Unusual geochemistry of hydrothermal vents on submarine arc volcanoes: Kasuga Seamounts, Northern Mariana Arc
Unusual geochemistry of hydrothermal vents on submarine arc volcanoes: Kasuga Seamounts, Northern Mariana Arc
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海底弧火山热液喷口的异常地球化学：北马里亚纳弧春日海山
DOI：
10.1016/0012-821x(93)90080-s
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发表时间：
1993
影响因子：
5.3
通讯作者：
H. Yeh
中科院分区：
文献类型：
--
作者：
G. McMurtry;P. Sedwick;P. Fryer;D. Vonderhaar;H. Yeh
位于马里亚纳群岛北方岛弧的深海热液研究所阿尔文迪夫斯从Kasuga 2和Kasuga 3海山的顶部区域回收了温暖的热液流体，以及元素硫、铁和锰氧化物和绿脱石的热液矿床。与其他海底热液相比，从春日2海山取样的富含气体的39°C喷口流体的成分是不寻常的，因为相对于周围海水，它富含27%的Mg 2+和17%的SO 42 −，并耗尽64%的Ca 2+。溶解的二氧化碳浓度升高（根据pH值和AT计算）、HCO 3 −和SO 42+，以及几乎不含H2S，表明该样品的不寻常成分可能是由于海底下火山CO2和SO2添加到海水热液中，导致：（1）“化学风化”反应，即火成岩或蚀变相受到CO2的侵蚀，将Mg 2+和其他阳离子、Si和HCO 3 −加入溶液中;（2）SO2水解为SO 42-和S（0），向流体中加入过量的SO 42-，并产生轻微的δ 34 S信号，导致元素硫在海底喷口沉积。饱和状态计算表明，在流体中的Si和Ca 2+的浓度可以控制在饱和与无定形二氧化硅和白云石分别。从Kasuga 3收集的9.3°C流体的来源很难确定，因为它的成分接近环境海水，并显示出高温和低温海水-岩石反应的可能证据。从春日3号山顶回收了绿脱石和铁锰氧化物的带状和夹层沉积物，氧同位素地质温度测定表明绿脱石的形成温度为22°C。
DSRVAlvindives in the Northern Mariana island arc recovered warm hydrothermal fluids from the summit areas of seamounts Kasuga 2 and Kasuga 3, as well as hydrothermal deposits of elemental sulfur, Fe- and Mn-oxides, and nontronite. The composition of a gas-rich ∼ 39°C vent fluid sampled from Kasuga 2 Seamount is unusual compared to other submarine hydrothermal fluids in that it isenrichedby 27% in Mg2+and 17% in SO42−, anddepletedby 64% in Ca2+, relative to ambient seawater. The elevated concentrations of dissolved CO2(calculated from pH andAT), HCO3−and SO42+, and near absence of H2S, suggest that the unusual composition of this sample may result from the sub-seafloor addition of volcanic CO2and SO2to a seawater-derived hydrothermal fluid, resulting in: (1) ‘chemical weathering’ reactions, whereby igneous minerals or alteration phases are attacked by CO2, adding Mg2+and other cations, Si, and HCO3−into solution; and (2) hydrolysis of SO2to SO42−and S(0), adding excess SO42−with a light δ34S signature to the fluid and causing deposition of elemental sulfur at the seafloor vents. Saturation-state calculations suggest that the concentrations of Si and Ca2+in the fluid may be controlled at saturation with amorphous silica and dolomite respectively. The origin of the 9.3°C fluid collected from Kasuga 3 is difficult to determine because it is compositionally close to ambient seawater and shows possible evidence of both high- and low-temperature seawater-rock reaction. Banded and interlayered deposits of nontronite and Fe- and Mn-oxides were recovered from the Kasuga 3 summit, with oxygen-isotope geothermometry suggesting a formation temperature of ∼ 22°C for the nontronite.