Fluid Infiltration Through Oceanic Lower Crust in Response to Reaction Induce d Fracturing: Insights From Serpentinized Troctolite and Numerical Models
Fluid Infiltration Through Oceanic Lower Crust in Response to Reaction Induce d Fracturing: Insights From Serpentinized Troctolite and Numerical Models
复制标题
流体渗透穿过海洋下地壳对反应引起的断裂的响应：来自蛇纹石化和数值模型的见解
DOI：
10.1029/2020jb020268
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
and Oman Drilling Project Phase Science Party
中科院分区：
文献类型：
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作者：
Kazuki Yoshida;Atsushi Okamoto;Hiroyuki Shimizu;Ryosuke Oyanagi,Noriyoshi Tsuchiya;and Oman Drilling Project Phase Science Party
流体穿透辉长岩下地壳的机制对大洋岩石圈的水化作用具有重要意义。在阿曼蛇绿岩中，保存了在快速扩张的山脊上形成的整个大洋岩石圈序列，层状辉长岩和英安岩层广泛地蛇纹岩。本文描述了从阿曼钻探项目CM1a遗址中发现的蛇纹岩和橄榄辉长岩的特征结构。在沸石中，橄榄石网状结构普遍发育，并以两种类型的矿脉为特征：早期蜥蜴石+新水镁石+新磁铁矿和晚期富铝荔枝石+新磁铁矿。这些矿脉表明在350℃时蛇纹岩开始形成，并在蛇纹岩的后期阶段从斜长石中获得硅和铝的供应。蛇纹化橄榄石颗粒周围的斜长石通常表现为放射状破裂。应用离散元方法对流体流动、反应和破裂的耦合进行了数值模拟，结果表明，蛇纹化过程中橄榄石颗粒的体积膨胀导致橄榄石及其周围斜长石同时破裂，大洋岩石圈冷却过程中的热应力也可能在蛇纹岩化之前导致优先的橄榄石破裂。模拟还预测了一个连接橄榄石颗粒的自组织裂隙网络，并穿过富含橄榄石和贫橄榄石的层，导致在蛇纹岩作用期间渗透率增加。我们的结果表明，反应诱导破裂在海水通过下地壳渗入大洋岩石圈内的地幔中起着至关重要的作用。
The mechanisms of fluid penetration through the gabbroic lower crust are important for the hydration of oceanic lithosphere. In the Oman ophiolite, which preserves an entire sequence of oceanic lithosphere formed at a fast‐spreading ridge, the layered gabbros and dunites are extensively serpentinized. In this paper, we describe the characteristic textures of serpentinized troctolite and olivine gabbros recovered from the CM1A site of the Oman Drilling Project. In the troctolite, an olivine mesh texture is pervasively developed and is characterized by two types of veins: early lizardite + brucite + magnetite and late Al‐rich lizardite + magnetite. These veins suggest the initiation of serpentinization at <350°C and a supply of Si and Al from plagioclase during the later stages of serpentinization. Plagioclase surrounding serpentinized olivine grains commonly shows radial fracturing. Numerical simulations using the discrete element method applied to coupled fluid flow, reaction, and fracturing reveal that volume expansion of olivine grains during serpentinization results in the simultaneous fracturing of olivine and surrounding plagioclase, and that the thermal stress during cooling of oceanic lithosphere might also cause preferential olivine fracturing prior to serpentinization. The simulations also predict a self‐organizing fracture network that connects the olivine grains and passes through both olivine‐rich and olivine‐poor layers, resulting in permeability enhancement during serpentinization. Our results suggest that reaction‐induced fracturing plays an essential role in the infiltration of seawater through the lower crust and into the mantle within oceanic lithosphere.