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Late Permian-early Middle Triassic back-arc basin development in West Qinling, China

机译：西秦岭晚二叠世-早中三叠世背弧盆地发育

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摘要

The Late Permian-early Middle Triassic strata of the northern West Qinling area, northeastern Tibetan Plateau, are composed of sediment gravity flow deposits. Detailed sedimentary facies analysis indicates these strata were deposited in three successive deep-marine environments. The Late Permian-early Early Triassic strata of the Maomaolong Formation and the lowest part of the Longwuhe Formation define a NW-SE trending proximal slope environment. Facies of the Early Triassic strata composing the middle and upper Longwuhe Formation are consistent with deposition in a base-of-slope apron environment, whereas facies of the Middle Triassic Anisian age Gulangdi Formation are more closely associated with a base-of-slope fan depositional environment. The lithofacies and the spatial-temporal changes in paleo-current data from these strata suggest the opening of a continental margin back-arc basin system during Late Permian to early Middle Triassic time in the northern West Qinling. U-Pb zircon ages for geochem-ically varied igneous rocks with diabasic through granitic compositions intruded into these deep-marine strata range from 250 to 234 Ma. These observations are consistent with extensional back-arc basin development and rifting between the Permian-Triassic Eastern Kunlun arc and North China block during the continent-continent collision and underthrusting of the South China block northward beneath the Qinling terrane of the North China block. Deep-marine sedimentation ended in the northern West Qinling by the Middle Triassic Ladinian age, but started in the southern West Qinling and Songpan-Ganzi to the south. We attribute these observations to southward directed rollback of Paleo-Tethys oceanic litho-sphere, continued attenuation of the West Qinling on the upper plate, local post-rift isostatic compensation in the northern West Qinling area, and continued opening of a back-arc basin in the southern West Qinling and Songpan-Ganzi. Rollback and back-arc basin development during Late Permian to early Middle Triassic time in the West Qinling area explains: the truncated map pattern of the Eastern Kunlun arc, the age difference of deep-marine sediment gravity flow deposits between the Late Permian-early Middle Triassic northern West Qinling and the late Middle Triassic-Late Triassic southern West Qinling and Songpan-Ganzi, and the discontinuous trace of ophiolitic rocks associated with the Anyemaqen-Kunlun suture.
机译：西秦岭北部，青藏高原东北部的晚二叠世-早中三叠世地层，由沉积物重力流沉积物组成。详细的沉积相分析表明这些地层沉积在三个连续的深海环境中。毛茂龙组的二叠纪晚期-早三叠世地层和龙屋河组的最低部分定义了西北向东南的近端斜坡环境。隆起河组中段和上段的早三叠世地层相与斜坡基底围岩环境中的沉积相一致，而中三叠纪阿尼西时代古浪底组相与扇底扇状沉积相密切相关。环境。这些地层的岩相和古流数据的时空变化表明，西秦岭北部在二叠纪晚期至中三叠世时期已建立了大陆边缘背弧盆地系统。地球化学变化的火成岩的U-Pb锆石年龄从250到234 Ma介于这些深海地层中，具有成岩质至花岗质成分。这些观察结果与大陆-大陆碰撞和华南地块北下的秦岭地层以下北的华南地块碰撞和逆冲作用期间二叠系-三叠纪东部昆仑弧和华北地块之间伸展的弧后盆地发育和裂谷相一致。深海沉积在中三叠纪拉迪尼时期结束于西秦岭北部，但开始于西秦岭南部和南部的松潘甘孜。我们将这些观测值归因于古特提斯海洋岩石圈向南定向回滚，上板块西秦岭的持续衰减，西秦岭北部地区的局部裂谷后等静压补偿以及后弧盆地的持续开放在西秦岭南部和松潘甘孜州。西秦岭地区晚二叠世至中三叠世时期的回滚和后弧盆地发育解释：东昆仑弧的截断图型，二叠纪晚期至中早之间深海沉积物重力流沉积的年龄差异西秦岭的三叠纪北部和西秦岭的晚三叠世晚期，西秦岭南部和松潘-甘孜，以及与阿尼玛琴-昆仑缝合线有关的不连续的蛇绿岩痕迹。

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  • 来源
    《Journal of Asian earth sciences》 |2014年第15期|116-129|共14页
  • 作者

    Lin Li; Qingren Meng; Alex Pullen; Carmala N. Garzione; Guoli Wu; Yanling Wang; Shouxian Ma; Liang Duan;

  • 作者单位

    Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China,Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA;

    Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;

    Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA,Department of Geoscience, University of Arizona, Tucson, AZ 85721, USA;

    Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA;

    Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;

    Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA;

    Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;

    Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;

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  • 正文语种 eng
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  • 关键词

    West Qinling; Triassic; Paleo-Tethys; Deep-marine sedimentation; Back-arc rift basin; Rollback tectonics;

    机译：西秦岭三叠纪;古特提斯深海沉积;后弧裂谷盆;回滚构造;

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