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的超细基质是熔融成因还是粉碎成因，(2)了解PT稀有的原因，以及(3)讨论前两个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的基质是细粒的，很难确定其来源。然而，这个项目的结果是找到了一种全新的方法来测试破碎来源的有效性，这是基于对PT中包含的碎屑的尺寸分布的分析(Shimamoto和Nagahama，1991,1992)。它们表明，澳大利亚中部马斯格雷夫山脉PT中含有的碎屑服从指数型大小分布，分维为1.5。这一尺寸分布预测，超细晶基质的面积应为4-5%，而PT的基质面积约为60%。因此，矩阵的主要部分不能为…更多的被视为压榨产品。这一结果与碎屑微颗粒发育和碎屑侵蚀结构等结构证据一起，有力地表明了假玄武岩基质的熔融成因。这一结果得到了基于来自另外两个地方的碎屑(Nagahama等人，1994)修正的分形粒度分布的最新分析的补充。我们还设计和建造了一台新的高速摩擦试验机来研究实验室中假硅质岩的产生过程。这就是这个项目的主要任务，我们已经成功地生产出了与天然假晶石非常相似的摩擦熔体。高速摩擦实验的结果如下。(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)花岗岩摩擦熔体因石英最耐摩擦熔融而亏损SiO_2，(4)辉长岩摩擦熔体的温度高于1,300ﾟ℃，(5)摩擦加热时升温过快的热破裂作用是假黄长岩中碎屑形成的重要原因。结果(3)与某些天然假黄晶的结果一致。较少

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