北淮阳东段西汤池岩体地球化学特征、锆石U-Pb定年及成因

Geochemical characteristics,zircon U-Pb dating and its genesis of the Xitangchi rock mass in the eastern section of North Huaiyang area,Anhui Province

西汤池岩体位于安徽北淮阳地区舒城县西汤池一带。西汤池似斑状二长花岗岩具高硅、富碱质特征,为铝饱和碱性系列岩石。稀土元素含量中等,(La/Yb)_N与HREE/LREE值较高,重稀土相对轻稀土亏损明显,Eu呈弱负异常,属轻稀土富集型。大离子亲石元素(Rb、K、La、Nd等)明显富集,而高场强元素(Nb、Ta、P、Ti等)亏损。通过LA-ICP-MS锆石U-Pb定年,获得西汤池二长花岗岩^(206)Pb/^(238)U年龄为(125.5±1.6)Ma,为早白垩世岩浆活动的产物。基于前人关于北淮阳地区区域地质背景方面的研究成果和本次地球化学构造环境判别方面的研究,认为西汤池二长花岗岩属A_1型花岗岩,形成于后碰撞的伸展构造环境。

Located in Xitangchi,Shucheng County,North Huiayang area,Anhui Province,Xitangchi rock mass is porphyroid monzogranite with high silica and high alkali,aluminum saturated rock of alkaline series. It is LREE-rich rock,with medium content of rare earth element,and high value of（ La/Yb）N and HREE/LREE. Its HREE is significantly depleted compared to LREE,and Eu shows weakly negative anomaly. It is quite enriched in large ion lithophile element such as Rb,K,La,Nd,etc,and depleted in high field-strength element such as Nb,Ta,P,Ti,etc. Zircon U-Pb dating by LA-ICP-MS shows that the age of the Xitangchi monzonite granite by-（206）Pb/-（238）U is（ 125.5±1.6） Ma,a production of the Early Cretaceous magma activity. Based on previous studies of geological setting of North Huaiyang area and the present geochemical research on the structural environment discrimination,it is believed that the Xitangchi monzonite granite is A1-type granite,formed in extensional structural environment of post-collision.