帕米尔构造结中新生代构造地貌演化及对塔里木盆地海退的影响

摘要

Robust constraints on Mesozoic-Cenozoic tectonic and topographic processes of the Pamir syntaxis is crucial to understanding the orogenesis and geodynamics of the Tibetan Plateau,as well as their impacts on the climate changes of Central Asia in the past.This review paper emphasized on the compilation of research progress on onset timing and evolution of major structures,burial and exhumation of the gneiss dome systems,as well as metamorphism and magmatism in the Pamirs and adjacent areas in recent decade,which are central to the topics of Mesozoic-Cenozoic morphtectonic evolution of the Pamir syntaxis,and Cenozoic incursions of the Tarim Sea.Episodic geodynamic scenarios were proposed to account for tectonic and topographic development of the PamirWest Kunlun Mountains from the Permian to the Late Miocene.It is confirmed that the Pamir-West Kunlun Mountain belts are long-lived topographic expression dating back to Triassic-Early Jurassic times,and have experienced Middle-Late Mesozoic to Early Cenozoic rejuvenation and Late Oligocene-Miocene outward and upward expansion.The Eocene deformation of the Pamir-West Kunlun Mountains was minor compared with thickening of the crust initiated at ca.37 ～ 35 Ma.Notably,large-scale northward indentation of the Pamirs did not occur until the Late Oligocene,responsible for the formation of orocline structures of the Pamir syntaxis.A model of double-sided lithospheric wedge model primarily driven by breakoff of the Indian crustal slab was built up to explain widespread intense tectonism in the Pamirs,featured by synchroneity of initial deformation of major structures,intense rock exhumation and burial peak metamorphism,associated with coeval magmatism across western Tibet.To the north the Pamir-West Kunlun Mountains,two steps of westward retreat of Paratethys Sea from the Tarim Basin took place at ca.41 ～ 40 Ma and ca.39 ～ 37 Ma in time order.The timing of latest regression of Paratethys from the Tarim Basin partially overlapped with Eocene magmatism of the central Pamir and the onset of significant crustal thickening of central and southern Pamirs from ca.37～35 Ma ago,implying potential impacts of regional tectonics on final sea retreat in the Tarim Basin.In addition,the oscillation of marine regression and transgression in Central Asia keeps pace with the drop-and-rise pattern of global sea level due to climate change,suggesting a role of climate change playing on the retreat of Tarim Sea in a long-term period.Therefore,both mechanisms of crustal thickening and descending of global sea level due to global cooling could control the final regression of the Tarim Sea.The relative contribution of tectonism and climate change to sea retreat from Central Asia still needs to be further evaluated.%对帕米尔构造结中新生代构造变形和地貌演化过程的精细约束是揭示青藏高原造山历史和动力学机制,以及中亚古环境变迁控制因素的关键.文章重点总结了近十年来与帕米尔中新生代构造地貌演化,以及塔里木盆地新生代海侵海退相关的研究成果,包括主要断裂构造、穹窿埋藏和剥露、岩浆变质作用,刻画了帕米尔-西昆仑从二叠纪末期到中新世中晚期的构造地貌发展的动力学过程.研究表明,帕米尔-西昆仑山脉从三叠纪-侏罗纪早期就已经出现,经历了中生代中晚期和新生代早期的活化造山和晚渐新世-中新世向外和向上生长过程.帕米尔构造结始新世的构造变形比较微弱,其地壳的强烈增厚始于37～35 Ma,帕米尔向北的大规模楔入和弧形构造的形成均发生在晚渐新世(约27～ 25 Ma)以来.晚渐新世-早中新世是帕米尔构造结强烈变形期,大型断裂的初始活动、岩石剥露和岩浆变质可用印度板块断离引起的地壳物质向南北两侧双向楔冲的动力学模型来解释.帕米尔-西昆仑山前的塔里木盆地分别经历了约41～40 Ma和39～ 37 Ma两次幕式向西的海退过程.特提斯洋最终退出塔里木-阿莱依-塔吉克盆地的时间(约39～37 Ma)与中帕米尔始新世岩浆作用及中-南帕米尔地壳开始强烈增厚的时间(约37～ 35 Ma)略有重叠,暗示构造对塔里木盆地最终海退可能存在一定影响.但从长时间尺度来看,中亚地区海侵和海退震荡波动与气候变化引起的全球海平面升降变化的规律是一致的,说明气候变化对塔里木海退的长期影响.据此,特提斯洋最终退出塔里木盆地可能是帕米尔地壳加厚和气候变冷引起的全球海平面下降共同作用的结果,而构造和气候对塔里木海退的相对贡献则还需要进一步评估.