Pseudotachylyte (Pt) veins associated with ancient fault zones are considered as reliable palaeoseismic indicators as they are produced by a combination of cataclasis and frictional melting of the host rock during rapid (seismic rate) fault slip. In spite of a large amount of work done on pseudotachylytes, several issues related to the frictional melting process are not completely resolved for example, the nature and origin of domain‐scale chemical heterogeneity of the Pt matrix, the contribution of different minerals of the host rocks in forming the melt product, temperature variation in different domains of the Pt veins, among others. To revisit these issues, pseudotachylyte veins hosted entirely within pelitic gneisses (Pt‐I) and those formed along the contact of gneisses with intrusive meta‐dolerite dykes (Pt‐II) within the Sarwar‐Junia Fault Zone in Rajasthan, India, are studied in detail using optical and scanning electron microscope, X‐ray diffraction (XRD), X‐ray fluorescence, and electron probe micro‐analyser, with an intention to better understand the evolution of the microstructures and the heterogeneous chemical character of the pseudotachylyte veins and their host rocks. Unequivocal melt‐origin microstructures (e.g., microlites, spherulites, melt flow structure) are observed in the pseudotachylyte matrix, and an indirect evidence of amorphous (glass?) phase is found through XRD. The Pt‐matrix is more mafic than the host rock or the bulk Pt‐vein, irrespective of the rock types involved, indicating preferential melting of mafic minerals of the host rock(s). Microdomain‐scale variation in mineralogical and chemical character of Pt‐matrix suggests co‐existence of melts of different composition which remained unmixed due to rapid quenching of the melt. Mineral chemistry of fine microlites and spherulites within the Pt‐matrix differs significantly from the corresponding parent mineral grains in the respective host rocks suggesting their formation by direct crystallization from a melt phase. Formation of microlites by devitrification of solidified glass is discounted due to the absence of fluid activity, and due to the spatial distribution of finer microlites (near the Pt‐vein boundary), and coarser spherulites (near the centre). It is surmised that frictional heating attains different temperatures within a single Pt‐vein, and in adjacent Pt‐veins, and the constituent minerals melt selectively as the temperature rises beyond the melting points of different constituent minerals of the host rock. Neither preferential crushing of mafic minerals followed by bulk melting, nor eutectic (equilibrium) melting of the host rock can explain the strongly heterogeneous character of pseudotachylyte melt observed in this study.

中文翻译：

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印度Sarwar-Junia断层带假速溶脉的微观结构和地球化学：对地震断层带的摩擦熔融过程的启示

与古代断层带相关的假速溶（Pt）脉被认为是可靠的古地震指示剂，因为它们是由快速（地震速率）断层滑脱过程中基岩的催化作用和摩擦融化共同产生的。尽管在假速溶电解质上进行了大量工作，但与摩擦熔化过程相关的一些问题仍未完全解决，例如，Pt基质的域尺度化学异质性的性质和起源，基质中不同矿物的贡献形成熔体产物的岩石，铂脉不同区域的温度变化等。为了重新审视这些问题，在印度拉贾斯坦邦的Sarwar-Junia断层带中，完全包裹在胶质片麻岩（Pt-I）内以及沿片麻岩与侵入性变长石脉（Pt-II）接触形成的假速溶质脉进行了详细研究。扫描电子显微镜，X射线衍射（XRD），X射线荧光和电子探针显微分析仪，目的是更好地了解假速溶脉及其宿主岩石的微观结构演变和非均质化学特征。在准速溶物基质中观察到明确的熔体起源的微结构（例如，微晶，球晶，熔体流动结构），并且通过XRD间接发现了非晶相（玻璃？）相。无论涉及的岩石类型如何，Pt矩阵都比基质岩石或块状Pt静脉更具铁镁铁质。表明基质岩石中的镁铁质矿物优先熔化。Pt基质的矿物学和化学特征的微域尺度变化表明，不同成分的熔体共存，由于熔体的快速淬火，它们保持未混合状态。Pt基质中的微细微球和球晶的矿物化学与相应宿主岩中相应的母体矿物晶粒有显着差异，表明它们是通过从熔融相直接结晶而形成的。由于没有流体活性，并且由于较细的微晶（靠近铂脉边界）和较粗的球晶（靠近中心）的空间分布，使得凝固玻璃失透形成的微晶被打折。据推测，摩擦加热在一个铂金脉络内可达到不同的温度，并且在相邻的铂脉中，随着温度升高超过母岩中不同组成矿物的熔点，组成矿物选择性地熔化。既不优先粉碎镁铁质矿物然后大量熔化，也不共晶（平衡）的熔化可以解释本研究中观察到的假速溶质熔体的强烈非均质特征。