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Mesozoic-Cenozoic tectonic relationships between the Kuqa subbasin and Tian Shan, northwest China: constraints from depositional records

机译：库车盆地与中国西北天山之间的中，新生代构造关系：沉积记录的约束

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摘要

Stratigraphic profiles in the Kuqa subbasin, located along the southern flank of the Tian Shan, northwest China, display similar Mesozoic-Cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts, sandstone framework grains and detrital heavy minerals. The similarity of these time-series profiles resulted from orogenesis and intracontinental deformation of the provenance area, the (ancestral) Tian Shan. Mineralogical maturities of conglomerates and sandstones increase from Triassic to Middle Jurassic and decrease from Upper Jurassic-Lower Cretaceous to Tertiary. This trend parallels a similar decrease in maturity in detrital heavy minerals. Zircon, rutile and tourmaline dominate in Middle-Upper Triassic to Middle Jurassic sandstone, whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the Tertiary, especially in Miocene and Pliocene strata. These compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from Cretaceous to Miocene. Since the Pliocene, large-scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward. Based on the Mesozoic-Cenozoic depositional records, the tectonic evolution of the Tian Shan-Kuqa subbasin may be divided into five phases. (1) In Early Triassic, following compression and uplift since Permian, gravelly braided river-alluvial plain depositional systems developing in the Kuqa subbasin, characterized by sands of mixed orogenic provenance type derived from the ancestral Tian Shan. (2) From Middle Triassic to Middle Jurassic, sediment composition of the Kuqa subbasin reflects arc orogen and mixed orogenic sand types, with extensive planation of the ancestral Tian Shan and the development of relatively stable coal-bearing depositional environments. (3) Renewed compression-uplift of the Tian Shan occurred in Late Mesozoic, especially in Cretaceous, with most detrital modes of the Kuqa subbasin indicating provenance attributes akin to the South Tian Shan. (4) Further intensive compression-uplift and, probably, southward (basinward) propagation of the South Tian Shan occurred during Miocene; and (5) supracrustal gravity gliding and collapse occurred in the Tian Shan-Kuqa subbasin probably due to intensive deep compression, with rejuvenated uplift and probable southward (basinward) structural propagation of the South Tian Shan developing since Pliocene. Observed changes in sediment composition and depositional environment since Pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the Tian Shan. Moreover, all depositional records in the Kuqa subbasin seem to reflect west to east differences in provenance along the Tian Shan, probably indicating greater exhumation depth in the western Tian Shan than that in the eastern Tian Shan since Early Cretaceous.
机译：位于中国西北天山南侧的库车盆地的地层剖面显示，砾岩，砂岩骨架颗粒和碎屑重矿物中存在相似的中，新生代成分成熟度演化序列。这些时间序列轮廓的相似性源于起源地（祖先）天山的造山作用和大陆内变形。砾岩和砂岩的矿物学成熟度从三叠纪到中侏罗纪增加，而从上侏罗纪-下白垩纪到第三纪逐渐减少。这种趋势与碎屑重矿物的成熟度下降类似。锆石，金红石和碧玺在中上三叠统至中侏罗统砂岩中占主导地位，而不稳定的角闪石和辉石则在第三纪的重矿物组合中占主导，特别是在中新世和上新世地层。这些组成趋势与冲积沉积锋面和沉积沉积中心从白垩纪向中新世的逐渐南移同时出现。自上新世以来，冲积沉积系统发生了大规模的南移，而沉积沉积中心则向北移动。根据中，新生代沉积记录，田山—库车次盆地的构造演化可分为五个阶段。 （1）在三叠纪早期，由于二叠纪以来的挤压和隆升，在库车次盆地发育了砾石辫状的河冲积平原沉积系统，其特征是源自祖先天山的混合造山物源型砂。 （2）从中三叠世到中侏罗世，库车亚盆地的沉积物成分反映了弧造山带和混合造山带的砂类型，祖先天山的广泛展布和相对稳定的含煤沉积环境的发展。 （3）在中生代晚期，特别是在白垩纪，天山重新出现了压缩隆升，其中库车次盆地的大部分碎屑模式表明了物源属性类似于南天山。 （4）中新世期间，南天山进一步发生强烈的压缩隆升，并可能向南（向北）传播； （5）天山—库车次盆地发生上地壳重力滑移和塌陷，可能是由于深部强烈的压缩作用，上新世以来南天山恢复了兴旺的隆升作用，并可能向南（向北）构造扩展。自上新世以来观测到的沉积物成分和沉积环境的变化，除了天山的强烈隆升外，还受到频繁而突然的气候变化的控制。此外，库车次盆地的所有沉积记录似乎都反映了天山沿东西向的物源差异，这可能表明自早白垩世以来，天山西部的发掘深度比东天山的发掘深度大。

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