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首页> 外文期刊>Contributions to Mineralogy and Petrology >Serpentinization, element transfer, and the progressive development of zoning in veins: evidence from a partially serpentinized harzburgite
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Serpentinization, element transfer, and the progressive development of zoning in veins: evidence from a partially serpentinized harzburgite

机译：蛇纹石化，元素转移和静脉区划的逐步发展：部分蛇纹石化的Harzburgite的证据

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Serpentinization is an important geochemical process that affects the chemistry and petrophysical properties of the oceanic lithosphere and supports life through abiogenic formation of hydrogen. Here, we document through detailed mineralogical evidence and equilibrium thermodynamic models the importance of water (H2O) and silica (SiO2) activities on mineral assemblages produced during progressive serpentinization of a harzburgite. We describe a harzburgite from the Santa Elena Ophiolite in Costa Rica that is similar to 30 % serpentinized. Serpentine + brucite +/- magnetite veins occur in olivine, Al-rich serpentine + talc veins occur in orthopyroxene, and Al-rich serpentine +/- talc +/- brucite veins occur at the boundary of orthopyroxene and olivine. Bulk vein chemistry and element distribution maps demonstrate distinct chemical zonations within veins and chemical gradients between orthopyroxene- and olivine-dominated areas. Specifically, the sample records (1) varying brucite composition depending on whether or not it is associated with magnetite, (2) formation of magnetite from Fe-rich brucite (+/- Fe-rich serpentine) during olivine hydration, where magnetite coexists with brucite Mg#96 and serpentine Mg#99, (3) chemical gradients in Si, Al, Cr, and Ca within and between orthopyroxene- and olivine-hosted veins, and 4) local (different) equilibrium assemblages within different zones of veins. The studied sample preserves rarely observed textures documenting continuous replacement of olivine, rather than individual vein generations and overprinting that is typically observed in more intensely serpentinized peridotites. Furthermore, the presence of a discrete sequence of vein textures and mineralogy allows direct comparison between mineral textures and equilibrium thermodynamic models and permits new insights into mineral reactions during serpentinization.
机译：蛇纹石化是一个重要的地球化学过程，它会影响海洋岩石圈的化学和岩石物理特性，并通过非生物形成氢来维持生命。在这里，我们通过详细的矿物学证据和平衡热力学模型证明了水（H2O）和二氧化硅（SiO2）活性对于在逐步蛇纹石化蛇纹石过程中产生的矿物组合的重要性。我们描述了哥斯达黎加的圣埃琳娜蛇绿蛇纹石的蛇纹石，类似于蛇纹石的30％。蛇纹石+水镁石+/-磁铁矿脉出现在橄榄石中，富铝蛇纹石+滑石脉出现在邻辉石中，富铝蛇纹石+/-滑石+/-水镁石脉出现在邻辉石和橄榄石的边界处。体静脉化学和元素分布图显示出在静脉内的不同化学区带以及在邻苯二酚和橄榄石为主的区域之间的化学梯度。具体而言，样品记录（1）取决于是否与磁铁矿相关的水镁石成分，（2）橄榄石水化过程中富铁水镁石（+/-铁富集的蛇纹石）形成的磁铁矿与磁铁矿共存。水镁石Mg＃96和蛇纹石Mg＃99，（3）邻苯二甲醚和橄榄石寄主静脉内和之间的Si，Al，Cr和Ca中的化学梯度，以及4）不同静脉区域内的局部（不同）平衡组合。所研究的样品保留了很少观察到的纹理，这些纹理记录了橄榄石的连续替换，而不是通常在更强烈蛇纹石化的橄榄岩中通常观察到的单个静脉生成和叠印。此外，静脉纹理和矿物学的离散序列的存在允许在矿物纹理和平衡热力学模型之间进行直接比较，并允许在蛇纹石化过程中对矿物反应提供新的见解。

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