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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Massive barite deposits and carbonate mineralization in the Derugin Basin, Sea of Okhotsk: precipitation processes at cold seep sites
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Massive barite deposits and carbonate mineralization in the Derugin Basin, Sea of Okhotsk: precipitation processes at cold seep sites

机译：鄂霍次克海Derugin盆地中大量的重晶石矿床和碳酸盐矿化：冷渗漏点的降水过程

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摘要

An area of massive barite precipitations was studied at a tectonic horst in 1500 m water depth in the Derugin Basin, Sea of Okhotsk. Seafloor observations and dredge samples showed irregular, block- to column-shaped barite buildups up to 10 m high which ere scattered over the seafloor along an observation track 3.5 km long. High methane concentrations in the water column show that methane expulsion and probably carbonate precipitation is a recently active process. Small fields of chemoautotrophic clams (Calyptogena sp., Acharax sp.) at the seafloor provide additional evidence for active fluid venting. The white to yellow barites show a very porous and often layered internal fabric, and are typically covered by dark-brown Mn-rich sediment; electron microprobe spectroscopy measurements of barite sub-samples show a Ba substitution of up to 10.5 mol% of Sr. Rare idiomorphic pyrite crystals (～1%) in the barite fabric imply the presence of H_2S. This was confirmed by clusters of living chemoautotrophic tube worms (1 mm in diameter) found in pores and channels within the barite. Microscopic examination showed that micritic aragonite and Mg-calcite aggregates or crusts are common authigenic precipitations within the barite fabic. Equivalent micritic carbonates and barite carbonate cemented worm tubes were recovered from sediment cores taken in the vicinity of the barite build-up area. Negative δ~(13)C values of these carbonates (> -43.5‰ PDB) indicate methane as major carbon source; δ~(18)O values between 4.04 and 5.88‰ PDB correspond to formation temperatures, which are certainly below 5℃. One core also contained shells of Calyptogena sp. at different core depths with ~(14)C-ages ranging from 20680 to > 49080 yr. Pore water analyses revealed that fluids also contain high amounts of Ba; they also show decreasing SO_4~(2-) concentrations and a parallel increase of H_2S with depth. Additionally, S and O isotope data of barite sulfate (δ~(34)S: 21.0-38.6‰ CDT; δ~(18)O: 9.0-17.6‰ SMOW) strongly point to biological sulfate reduction processes. The isotope ranges of both S and O can be exclusively explained as the result of a mixture of residual sulfate after a biological sulfate reduction and isotopic fractionation with 'normal' seawater sulfate. While massive barite deposits are commonly assumed to be of hydrothermal origin, the assemblage of cheomautotrophic clams, methane-derived carbonates, and non-thermally equilibrated barite sulfate strongly implies that these barites have formed at ambient bottom water temperatures and form the features of a Giant Cold Seep setting that has been active for at least 49000 yr.
机译：在鄂霍次克海德鲁金盆地的水深1500 m的构造地壳中研究了大量重晶石沉淀区域。海底观测和挖泥样品显示不规则，块状至柱状的重晶石堆积物，高达10 m高，它们沿着3.5公里长的观测轨迹散布在海底。水柱中较高的甲烷浓度表明，甲烷排放以及可能的碳酸盐沉淀是最近活跃的过程。海底的化学自养蛤fields（Calyptogena sp。，Acharax sp。）的小区域为主动排泄流体提供了额外的证据。白色至黄色的重晶石显示出非常多孔的内部织物，通常是分层的，并且通常被深棕色的富含锰的沉积物所覆盖。重晶石子样品的电子微探针光谱测量表明，Ba置换占Sr的10.5 mol％。重晶石织物中的稀有亚纯黄铁矿晶体（〜1％）表明存在H_2S。在重晶石的孔和通道中发现的成群的化学自养管蠕虫（直径1毫米）证实了这一点。显微镜检查表明，在重晶石辉长岩中，闪粉性文石和镁方解石聚集体或地壳是常见的自生沉淀。从重晶石堆积区附近采集的沉积物岩心中回收了同等的碳酸盐碳酸盐岩和重晶石碳酸盐胶结蜗杆。这些碳酸盐（> -43.5‰PDB）的δ〜（13）C负值表明甲烷是主要碳源。 PDB的δ〜（18）O值在4.04至5.88‰之间，对应地层温度，肯定低于5℃。一个核还包含Calyptogena sp。的壳。 〜（14）C年龄范围从20680到> 49080 yr处于不同的岩心深度。孔隙水分析表明，流体中还含有大量的Ba; Ba含量较高。它们还显示出SO_4〜（2-）浓度降低，H_2S随深度平行增加。另外，重晶石硫酸盐（δ〜（34）S：21.0-38.6‰CDT;δ〜（18）O：9.0-17.6‰SMOW）的S和O同位素数据强烈指出了生物硫酸盐的还原过程。 S和O的同位素范围可以专门解释为生物硫酸盐还原和“常规”海水硫酸盐的同位素分馏后残留硫酸盐的混合物的结果。通常认为块状重晶石沉积物是热液来源的，化肥自生蛤，甲烷衍生的碳酸盐和非热平衡重晶石硫酸盐的组合强烈暗示这些重晶石是在周围底部水温下形成的，并形成巨人的特征。已激活至少49000年的冷渗漏设置。

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