Tectonic setting for Tsunemori Formation in the Permian accretionary complex of the Akiyoshi Belt, Southwest Japan
Tectonic setting for Tsunemori Formation in the Permian accretionary complex of the Akiyoshi Belt, Southwest Japan
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日本西南部秋吉带二叠纪增生杂岩中常盛组的构造背景
DOI：
10.1016/j.heliyon.2018.e01084
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Y.
中科院分区：
文献类型：
--
作者：
Wakita;K.;Yoshida;R.;Fushimi;Y.
本研究的目的是重新审视常森组的年龄、沉积环境和构造环境。这项研究为常盛组的形成提供了新的构造模型，常盛组是了解日本晚二叠世俯冲和增生过程的关键地层。根据本研究报道的放射虫，例如Follicuculluscf.scholasticusOrmiston和Babcock，恒盛组的沉积年龄为中二叠世晚期至晚二叠世早期。本文反驳了先前关于 Akiyoshi 石灰岩海沟处环礁碳酸盐塌陷的理论。常森组的沉积岩大部分没有普遍剪切，与典型增生杂岩的沉积岩相比变形较小。常森组浊积岩序列中不存在层位平行或近平行逆冲。浊积泥岩和卵石泥岩缺乏裂变性和鳞片解理。变形样式、再加工化石的出现、钙铁矿和石灰岩角砾岩的存在表明常森组不是增生楔的一部分，而可能是前弧或斜坡盆地沉积。改造化石、钙铁矿、石灰岩角砾岩的存在表明，常森组物源的一部分是暴露在弧沟间隙处的石灰岩，这些石灰岩向上移动到达弧沟间隙，在该处秋吉灰岩将其碎片和块体提供到弧前和/或斜坡盆地中。因此，常森组是弧前盆地和/或斜坡盆地的沉积物，而不是海沟沉积物。
The purpose of this study is to reexamine the age, depositional environment, and tectonic setting of the Tsunemori Formation. This study provides a new tectonic model on the formation of Tsunemori Formation, which is a key formation to understand the Late Permian subduction and accretionary processes in Japan. The sedimentation age of the Tsunemori Formation is late Middle Permian to early Late Permian, based on radiolarians, such asFollicuculluscf.scholasticusOrmiston and Babcock reported in this study. This paper disproves the previous theory of atoll carbonates collapse at the trench for the Akiyoshi Limestone. Most of sedimentary rocks of the Tsunemori Formation is not pervasively sheared, are less deformed compared with sedimentary rocks of the typical accretionary complexes. There is no layer parallel or sub-parallel thrusting in the turbidite sequences of the Tsunemori Formation. Mudstone of turbidite and pebbly mudstone is lack of fissility and scaly cleavages. The styles of deformation, occurrence of reworked fossils, presence of calcarenite and limestone breccia suggest that the Tsunemori Formation was not a part of accretionary wedges, but possibly was fore arc or slope basin deposits. Presence of reworked fossils, calcarenite, limestone breccia suggest that a part of the provenance of Tsunemori Formation are limestone exposed at the arc trench gap, which was moved upward to reach the arc trench gap where the Akiyoshi Limestone provides its fragments and blocks into forearc and/or slope basins. Therefore, Tsunemori Formation is a deposit in the forearc basin and/or slope basin rather than trench deposits.