The Mechanism of Pseudotachylyte Generation and the Elucidation of the State-of-Stress Problem

本研究项目的主要任务是：(1)确定PT的超细基质是熔体起源还是挤压起源，(2)了解PT罕见的原因，以及(3)讨论前两项任务的结果对应力状态问题的影响。该项目的主要成果如下：PT的基体粒度非常细，很难确定其来源。然而，这个项目的结果是发现了一种全新的方法，基于对PT中所含碎屑的大小分布的分析，来检验粉碎起源的有效性（Shimamoto和Nagahama， 1991,1992）。他们发现，来自澳大利亚中部马斯格雷夫山脉的铂中包含的碎屑服从分形维数为1.5的幂律大小分布。这种尺寸分布预示着超细晶基体的面积约为4- 5%，而PT基体的面积约为60%。因此，不能将基体的大部分视为破碎产物。这一结果，连同微岩的发育和碎屑的腐蚀结构等结构证据，有力地表明假长柄岩基质的熔融起源。这一结果已被更新的分析所取代，该分析基于来自其他两个地区的碎屑的改进分形尺寸分布（Nagahama et al., 1994）。我们还设计并建造了一台新的高速摩擦试验机，在实验室中研究了假羧酸盐的生成过程。这是这个项目的主要任务，我们已经成功地生产出了与天然伪聚乳酸非常相似的摩擦熔体。高速摩擦试验结果如下：(1)摩擦熔融是一种不平衡现象，(2)熔融温度较低且对快速加热稳定性较差的矿物在摩擦熔融过程中优先熔融，(3)花岗岩的摩擦熔体在sio2中被耗尽，因为石英最耐摩擦熔融，(4)辉长岩的摩擦熔体在1300ºC以上用光测温仪测得。(5)摩擦加热过程中温度快速上升导致的热破裂对假木石中碎屑的生成起重要作用。结果(3)与一些天然假木质素的结果一致。少

The main tasks of the present research project have been (1) to determine whether the ultrafine matrix of PT is of melt origin or of crush origin, (2) to understand why PT are rare, and (3) to discuss the implications of the results from the former two tasks for the state-of-stress problem. The major results from the project are as follows.The matrix of PT is so fine-grained that it is not easy to delineate its origin. However, an entirely new method was found as a result of this project for testing the validity of the crush origin based on the analysis of the size distribution of clasts contained in PT (Shimamoto and Nagahama, 1991,1992). They showed that clasts contained in PT from the Musgrave Range, central Australia, obey a power-law size distribution with a fractal dimension of 1.5. This size distribution predicts that the ultrafine-grained matrix should occupy an area of 4-5 %, whereas the area of the matrix of PT amounts to about 60 %. Hence, the major part of the matrix cannot … More be regarded as the crush products. This result, together with textural evidence such as the development of microlites and corroded textures of clasts, strongly suggests the melt origin of the matrix of pseudotachylytes. This result has been substatiated with updated analysis based on a modified fractal size distribution of clasts from two other localities (Nagahama et al., 1994).We also have designed and built a new high-speed frictional testing machine to study the pseudotachylyte generating processes in laboratory. This was the major task for this project, and we have successfully produced frictional melt that is very similar to natural psedotachylytes. The findings from high-speed friction experiments are as follows. (1) Frictional melting is a disequilibrium phenomenon, (2) minerals with low melting temperature and presumably with less stability to rapid heating preferentially melt during the frictional melting, (3) frictional melt of granite is depleted in SiO_2 because quartz is most resistent to frictional melting, (4) temperature above 1,300 ﾟC was measured for the frictional melt of gabbro using a photo thermometer, and (5) thermal fracturing due to rapid temperature rise during frictional heating is important in the generation of clasts contained in pseudotachylytes. The results (3) is consistent with the results for some natural pseudotachylytes. Less