岩浆过程和热液蚀变对深海橄榄岩地球化学特征的影响

THE INFLUENCE OF MAGMATIC PROCESS AND HYDROTHERMAL ALTERATION ON THE GEOCHEMICAL CHARACTERISTICS OF ABYSSAL PERIDOTITES

在慢速-超慢速扩张洋中脊环境中,深海橄榄岩常出露于洋中脊的末端与转换断层附近。其出露和蚀变对大洋岩石圈流变学性质、海洋地球化学储库和洋中脊生态系统等方面都有着重要的影响。深海橄榄岩被动抬升至海底的过程中,经历了减压部分熔融,与迁移熔体、循环海水发生物质和能量交换等复杂地质过程。了解深海橄榄岩地球化学特征形成机制对探讨深海橄榄岩的岩石成因、蛇纹石化过程、海底超镁铁质岩石中热液系统的发育和热液成矿机制等具有重要意义。基于前人的研究成果,介绍了洋中脊深海橄榄岩出露的机制,探讨了岩浆过程和热液蚀变对其地球化学特征的影响和元素在热液蚀变中的迁移性,认为深海橄榄岩的稀土配分样式受到岩浆作用和热液蚀变的共同作用,而前者作用更显著。

Abyssal peridotites usually occur at the end of the slow-ultraslow spreading ridges and the places near transform faults. Their exposure and the alteration thereby have important consequences to the rheol- ogy of oceanic lithosphere, the geochemical budgets of the ocean and the activities of microbial communi- ties. They have undergone geological processes such as partial melting, reactions with the porous melt and penetrative seawater during the ascent from the upper mantle via the detachment faults. The geochemical characteristics of abyssal peridotites, therefore, are of importance in discussing their petrogenesis, serpen- tinization, generation of the ultramafic hosted hydrothermal system and hydrothermal mineralization. Based on the previous studies, we reviewed the exposure and alteration of abyssal peridotites along mid-o- cean ridges systematically. The effects of magmatic processes and hydrothermal alteration on the geochem- ical characteristics of abyssal peridotites, together with the element mobility during alteration, are also discussed. Finally, we proposed that the REE pattern of abyssal peridotite is controlled by both the mag- matic process and alteration. However, the magmatic process should be more significant than alteration on modifying the REE patternss.