滇西盈江地区新生代辉长岩地球化学特征及其构造意义

Recent studies show that the Tengchong block and its surrounding areas is an important component part of the Tibet Plateau. The region is not only the composition of the Tethyan tectonic domain, but also strongly related with the collision of two-continent after subduction of Neo-Tethys, the lifting of Tibetan Plateau. However, the time of the collision of India with the Asian continent, the Neo-Tethys closed in the end, collisional orogeny and the extention, as well as crust-mantle interaction mechanisms were still poorly defined. The age, petrogenesis and tectonic setting of the Yingjiang Cenozoic gabbro play an important role on understanding the interaction of the crust-mantle evolution of the Tibet Plateau and the transformation of the tectonic regime. The aim of this project is based on the field, petrology and geochemistry of Yingjiang Cenozoic gabbro, to establish the temporal and spatial of the Cenozoic magmatic rocks, the petrogenesis and its tectonic environment, and to probe into the relationship between evolution of Neo-Tethyan on the south-eastern of Tibetan and the mechanism of the crust-mantle interaction.

近年来的研究表明腾冲地块及其周边地区，是青藏高原的重要组成部分。该地.区不仅是特提斯构造域的组成，而且是与新特提斯闭合后两大陆碰撞、青藏高原隆升相关的.地质作用强烈改造的地区。然而，有关印度与亚洲大陆的碰撞时间，新特提斯最终闭合、碰.撞造山、造山后伸展的精细时空问题以及不同演化阶段壳幔相互作用机制问题都没有得到有.效的约束。滇西盈江地区新生代辉长岩体形成时代的确定、岩石成因及其大地构造背景的研.究对了解青藏高原侧面碰撞带新生代岩浆作用与新特提斯的演化过程中的壳幔相互作用和.构造体制的转换关系具有非常重要的地质意义。本项目将对滇西盈江地区新生代辉长岩体进.行系统的野外地质、岩石（相）学、元素和同位素地球化学研究，确立该区新生代岩浆岩的.时空分布特征、岩石成因及其形成的大地构造环境，探讨他们的形成与整个侧面碰撞带新特.提斯演化的关系以及演化过程中壳-幔相互作用的机制。

对滇西盈江地区5个辉长岩体的锆石进行激光ICPMS U-Pb定年，结果显示为新生代岩浆作用，与该区出露的花岗岩同期。5个岩体得出较为一致的结果，侵位年龄~53 Ma；对辉长岩的主微量元素和Sr、Nd同位素研究结果显示，滇西盈江地区新生代辉长岩具有弧岩浆地球化学特征。高黎贡-腾梁-盈江地区最年轻的岩浆作用（~53Ma）主要出露于盈江以西，靠近中缅边境。这一期岩浆活动的时间与冈底斯带的主要岩浆活动期相一致。在岩石地球化学性质上，该期岩浆作用主要有辉长岩及花岗岩，具有十分宽泛的成分变化范围，花岗岩总体上显示了介于I型和S型的过渡型类型，辉长岩具有弧岩浆地球化学特征。最为重要的，从东往西，岩石中锆石的Hf同位素比值由负值逐渐变正，说明越靠近缝合带岩浆源区的地幔贡献越大。这些特征说明研究区~53 Ma的岩浆作用代表了与新特提斯洋俯冲有关的大陆边缘弧岩浆作用。