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

1.深部花岗岩的勘探为了验证增生杂岩地体中的深部花岗岩，建立了泥岩中挥发性元素(B、F、Cl)的X射线荧光分析技术。利用这一技术对坦巴地体进行了研究，证实了龟冈北部地区挥发性元素的高度集中，表明存在深部花岗岩。在前白垩纪地体中发现了新的大型地质构造(1)京都北部大江町地区的Maizuru和Akiyoshi带之间发现了一条大规模的高角度断裂带。(2)冈山县卡加米诺地区的Maizuru带形成的低角度推覆覆盖了三根变质岩。(3)2000年10月爆发的鸟取西部地震震中所在的Kohfu-cho地区的前白垩纪地体由周周变质混杂建造组成，(4)岛根县Hikimi-cho地区两条WNW-ESE向断裂中的Maizuru带夹有异地Kanmon群。这表明沿麦祖鲁带存在早白垩世大型扭动断裂。从几何角度来说，严格地说，活动断裂系统不是块状结构。中部至东部近海地区，增生复式地壳被形成骨架结构的花岗岩壳所包围，活动断裂多发育在花岗岩壳或其边缘。西金基地区花岗质结壳和增生杂岩结壳具有明显的WNW-ESE向带状展布。一些活动断裂沿上述带状展布呈平行排列。大部分活动断裂被形成于九州北部的晚白垩世古断裂重新激活。它们显示了应力场转换引起的位移感的反转。

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.