Evolutionary process of Beppu Bay in central Kyushu, Japan: a quantitative study of the basin-forming process controlled by plate convergence modes
Evolutionary process of Beppu Bay in central Kyushu, Japan: a quantitative study of the basin-forming process controlled by plate convergence modes
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DOI：
10.1186/1880-5981-66-74
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发表时间：
2014-07-22
影响因子：
3
通讯作者：
Takemura, Keiji
中科院分区：
文献类型：
--
作者：
Itoh, Yasuto;Kusumoto, Shigekazu;Takemura, Keiji
这一综合构造研究揭示了活动边缘的成盆和变形过程。日本西南部是受菲律宾海板块斜向俯冲影响的岛弧，岛弧的斜向俯冲引起了横贯弧的中构造线（MTL）的右向滑动。别府湾是MTL最西端的构造凹陷，上新世/更新世沉积物由高到低依次为下（5 ~ 0.7 Ma）、上（0.7 ~ 0.3 Ma）和辅助上（0.3 Ma）单元。详细的地震解释表明，盆地深处的主要构造是一个较老的半地堑和一个较年轻的拉分凹陷，这是由于晚第四纪断层的走滑速率增强而在MTL的右行部发育的。随着收缩期的出现，拉离期内的沉积物被后来的反转事件所变形。数值模拟成功再现了盆地低角度滑脱上盘的明显变形。基于离散元方法，认为变形沉积层的构造差异是由断层倾角的不同引起的。别府湾及西南海域其他地区构造格局的显著时间变化可能与约6 Ma以来菲律宾海板块的瞬态辐合模式（包括欧拉极的迁移）有关。
This integrated tectonic study reveals the basin-forming and deforming processes on an active margin. Southwest Japan (SWJ) is an island arc under the influence of oblique subduction of the Philippine Sea plate, which has provoked dextral slips on the arc-bisecting Median Tectonic Line (MTL). Plio-/Pleistocene sediments in Beppu Bay, a tectonic depression at the westernmost portion of the MTL, are categorized into lower (5 similar to 0.7 Ma), upper (0.7 similar to 0.3 Ma), and an auxiliary uppermost (0.3 Ma similar to present) unit in ascending order. Detailed seismic interpretation demonstrates that major structures in the deep interior of the basin are an older half-graben under a strong N-S extensional regime and a younger pull-apart sag that developed in a right-stepping part of the MTL as a result of late Quaternary-enhanced strike-slip rates on the fault. Sediments within the pull-apart have been deformed by later inversion events as a contraction phase arose. Conspicuous deformation of the hanging wall of the low-angle detachment of the basin was successfully reproduced by numerical modeling. Based on a discrete element method, this suggests that structural differences in the deformed sedimentary layers are caused by differences in the dip angles of the faults. Remarkable temporal changes in tectonic regimes around Beppu Bay and other areas of SWJ are probably related to transient modes of convergence, including the migration of the Euler pole, of the Philippine Sea plate since ca. 6 Ma.