江西北部五里街地区横山花岗岩的LA-ICP-MS锆石U-Pb年龄、地球化学及成因研究

LA-ICP-MS Zircon U-Pb Age,Geochemistry and Genesis of the Hengshan Granite in Wulijie,Northern Jiangxi Province

横山花岗岩岩体位于江西北部、幕阜山-五里街岩带东段,岩性主要为黑云母二长花岗岩、二云母二长花岗岩、白云母二长花岗岩、钾长花岗岩。对横山花岗岩中的黑云母二长花岗岩、二(白)云母二长花岗岩、钾长花岗岩进行了详细的锆石U-Pb年龄、岩相学、地球化学研究。研究表明,采用LA-ICP-MS锆石U-Pb定年,测得横山岩体中的中细粒黑云母二长花岗岩的年龄为(143.3±1.8)Ma,细粒二云母二长花岗岩年龄为(139.8±2.0)Ma,细中粒斑状白云母二长花岗岩年龄为(135.6±1.6)Ma,细粒黑云母钾长花岗岩的年龄为(135.0±1.1)Ma,均形成于燕山晚期早白垩世。横山花岗岩为高钾钙碱性强过铝质的S型花岗岩,具有高硅(SiO_(2)含量68.80%~75.78%)、富碱((K_(2)O+Na_(2)O)含量6.93%~8.51%)、过铝质(Al_(2)O_(3)含量12.82%~15.64%)的特征及较高的分异指数,轻重稀土分馏明显,呈左高右低的深V形,Eu表现为明显的亏损,表明岩浆是经历多阶段分离结晶、高度分异的结果。岩石成因与陆内俯冲造山过程中岩石圈增厚有关,形成于燕山期陆内活化造山-局部伸展的碰撞后拉张减压的构造环境,岩浆来源于地壳物质的部分熔融。

The Hengshan granite located in the north of Jiangxi province,in the eastern section of the Mufushan-Wulijie rock belt,which the lithology is mainly biotite monzogranite,muscovite-biotite monzogranite,muscovite monzogranite,K-feldspar granite.Detailed zircon U-Pb age,petrographic and geochemical studies have been carried out on the biotite monzogranite,muscovite monzogranite and K-feldspar granite of the Hengshan granite.Using LA-ICP-MS zircon U-Pb dating method,the age of the medium-fine-grained biotite monzogranite of the Hengshan pluton is measured to be(143.3±1.8)Ma,and the age of the fine-grained muscovite-biotite monzogranite is(139.8±2.0)Ma.The age of the medium-fine grained porphyritic muscovite monzogranite is(135.6±1.6)Ma,which show that they are and the age of the fine-grained biotite K-feldspar granite is(135.0±1.1)Ma,originated in the late Yanshanian-early early Cretaceous.The Hengshan granite is a high-potassium calc-alkaline strong peraluminous S-type granite with high silicon(SiO_(2)content of 68.80%to 75.78%),high alkali((K_(2)O+Na_(2)O)content of 6.93%to 8.51%),high aluminum(Al_(2)O_(3)content of 12.82%to 15.64%),and high differentiation index.The Hengshan granite are enriched in LREE,and depleted in HREE,with strong negative Eu anamolies,which suggests its magma are highly fractionated.This granite is originated from the partial melting of crustal materials in the intracontinental activated orogeny process to local extensional post-collision extensional decompression in Yanshanian period that is related to the thickening of the lithosphere during intracontinental subduction orogeny.