准噶尔盆地构造演化与动力学背景再认识

Further Researches on the Tectonic Evolution and Dynamic Setting of the Junggar Basin

准噶尔盆地是中国西部重要的含油气盆地,关于其演化历史,至今尚存在争议。地球物理资料分析表明,准噶尔盆地地质结构在平面和剖面上具前陆盆地系统的结构特征。本文运用前陆盆地理论,通过压陷挠曲作用,以演化动力为背景,将准噶尔盆地分为5个演化阶段:①碰撞成盆阶段;②压陷挠曲阶段;③挠曲坳陷阶段;④坳陷沉降阶段;⑤再生前陆盆地阶段。石炭纪至二叠纪,准噶尔地块周围海槽先后关闭,发生陆陆碰撞。首先是西北缘:早石炭世末期形成西北缘界山的雏形;其次是东北缘:晚石炭世中晚期,形成了克拉美丽造山带;最晚是南缘:于早二叠世晚期风城组沉积期,形成南缘界山。随着周缘界山的隆升,准噶尔盆地形成三大前陆盆地系统。三叠纪至古近纪,板块挤压作用减弱,准噶尔盆地由强烈压陷期逐渐进入坳陷沉降阶段。新近纪至第四纪,受喜马拉雅运动的影响,北天山快速、大幅度隆升,准噶尔盆地南缘再次挠曲下沉,形成近EW向的再生前陆盆地。多期演化造就了盆地具有多套生、储、盖组合和多期次成藏,为油气的富集创造了条件。

There still exist some different opinions concerning the evolution of Junggar basin, an important oil-bearing basin in wes-tern China. An analysis of geophysical data shows that geological structures of Junggar basin in plane and in profile have the foreland basin features. Based on the dynamic setting, the authors utilized the foreland basin systems and pressure-flexure action to divide the evolution of the Junggar basin into five stages: ① collision-basin-forming stage; ② pressure-flexure stage; ③ flexure-depression stage; ④ depression-sedimentation stage and ⑤ foreland basin regeneration stage. From Carboniferous to Permian, the ocean troughs around Junggar massif were closed early or late and continent-continent collision took place. At first, the northeastern part was formed during the late period of Early Carboniferous. Then Kelameili orogenic belt was developed in the northwest during middle and late periods of Late Carboniferous. Finally, the southern part was formed during the late period of Early Permian. With the uplift of marginal mountains, three foreland basin systems were formed in Juggar basin. From Triassic to Palaeogene, the plate squeezing action weakened and Junggar basin gradually entered a depression-subsidence phase from the intense compressive phase. From Neogene to Quaternary, North Tianshan Mountains were uplifted quickly and extensively under the influence of Himalayan movement. The southern part subsided again and formed the regenerated foreland basin from west to east. As a result of such a complex evolution, Junggar basin developed more than one sets of source-reservior-caprock assemblages and multiple periods of hydrocarbon accumulation, which provided favorable conditions for oil and gas accumulation.