滇西腾冲—梁河地区花岗岩的年代学、地球化学及其构造意义
Geochronology and geochemistry of granites in the Tengliang area, western Yunnan: Tectonic implication
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摘要: 滇西腾冲-梁河地区位于喜马拉雅东构造结的东侧，区域内广泛分布的中、新生代花岗岩（简称腾梁花岗岩）由古永岩群、宾榔江岩群的若干个花岗岩体组成，以岩基、岩株、岩墙状态产出。花岗岩呈现带状沿着一系列北北东向弧形断裂平行分布，展示明显的同构造剪切被动侵位和岩墙扩展侵位特征。岩浆锆石SHRIMP U-Pb定年结果显示，东侧的古永岩群花岗岩结晶年龄为白垩世晚期（76~68Ma）；而西侧的槟榔江岩群花岗岩结晶年龄为稍晚的始新世（53Ma）。腾梁花岗岩主要为中、粗粒黑云母二长花岗岩、黑云母条纹长石花岗岩、伟晶花岗岩，缺少典型的富铝矿物。地球化学特征表明腾梁花岗岩是起源于中下地壳的过铝-强过铝高钾钙碱性花岗岩，源岩是富含泥质的硬砂岩，并具有岛弧-后碰撞花岗岩特征。由于喜马拉雅新特提斯封闭及印度陆块与亚洲陆块的陆陆碰撞发生于65Ma, 进一步推测腾梁花岗岩是新特提斯封闭到陆陆碰撞造成陆壳增厚所引起的中下地壳部分熔融的产物。腾梁花岗岩是冈底斯的东延部分，但在形成机制上，与冈底斯花岗岩具有明显的差别。Abstract: The granitoids outcropped extensively in the form of batholiths, stocks, and dikes in the Tengchong-Lianghe area, east of Eastern Himalaya Syntaxis. The plutons (so called Tengliang granites) are composed of Guyong Group and Binglanjiang Group. The Tengliang granites are distributed along a number of NNE-extending faults. They show some shearing features related to syn-tectonic intrusion and dyke-developing emplacement. SHRIMP zircon U-Pb dating reveals two episodes of magmatism of Late Cretaceous (76~67Ma; Guyong Group) and Early Paleocene (53Ma; Bingliangjiang Group). The Tengliang granites are composed of biotite monzonogranite, biotite perthite granite, pegmatite, with no typical peraluminous minerals. Characterized by high-potassium, peraluminous to strongly peraluminous, they were generated from lower to middle crust by partial melting of metapelite. The partial melting was induced by crustal thickening related to the subduction of Neo-Tethyan plate and subsequent collision between India and Asia continents. It is suggested that the Tengliang granites are the eastward extending part of Gandese batholith, but have different genesis.
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Key words:
- Tengliang granites /
- U-Pb dating /
- Neo-Tethys /
- Continent-continent collision
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