【作者】 李世琴；

【导师】 汪新；

【作者基本信息】 浙江大学 ， 构造地质学， 2009， 博士

【摘要】 本文依据石油勘探二维地震剖面,结合地表地质调查、遥感影像解译和钻测井数据,建立库车前陆盆地中-西段区域构造剖面,确定库车秋里塔格构造带中-西段挤压盐构造特征;利用轴面分析以及深度隆升（Depth-relief method）和厚度隆升方法（Thickness-relief method）,计算剖面的构造缩短量;根据库车盆地西段新生界6-8km厚的同构造沉积地层几何形态恢复,结合地层磁性年代学数据,分析库车盆地西段的盐构造演化历史,进而揭示南天山库车山前带新生代构造演化过程。库车盆地新生代沉积两套膏盐岩:古-始新统库姆格列木组(E_1-2km)盐岩和中新统吉迪克组(N_lj)盐岩,库姆格列木组盐岩分布在库车盆地西部,吉迪克组盐岩分布在库车盆地东部。库车地区的构造变形与这两套膏盐活动密切相关,盐岩的分布范围及其活动特征控制了盆地的构造变形特征、变形机制和变形序列。秋里塔格中段构造结位于库姆格列木组盐岩和吉迪克组盐岩交汇处,其构造变形受三个滑脱面:中新统吉迪克组盐岩、古-始新统库姆格列木组盐岩和侏罗系（J）煤层控制。构造结东部发育两个滑脱面,它们分别是中新统吉迪克组盐岩和侏罗系煤层,形成浅层的滑脱褶皱和深层的断层转折褶皱,深、浅层背斜叠加在一起,构成库车塔吾复合背斜;构造结西部发育一个滑脱面:库姆格列木组盐岩,盐岩聚集形成南秋里塔格盐背斜。库车塔吾背斜向西倾伏,背斜下伏沿吉迪克组盐岩和侏罗系煤层发育的断层滑移量向西减小。南秋里塔格背斜向东倾伏,背斜下伏沿库姆格列木组盐岩发育的断层滑移量向西增大。构造结地区三个滑脱面交汇:①东、西段卷入变形的断层和褶皱在此发生了叠加干涉;②断层的滑移量在此汇合转换;③库车塔吾背斜、南秋里塔格背斜和托克拉克坦背斜在此交汇,交汇处发育多个高角度的逆冲剪切断层和表皮褶皱,形成了秋里塔格中段复杂构造结。秋里塔格构造带西段,大量的外来库姆格列木组盐岩聚集在南秋里塔格背斜、北秋里塔格背斜、亚克里克背斜和米斯坎塔克背斜核部,盐下中生代地层未卷入变形,形成薄皮的挤压盐构造。薄皮挤压盐构造的形态受两个因素影响:①库姆格列木盐岩在秋里塔格构造带南缘尖灭,由此产生的摩擦阻力急速增加易于盐岩在尖灭线附近聚集;②库车盆地西段在挤压构造发生前就发育先存的盐底辟构造（Pre-existing salt diapir）,这些盐底辟构造在库姆格列木盐岩沉积后不久便开始发育,易于受到后期挤压变形的改造。如果盐底辟的发育时间很短,挤压变形之前已被较厚的地层覆盖,这种类型的盐底辟被挤压后将继续演化为盐丘背斜（Salt dome）,外来盐岩聚集在背斜核部,例如南秋里塔格背斜、北秋里塔格背斜。如果盐底辟的发育时间很长,挤压变形之前盐底辟之上仅沉积很薄的地层,这种类型的盐底辟被挤压后容易演化为盐推覆构造,例如却勒盐推覆体,盐底辟的北翼逆冲推覆到南翼之上,盐岩沿逆冲推覆面流至地表形成盐席。本文通过逐层恢复库车盆地西段新生界6-8km厚的同构造沉积地层几何形态,发现新生代天山自20-25 Ma开始重新活动以来,南天山库车盆地西段的构造缩短变形直到中新世早期仍主要集中在北部单斜带,库车山前大规模的挤压变形发生在上新世（5-6Ma）以后。在挤压构造发生之前,库车盆地西段主要发生膏盐岩的塑性流动,形成相关盐构造。上新世开始的大规模挤压变形是形成大宛齐背斜、秋里塔格构造带和秋里塔格南缘隐伏滑脱褶皱的主要原因。本文计算出库车盆地西段的构造缩短量为～23 km,如果依据前人的观点:天山的隆升始于20-25 Ma,由此得到天山隆升以来库车山前的构造缩短率为～1.15/0.92 mm/yr,这与GPS测量的天山（80-85°E范围）现今缩短率～7-8 mm/yr不相符。本文对库车盆地西段两条构造平衡剖面的正演恢复结果显示,上新世（5.2/5.8 Ma）到更新世（2.58 Ma）,库车盆地西段的构造缩短量为～9 km,平均缩短率～3.4/2.8 mm/yr;更新世（2.58 Ma）以来,库车盆地西段的构造缩短量为～14 km,平均缩短率～5.4 mm/yr。显然,库车山前的构造缩短主要发生在上新世以后,其构造缩短率与GPS测量的天山（80-85°E范围）现今缩短率～7-8mm/yr相符。因此,本文推断天山隆升以来至少经历了两次构造加速事件:分别是早上新世和早更新世。更多还原

