key words: Songnan low uplift, granite, geochronology, geochemistry, tectonic environment, Qiongdongnan basin