Serpentinization of abyssal peridotites from the MARK area, Mid-Atlantic Ridge: Sulfur geochemistry and reaction modeling
Serpentinization of abyssal peridotites from the MARK area, Mid-Atlantic Ridge: Sulfur geochemistry and reaction modeling
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DOI：
10.1016/s0016-7037(02)01142-0
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发表时间：
2003-02-01
影响因子：
5
通讯作者：
Shanks, WC
中科院分区：
文献类型：
--
作者：
Alt, JC;Shanks, WC
对MARK（Mid-Atlantic Ridge，Kane Fracture Zone）地区蛇纹化橄榄岩的不透明矿物学、硫含量和同位素组成进行了研究，以了解蛇纹化的条件，并评估该过程作为海水硫的汇。蛇纹岩含有富硫的次生矿物组合，硫含量高（高达1wt%）δ（34）硫化物含量升高（3.7 ~ 12.7ppm）。地球化学反应模型表明，海水橄榄岩在300至400 ℃的相互作用单独不能解释高硫含量和高δ（34）S（硫化物）。这需要一个多阶段的反应，即在高温（约400 ℃）下与海水反应时，硫化物从辉长岩中浸出，随后在约300 ℃下橄榄岩的蛇纹石化过程中硫化物沉积。蛇纹石化作用产生高度还原条件和大量的H，并导致海水碳酸盐部分还原为甲烷。后者是通过在250 ℃以上的温度下形成富含C-13（高达4.5%）的碳酸盐脉来记录的。虽然不同的过程产生不同的硫同位素效应在其他海洋蛇纹岩，硫是一致的添加到深海橄榄岩在蛇纹石化。从大洋地壳和蛇绿岩钻探和疏浚的蛇纹岩数据表明，大洋橄榄岩是0.4 - 6.0 × 10（12）g海水S yr（-1）的汇。这是可比的硫交换，发生在热液系统中的镁铁质洋壳在米氏脊和脊的侧翼和金额的2%至30%的河流硫酸盐来源和沉积硫化物汇在海洋中。蛇纹岩中硫的高浓度和改变的同位素组成可能对缓慢扩张的地壳俯冲过程中的地幔交代作用具有重要意义。版权所有（C）2003 Elsevier Science Ltd.
The opaque mineralogy and the contents and isotope compositions of sulfur in serpentinized peridotites from the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) area were examined to understand the conditions of serpentinization and evaluate this process as a sink for seawater sulfur. The serpentinites contain a sulfur-rich secondary mineral assemblage and have high sulfur contents (up to 1 wt.%) and elevated delta(34)sufide (3.7 to 12.7parts per thousand). Geochemical reaction modeling indicates that seawater-peridotite interaction at 300 to 400degreesC alone cannot account for both the high sulfur contents and high delta(34)S(sulfide). These require a multistage reaction with leaching of sulfide from subjacent gabbro during higher temperature (similar to400degreesC) reactions with seawater and subsequent deposition of sulfide during serpentinization of peridotite at similar to300degreesC. Serpentinization produces highly reducing conditions and significant amounts of H, and results in the partial reduction of seawater carbonate to methane. The latter is documented by formation of carbonate veins enriched in C-13 (Up to 4.5%) at temperatures above 250degreesC. Although different processes produce variable sulfur isotope effects in other oceanic serpentinites, sulfur is consistently added to abyssal peridotites during serpentinization. Data for serpentinites drilled and dredged from oceanic crust and from ophiolites indicate that oceanic peridotites are a sink for up to 0.4 to 6.0 X 10(12) g seawater S yr (-1). This is comparable to sulfur exchange that occurs in hydrothermal systems in mafic oceanic crust at midocean ridges and on ridge flanks and amounts to 2 to 30% of the riverine sulfate source and sedimentary sulfide sink in the oceans. The high concentrations and modified isotope compositions of sulfur in serpentinites could be important for mantle metasomatism during subduction of crust generated at slow spreading rates. Copyright (C) 2003 Elsevier Science Ltd.