【Abstract】 This thesis focuses on the salt tectonics and synkinematic strata in the middle to western Kuqa foreland basin. Integrating surface geology, well data and a grid of seismic reflection profiles, thirteen balanced cross sections were constructed in this paper. Shortening displacements of several profiles were calculated by the axial surface analysis, the Depth-relief method or the Thickness-relief method respectively, and the Cenozoic synkinematic strata (6-8 km thick) in the western Kuqa basin were bed-by-bed restored. According to the shortening displacements and the shape of the synkinematic strata, in combination with the previous magnetostratigraphic data, the salt tectonics evolution and the Cenozoic histories of the Tian Shan were discussed in this paper.The Kuqa basin deposited two sets of salt. They are the Paleocene-Eocene Kumugeliemu salt and the Miocene Jidike salt. The Kumugeliemu salt distributes in the western Kuqa basin, while the Jidike salt distributes in the eastern Kuqa basin.At the middle segment of the Qiulitage fold belt, there are three decollements: the Jurassic coal bed, the Paleocene-Eocene Kumugeliemu salt and the Miocene Jidike Salt involved in deformation. The Kuqadawu anticline is a detachment fold cored by the Jidike salt, which overlies a deep fault-bend fold with a lower decollement flat locates in Jurassic coal bed. The southern Qiulitage anticline is a thin-skinned salt anticline cored by the Kumugeliemu salt.Shortening displacement estimatation shows that the displacements of faults developed by the Jidike salt and the Jurassic coal bed decrease to west, while the displacement of the fault developed by the Kumugeliemu salt is converse. Furthermore, the Kuqadawu anticline plunges to west, the southern Qiulitage anticline plunges to east, so both of the Kuqadawu anticline and the southern Qiulitage anticline plunge with their underlying faults respectively. As a result, (1) the strara involved in deformation were superimposed, (2) the shortening displacements of the three decollements were converged and transformed, and (3) the Kuqadawu anticline, the southern Qiulitage anticline and the Tuokelaketan anticline converged in the middle segment of the Qiulitage fold belt, induced complex deformation over here.At the western segment of the Qiulitage fold belt, thin-skinned compression salt tectonics developed, comprising of numerous allochthonous Kumugeliemu salt. These thin-skinned salt teconics have been influenced by two factors: (1) the distal pinch-out of the Kumugeliemu salt located at south edge of the Qiulitage fold belt, which resulted in an increasing of frictional resistance, was prone to allochthonous salt accumulating in here. (2) Several pre-existing diapirs developed in the western Kuqa basin. These precursor diapirs initiated soon after the Kumugeliemu salt deposition, which had different growth histories, localized the contraction strain of later shortening. If a diapir had a short growth history and was overlain by a thick overburden, it was likely to evolve into a salt dome by later shortening, comprising a 3000-7000 m thickness of allochthonous salt. Conversely, if a diapir was overlain by a thin overburden, it was more likely to form a salt nappe, with northern flank of the diapir thrust over its southern flank.The shape of the synkinematic strata in the westerm Kuqa basin indicates that since the regeneration of the Tian Shan at 20-25 Ma, the shortening deformation of the western Kuqa basin mainly accumulated in the hinterland until the early Miocene, while the intense shortening deformation of the western Kuqa basin iniated since the early Pliocence/ late Miocene (5-6 Ma). Before compression deformation, the middle to western Kuqa bain developed early salt tectonics.The western Kuqa basin has -23 km of total shortening displacements. Accordingly, if the Tian Shan regerated at 20-25 Ma, we get a -1.15/0.92 mm/yr average shortening rate. This is very small than the shortening rate of the modern Tian Shan (-7-8 mm/yr in 80-85°E) estimated by GPS (Abdrakhmatov et al, 1996; Wang et al., 2001). However, two forward kinematic profiles in this paper illustrate that -9 km of the total shortening consumed during the end of Miocene (5.2/5.8 Ma) to the early Pleistocene (2.58 Ma), and -14 km have been absorbed since then, thus obtaining a -3.4/2.8 mm/yr average shortening rate from 5.2/5.8 Ma to 2.58 Ma, and a -5.4 mm/yr average shortening rate since the 2.58 Ma, which is concordant with the shortening rate of the modern Tian Shan estimated by GPS. Therefore, the modern Tian Shan had at least experienced two accelerated events, which began in the late Miocene/early Pliocene and early Pleistocene, respectively.更多还原