Abstract High pressure shock metamorphism in ordinary chondrites involves heating and melting of individual phases from shock entropy, pore collapse, frictional heating, and heat transfer. Numerical models using shock physics codes have recently been used to comprehend the mechanism of shock heating and melting in multiphase mesoscale models. Such models suggest that the formation of sulfide and metal melt veins in ordinary chondrites (shock-darkening) can be explained by preferential heating and melting of iron and iron sulfides during shock. However, those models usually dismissed heat transfer between heterogeneously shock heated phases. This leads to an underestimation of the degree of melting in phases that experienced low degrees of shock heating (e.g. iron metal) but are in direct contact with strongly shock heated phases (e.g. iron sulfides). In our study, we implemented a finite difference 2-D heat diffusion code to model heat diffusion among neighboring grains in shock heated multiphase meshes that represent typical textural relations of silicate, sulfide and metal grains in ordinary chondrites. Post-shock temperature maps for each textural model were calculated using the iSALE shock physics code and used as input for the diffusion code. We find that heat diffusion, not initial shock heating, is the principal cause for heating and melting of metals in eutectic contact with iron sulfides at ~50 GPa of pressure. In addition we study the effects of iron and troilite grain sizes, shock pressures and pre-shock porosities of the silicate matrix, and discuss the preservation of melt allowing melt migration in shock-darkened meteorites and the observation of metal-silicate intermixed melting. With our work, we demonstrate that the consideration of heat diffusion during and after shock is crucial for a better understanding of melting features in both experimentally and naturally shocked ordinary chondrites.

中文翻译：

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数值冲击普通球粒陨石中的热扩散及其对冲击熔化的贡献

摘要 普通球粒陨石中的高压冲击变质作用涉及来自冲击熵、孔隙坍塌、摩擦加热和传热的各个相的加热和熔化。使用激波物理代码的数值模型最近已被用于理解多相中尺度模型中激波加热和熔化的机制。这些模型表明，普通球粒陨石中硫化物和金属熔体脉的形成（冲击变暗）可以通过冲击期间铁和硫化铁的优先加热和熔化来解释。然而，这些模型通常不考虑异质冲击加热相之间的热传递。这导致低估了经历低度冲击加热的相（例如铁金属）但与强烈冲击加热的相（例如 硫化铁）。在我们的研究中，我们实施了有限差分二维热扩散代码来模拟冲击加热多相网格中相邻颗粒之间的热扩散，这些网格代表普通球粒陨石中硅酸盐、硫化物和金属颗粒的典型纹理关系。使用 iSALE 冲击物理代码计算每个纹理模型的冲击后温度图，并用作扩散代码的输入。我们发现热扩散，而不是初始冲击加热，是在~50 GPa 压力下与硫化铁共晶接触的金属加热和熔化的主要原因。此外，我们研究了铁和硫钛矿粒度、冲击压力和硅酸盐基质的冲击前孔隙度的影响，并讨论熔体的保存允许熔体在冲击变暗陨石中的迁移和金属-硅酸盐混合熔化的观察。通过我们的工作，我们证明了考虑冲击期间和之后的热扩散对于更好地理解实验和自然冲击普通球粒陨石的熔化特征至关重要。