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首页> 外文期刊>Journal of Asian earth sciences >Late Carboniferous (Kasimovian) closure of the South Tianshan Ocean: No Triassic subduction
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Late Carboniferous (Kasimovian) closure of the South Tianshan Ocean: No Triassic subduction

机译：南天山洋晚石炭世（Kasimovian）封闭：无三叠纪俯冲

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摘要

The proposed Triassic age of oceanic subduction and high-pressure/low-temperature (HP-LT) metamorphism in the South Tianshan orogen (STS) of the southwestern Central Asian Orogenic Belt needs to be re-examined on the basis of field relationship and precise age dating. Our biostratigraphic study in the Atbashi Range of southern Kyrgyzstan indicates that sedimentary strata unconformably overlie the HP-LT metamorphic rocks within the Turkestan suture zone and have a late Kasimovian (ca. 305 Ma) age. This constrains the minimum age of eclogite metamorphism in the HP-LT metamorphic complex. A Late Pennsylvanian to early Permian (Asselian) hinterland basin overlaps the margins of the Middle and South Tianshan and the ophiolitic suture between them, thus leaving no space for an oceanic basin in the northern STS in the late Permian or Triassic. In the south, overlap assemblages stitching the STS with the Tarim Craton consist of late Asselian to early Sakmarian limestones and early Permian rhyolites. Early Permian (ca. 295-265 Ma) post-collisional A-type granites and sub-alkaline plutons are widespread in the STS and are not affected by thrust deformation. These facts indicate that thrust packages of the STS were stacked together and welded to the margin of the Tarim Craton by the early Permian. The widespread occurrence of early Permian sub-alkaline granites is also not compatible with an oceanic accretionary wedge setting in the STS during the Permian or Triassic.Permian and Triassic zircon ages for subduction-related HP-LT metamorphic rocks and ophiolitic gabbro from the Atbashi and Djandjir ranges reported in two recent papers contradict geological relationships. A review of reported analytical data shows that anomalously young ages in all studied samples are based on geologically meaningless single zircon analyses and/or discordant data, which cannot be used for age calculation. The suggestion that an oceanic basin in the STS remained open and subduction continued until the Middle Triassic is erroneous because of insufficient consideration of basic regional geological relationships and incorrect interpretations of analytical results.
机译：中野西南造山带的西南天山造山带（STS）的海洋俯冲和高压/低温（HP-LT）变质的三叠纪拟议时代需要根据田间关系和精确性进行重新审查年龄约会。我们在吉尔吉斯斯坦南部Atbashi山脉进行的生物地层研究表明，沉积地层不整合地覆盖了Turkestan缝合带内的HP-LT变质岩，并具有晚期卡西摩维亚时代（约305 Ma）。这限制了HP-LT变质复合物中的榴辉岩变质的最小年龄。宾州晚期至二叠纪（阿塞拜疆）早期的腹地盆地与中天山南缘和南天山的边缘以及它们之间的砾岩缝合线交叠，因此在二叠纪晚期或三叠纪的北部STS没有留出空间。在南部，将STS与塔里木克拉通（Tarim Craton）缝合在一起的重叠组合物包括晚阿瑟尔（Asselian）到早期萨克马尔（Sakmarian）石灰石和早二叠纪流纹岩。早二叠世（约295-265 Ma）碰撞后的A型花岗岩和亚碱性岩体在STS中分布较广，不受推力变形的影响。这些事实表明，STS的推力组件堆叠在一起，并在二叠纪早期被焊接到塔里木克拉通的边缘。二叠纪或三叠纪早期二叠纪亚碱性花岗岩的广泛分布也与STS中的海洋增生楔形环境不相容。俯冲相关的HP-LT变质岩和来自Atbashi和最近两篇论文中报道的Djandjir范围与地质关系矛盾。对报告的分析数据的回顾表明，所有研究样品中的异常年龄都是基于无地质意义的单一锆石分析和/或不一致的数据，这些数据不能用于年龄计算。由于对基本区域地质关系的考虑不充分以及对分析结果的错误解释，STS的海盆一直保持开放并一直俯冲直到中三叠纪是错误的建议。

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