西藏冈底斯西段松多复式岩体锆石U-Pb定年及地球化学特征

冈底斯岩浆岩带的岩石成因和动力学过程对于揭示新特提斯洋俯冲、印度-亚洲大陆碰撞和之后的高原隆升具有重要意义.通过对松多区岩体地球化学和锆石LA-ICP-MS U-Pb定年研究,结果表明:二长花岗斑岩锆石206 Pb/238 U年龄为(44.5±1.6) Ma(95％置信度,n=18,MSWD=1.5),黑云二长花岗斑岩...

Zircon U-Pb age and geochemical characteristics of Songduo intrusive rock in the western Gangdese,Tibet

The petrogenesis and dynamic process of the Gangdise magmatic belt are of great significance to reveal the subduction of the Neo Tethys ocean,the collision between the Indian and Asian continents and the subsequent uplift of the plateau. According to the result of zircon LA-ICP-MS U-Pb dating,the zircon206 Pb/238 U age of monzonitic granite porphyry is 44.5 ± 1.6 Ma( 95% confidence level,n = 18,MSWD = 1.5),and that of biotite monzonitic granite porphyry is 50.3 ± 1.1 Ma( 95% confidence level,n =24,MSWD = 0.92),implying the products of early Eocene magmatism and representing the diagenetic age of the rocks in this area.The geochemical characteristics of the rocks indicate that the Songduo granite is a alkaline peraluminous I-type granite with high potassium and calcium. The Rittmann Index( σ) is 2.2 ~ 2.64. The distribution curve of rare-earth element is right inclined,with obvious negative Eu anomaly,enriched in large ion lithophile elements such as Nd,Th,La,U,and depleted in high field strength elements such as Ti,Nb,Ta. The ratio of Rb/Sr ranges from 0.37 to 0.53,which shows the characteristics of crust mantle contamination. Combined with previous studies,it is shown that the resistance of the subducted plate of the Neo-Tethys increased in the early Eocene. In the late evolution,the plate rotated and broke off,resulting in the partial melting of the upper mantle rocks,then the crust materials were melted to form mixed magma during the emplacement process,and in the rapid emplacement process,some crustal materials were mixed. Finally,the fine-grained granite porphyry in Songduo area was formed. These processes enriched the formation of Cenozoic magmatic tectonic diagenetic model and geochemical characteristics in the western Gangdese,Tibet.