Hydrothermal gases offshore Milos Island, Greece
Hydrothermal gases offshore Milos Island, Greece
复制标题
DOI：
10.1016/0009-2541(96)00023-x
复制
发表时间：
1996-08-27
期刊：
影响因子：
3.9
通讯作者：
Faber, E
中科院分区：
文献类型：
--
作者：
Botz, R;Stuben, D;Faber, E
热液从数英里外的古霍里湾的海底涌出。这些流体中的气体主要含有二氧化碳，但存在高达2%的甲烷浓度。二氧化碳的稳定碳同位素组成(接近千分之零)表明是无机碳源(下伏海相碳酸盐的解离)。大多数CH样品的碳和氢同位素都富含重物种(Delta(13)C=-9.4~-17.8 ppm；Delta D=-102~-189 ppm)，这被认为是通过CO2还原(Fischer-Tropsch反应)非生物生成CH4的特征。三个甲烷样品中的氘含量的贫乏(至-377‰)可能是由未知的地下岩石蚀变过程引起的。甲烷、氢和水之间的二次氢同位素交换过程很可能是计算出不切实际的甲烷形成温度的原因。我们发现，在古奥霍里湾海底浮现的热液中存在着过剩的氦，略有富含He-3。在计算过剩组分的同位素比率时，He-3/He-4(过剩)为3.6。得到了10(-6)。这表明过剩组分由大约1/3的地幔氦和2/3的放射性成因氦组成。我们推测，在流体上升到地表的过程中，地幔来源的成分被放射性成因的氦强烈稀释。
Hydrothermal fluids emerge from the seafloor of Paleohori Bay on Miles. The gases in these fluids contain mostly CO2 but CH4 concentrations up to 2% are present. The stable carbon isotopic composition of the CO2 (near 0 parts per thousand) indicates an inorganic carbon source (dissociation of underlying marine carbonates). The carbon and hydrogen isotopes of most CH samples are enriched in the heavy species (delta(13)C = -9.4 to -17.8 parts per thousand; delta D = -102 to -189 parts per thousand) which is believed to be characteristic for an abiogenic production of CH4 by CO2-reduction (Fischer-Tropsch reactions). Depletions in the deuterium content of three CH4 samples (to -377 parts per thousand) are probably caused by unknown subsurface rock alteration processes. Secondary hydrogen isotope exchange processes between methane, hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures.We show that excess helium, slightly enriched in He-3, is present in the hydrothermal fluids emerging the seafloor of Paleohori Bay. When the isotopic ratio of the excess component is calculated a He-3/He-4(excess) of 3.6 . 10(-6) is obtained. This indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium. We infer that the mantle-derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface.