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首页> 外文期刊>Contributions to Mineralogy and Petrology >Reaction-induced grain boundary cracking and anisotropic fluid flow during prograde devolatilization reactions within subduction zones
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Reaction-induced grain boundary cracking and anisotropic fluid flow during prograde devolatilization reactions within subduction zones

机译：在俯冲区内促进脱挥发反应期间的反应诱导的晶粒边界裂纹和各向异性流体流动

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摘要

Devolatilization reactions during prograde metamorphism are a key control on the fluid distribution within subduction zones. Garnets in Mn-rich quartz schist within the Sanbagawa metamorphic belt of Japan are characterized by skeletal structures containing abundant quartz inclusions. Each quartz inclusion was angular-shaped, and showed random crystallographic orientations, suggesting that these quartz inclusions were trapped via grain boundary cracking during garnet growth. Such skeletal garnet within the quartz schist formed related to decarbonation reactions with a positive total volume change (Delta V-t > 0), whereas the euhedral garnet within the pelitic schists formed as a result of dehydration reaction with negative Delta V-t values. Coupled hydrological-chemical-mechanical processes during metamorphic devolatilization reactions were investigated by a distinct element method (DEM) numerical simulation on a foliated rock that contained reactive minerals and non-reactive matrix minerals. Negative Delta V-t reactions cause a decrease in fluid pressure and do not produce fractures within the matrix. In contrast, a fluid pressure increase positive Delta V-t reactions results in hydrofracturing of the matrix. This fracturing preferentially occurs along grain boundaries and causes episodic fluid pulses associated with the development of the fracture network. The precipitation of garnet within grain boundary fractures could explain the formation of the skeletal garnet. Our DEM model also suggests a strong influence of reaction-induced fracturing on anisotropic fluid flow, meaning that dominant fluid flow directions could easily change in response to changes in stress configuration and the magnitude of differential stress during prograde metamorphism within a subduction zone.
机译：在翼展变质期间的脱挥石反应是俯冲区域内的流体分布的关键控制。日本Sanbagawa变质带内的富含Mn的石英血清中风的装饰物的特点是含有丰富的石英夹杂物的骨架结构。每个石英夹杂物是角形的，并且显示出随机结晶取向，表明这些石英夹杂物通过石榴石生长期间通过晶界开裂被捕获。在与阳性总体积变化（Delta V-T> 0）的脱碳反应中形成的石英肌肉内的这种骨骼石榴石，而由于与负二ΔV-T值的脱水反应形成的骨质色肌内的Euhedral石榴石。通过对叶片岩石上的不同元素法（DEM）数值模拟来研究变质脱挥发反应期间的耦合水文 - 化学 - 机械过程。含有反应性矿物质和非反应性基质矿物质的不同元素法（DEM）数值模拟。阴性δV-T反应导致流体压力降低，不会在基质内产生裂缝。相反，流体压力增加阳性δV-T反应导致基质的水加压。这种压裂优先沿晶界发生，并导致与裂缝网络的发展相关的情节流体脉冲。石榴石内的晶界骨折内的沉淀可以解释骨骼石榴石的形成。我们的DEM模型还表明反应诱导的压裂对各向异性流体流动的强烈影响，这意味着主导的流体流动方向可以容易地改变俯冲区内的衍生变质期间的压力配置和差分应力的大小。

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