印度尼西亚塔里亚布岛花岗岩的Rb-Sr年代学、地球化学及地质意义

印度尼西亚塔里亚布岛花岗岩位于东南亚陆缘壳体北缘。全岩Rb-Sr等时线测年结果表明,该花岗岩形成于中晚三叠世((227±2)Ma),Isr=0.716 67±0.002 40,属印支期的壳源S型花岗岩。岩石类型以二长花岗岩为主,富硅(w(SiO2)=75.92%～77.38%)、富碱(w(Na2O+K2O)>7%)、富钾(K2O/Na2O>7),贫钙、镁和铁。稀土及微量元素方面富Rb、K、Th、U、Ta和Nb,贫Ba、Sr、P、Ti和Cr,具强烈的铕负异常(δ(Eu)=0.13～0.52)及铈负异常(δ(Ce)=0.43～0.79),反映出其经历过彻底的岩浆演化分异和斜长石分离结晶过程。结合区域地质背景,晚三叠世前塔里亚布岛位于新几内亚岛北缘,尚未从冈瓦纳大陆分离。塔里亚布岛花岗岩形成于泛大洋洋壳对冈瓦纳大陆陆壳北东部边缘碰撞后的拉张-伸展环境,与该岛铁多金属矿田同属本次构造-岩浆-成矿事件的产物。

Rb-Sr geochronology, geochemistry and geological implications of granite from Taliabu Island, Indonesia

The granite from Taliabu Island of Indonesia is situated in the north margin of Southeast Asia continental margin crustobody.The data of the whole rock Rb-Sr isotopic isochron show that the granite was formed in Middle to Late Trassic((227±2) Ma),Isr=0.716 67±0.002 40.It belongs to Indo-Chinese epoch and S-type granite from crust source.The rock type is mainly monzogranite.Geochemically,the granite is rich in silica(w(SiO2)=75.92%-77.38%),alkali(w(Na2O+K2O)>7%) and potassium(K2O/Na2O>7),poor in calcium,magnesium and iron,and shows the enrichment of Rb,K,Th,U,Ta,Nb,and depletion of Ba,Sr,P,Ti and Cr,with an intensive negative Eu anomaly(δ(Eu)=0.13-0.52),and negative Ce anomaly(δ(Ce)=0.43-0.79).These geochemical characteristics indicate that the magma have gone through complete evolution and fractional crystallization of plagioclase.Combined with the regional geological setting,Taliabu Island is located in the north margin of New Guinea island which is not separated from Gondwana.The granite was formed in a post-collision extensional tectonic setting between the Panthalassa and the northeast margin of Gondwana.The granite is the same product with the Fe-polymetallic orefield in Taliabu island by the tectonism- magmatism-mineralization event.