Geochemical Studies on Mg-bearing Carbonates in Ryukyu Islands and Okinawa Trough.

对主要采集于竹岛和冲绳海槽弧后盆地海底热液点的碳酸盐沉积物及相关物质进行了地球化学研究。研究结果总结如下:[A]竹岛海底热液点：(1)由水肺潜水员在竹岛珊瑚礁底部（约22m深）采集碳酸盐沉积物、温泉水和伴生气样本。(2)碳酸盐沉积物由有孔虫、贝壳或珊瑚骨架碎片组成。深色的次生碳酸盐覆盖在沉积物的孔隙中。暗区白云石比例及Hg、as、Sb、Ba、Fe、Mn、Cd、U等重金属含量异常高。(3) Taketomijime热液遗址沉积物的化学和矿物学特征与鹿儿岛湾相似，认为与邻近地区的火山活动有关。(4)频繁的地震活动……自1991年1月23日至今，位于竹岛热点以西约30公里处的岛内岛观测到更多的地震活动。因此，竹岛温泉活动与伊洛莫特地震活动之间是否存在关联将是一个重要的问题。应监测水温、水的化学成分和伴生气体。[B]冲绳海槽热液位置：(1)1989年和1990年用“SINKAI2000”号潜航器在冲绳海槽Iheya深采集碳酸盐沉积物。(2) x射线衍射和中子活化分析表明，这些碳酸盐主要由方解石、菱铁矿（MnCO3）和钾土（CaMn (CO3) 2）组成，富含锰、砷、汞和银。(3)另一方面，1989年从Izena深层收集了硫酸盐和硫化物沉积物。伽玛能谱分析表明，在含硫酸钡的沉积物中，Ra-226、Ra-228及其子核的活度极高。这些沉积物是近年来热液活动形成的。(4)在Izena深层热液站点观测到液态CO2和固体气体水合物CO2。少

Geochemical studies on carbonate sediments and related materials collected mainly from submarine hydrothermal sites of Taketomijima-Island and Okinawa Trough back arc basin have been carried out. The research results are summarized as follows.[A] Taketomijima submarine hydrothermal sites:(1) Samples of carbonate sediments, hot spring water and associated gas were collected from the bottom of coral reef of Taketomijima (ca. 22m in depth) by scuba divers.(2) The carbonate sediments are composed of foraminifera test, shell or fragments of coral skeleton. The dark colored secondary carbonates covered the cavity of pores of sediments. The proportion of dolomite and content of heavy metals such as Hg, As, Sb, Ba, Fe, Mn, Cd and U are abnormally high in the dark portion.(3) The chemistry and mineralogy of sediments of Taketomijime hydrothermal site is analogous to that of Kagosima-bay which is considered to be related to the volcanic activity of the adjacent area.(4) Frequent earthquake activ … More ity has been observed from January 23, 1991 until now at Iriomotejima Island, which is located ca. 30 Km west of Taketomijima hot spot. It will be important whether Taketomijima hot spring activity and Iriomote earthquake activity are related each other or not. The water temperature, chemical composition of water and associated gas should be monitored.[B] Okinawa Trough hydrothermal sites :(1) The carbonate sediments are collected from Iheya deep of Okinawa Trough by research submersible 'SINKAI2000' in 1989 and 1990.(2) X-ray diffraction and neutron activation analysis revealed that these carbonates are mainly composed of calcite, rhodechlosite (MnCO3) and kuthonite (CaMn (CO3) 2) and rich in Mn, As, Hg, and Ag.(3) On the other hand, sulphate and sulphide sediments are collectd from Izena deep in 1989. The gamma-ray spectroscopy showed that activity of Ra-226, Ra-228 and their daughter nucleides is extremly high in barium sulphate containing sediments. These sediments are deposited by hydrothermal activity in recent years.(4) Liquid CO2 and solid gas hydrate of CO2 were observed at Izena deep hydrothermal sites. Less