The paleo-continental reconstruction of Asia during the Permian–Triassic boundary indicates major tectonic readjustments between multiple continental blocks in the north of North China Craton (NCC) due to complex plate subduction system(s). One of the major consequences was the closure of the Paleo-Asian Ocean. In a similar time frame, Proto-Japan was also evolving through plate-subduction with the opening of the Maizuru back-arc basin. The spectacular linear near-continuous belt of the Maizuru Terrain in the Inner Zone of Southwest Japan holds the rock record of the opening of the back-arc basin, sediment-fill in this basin culminating into closure-related pulsative debris flow deposits (i.e. the Tonoshiki Formation). However, the exact deformation mechanism(s), paleo-stress regime, their mesoscopic to microscopic rock record, and exact timing hold the keys to connecting the closure event of the Maizuru back-arc basin and the possible tectonics, in particular the closure of the PAO in Asia. With this aim, we report here the micro- to -structural geological records of rock units of the Maizuru Terrane which indicate evidence of (1) pre-depositional hydrofracturing, (2) extensive -lithification fracture-vein formation due to (3) broad WNW-ESE to E-W compressional paleostress regime using the fracture-vein analysis, (4) deformational e-twin development with the dominance of Type II twin indicating a maximum temperature of 300 °C with no evidence of overprinting. This brittle deformation affected all the lithounits of the Maizuru back-arc basin but not the overlying units deposited after the basin closure. New U-Pb detrital zircon age data of the rocks belonging to the Maizuru Group and also the overlying Fukumoto Formation fixes the age of the above-mentioned deformation event at ∼ 250 Ma. All these data help to assess the possible paleo-position of Proto-Japan and a clear tectonic scenario between the NCC, the Central Asian Orogenic Belt, and the Khanka-Jiamusi Massif in East Asia.

中文翻译：

---

古生代舞鹤弧后盆地是如何以及何时闭合的？对东亚大陆边缘构造的影响


二叠纪-三叠纪边界期间亚洲的古大陆重建表明，由于复杂的板块俯冲系统，华北克拉通（NCC）北部多个大陆块之间发生了重大构造调整。主要后果之一是古亚洲洋的关闭。在相似的时间范围内，随着舞鹤弧后盆地的开放，原始日本也通过板块俯冲而演化。日本西南部内区舞鹤地形壮观的线性近连续带保持着弧后盆地开口的岩石记录，该盆地中的沉积物充填最终形成与闭合相关的脉动泥石流沉积物（即登敷组）。然而，确切的变形机制、古应力状态、介观到微观的岩石记录以及准确的时间是将舞鹤弧后盆地闭合事件与可能的构造联系起来的关键，特别是亚洲的 PAO。为此，我们在这里报告了舞鹤地体岩石单元的微观到构造地质记录，这些记录表明了以下证据：(1) 沉积前水力压裂，(2) 由于 (3) 广泛的岩化缝脉形成使用裂缝脉分析的 WNW-ESE 到 EW 压缩古应力状态，(4) 变形电子孪晶发育，以 II 型孪晶为主，表明最高温度为 300 °C，没有叠印证据。这种脆性变形影响了舞鹤弧后盆地的所有岩体，但不影响盆地闭合后沉积的上覆岩体。 舞鹤群岩石和上覆福本组岩石的新 U-Pb 碎屑锆石年龄数据将上述变形事件的年龄确定为 ∼ 250 Ma。所有这些数据有助于评估原日本可能的古位置以及华北克拉通、中亚造山带和东亚兴佳-佳木斯地块之间的清晰构造情景。