龙门山冲断带构造特征与油气勘探远景研究

1、龙门山冲断带构造特征与油气勘探远景研究        【中文摘要】龙门山冲断带位于四川盆地西侧,扬子准地台和松潘甘孜褶皱带分界线上,主要为一条NESW向大型构造带,由众多北东向、南北向和少量的北西向及断裂组成,构造特征复杂多变,不同地带的构造控制因素不一致。本论文正是从构造学作为切进点来讨论,从构造的运动学、几何学及动力学等因素讨论了构造样式的组合和分布特征,及其对油气分布的控制作用,重点探讨构造差异性,同时在分析、盆山耦合动力学、构造演化等对于油气的影响作用的基础上,最后综合评价有利勘探区带。从现今构造面貌来看,

2、后期构造的叠加和改造具有普遍性,并且由于改造的方式和部位不同,造成现今复杂的构造面貌。龙门山冲断构造带各期构造的发展,都从深部基底及以下岩块的抬升推覆,造成了相当规模的向盆地方向的构造侵位。在前山地区出现了以台阶状断层控制的叠瓦断片为特征的消减带和以褶皱为主的传播带,以及可能出现的以反冲断层和相关褶皱组成的反冲褶皱带。现今的构造面貌均叠加复合了早期的形变。对早期形变的改造,剖面上主要表现上叠,出现新地层的形变,与老褶皱发育部位不同。平面上构造侵位,切割前期的形变,或使前期形变更加紧闭。龙门山冲段带明显的构造特征总体表现为差异性。由南向北具有分段性差异,不同构造段落具有不同的构造特征;自西向东有

3、分带性差异,几条主要大型断裂控制了不同的构造形变带;纵向上表现出分层性差异,各构造层次分别代表不同构造时期的形变特征。在构造样式分布上,印支晚期的叠瓦状逆冲推覆与断层转折褶皱主要分布于龙门山前北段,南段大邑地区保存了印支期生长断层转折褶皱。燕山喜山期前陆方向构造消减褶皱带发生在上述逆冲推覆带的下盘,各断层基本上隐伏于侏罗系以下,构造活动发生于燕山喜山期,但时间上稍晚于逆冲推覆构造。构造成由于龙门山向东挤压时部分断层转向前陆盆地方向传递所致,为逐渐消减其位移量,多形成以断层传播褶皱和局部协调性反冲断层为主的构造类型,也有在滑动过程中分叉为多条分支状断层并逆冲至地表形成次级规模的推覆褶皱。山前叠瓦

4、状逆冲推覆带是龙门山与四川盆地构造结合部的最前排断裂带,主要发生于喜山期,由两个主要的逆冲推覆构造组成,白水河逆冲断裂带和宝兴南彭灌安县逆冲断裂带,两者呈叠瓦状排列。从构造动力来源和应力开释表现形式的角度来看,北川映秀大断裂北西的后山带是龙门山冲断带形成的动力来源,构造表现为由深部向浅层逆冲、冲断;前山为主要应力开释带,表现为以深部发育的台阶状断层所控制的一系列逆掩、推覆构造体系。自印支期以来,在台阶状断层的控制下,总体由深层向浅层递进推覆的形变过程,其间又叠加了后期的构造形变的形迹和面貌,形成了现今龙门山十分复杂的构造格式。在构造演化上有具有由南向北依次发展起来,主要构造形成期具有滞后性的特

5、征。印支期大规模的推覆侵位首先产生于北段地区,燕山期,大规模台阶状逆掩断层向盆地的侵位多发于中段及其以南地区,喜山期龙门山造山带强烈隆升,大规模推覆侵位主要发生于南段地区。龙门山冲段带具有丰富油气资源,勘探潜力大,目前已在部分构造上取得了较好的油气成果,通过综合评价出三个有利勘探区带,展示了该带良好的勘探远景。');【Abstract】 The Longmenshan thrust belt locates in the west side of Sichuan basin, the boundary of Yangzi metaplatform and Songpan-Ganzi b

6、ow area. It is a huge structure belt extending from NESW and composed of several faults with NE, NW and little SW aligement. The tectonic character is complicated, and different part with different tectonic control factor. The text analyze the tectonic pattern assemblage, distribution character and

7、its effect on oil and gas distribution. The main goal is the tectonic difference. Meanwhile at the base of basin and range couple mechanism and tectonic evolution's influence on oil and gas accumulation, the text finally have evaluated the potential available area for exploration.It can be concl

8、uded from today's tectonic pattern, the later overlapping of tectonic movement and reforming are common. And because of different part with different pattern of reforming, the structure is rather complex today. The Longmen mountain thrust's movement in each episode were from the thrust of de

9、ep basement and block and cause the tectonic emplacement to the basin with considerable scale. There are consumering zone and propagation which are marked with imbricated passage in the front range. And also there are recoil faults and recoil bow area. The tectonic features today are overlapped with

10、 early deformation. As for early deformation, the main phenomenon are represented as the deformation of new layer, which are different with old layers. The tectonic emplacement in plane and the deformation before the cutting ,or made the early deformation become more close.The mainly character of Lo

11、ngmen mountain thrust belt is divergence. From south to north, different tectonic section has their own tectonic character; From west to east, several main fault control the different tectonic deformation belt; In vertical, each tectonic layer represents the deformation of different episode. As for

12、tectonic pattern, the imbricate thrust and fault reversing fold of late Indosinian distribute mainly in north section of Longmenshan mountain, and the Gulf-Coast-type fault transition fold are preserved in Dayi of south section. The tectonic subduction fold belt of Yanshan-Himalayan movement develop

13、ed in the downdip block of thrust belt, each fault are commonly below Jurassic system, and the tectonic movement happened during Yanshan-Himalayan episode, but little later than thrust-decken structure.To decrease the stress to the foreland basin, the main tectonic pattern are fault propagating fold

14、 and local recoil fault. Still there are some branched faults thrusting to the su*ce and became secondary thrust fold. Imbricate deckenbau belt is at foremost fault belt in joint of Longmen mountain and Sichuan basin. It occurs during Himalayan episode and formed with two major thrust belt: Baishuih

15、e thrust fault belt and South Baoxing-Pengguan-Anxian thrust fault belt, which lays overlapping. Regarding the source and the expressing pattern of tectonic sfault tress, the back belt of Beichuan-Yingxiu big fault is the source. The tectonic character shows the fault thrusts from deep to shallow la

16、yer; The front range is the main belt to release the stress. From Yanshan episode, at the control of the bench fault, the thrust developed form deep to shallow and was overlapped by later tectonic deformation. All those above form the complex tectonic framework of Longmen mountain.The tectonic evolu

17、tion developed gradually from south to north and the main episode for formation is delayed. The huge thrust of indosinian first occurred in north section, while the bench thrust emplacing to basin with large scale of Yanshan episode occurred in middle and south part. The intense uplift of Himalayan caused large emplacement in so