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西太平洋典型弧后盆地的地质构造、岩浆作用与热液活动
曾志刚,张玉祥,陈祖兴,马瑶,王晓媛,张丹丹,李晓辉
中国科学院海洋研究所海洋地质与环境重点实验室;青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室,中国科学院海洋研究所海洋地质与环境重点实验室; 中国科学院大学,中国科学院海洋研究所海洋地质与环境重点实验室;中国科学院大学,中国科学院海洋研究所海洋地质与环境重点实验室,中国科学院海洋研究所海洋地质与环境重点实验室;青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室,中国科学院海洋研究所海洋地质与环境重点实验室; 中国科学院大学,中国科学院海洋研究所海洋地质与环境重点实验室;中国科学院大学
摘要:
研究了西太平洋典型弧后盆地冲绳海槽和马努斯海盆的区域地质背景、岩浆岩、喷口流体、热液柱、沉积物以及多金属硫化物。结果表明,冲绳海槽在构造和地球物理特征上南北分异,从北向南地壳厚度减薄,南部重力异常变化大,发育条带状磁异常,中部则具有最高的热流值。马努斯海盆的重力异常变化较小,磁力异常呈东西向展布,海底扩张中心附近出现磁异常条带。马努斯海盆已出现洋壳,冲绳海槽的地壳属于过渡性地壳,在中南部的地堑中可能已出现洋壳。 冲绳海槽与马努斯海盆玄武岩的岩浆是由地幔源区部分熔融产生的原始岩浆与板块俯冲组分混合构成。中酸性岩与基性岩具有相同的岩浆物质来源,是玄武质岩浆结晶分异的产物。与马努斯海盆火山岩相比,冲绳海槽火山岩存在不同程度的地壳混染。 冲绳海槽的喷口流体为富含金属元素(Mn、Fe、Zn、Pb)的酸性高温(高达320 °C)流体,其热液柱中的Zn2 、Cd2 、Pb2 、Cu2 离子浓度明显高于正常海水。马努斯海盆的热液柱呈现出CH4、Mn、Al、δ3He正异常及pH负异常的特征。与马努斯海盆PACMANUS热液区的喷口流体(220–276 °C、pH = 2.5–3.5)相比,DESMOS热液区的喷口流体温度(≥88–120 °C)相对较低,酸性更强(pH ≤ 2.1),二者较低的δ34SH2S和δD值表明岩浆演化过程中有酸性挥发分进入岩浆流体。冲绳海槽与马努斯海盆含金属沉积物的分布及其元素含量特征具有差异,相应地,两个弧后盆地含金属沉积物中的微生物群落也不同。冲绳海槽和马努斯海盆热液区均具富Zn型、Ba-Pb-Zn型、Si-硫化物型和Si-硫化物-硫酸盐型热液产物。与冲绳海槽的多金属硫化物相比,马努斯海盆中多金属硫化物的Pb和Au含量较低。
关键词:  海底热液活动  岩浆作用  地质构造  冲绳海槽  马努斯海盆  弧后盆地
DOI:10.12036/hykxjk20160725003
分类号:
基金项目:中国科国家重点基础研究发展计划(973计划)(编号:2013CB429700);国家杰出青年科学基金(编号:41325021),中国科学院战略性先导科技专项(编号:XDA11030302),泰山学者工程专项和青岛海洋科学与技术国家实验室鳌山人才计划项目经费资助
Geological Tectonics, Magmatism and Seafloor Hydrothermal Activity in the Back-Arc Basins of the Western Pacific
Zeng Zhigang,Zhang Yuxiang,Chen Zuxing,Ma Yao,Wang Xiaoyuan,Zhang Dandan and Li Xiaohui
CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; University of Chinese Academy of Sciences,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; University of Chinese Academy of Sciences,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; University of Chinese Academy of Sciences,CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Abstract:
The regional geological setting, magmatic rock, vent fluid, hydrothermal plume, metalliferous sediment and polymetallic sulfide of the Okinawa trough and the Manus basin in the western Pacific have been studied. The Okinawa Trough has different tectonic and geophysical characteristics from the north to the south with crustal thickness decreases. The southern part of the trough shows variable gravity anomalies and linear magnetic anomalies, while the middle part has the highest heat flow value. The gravity anomalies in the Manus Basin show small variations while the magnetic anomalies show a pronounced E-W trend, and there exist linear magnetic anomalies near the seafloor-spreading center. Oceanic crust has already appeared in the Manus Basin, while the most part of the crust in the Okinawa Trough belongs to transitional crust, and oceanic crust probably appears in some grabens in the middle and southern part. The magma source of basalts from Okinawa trough and Manus basin are both formed by partial melting of mantle source and mixed with subduction composition. Intermediate-acid volcanic rocks with the same magma source of basalt, are products of crystallization differentiation of the basaltic magma. Compared to Manus basin volcanic rocks, volcanic rocks in the Okinawa trough are affected by different degree of crustal contamination. Vent fluid in Okinawa Trough was high temperature (up to 320℃), acid fluid and enriched in metal elements (e.g., Mn, Fe, Zn and Pb). Concentration of Zn2 , Cd2 , Pb2 and Cu2 in hydrothermal plume of Okinawa Trough was significantly higher than that in seawater. The Manus hydrothermal plume showed positive CH4, Mn, Al and δ3He anomalies and a negative pH anomaly. Compared with the vent fluid (220-276°C, pH=2.5-3.5) of PACMANUS hydrothermal field, the vent fluid of DESMOS hydrothermal field was lower temperature (≥88-120℃) and more acid (pH≤2.1). The lower values of δ34SH2S and δD implied the mixing of acid volatile component and magmatic fluid. The distribution and element concentrations of the metalliferous sediments from the Okinawa trough and the Manus basin are different, and the microbial community in the metalliferous sediments from the two areas aslo are different. The hydrothermal products were divided into four types: Zn-rich type, Ba-Pb-Zn type, Si-sulfide type and Si-sulfide-sulfate type in the Okinawa trough and the Manus basin. The Pb and Au concentrations of the polymetallic sulfides in the Manus basin are significantly lower than that in the Okinawa trough.
Key words:  Seafloor hydrothermal activity  magmatism  geological tectonics  Okinawa trough  Manus basin  back-arc basins
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