滇西高黎贡带～40Ma OIB型基性岩浆活动:消减特提斯洋片与印度板块断离的产物?  

～40 Ma OIB-type mafic magmatism in the Gaoligong belt:results of break-off between subducting Tethyan slab and Indian plate?

作　　者：蓝江波[1] 徐义刚[1] 杨启军[1] 黄小龙[1] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室

出　　处：《岩石学报》2007年第6期1334-1346,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2002CB412603)资助。

摘　　要：滇西高黎贡带基性岩脉形成于40～42Ma,以高FeO、TiO2,低K2O含量为特征.虽然多数样品经历了不同程度的地壳混染,少量样品的Nb/La大于1,La/Yb比值较小和Mg#值较高,显示了似洋岛玄武岩（OIB）的地球化学特征,从而为研究区提供了软流圈上涌的岩石学证据.模拟计算进一步暗示高黎贡基性岩脉的源区在尖晶石相橄榄岩中（＜70km）,说明软流圈地幔上涌到很浅的部位,这与目前青藏高原巨厚的岩石圈（＞150km）形成鲜明对比.因此,～40Ma高黎贡基性岩浆活动记录了研究区陆一陆碰撞后特殊的构造演化阶段.高黎贡带基性岩脉与达孜-甲马基性次火山岩在形成时间和地球化学性质上一致,两者均代表了碰撞后消减特提斯洋片与印度板块断离过程中软流圈上涌熔融的产物.The marie dykes in the Gaoligong belt were emplaced at 40 and 42 Ma. They are characterized by high FeO, TiO2 and low K2O contents. Despite the various degree of crustal contamination, a few samples have Nb/La 〉 1, low La/Yb and high Mg#, sharing the geochemical features of oceanic island basalts. This provides the petrological evidence for the Eocene asthenospheric upwelling in the studied area. Trace element modeling further indicates that the Gaoligong basaltic rocks were derived from a spinelfacies mantle, suggesting a shallow level （〈70km） reached by the upwelling asthenosphere. This shallow asthenospheric source is in great contrast with the current thickness of the lithosphere beneath the Tibetan Plateau （ 〉 150km）. Therefore, the - 40 Ma magmatism represents the response to specific stage of the post-collisional tectonic evolution. The Gaoligong mafic dykes are similar to the sub-volcanic rocks from Dazi-Jiama in terms of geochemistry and emplacement age. These rocks are interpreted as products of the partial melting of the upwelling asthenosphere in the course of the break-off of subducting Tethys slab and Indian continental plate.

关 键 词：高黎贡带 基性岩脉 板片断离 软流圈上涌 

分 类 号：P588.124[天文地球—岩石学]