库车前陆褶皱—冲断带前缘大型盐推覆构造

A Large-scale Salt Nappe Complex in the Leading Edge of the Kuqa Foreland Fold-Thrust Belt, Tarim Basin, Northwest China

塔里木盆地北部库车前陆褶皱-冲断带构造-地层层序可划分为中生界盐下层序、古新统一始新统盐层层序和渐新统一第四系盐上层序。盐岩层序的岩性主要为灰白色、浅灰色盐岩、膏岩、泥灰岩和紫红色碎屑岩,厚110～3000 m。盐岩层的存在使库车前陆褶皱-冲断带发育-系列盐相关构造,其中最引人注目的是盐推覆构造。野外地质调查、地震资料解释、遥感资料和钻井资料揭示,沿库车前陆褶皱-冲断带前缘西秋立塔克山发育大型盐推覆构造,总体呈近东西走向,并略呈往西南凸出的弧形展布,沿走向延伸超过200km,由北往南逆冲推覆距离达30km以上。主断层沿古新统-始新统盐岩层发育,外来推覆体由古新统-始新统盐层层序和渐新统-第四系盐上层序组成,表现为受断层控制的单面山,逆冲推覆在原地中生代-新生代地层之上。地质分析和剖面复原结果表明,盐推覆构造主要形成于新近纪末期以来的喜马拉雅晚期阶段,现今仍具有强烈的活动性。由于不均匀推覆作用,在盐推覆构造的不同地段,逆冲推覆距离、冲断层产状、外来岩系和原地岩系的叠置关系以及盐相关构造的发育都有较大差异,显示出走向上分段性特点。库车前陆褶皱-冲断带前缘盐推覆构造的形成演化受区域挤压作用、重力滑动和重力扩展作用控制。

The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt, northern Tarim basin, Northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene—Eocene salt sequence and the Oligocene—Quaternary supra-salt sequence. The salt sequences are mainly composed of light gray halite, gypsum and marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold-thrust belt, in which the most fascinating structure is the salt nappe complex. Based on field observations, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east—west for over 200 km and occurs along the western Qiulitag Mountain. Its thrusting displacement is more than 30 km. The salt nappe complex occurs as an arcuate zone projecting southwestward along the leading edge of the Kuqa foreland fold-thrust belt. The major thrust fault is developed along the salt beds of the Paleocene—Eocene. The allochthonous nappes are large N-dipping faulting monoclines composed of Paleocene—Pliocene sediments, thrusting on the autochthonous Meso-Cenozoic successions. According to the geological analysis and cross-section restoration, the salt nappes were mainly formed in the late Himalayan stage since the end of Neogene and are still active intensively at present. Because of the inhomogeneous thrusting, there are great differences in the displacement and occurrence of the thrust, the superimposition of the allochthonous and autochthonous sequences, and the development of the salt-related structures, indicating a feature of segmentation along the salt nappes. The salt nappe complex in the Kuqa foreland fold-thrust belt is controlled by regional compression, and gravitational gliding and spreading.