滇东南马关新生代玄武岩中橄榄岩包体的含水性及深部动力学意义

Researchers have carried out many studies on water contents in mantle-derived peridotite xenoliths from East China, but less from Tethyan domain in Southwest China. This project will foucus on the Cenozoic Mantle-derived Xenocrysts in Maguan peridotite, which locates at the junction among the Yunnan-Tibet Tethyan domain, western Yangtze Craton, and South China fold belt which, to determine water contents and distribution in lithospheric mantle through in-situ micro-Fourier transform infrared spectroscopy, and combining with trace elements and H-O-Sr-Nd-Pb isotopes, to constrain magma origin and trace the influence on lithospheric mantle magmatism aroused by the Tethyan orogenesis, the Tibet plateau lava flow or the Yangtze Craton subduction. Subsequently we will explore the mutual influence between hydrous lithospheric mantle and the geotectonic evolution or deep dynamics of the Tethyan domain.

前人对我国东部地区岩石圈地幔含水性开展过较多研究，但对我国西南部的特提斯构造域的地幔含水性研究还十分薄弱。本项目拟选取处于滇藏特提斯造山带、扬子板块西缘与华南褶皱系三者结合部位的马关地区出露的新生代玄武岩中幔源橄榄岩包体为研究对象，利用原位显微傅立叶变换红外光谱分析方法获取该区岩石圈地幔水的含量及分布，结合微量元素及H-O-Sr-Nd-Pb同位素分析, 来制约新特提斯造山作用、青藏高原深部物质流以及扬子板块西缘俯冲对该区岩石圈地幔岩浆活动的影响，探讨岩浆起源及岩浆源区性质，揭露特提斯构造背景下岩石圈中水与地质构造环境演化及深部动力过程的相互影响。

获得马关地区新生代玄武岩幔源橄榄岩包体中橄榄石、单斜辉石、斜方辉石、巨晶单斜辉石以及全岩的结构水含量分别为2-12ppm、141-600ppm、85-207ppm、318-693ppm和37-137ppm，数据表明研究区岩石圈富水。新生代时期，到达软流圈和地幔过渡带边界的新特提斯俯冲洋壳为岩浆熔融动力，玄武岩的高含水量暗示地幔过渡带是玄武岩岩浆源区。由于新特提斯俯冲洋壳的加入，导致部分地幔橄榄岩逐渐从亏损难熔的特征向饱满肥沃转变。证据并不支持研究区玄武岩归属于峨嵋山大火成岩省。