The tectonic environments of the Late Neoproterozoic-Early Paleozoic and its tectono-sedimentary response in the Tarim Basin

Abstract

塔里木盆地上新元古界-下奥陶统是我国超深层油气勘探的重要领域，但其盆地动力学研究程度低、认识分歧大，制约了塔里木盆地超深层油气地质评价。本文综合近年地质学、地球化学与地球物理资料，探讨塔里木盆地晚新元古代-早古生代板块构造环境及其构造-沉积响应，提出以下5个方面认识：（1）新元古代-早古生代经历了前展-后撤-前展俯冲的板块构造演化；（2）南华纪发育后撤俯冲机制下的大陆裂谷沉积体系，不同于地幔柱机制；（3）震旦纪-寒武纪不是裂谷盆地的连续沉积，而是发育后撤-前展俯冲转换期的前寒武纪大不整合面；（4）寒武纪-奥陶纪，塔里木盆地缺乏被动大陆边缘背景，发育一套碳酸盐台地沉积，而且随着原特提斯洋闭合的前展俯冲作用增强，导致了中奥陶世晚期台地从东西分异转向南北分异的沉积演变；（5）晚奥陶世末在前展俯冲造山作用下形成复理石快速充填的类前陆盆地，但没有形成碰撞造山作用下的磨拉石前陆盆地。研究认为，塔里木板块晚新元古代-早古生代多期幕式后撤-前展俯冲机制形成了南华纪强伸展→震旦纪末挤压与寒武纪-早奥陶世弱伸展→中奥陶世晚期-志留纪强挤压的两大构造旋回，并造成了构造-沉积演化的差异性，不同于经典的威尔逊旋回模式及其成盆动力学机制。;The Upper Neoproterozoic-Lower Ordovician stratum of the Tarim Basin is an important ultra-deep hydrocarbon exploration target in China. However, only a few studies on basin dynamics have been carried out in this area, which greatly constrain the geological evaluation of ultra-deep hydrocarbon potential. Integrated with recent geological, geochemical and geophysical data, this paper discusses the Late Neoproterozoic-Early Paleozoic tectonic environments of the Tarim Basin and their tectonic-sedimentary responses. The results show that: (1) during the Neoproterozoic-Early Paleozoic Era, an advancing-retreating-advancing subduction evolution occurred in the Tarim Bain; (2) in the Nanhua Period, a continental rift depositional system developed in the basin by the retreating-subduction mechanism that differs from the mantle plume mechanism; (3) the Sinian-Cambrian of Tarim Basin was not a continuous sedimentary succession of a rift basin, but a Precambrian Great Unconformity during the transition period from retreating to advancing subduction; (4) in the Cambrian-Ordovician, the Tarim Basin is lack of a passive continental margin environment, while a carbonate platform occurred in it; and a transition switched from E-W to S-N trending differentiations of the platform in the late Middle Ordovician by the increasing advancing subduction following the Proto-Tethys Ocean closure; (5) at the end of the Late Ordovician, rapid flysch-filling para-foreland basin formed by the advancing subduction orogeny rather than molasse-filling foreland basin by a collisional orogeny. In conclusion, the Late Neoproterozoic-Early Paleozoic multi-episodic retreating-advancing subduction mechanism formed two tectonic cycles of strong extension in Nanhua Period to compression in the Late Sinian, and weak extension during the Cambrian-Early Ordovician to strong compression during the late Middle Ordovician-Silurian, which led to the varied tectono-sedimentary evolution in the Tarim Plate. This geological evolution is different from the classical Wilson Cycle and its basin dynamic mechanism.