高级检索

    藏北日土地区南羌塘地块晚石炭—早二叠世海相裂谷盆地沉积序列:冈瓦纳大陆北缘初始裂解的沉积响应

    The marine rifted successions of the Late Carboniferous–Early Permian deposits from the South Qiangtang Block in the Rutog area, Northern Xizang: Sedimentary records of a rifting process on the northern Gondwana margin

    • 摘要: 南羌塘地块被广泛认为是晚古生代亲冈瓦纳的基梅里大陆的一部分,其构造演化历史与冈瓦纳北缘裂解及班公湖–怒江中特提斯洋的打开关系密切。虽然众多研究成果显示,南羌塘地块在早二叠世从冈瓦纳大陆北缘裂解而来,但这在盆地沉积响应上却没有得到确切的证实。本文通过研究藏北日土地区晚石炭—早二叠世受冰期影响的4类16个岩相、6类沉积环境特征和不同沉积作用演化阶段,划分出受盆地基底构造沉降控制和气候影响的5个沉积充填序列,并分析其所反映的沉积物供应与可容空间变化,揭示沉积充填序列形成过程中的构造–气候控制因素。研究表明,序列Ⅰ在晚石炭世—早二叠世阿舍尔期沉积,表现为冰川沉积物补偿了盆地基底沉降形成的沉积可容空间,是同裂谷早期阶段构造活动与气候共同作用的结果;在萨克马尔期至亚丁斯克早期,以展金组为代表的冰海相海侵退积序列(序列Ⅱ)和以曲地组为代表的海退进积–加积序列(序列Ⅲ),分别反映同裂谷活动第一幕高峰期和停滞期;亚丁斯克晚期至空谷期,以吞龙共巴组下段为代表的海侵加积–退积序列(序列Ⅳ)和以吞龙共巴组上段为代表的加积–进积序列(序列Ⅴ)则分别指向同裂谷活动第二幕高峰期和减弱期。因此,藏北日土地区南羌塘地块晚石炭—早二叠世沉积充填序列是冈瓦纳大陆北缘裂解过程的沉积响应,早二叠世是班公湖–怒江中特提斯洋初始打开的关键时期。

       

      Abstract: The South Qiangtang Block (SQB) is widely acknowledged as part of the Cimmerian Continent, which rifted away from the northern Gondwana margin during the Early Permian, marking the initial opening of the Bangong-Nujiang Meso-Tethys Ocean. However, the sedimentary response to this rifting event remains unconfirmed, leaving the event ambiguous. In this study, five sedimentary successions are identified in the Rutog area, Northern Xizang, each characterized by distinct facies that record different stages in the tectonic evolution and climatic influences on the basin, along with associated changes in the rates of basin subsidence and sediment accommodation. Succession Ⅰ, formed in the Late Carboniferous to Asselian age, shows that glaciomarine sediments compensated for the sediment accommodation generated by the basin subsidence, resulting from tectonic activities and climatic factors in the early stage of the syn-rift. During the Sakmarian to early Artinskian age, the glaciomarine retrogradational sequence represented by the Zhanjin Formation (Succession Ⅱ) and the following progradational-aggradational sequences represented by the Qudi Formation (Succession Ⅲ) mark the climax and standstill stages of the first episode of the syn-rift tectonic activities, respectively. In the late Artinskian to Kungurian age, the second episode of syn-rift is manifested by the Succession Ⅳ and Ⅴ. And the former retrogradational sequence (Succession Ⅳ), reflected in the lower part of the Tunlonggongba Formation, indicates a climax stage of syn-rift tectonic activity, while the latter aggradational-progradational sequences (Succession Ⅴ), represented by the upper part of the Tunlonggongba Formation, mark a stage of tectonic quiescence. Therefore, these Early Permian sedimentary successions in the SQB are best explained by the tectonic subsidence resulting from the rifting of the SQB from the Gondwana margin, suggesting an early Permian timeline for the initial opening of the Bangong-Nujiang Meso-Tethys Ocean.

       

    /

    返回文章
    返回