The origin of ancient banded iron formation （BIF） has remained unclear for a long time. How the precipitation process occurred and what the environmental condition was have been widely discussed among scientists, because the period when the major BIFs deposited （-2.8 to 1.8Ga） is the same time when biosphere and atmosphere significantly changed. Based on the discovery of modern seafloor hydrothermal vents, it is possible that reductive environment controlled by vent system is related to the environment where BIF was deposited. According to matter source.
热液羽流的扩散过程常常记录于其下的热液沉积物中。研究热液羽流的沉积学记录有利于在现代洋底寻索所动热液喷口的位置,甚至还可为陆地类似成因矿床的发现提供有价值的线索。本文报道了来自Juan de Fuca洋脊(Jd FR)Endeavour段的8个按规律采样的羽流末端沉积物样品的矿物学和地球化学分析结果。分步化学淋滤结果表明,热液来源物质直接对于该沉积物的贡献最少为23.03–33.
The rare earth element(REE)geochemistry of hydrothermal vent systems has been investigated intensively,but few studies have been carried out on marine shallow-water hydrothermal systems like that at Kueishantao.Here we present novel data sets of REE in hydrothermal fluids from Kueishantao,off northeastern Taiwan.The total REE(REE)concentrations of yellowish fluids are similar to those of whitish fluids,813–1212 ng/L,and are significantly higher than that of ambient seawater.The yellowish fluids have chondrite-normalized REE(REEN)distribution patterns with slight convex-downward curvatures at Eu;and the REE patterns of the whitish fluids are smooth at Eu,which is related to the lower temperature and more oxidizing conditions.The Kueishantao hydrothermal fluids are slightly enriched in light REE(La-Nd)relative to the heavy REE(Gd-Lu).The behaviors of REE in both yellowish and whitish fluids are affected by the short time of water-rock interaction.The REE distributions in the yellowish fluids are also affected by very low pH(2.81 and 2.29),boiling of the fluid and precipitation of native sulfur.In the whitish fluids,adsorption by small particles and formation of REE-chloride complexes has played a role in the distribution of REE.
WANG XiaoYuanZENG ZhiGangCHEN ShuaiYIN XueBoCHEN Chen-Tung Arthur
