During the DY105-12, 14cruise (R/V DAYANG YIHAO, November 2003) on East Pacific Rise (EPR) 12-13°N, the submarine hydrothermal activity was investigated and the CTD hydrocast was carried out at EPR12°39''N—12°54''N. From the temperature anomalies and the concentrations of magnesium, chlorine, bromine in seawater samples, we discover that magnesium depletes 9.3%—22.4%, chlorine and bromine enrich 10.3%—28.7% and 10.7%—29.0% respectively relative to normal seawater at the stations which have chemistry anomalies, moreover temperature and chemistry anomalies are at the same layer. The depletion of magnesium in the plume may be caused by a fluid lacking of magnesium which rises after the hydrothermal fluid reaches the equilibrium with ambient seawater, the enrichment of chlorine and bromine might be the result of inputting later brine which is generated by phase separation due to hydrothermal activity. In addition, the Br/CI ratio in the abnormal layers at the survey area is identical to that in seawater, which implies that halite dissolution (or precipitation) occurs neither when the fluid is vented nor when hydrothermal fluid entraining ambient seawater rises to form plume. From the abnormal instance at E55 station, it is very possible that there might exist a new hydrothermal vent site.
WANG XiaoYuan1,2, ZENG ZhiGang1, LIU ChangHua1,2, YIN XueBo1, YU ShaoXiong1,2, YUAN ChunWei1,2, ZHANG GuoLiang1,2 & WANG XiaoMei1,2 1 Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Acadamy of Sciences, Qingdao 266071, China
Analyses of rare earth and trace element concentrations of native sulfur samples from the Kueishantao hydrothermal field were performed at the Seafloor Hydrothermal Activity Laboratory of the Key Labo-ratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences. Using an Elan DRC II ICP-MS, and combining the sulfur isotopic compositions of native sulfur samples, we studied the sources and formation of a native sulfur chimney. The results show, when comparing them with native sulfur from crater lakes and other volcanic areas, that the native sulfur content of this chimney is very high (99.96%), the rare earth element (REE) and trace element constituents of the chimney are very low (ΣREE<21×10?9), and the chondrite-normalized REE patterns of the native sulfur samples are similar to those of the Kueishantao andesite, implying that the interaction of subseafloor fluid-andesite at the Kueishantao hydrothermal field was of short duration. The sulfur isotopic compo-sitions of the native sulfur samples reveal that the sulfur of the chimney, from H2S and SO2, originated by magmatic degassing and that the REEs and trace elements are mostly from the Kueishantao ande-site and partly from seawater. Combining these results with an analysis of the thermodynamics, it is clear that from the relatively low temperature (<116 ℃ ), the oxygenated and acidic environment is favorable for formation of this native sulfur chimney in the Kueishantao hydrothermal field.
ZENG ZhiGang1, LIU ChangHua1,2, CHEN ChenTung A3, YIN XueBo1, CHEN DaiGeng1,2, WANG XiaoYuan1,2, WANG XiaoMei1,2 & ZHANG GuoLiang1,2 1 Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
