Abiotic methane flux from the Chimaera seep and Tekirova ophiolites (Turkey): Understanding gas exhalation from low temperature serpentinization and implications for Mars
Abiotic methane flux from the Chimaera seep and Tekirova ophiolites (Turkey): Understanding gas exhalation from low temperature serpentinization and implications for Mars
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DOI：
10.1016/j.epsl.2011.08.001
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发表时间：
2011-10-01
影响因子：
5.3
通讯作者：
Hosgormez, Hakan
中科院分区：
文献类型：
--
作者：
Etiope, Giuseppe;Schoell, Martin;Hosgormez, Hakan
到目前为止，只有菲律宾、阿曼、新西兰和土耳其四个国家记录了蛇绿岩低温蛇纹化作用向大气中排放非生物甲烷（CH 4）。蛇纹石化作用产生大量的氢（H-2），其理论上可与CO2或CO反应以形成烃（费-托型合成，FTT）。类似的机制已经被用来解释在火星上检测到的CH 4，因此，了解地球上蛇绿岩气体的流量和呼出方式可能有助于破译火星上潜在的脱气作用。这项工作报告的第一个直接测量的气体（甲烷，二氧化碳）通量以往任何时候都在陆上蛇绿岩与现今的蛇纹石化。我们调查了土耳其Cirali的Tekirova蛇绿岩，该蛇绿岩中有Chimaera渗漏，这是一个从5000 m（2）宽蛇绿岩露头中的裂缝中流出的气体喷口系统。在该场址，每年至少有150-190吨甲烷释放到大气中。C1-C5烷烃、CO2和N-2的分子和同位素组成与源岩成熟度数据和热成因气形成模型相结合，表明主要的非生物组分（类似于80-90%）与热成因气混合。非生物富含H-2的气体可能在低于50摄氏度的温度下形成，这是由H-2的低氘/氢同位素比率（Δ D-H2：-720%4）所暗示的，与该地区的低地热梯度一致。非生物气体合成必须非常快速和有效，以连续产生相当于>100 t CH 4 yr（-1）的长期（> 2000年）排放量的气体，否则必须存在加压气体积累。在同一个蛇绿岩建造，3公里以外的嵌合体，我们检测到一个不可见的微渗漏的非生物CH 4的流量从0.07到1 g m（-2）d（-1）。在火星上，类似的通量能够维持在2003年北方夏季（10（4）或10（5）吨年（-1））在大锡尔蒂斯和尼利槽沟的广泛的橄榄石基岩和含水硅酸盐露头上明显识别出的甲烷羽流;只有一个像嵌合体一样的渗漏，或者更实际地说，一个微弱的，空间上分散的微渗漏，足以维持火星大气中的甲烷含量。(C)2011 Elsevier B. V.保留所有权利。
The emission of abiotic methane (CH4) into the atmosphere from low temperature serpentinization in ophiolitic rocks is documented to date only in four countries, the Philippines, Oman, New Zealand, and Turkey. Serpentinization produces large amounts of hydrogen (H-2) which in theory may react with CO2 or CO to form hydrocarbons (Fischer-Tropsch Type synthesis, FTT). Similar mechanisms have been invoked to explain the CH4 detected on Mars, so that understanding flux and exhalation modality of ophiolitic gas on Earth may contribute to decipher the potential degassing on Mars. This work reports the first direct measurements of gas (CH4, CO2) flux ever done on onshore ophiolites with present-day serpentinization. We investigated the Tekirova ophiolites at Cirali, in Turkey, hosting the Chimaera seep, a system of gas vents issuing from fractures in a 5000 m(2) wide ophiolite outcrop. At this site at least 150-190 t of CH4 is annually released into the atmosphere. The molecular and isotopic compositions of C-1-C-5 alkanes, CO2, and N-2 combined with source rock maturity data and thermogenic gas formation modelling suggested a dominant abiotic component (similar to 80-90%) mixed with thermogenic gas. Abiotic H-2-rich gas is likely formed at temperatures below 50 degrees C, suggested by the low deuterium/hydrogen isotopic ratio of H-2 (delta D-H2: -720%4, consistent with the low geothermal gradient of the area. Abiotic gas synthesis must be very fast and effective in continuously producing an amount of gas equivalent to the long-lasting (>2 millennia) emission of >100 t CH4 yr(-1), otherwise pressurised gas accumulation must exist. Over the same ophiolitic formation, 3 km away from Chimaera, we detected an invisible microseepage of abiotic CH4 with fluxes from 0.07 to 1 g m(-2) d(-1). On Mars similar fluxes could be able to sustain the CH4 plume apparently recognised in the Northern Summer 2003 (10(4) or 10(5) t yr(-1)) over the wide olivine bedrock and outcrops of hydrated silicates in the Syrtis Major and Nili Fossae; just one seep like Chimaera or, more realistically, a weak, spatially sporadic microseepage, would be sufficient to maintain the atmospheric CH4 level on Mars. (C) 2011 Elsevier B.V. All rights reserved.