Constraints of the Yanshanian dynamic background in the northeastern Hunan:Chronology and geochemical characteristics of granitic intrusive rocks in the Jinjing area
The Yanshanian intrusive rocks in the northeastern Hunan are widely developed within a longtime span,but their stages of magmatic activity are very limitedly studied,and the tectonic setting of those magmatic events is also controversial.In this article,we conducted a study on the chronology and geochemistry of granitic intrusive rocks in the Jinjing area of the northeastern Hunan,defined stages of magmatic activity,and explored the tectonic settings and dynamic mechanisms of magmatic activities.The results show that intrusive rocks have zircon SHRIMP U-Pb ages of 165～160 Ma and 155～150 Ma,indicating that there are two stages of magmatic activities(Late Jurassic).The intrusive rocks are characterized with rich Si,Al,and K contents and high ASI values.They generally belong to the high-K calc-alkaline series of strong peraluminous granite.Their Ba,Nb,Sr,P and Ti are significantly or strongly depleted,and Nb is significantly depleted relative to Ta.They have enriched LREE,with weak-medium negative Eu anomalies.They have ISr values varying from 0.713 83 to 0.729 19,εNd(t)values varying from-10.98 to-8.47 with Nd model ages(tDM2)of 1.64～1.83 Ga.Geochemical data show that the acid intrusive rocks were mainly sourced from the metamorphosed mudstones and greywackes in the middle and upper parts of crust,with little basic rocks of the lower crust.They generally belong to the S-type granite.Based on petrogeochemistry and regional tectonic characteristics,it is proposed that the 165～160 Ma aged magmatic activities in the Jinjing area were mainly related to the decompression melting of the thickened middle-upper crust,whereas the 155～150 Ma aged magmatic activities were related to the decompression melting of the thickened middle-upper crust and the upwelling of asthenosphere caused by the collapse of the subducted paleo-Pacific plate.
万方数据
维普
