大兴安岭阿尔山橄榄岩捕虏体硫化物原位Re-Os同位素组成研究

As the low-density and Mg-rich residue after basaltic melt extraction, the formational age and evolutionary history of the lithospheric mantle play a key role in studying the formation and evolution of the crust. Compared with traditional isotopic systems (such as Rb-Sr, Sm-Nd), Re-Os system is currently the most reliable method to date the lithospheric mantle. Recently, the LAM-MC-ICPMS was gradually used for in situ Re-Os analysis of the sulfide contained in peridotites. In contrast with bulk rock analysis, in situ study of Re-Os system of sulfide can deepen and detailed the knowledge about the multi-geological process that the lithospheric mantle experienced. This study intend to select the peridotite xenoliths hosted by the alkali basalts from the Aershan area, the Great Xing’an Range, as the studied object, on the basis of detailed petrographic observations, major- and trace- element compositions of bulk rock and minerals, focusing on the occurrence, composition and in situ Re-Os isotopic compositions of single sulfide, , discuss the formational time and evolutionary process of the lithospheric mantle beneath this area, reveal the correlations of tectono-thermal events which the deep mantle and shallow crust underwent respectively, Through combining with regional geological data and previous research on the peridotite xenoliths from eastern China, we further provide some constrains and implications on the lithosphere evolution of the Great Xing'an Range, even for the Northeastern China.

岩石圈地幔是伴随着玄武质熔体抽取而形成的低密度富镁残留，其形成年龄和演化历史是地球固体科学研究的关键问题之一。与传统的Rb-Sr、Sm-Nd等同位素体系相比，Re-Os体系是目前岩石圈地幔定年的最理想工具。近年来，LAM-MC-ICPMS原位分析技术被逐渐的用来研究橄榄岩硫化物的Re-Os同位素组成。与全岩分析相比，对硫化物Re-Os体系的研究能够更好的揭示岩石圈地幔多期次地质过程。项目以大兴安岭中部阿尔山橄榄岩捕虏体为研究对象，在对样品进行的岩相学观察和全岩、矿物主微量元素分析的基础上，侧重对其硫化物的产状、组成（尤其是Re和铂族元素）和原位Re-Os同位素体系的研究，探讨该区岩石圈地幔的年龄及演化历史、深部地幔和浅部地壳构造热事件的耦合关系，并结合我国东部橄榄岩捕虏体的研究成果，对不同构造单元岩石圈地幔改造过程的异同，以及大兴安岭乃至整个中国东北岩石圈的演化提供一些约束和启示。

岩石圈地幔的形成和演化历史是固体地球科学研究的关键问题之一。与华北克拉通相比，人们对中亚造山带东部岩石圈地幔的认识仍显薄弱。本项目对大兴安岭中部阿尔山地区橄榄岩捕虏体进行了系统的岩相学和地球化学组成研究，识别出了饱满、弱交代，适度难熔、强交代与过渡类型的三类橄榄岩包体，总结了中亚造山带东部岩石圈地幔的性质与演化模式。认为该造山带东部岩石圈地幔以新生饱满物质与古老难熔残余共存为特征，且浅部以饱满型地幔为主，软流圈物质上涌对该造山带地幔演化起了重要作用。由于所获硫化物颗粒在大小与数量上难以满足原位Re-Os同位素组成测试要求，进而无法精确限定岩石圈地幔形成年龄与多期次演化过程的时限。项目后期转为研究阿尔山橄榄岩捕虏体单斜辉石海绵结构的产状、矿物组成、含量、相互关系与化学成分，提出了地幔单斜辉石海绵结构成因的复杂性，揭示了研究区岩石圈地幔经历了多期次的熔体抽取与交代过程。不同构造单元、不同时空背景下橄榄岩捕虏体的对比可以加深对岩石圈地幔形成和演化过程的理解，本项目参与并资助了针对华夏西部、江西安远地区橄榄岩捕虏体的研究工作，认为安远地区的陆下岩石圈地幔表现为饱满与适度难熔物质共存。这种不均一性是熔-岩反应，侵蚀作用和上涌软流圈物质冷却转变置换的综合结果。

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