冲绳海槽南部海底热液活动区地形地貌特征及成因分析

Topographic features of the hydrothermal field and their genetic mechanisms in southern Okinawa Trough

为了进一步理解构造地质过程对弧后盆地热液活动及成矿作用的影响和控制,以实测和收集的多波束资料为基础,对冲绳海槽南部多个海底热液活动区的地形地貌特征进行了精细刻画。结合前人研究成果,从构造地质学的角度分析了热液区地形地貌的成因机制。结果表明,冲绳海槽南部热液区均为海底火山成因地貌,不同热液区的海底地貌分属于不同类型岩浆作用的产物:D海丘受岛弧和弧后盆地岩浆作用的双重影响,A海丘群由岛弧为主的多源岩浆作用产生,C海丘和B海丘群属于琉球火山岛弧,雨花海丘形成于造山期后地壳伸展导致的岩浆上涌。冲绳海槽中央地堑与琉球火山岛弧的交汇处有利于形成大规模岩浆和地热活动。琉球火山岛弧的岩浆活动存在时空迁移,与海槽构造演化过程中由分散式裂陷向中心式裂陷的转换有关。唐印热液区的存在表明台湾北火山带在槽底北缘及陆坡区仍具有较强的岩浆和地热活动性,是未来冲绳海槽南部海底热液调查的重要靶区之一。

In order to better understand the role of tectonic processes in submarine hydrothermal activity and mineralization in back-arc basins, we documented herewith the multi-beam sounding data from the southern Okinawa Trough and detailedly depicted the topographic features of some hydrothermal fields concerned. Combined with the results in previous publications, we analyzed the genetic mechanisms of the topographic features from the viewpoint of tectonics. Topographic features in all of the hydrothermal fields are formed by submarine volcanism. Nevertheless, features of different hydrothermal fields are essentially depending upon the distinct types of magmatism. The D Knoll was influenced by both the arc and back-arc magmatisms;the A Knolls were formed by multi-source magmatism predominated by arc magmatism;the C Knoll and the B Knolls are part of the Ryukyu Volcanic Arc;and the Yuhua Knoll was generated by the magmatism induced by the post-collisional lithospheric extension. The intensity of the Ryukyu Volcanic Arc magmatism shows a trend of migration both temporally and spatially, which may be attributed to the transition from disperse rifting to the focus rifting. The occurrence of the Tangyin hydrothermal field indicates that the magmatism of the Northern Taiwan Volcanic Zone in the continental slop region is strong enough to drive vigorous hydrothermal circulation. Thus this region is an important target area for hydrothermal surveys in the future.