安徽九华山柯村花岗斑岩锆石U-Pb年代学、地球化学特征及地质意义

Chronology and geochemistry of the Kecun granite porphyry in the Jiuhuashan area,Anhui Province and their geological implications

柯村花岗斑岩位于九华山国家地质公园西部,九华山岩体西侧。LA-ICP-MS锆石U-Pb年代学研究表明:该花岗斑岩的侵入时间为125.8±0.9 Ma,与九华山岩体的侵入时间相近,属于早白垩世岩浆活动的产物;九华山柯村花岗斑岩富硅、富碱、富集不相容元素,亏损Sr、Ba、Ti等元素,具有较高的10 000×Ga/Al值和锆石饱和温度,地球化学特征与A型花岗岩相似,形成于伸展构造环境,表明在125 Ma左右,皖南地区已经由早期相对挤压的构造环境转变为伸展构造环境。

Kecun granite porphyry is located in the western part of Jiuhuashan National Geopark and in the west side of Jiuhuashan granite. Study of LA-ICP-MS zircon U-Pb dating indicates that granite porphyry emplaced at 125.8±0.9 Ma, close to the intrusion age of Jiuhuashan granite, suggesting that it should be the product of early Cretaceous magmatic activity. The Kecun granite porphyry is enriched in SiO 2, total alkalis and incompatible elements, depleted in Ba, Sr and Ti, and has high 10 000 ×Ga/Al values and zircon saturation temperature. All of these features are similar to geochemical characteristics of A-type granite, indicating that the Kecun granite porphyry was formed in an extensional tectonic setting. This study can conclude that the tectonic environment of southern Anhui Province might have transformed from early compression to extensional tectonic settings at ca. 125 Ma.