Tectonic relationships between ductile shear zone and brittle fault zone in the upper crust

该项目的目的是研究含假玄武玻璃岩的碎屑断层与上述韧性剪切带的构造关系，分析糜棱岩的面理和地震脆性断层的滑动面，运动趋势和方向，以及糜棱岩和地震断层的剪切和滑动条件。研究区域仅限于下地壳变质岩被出露的逆冲断层沿着，即八幡滨大岛、龙屋边缘糜棱岩带和日高变质带。在八幡滨大岛变质岩片中，除了含有地震断层的假玄武玻璃岩外，还识别出四个阶段的糜棱岩化。部分假玄武玻璃以韧性变形方式变形。对假玄武玻璃断裂的详细观察表明，地震破裂多发生在韧脆性过渡带内。地震断层作用和叠加的韧性变形与深壳变质层大岛变质杂岩逆冲到三钵川片岩上有关，是地壳深部形成糜棱岩Ⅱ的连续运动。在长野县南部和田地区的Ryoyo边缘糜棱岩带中，沿着与糜棱岩面理相似的脆性断层，在石英-二长糜棱岩中新发现了假玄武玻璃岩脉。糜棱岩退变质为低绿片岩相矿物，假玄武玻璃中含有少量球粒。这些结果表明，假玄武玻璃岩形成于地壳较浅的地带，但其滑动面的运动方向与上述糜棱岩相同。这也可能表明地震断层作用与地壳深部变质岩的逆冲运动有关。

The project was aimed to investigate the structural relation of pseudotachylite bearing scismic faults with respect to foregoing ductile shear zones, analysing the foliation of mylonites and slip planes of seismic brittle faults, trends and sense of movement, and shear and slip conditions of mylonite and seismic faults, respectively. The research areaa are limited to thrust faults along which lower crustal metamorphic rocks were exhumed ; namely, Yawatahama Oshima island, the Ryoke marginal mylonite zone, and the Hidaka metamorphic belt. In the Yawatahama Oshima metamorphic sheet, four stages of mylonitization are identified, in addition to the pseudotachylite bearing seismic faulting. A part of the pseudotachylite was deformed in a ductile manner. Detailed observation of the pseudotachylite fautls revailed that the seismic rupturing multiplly took place within a zone of ductile and brittle transition. The seismic faulting and overprinted ductile deformation are related to the thrusting of Oshima metamorphic complex, deep crustal metamorphic layers, onto the Sambagawa schists, which is a continuous movement to form the mylonite II in the deep crust. This is significant to mean that inland earthquakes takes place along thrust faults by which crustal blocks tectonically exhume.In the Ryoke marginal mylonite zone of Wada area, southern Nagano prefecture, pseudotachylite veins were newly found in quartz-diorite mylonite along brittle faults paralell to mylonite foliation. The mylonite is retrogessively altered to low greenschist facies minerals, and the pseudotachylite contains a small amount of spherulite. These show that the psudotachylite was formed in a relatively shallow zone of the crust, but the sense of movement of the slip planes is the same as that of foregoing mylonite. It may also indicate that the seismic faulting is related to thrust mevement of the deep crustal metamorphic rocks.