Geological background of the Kairei and Edmond hydrothermal fields along the Central Indian Ridge: Implications of their vent fluids' distinct chemistry
Geological background of the Kairei and Edmond hydrothermal fields along the Central Indian Ridge: Implications of their vent fluids' distinct chemistry
复制标题
DOI：
10.1111/j.1468-8123.2008.00223.x
复制
发表时间：
2008-11-01
期刊：
影响因子：
1.7
通讯作者：
Takai, K.
中科院分区：
文献类型：
--
作者：
Kumagai, H.;Nakamura, K.;Takai, K.
富含氢的热液区，如印度洋的热液区，可能对地球上生命的早期演化产生了影响，因此引起了人们的兴趣，因为它们可能是古代生态系统的代表。印度洋的Karei和Edmond热液区相距160公里，但表现出不同的流体化学：Karei流体富含氢; Edmond流体贫氢。在这一区域，中印度洋脊显示出中等的扩张速率，48毫米年（-1）的全速率，在那里的热液场发生。Karei油田喷口流体显示出持续高浓度的H-2。在富氢热液区中，海雷田似乎是独一无二的：大多数类似的富氢热液活动发生在沿着缓慢扩张的山脊，< 40 mm年（-1）。对Karei和Edmond热液田的地质和构造方面进行了研究，试图阐明对制氢的地质限制。从潜水器上对海雷附近海底进行的目视观测显示，在喷口区15公里范围内暴露出富含橄榄石的深成岩石和橄榄石辉长岩-橄榄岩-纯橄榄岩组合，在大洋核杂岩上有蛇纹石化超镁铁质地幔岩。OCC地区可能是产生富H-2喷口流体的海雷热液活动的补给带。Karei油田30公里范围内混乱的海底反映了那里持续了100万年的岩浆匮乏状况。不对称的地磁和重力异常附近的Karei字段可以用来推断，斑片状富含橄榄石的侵入体分散在地幔超镁铁岩，渗透海水与岩浆和超镁铁岩或富含橄榄石的岩石反应。围绕Karei气田的非均匀最上层岩石圈包含浅的富含橄榄石的岩石相，通过蛇纹化作用向喷口流体提供了丰富的H-2。富氢的Karei气田由玄武岩承载，富含镁铁质-超镁铁质橄榄石岩性;普通的贫氢埃德蒙气田由正常玄武岩岩性承载。这里报告的两个领域的对比地球化学特征也可以在年轻地球的古老岩石中找到。这表明，岩石控制的氢生成可能已经运行了很长一段时间，并与地球上生命的起源有关。
Hydrogen-rich hydrothermal areas, such as those in the Indian Ocean, may have had an influence on early evolution of life on Earth and thus have attracted interest because they may be a proxy for ancient ecosystems. The Kairei and Edmond hydrothermal fields in the Indian Ocean are separated by 160 km, but exhibit distinct fluid chemistry: Kairei fluids are hydrogen-rich; Edmond fluids are hydrogen-poor. At this region, the Central Indian Ridge shows an intermediate spreading rate, 48 mm year(-1) as full rate, where the hydrothemal fields occur. Kairei field vent fluids show persistently high concentrations of H-2. The Kairei field seems to be unique among hydrogen-enriched hydrothermal regions: most similar hydrogen-rich hydrothermal activity occurs along slowly spreading ridge, < 40 mm year(-1). The geological and tectonic aspects of the Kairei and Edmond hydrothermal fields were studied to try to elucidate geological constraints on hydrogen production. Visual observations of the seafloor near Kairei from a submersible revealed olivine-rich plutonic rocks with olivine gabbro-troctolite-dunite assemblages exposed within 15 km of the vent field, with serpentinized ultramafic mantle rocks on the Oceanic Core Complex (OCC). The OCC area might be a recharge zone of Kairei hydrothermal activity producing H-2-rich vent fluids. The chaotic seafloor within 30 km of the Kairei field reflects a magma-starved condition persisting there for 1 Myr. Asymmetric geomagnetic and gravity anomalies near the Kairei field can be used to infer that patchy olivine-rich intrusions are scattered within mantle ultramafics, where infiltrated seawater reacts with magma and ultramafic rocks or olivine-rich rocks. The heterogeneous uppermost lithosphere containing shallow olivine-rich rock facies surrounding the Kairei field provides abundant H-2 into the vent fluid through serpentinization. The hydrogen-rich Kairei field is hosted by basalt, with mafic-ultramafic olivine-rich lithology; the ordinary, hydrogen-poor Edmond field is hosted by a normal basaltic lithology. The contrasting geochemical signatures of the two fields reported here can also be found in ancient rocks from a juvenile Earth. This suggests that lithology-controlled generation of hydrogen may have operated for a long time and be relevant to the origin of life on Earth.