青藏高原东缘保山地块沧源新生代中酸性侵入岩年代学、岩石成因与地块挤出

Chronology,Petrogenesis and Links with Extrusion Tectonics of Cangyuan Cenozoic Intermediate to Acid Intrusive Rocks in Baoshan Block,Eastern Tibetan Plateau

为探讨保山地块新生代岩浆侵位时代,揭示其成因和形成动力学机制,重建保山地块新生代演化历史,对保山地块东南缘沧源新生代岩浆岩中部分中酸性岩体和岩墙开展了岩石学、锆石U-Pb年代学和地球化学研究。结果表明,沧源地区新生代中酸性岩体和岩墙均侵位于40~41Ma,与澜沧新生代花岗质侵入岩年龄相当,为保山地块新生代早期岩浆活动的重要组成。沧源和澜沧新生代岩浆岩总体具有较强的轻-重稀土、特别是中-重稀土分馏,无明显Sr、Eu负异常,具高的Sr/Y、La/Yb、Gd/Yb值,与C型埃达克岩类似。样品的86Sri/87Sri为0.7065~0.7103,εNd(t)为-3.6^-5.6。沧源新生代岩浆岩很可能来自石榴斜长角闪岩源区在30~40km深度的部分熔融。通过岩相学和地球化学分析,首次在沧源新生代岩浆岩中识别出~41Ma的A型花岗岩。结合区域构造-岩浆研究成果,认为沧源-澜沧新生代岩浆带与青藏高原碰撞导致的东部岩石圈块体南东向挤出作用存在密切联系。

In order to investigate the geochronology, petrogenesis and geodynamicsettingof the Cenozoic igneous rocks in Baoshan block, we have concentrated on the petrology, zircon U-Pb chronology and whole-rock geochemical composition of the Early Cenozoic igneous rock in Cangyuan, southeastern Baoshan block. The results of dating indicate that the interme- diate to flesic intrusions and dykes in Cangyuan emplaced at 40-41 Ma, synchronous with those in Lancang region. The Early Cenozoic igneous rock in Cangyuan and Lancang exhibits high Sr/Y, La/Yb, Gd/Yb ratios and significant REE fractionation, with no significant Sr, Eu negative anomaly, similar to C-type adakite. They have enriched initial ^86Sr/^87Sr ratios of 0. 7065-0. 7103, and（t）values of -3.6 to -5.6. We infer that the Cangyuan Cenozoic magmatism resulted from partial melting of garnet amphibolite in lower crust at a depth of 30-40 km. In addition, we report for the first time that there has -41 Ma A-type granite in Cangyuan region in this study. The early Cenozoic igneous rock in both Cangyuan and Lancang have close spatial, temporal and possibly has genetic linkage with the eastward extrusion of Tibet.