海底热液成因含金属沉积物的研究现状及展望

Reviews and prospects of submarine metalliferous sediments of hydrothermal origin

海底热液成因含金属沉积物广泛分布于全球各大洋与弧后活动扩张中心、大洋玄武岩上覆沉积层的底部以及板内火山的顶部等区域。块状硫化物烟囱体经氧化蚀变发生再沉积作用、热液羽流的扩散和沉降作用或低温弥散流的直接沉淀均可形成含金属沉积物。尽管不同热液区的含金属沉积物在矿物和化学组成上具有一定的差异,但其相对正常远洋沉积物均表现为富含Fe、Mn并亏损Al和Ti等组分,其中的主要矿物通常为结晶程度较差的铁锰氧化物/氢氧化物和富铁蒙脱石(绿脱石)。自二十世纪七十年代末发现现代海底热液活动以来,大量的研究不仅基本明确了含金属沉积物的形成机制,还在与之相关的微生物矿化作用和自生黏土矿物的成因研究等方面取得了重要的进展。对含金属沉积物开展综合研究,确定其鉴别分类标准,既能丰富人们对海底热液循环系统、热液活动对全球海洋热和化学通量的贡献以及对海底深部生物圈的认识,也可为寻找多金属硫化物矿床、揭示古板块中类似矿床的成因和分布规律以及探索古海洋环境演化等提供重要信息。

Submarine metalliferous sediments of hydrothermal origin occur widely in the global ocean and back-arc spreading centers,and basal sedimentary layers overlie oceanic basalts and the top of intraplate volcanos.Metalli-ferous sediments may be formed by oxidative weathering and re-deposition of massive sulfide chimneys,hydro-thermal plume diffusion and sedimentation,or direct precipitation from low-temperature diffusive flows.These sediments are mainly composed of poorly crystallized Fe-Mn oxide/oxyhydroxides and Fe-rich smectite(non-tronite).Although obvious regional differences in the composition of metalliferous sediments from various hydro-thermal fields have been observed,the sediments are usually characterized with more metallic elements,such as Fe and Mn,and less Al and Ti compared with pelagic sediments.Since the discovery of modern submarine hydrother-mal activity in the late 1970s,the formation mechanism of metalliferous sediments has been clarified,and important advances in the microbial mineralization and origins of authigenic clay minerals have been made.A comprehensive study of metalliferous sediments and detailed explication of their identification criteria can not only enrich the cur-rent understanding of seafloor hydrothermal systems and their heat and chemical fluxes to the global ocean as well as the understanding of deep sea biosphere,but also provide insights into the development of polymetallic sulfide deposits,reveals the origin and distribution of the ancient analogs of these sediments on paleo-plates as well as in-formation to explore the evolution of the paleo-oceanographic environment in the future.