Basement structure and active fault system in the Inner zone of Southwest Japan

1. 建立了用XRF分析泥岩中挥发性元素（B、F、Cl）的方法，对增生复杂地体中的深部花岗岩进行了验证。利用这一技术对坦巴地块进行了研究，证实了龟冈北部地区挥发性元素的高浓度，表明存在深部花岗岩。前白垩世地系新发现的大型地质构造(1)在京都市北部五草地区的Maizuru和Akiyoshi带之间发现了大型高角度断裂带。(2)冈山县鹿神町地区三广变质岩上覆有一低角度推覆的舞鹤带地层。(3) 2000年10月西鸟取县地震震中地区科府町地区的前白垩世地体由周变质混杂岩组成，可与飞驒-盖连带相对应。(4)岛根县Hikimi-cho地区的两条WNW-ESE走向断裂内嵌在Maizuru带内的异域Kanmon群。这表明迈祖鲁带存在早白垩世大型扳手断裂。从几何上严格地说，活动断裂系统不属于块体构造。中部至近基地区东部，增生杂壳被花岗质壳包围，形成格架构造，花岗质壳及其边缘发育大量活动断裂。近基西部花岗岩地壳和增生杂岩地壳呈WNW-ESE向分带排列。部分活动断层沿上述带状排列呈平行走向。大部分活动断裂是由晚白垩世形成的古断裂重新激活的。它们表现出由应力场转换引起的位移感反转。

1. Exploration of deep-seated graniteAnalytical technique for the volatile elements (B, F, Cl) in mudstone by XRF was developed with the purpose of verifying deep-seated granite in the accretionary complex terrane. Tamba terrane was examined using this technique, and confirmed that the high concentration of those volatile elements in northern Kameoka area showing the existence of deep-seated granite.2. Newly found large scale geologic structure in the Pre-Cretaceous Terranes(1) A large-scale high angle fracture zone was found between the Maizuru and Akiyoshi zones in Ooe-cho area, northern Kyoto Prefecture.(2) The Sangun metamorphic rocks are overlain by a low angle nappe of the Maizuru zone fomations in the Kagamino-cho area, Okayama Prefecture.(3) The Pre-Cretaceous Terranes in Kohfu-cho area where the epicentral region of the Western Tottori earthquake outbreaked in October 2000, are composed of weekly metamorphosed melange formations, and they can be correlated to the Hida-gaien zone.(4) Allochthonous Kanmon Group is intercalated in the Maizuru zone embedded in two WNW-ESE trending faults in the Hikimi-cho area, Shimane Prefecture. This suggests the existence of the early Cretaceous large-scale wrench fault along the Maizuru zone.3. SummaryGeometrically strictly to say, the active fault system is not in a block structure. Accretionary complex crust is surrounded by the granitic crust forming frame work structure in the Chubu to eastern Kinki district, at where much of active faults develop in the granitic crust or its marginal part. WNW-ESE trending zonal arrangement of granitic crust and accretionary complex crust is distinct in the western Kinki. Some active faults show parallel alignment along the above mentioned zonal arrangement. Most of active faults had re-activated by the ancient faults formed in late Cretaceous in the Chugoku to northern Kyushu. They show inversion of displacement sense caused by the conversion of the stress field.