老挝南部波罗芬高原晚新生代玄武岩及其地幔捕虏体地球化学特征

Geochemical composition of continental basalts and their mantle xenoliths can provide the best proxy record available for study of chemical-physical evolution of deep continental lithosphere and underlying mantle. Late Cenozoic continental basalts are widely distributed in the Indochina Peninsula of Southeast Asia. They are not only rich in mantle xenoliths, but also contain a huge amount of iron, bauxite, and gem resources, which have drawn strong interesting for research. However, geological research on the late Cenozoic basalts and mantle xenoliths is still limited in Laos. In view of the important scientific significance of rocks mentioned above, and considering increasing competition of mineral resources and research imbalance of this area, we plan to study geochemistry of late Cenozoic basalts and mantle xenoliths in the Bolaven Plateau, southern Laos. This proposal aims to genesis of basalts, including composition of mantle source, degree of partial melting, P-T conditions of melting, and role of crustal contamination, by means of geochemical techniques. Taking basalts and mantle xenoliths as "rock probe", we try to clarify the properties and geological processes in the mantle source region and further, to constrain mechanism of deep mantle dynamics behind basalt genesis in the framework of geological evolution and spatial-temporal distribution of basalts in Indochina Peninsula. Geochemical data obtained in this proposal are extremely necessary for understanding tectonic setting of late Cenozoic basalts in Indochina Peninsula and adjacent regions.

大陆玄武岩及其地幔捕虏体的地球化学组成很好的反演了岩石圈和深部地幔的化学和物理演化历史，是地球科学家研究岩石圈和深部地幔的有效途径。广泛分布于东南亚中南半岛的晚新生代玄武岩不仅富含地幔捕虏体，而且与铁、铝土、宝石资源相关，备受关注。特别是老挝，资源开发和地质研究程度极低。鉴于新生代大陆玄武岩及地幔捕虏体研究的重要科学意义，以及地区资源竞争日趋激烈的局势，针对地区研究不平衡的现状，拟对老挝南部波罗芬高原晚新生代玄武岩及其地幔捕虏体进行地球化学研究。运用元素地球化学和同位素示踪技术，探讨玄武岩成因（地幔源区组成、部分熔融程度、温压条件、地壳混染）。利用玄武岩和地幔捕虏体的“岩石探针”作用，反演地幔源区属性和深部地质作用过程。在中南半岛区域地质演化背景和玄武岩时空分布框架下，阐明玄武岩成因背后蕴涵的地幔动力学机制，为中南半岛及邻区晚新生代玄武岩成因研究提供基础数据。

大陆玄武岩及其地幔捕虏体的地球化学组成很好的反演了岩石圈和深部地幔的化学和物理演化历史，开展这些岩石的地球化学研究是地球科学家认识岩石圈和深部地幔的有效途径。广泛分布于东南亚中南半岛的新生代玄武岩富含地幔捕虏体，对于揭示岩石圈和深部地幔属性及地质过程具有重要意义。项目分析了老挝和柬埔寨的新生代拉斑和碱性玄武岩的主量、微量元素及Sr-Nd-Pb同位素数据，及柬埔寨东南部尖晶石二辉橄榄岩的矿物主量、微量元素数据。中南半岛新生代玄武岩具有亏损的同位素组成（εNd >0），但其富集不相容元素，其地球化学组成类似于OIB，同位素和不相容元素之间出现“解耦”。富集的不相容元素特征与近期的由低部分熔融程度熔体参与的地幔交代事件相关。玄武岩来源于软流圈地幔减压熔融，其动力学机制是印度-欧亚板块碰撞和西太平洋板块、印度洋板块俯冲拖拽联合作用下的中南半岛软流圈地幔南东向挤出构造。柬埔寨东南部地幔橄榄岩的环带橄榄石和单斜辉石从核部亏损逐渐到边部富集微量元素的特点，以及环带矿物边部越不相容元素越富集的特征，表明橄榄岩受到了硅酸盐熔体的交代作用。