Serpentinization of mantle peridotites has first order effects on the rheology and tectonic behavior of the oceanic lithosphere, on the global water cycle, and on the biosphere at mid-oceanic ridges. Investigating serpentinization of abyssal peridotites is limited by the scarce occurrences of peridotites at or close to the ocean floor at slow and ultra-slow ridge environments where peridotite is exposed by long-lived detachments. The processes controlling hydration of the upper mantle below a thick magmatic crust at fast spreading ridges are poorly constrained. Here we present results based on samples from cores drilled in peridotites from the Samail ophiolite obtained during the Oman Drilling Project. We describe an early generation of highly localized brittle faults ubiquitous through all the peridotite cores and investigate their relation to the main serpentinization event represented by mesh-textured serpentinites. We combine microstructural observations with mineral and bulk chemical analyses as well as oxygen isotope microanalyses obtained by secondary ion mass spectrometry (SIMS). Asymmetric wall rock damage, weakening of crystal preferred orientation (CPO) in small fault clasts, and intense fragmentation within the fault zones even in association with very small displacements suggest that the early stage faults represent seismic events and predate mesh formation. Hydration and mesh texture formation follows in the wake of this faulting. Serpentinization is associated with moderate enrichment of fluid mobile elements including B, Li, Rb and U, indicative of fluid rock interaction characterized by relatively low fluid/rock ratios. This is consistent with a scenario where serpentinization took place below a thick magmatic crust following an earthquake-induced permeability increase. The oxygen isotope compositions of mesh serpentine are consistent with off-axis serpentinization at temperatures in the range 200-250 °C

地幔橄榄岩的蛇纹石化对大洋岩石圈、全球水循环和大洋中脊生物圈的流变学和构造行为具有一级影响。研究深海橄榄岩的蛇纹石化受到在缓慢和超缓慢的山脊环境中橄榄岩在海底或靠近海底的稀少出现的限制，在这些环境中橄榄岩被长寿命的拆离所暴露。控制快速扩张脊处厚岩浆地壳下方上地幔水化的过程很少受到限制。在这里，我们展示了基于在阿曼钻探项目期间获得的 Samail 蛇绿岩橄榄岩中钻探的岩心样本的结果。我们描述了遍及所有橄榄岩岩心的早期高度局部化脆性断层，并研究了它们与以网状纹理蛇纹岩为代表的主要蛇纹石化事件的关系。我们将微观结构观察与矿物和大宗化学分析以及通过二次离子质谱 (SIMS) 获得的氧同位素微观分析相结合。不对称围岩损坏、小断层碎屑中晶体择优取向 (CPO) 的减弱以及断层带内的强烈破碎甚至与非常小的位移有关，这表明早期断层代表地震事件并早于网格形成。在此断层之后，水化和网状纹理的形成随之而来。蛇纹石化与流体流动元素的适度富集有关，包括 B、Li、Rb 和 U，表示以相对较低的流体/岩石比为特征的流体岩石相互作用。这与地震引起的渗透率增加后在厚岩浆地壳下发生蛇纹石化的情况一致。网状蛇纹石的氧同位素组成与在 200-250 温度范围内的离轴蛇纹石化一致 ℃