论文部分内容阅读
本文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源区地幔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Zn~(2+)、Cd~(2+)、Pb~(2+)、Cu~(2+)离子浓度明显高于正常海水。马努斯海盆的热液柱呈现出CH_4、Mn、Al、δ~3He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或120°C以上)相对较低,酸性更强(pH≤2.1),二者较低的δ~(34)S_(H_2S)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。
In this paper, we study the regional geological background, magmatic rocks, jet fluid, hydrothermal column, sediments and polymetallic sulphides in the Okinawa Trough and Manus Basin in the Western Central Pacific. The results show that the Okinawa Trough is characterized by north-south divergence in structure and geophysical characteristics. The thickness of the crust decreases from north to south. The gravity anomalies in the southern part of the Okinawa Trough change greatly. Magnetic anomalies are developed in the strip and the highest in the middle. The gravity anomalies in the Manus Basin are small, with anomalous magnetic anomalies extending east-west and magnetic anomalies appearing near the seafloor spreading centers. The oceanic crust has emerged in the Manus Basin, and the crust in the Okinawa Trough is a transitional crust that may have appeared in the graben in the central and southern parts of the country. The magma in the Okinawa Trough and Manus Basin basalts is composed of primitive magma and plate subduction components that are partially melted by the mantle of the source area. The acidic rocks and mafic rocks have the same source of magmatic material and are the product of crystallization differentiation of basaltic magmas. Compared with the Manus Basin volcanic rocks, there are some crustal contamination in the Okinawa Trough volcanic rocks. The spout fluid in the Okinawa Trough is acidic high temperature (up to 320 ° C) fluid rich in metal elements (Mn, Fe, Zn, Pb). The Zn 2+, Cd 2+ , Pb ~ (2 +) and Cu ~ (2+) were significantly higher than normal seawater. The hydrothermal column of the Manus Basin shows the features of positive anomalies CH_4, Mn, Al, δ ~ 3He and negative pH anomalies. Compared with the nozzle fluid (220 ~ 276 ° C, pH = 2.5 ~ 3.5) in the MANMAN basin PACMANUS hydrothermal zone, the temperature of the nozzle fluid in the DESMOS hydrothermal zone (88-120 ° C or above 120 ° C) Low and acidic (pH≤2.1). The lower values of δ ~ (34) S_ (H_2S) and δD indicate that there are acidic volatiles into the magmatic fluid during magmatic evolution. There are differences in the distribution of metal-bearing sediments and their elemental contents in the Okinawa Trough and the Manus Basin. Correspondingly, the microbial communities in the metal-bearing sediments of the two backarc basins are also different. The Okinawa Trough and Manus Basin hydrothermal zones are characterized by Zn-rich, Ba-Pb-Zn, Si-sulfide and Si-sulfide-sulfate hydrothermal products. Compared to the polymetallic sulphides in the Okinawa Trough, the Pb and Au concentrations of polymetallic sulphides in the Manus Basin are low.