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西域组是我国西部一重要并广泛引用的晚新生代地层,关于其年代和成因至今尚存争议。在西南天山喀什远源盆地喀什-阿图什褶皱带不同构造部位选择有代表性的5～6个晚新生代地层剖面开展了详细的沉积学、磁性地层年代学对比研究,据此限定了不同构造的起始变形时间以及西域砾岩的沉积年代。西域砾岩并非一年代地层单位,作为一岩石地层单位,其底界具有穿时特征,从山体(北)向喀什前陆盆地(南)逐渐变新。其底界年龄在盆地北部近源区约为15·5Ma[1],在盆地中部中源区约为8·6Ma[1],在盆地南部远源区的阿图什背斜为1·9Ma,喀什背斜为1·6～0·7Ma。这一穿时的砾岩沉积楔体的起始堆积起因于盆地北部边界逆冲断层(KBT)的活动。构造变形是由北南脉冲式迁移扩展的,其速率是非均匀的,在约15·5Ma至4·0Ma期间为1·4～3·4mm/a,在约4·0Ma以来剧增至>10mm/a。西域砾岩沉积前缘向南进积速率与构造变形前缘迁移速率有很好的一致性,但在时间上较构造变形可能滞后2·0Ma。这表明构造变形前缘向南的脉冲式扩展是西域砾岩进积并发生侧向和垂向上岩相突变的主因。
The Western Regions Formation is an important and widely cited late Cenozoic strata in western China. There are still controversies about its age and causes. In the southwest Tianshan Kashgar Yuanyuan basin Kashgar Atushu fold belt of different tectonic parts of the representative selection of 5 to 6 Late Cenozoic stratigraphic sections carried out detailed sedimentology, magnetic stratigraphic chronology comparative study, thus defining different The onset of tectonic deformation, and the age of conglomerate deposition in the western region. The conglomerate in the western region is not a primary strata unit. As a lithostratigraphic unit, the bottom boundary of the conglomerate has the characteristics of permutation and gradually changes from the mountain (north) to the Kashgar foreland basin (south). The bottom boundary age is about 15.5 Ma [1] in the northern part of the basin and about 8.6 Ma in the middle source area in the central part of the basin, and 1. 9 Ma in the far source area in the southern part of the basin , Kashi anticline is 1.6 ~ 0.7Ma. The initial accumulation of this weathered conglomerate sedimentary wedge arises from the activity of the northern boundary thrust (KBT) of the basin. Tectonic deformation is extended by north-south pulsed migration at a heterogeneous rate of 1.4-4.3 mm / a over a period of about 15.5 to 4.0 MPa and a dramatic increase to> 10 mm over about 4.0 mm / a. The depositional rate of sedimentary frontier in the western conglomerate has a good consistency with the migratory rate of tectonic deformation, but it lags behind that of structural deformation by 2.0 Ma in time. This indicates that the pulsatile expansion to the south of the tectonic deformation front is the main cause of lateral and vertical facies facies alteration in the western margin conglomerate.