Study on Pull-Apart Basin along Median Tectonic Line

沿着中央构造线（MTL）的泉沉积盆地（ISB）作为一个典型的走滑盆地，近年来引起了人们的广泛关注。本次研究的目的是明确ISB的形成机制和ISB的变形方式，长度约为300 km。所得结果摘要如下。ISB的划分：编制了MTL断裂系统和泉群（上白垩统）分布的构造图。根据该图，ISB可分为至少5个段（A-E）。虽然泉群的分布从A段（四国西部）到D段（泉山脉）是连续的，但设想了盆地与每个段（次盆地）相似的可能性。迄今为止，D段西段的裂变径迹年龄为77-72 Ma，而Radioralia（Archeodictyomitra Sp.）从E段（Gojo的远东）获得。 ...更多信息 (will提交）2。ISB的形成机制：还编制了MTL断层弯曲（Gojo弯曲）以西D段的构造图。在MTL的这个释放弯曲处，由左滑运动产生的双重构造变得清晰（地质学，第18卷，第392-394页，1990年;结构地质学，第35期，第65-70页，1990年）。ISB可以看作是MTL弯曲处的褶皱作用形成的拉分盆地。进一步探讨了拉分盆地的形成机制（《构造地质》1991年第36期，出版中）. ISB中的变形样式：D段泉群浊积岩相发育由重力作用引起的层面滑动所产生的不协调褶皱和小规模雁列断层等变形构造。通过对它们的测量，得到了沿层面的剪切应变（γ = 0.3- 1.4）沿着。利用扫描电子显微镜，确定了滑面上的滑移方向。根据其证据和沉积中心的迁移，盆地中的充填泉群的倾斜被认为是由沿MTL的走滑运动沿着引起的（日本地质学会关西分支会议录，第109期，第7页，1990年;日本地质学会年会，第97届，摘要，第346页，1990年;将提交）。少

The Izumi Sedimenatry Basin (ISB) along the Median Tectonic Line (MTL) has become of major interest lately as a typical strike-slip basin. The purpose of this study is to become clear formative mechanism for the ISB and deformational style in the ISB, attaining to about 300 km in length. A summary of the results obtained is shown below.1. Division of ISB : A tectonic map showing the MTL fault system and the distribution of the Izumi Group (Upper Cretaceous) was compiled. According to this map, the ISB is divisible into at least 5 segments (A-E). The possibility of a basin having liked with each segment (subbasin) is envisioned, though the distribution of the Izumi Group is continuous from segment A (west Shikoku) to segment D (Izumi Mountains). This study has hence tried to determine ages of some segments : Until now, the fission track age of 77-72 Ma from the western part of the segment D, and Radioralia (Archeodictyomitra Sp, etc.) from the segment E (far east of Gojo) were obtained. … More (will be submitted)2. Formative mechanism for ISB : A tectonic map in the segment D, west of a fault bend (Gojo bend) of the MTL, was also compiled. At this releasing bend of the MTL, duplex structures produced by left-slip movement have become clear (Geology, v. 18, p. 392-394, 1990 ; Structural Geology, no. 35, p. 65-70, 1990). The ISB can be regarded as a pull-apart basin formed by the duplexing at the MTL bend. The mechanism of pull-apart basin was further discussed (Structural Geology, no. 36, 1991, in press).3. Deformational style in ISB : Deformation structures, such as disharmonic folds and small-scale echelon faults, produced by gravity-induced bedding-plane slippages, are well developed in the turbidite facies of the Izumi Group in the segment D. By measuring for them, the shear stranin (gamma= 0.3--1.4) along the bedding plane was obtained. Using a scanning electron microscope, the slip direction on slickensides was determined. Judging from their evidence and the migration of depocenter, the tilting of the filling Izumi Group in the basin is thought to have been caused by strike-slip duplexing along the MTL (Geological Society of Japan, Kansai Branch Proceedings, no. 109, p. 7, 1990 ; Geological Society of Japan, Annual Meeting, 97th, Abstracts, p. 346, 1990 ; will be submitted). Less