【作者】 田小彬；

【导师】 刘树根；

【作者基本信息】 成都理工大学 ， 矿产普查与勘探， 2009， 硕士

【摘要】 龙门山陆内复合造山带北段地区是指以北川、安县为界向北东方向延伸的部分,以出露轿子顶杂岩和唐王寨向斜为主要特征,总体上表现为复杂的逆冲推覆构造。本文通过详细的野外地表构造特征调查,地表沥青分布特征调查,区域地震剖面的重新解释等工作,对龙门山北段地区的地表构造特征、地腹构造特征、形成演化过程、地表沥青分布特征以及该区的油气勘探前景进行了研究,并取得了一定成果。龙门山北段地区地表3条主干断裂厘定为青川—阳平关断裂、凉水—林奄寺断裂及马角坝—竹园坝断裂,这3条断裂均有多期变形,在不同时期具有不同的运动特征:前两者早期以韧性变形为主,晚期以脆性变形为主,马角坝—竹园坝断裂主要以脆性变形为主。依此3条主干断裂将龙门山陆内复合造山带北段及其邻区划分为:碧口微地块、后龙门山陆内造山带、前龙门山陆内造山带及川北复合前陆盆地4个构造单元,各构造单元构造变形特征差异显著,表现为自北西向南东,自造山带向盆地方向变形-变质作用明显减弱。在垂向上,依据地震剖面的解释可以把龙门山北段分为上、中、下3层构造:上构造层是以志留系和奥陶系、寒武系组成的叠瓦冲断系;中构造层是以中下二叠统、泥盆系、志留系、奥陶系和寒武系构成的相对平缓的构造层,构造缩短有限;下构造层以平缓反射为主要特征,由震旦系、南华系和基底构成。龙门山北段地区发育多种构造样式,主要有:叠瓦状冲断构造、双重构造、断层相关褶皱、背冲断块、飞来峰等。龙门山北段在印支期已基本成型,经历燕山期和喜马拉雅期构造进一强化,造就今日面貌:印支早期主要表现为海退;印支中期总体抬升,发生微弱褶皱;印支晚期强烈褶皱,冲断推覆;燕山期不均衡抬升,冲积扇发育;喜马拉雅期褶断强化,强烈推覆。龙门山北段由于强烈的构造运动,造成早期古油藏的破坏,地表沥青大量出露。在陕西宁强地区震旦系灯影组古油藏裂解成气藏后由于隆升剥蚀,沥青呈分散状分布于灯影组中;广元矿山梁地区沥青呈脉状,主要沿断裂和大的裂缝分布,表明其下的油藏由于断裂发育已遭一定程度破坏,甚至可能是完全破坏;而青川地区下寒武统的砾石状沥青则表明该区在晚震旦世时就有油气的生成和聚集。且这3种形态分布的沥青具有共同的来源,均来自于下震旦系陡山沱组。龙门山北段地区早期油气成藏条件优越,晚期由于强烈构造运动,圈闭保存条件变差,因此龙门山北段油气成藏主要受晚期构造作用的控制。而川北前陆盆地油气成藏主要受晚期构造圈闭和裂缝系统控制。龙门山北段前山带可能发现一些中、小型油气田,而其前缘地区梓橦凹陷的西侧斜坡带由于油气源充足且晚期变形较弱而具有良好的勘探前景。更多还原

【Abstract】 The northern segment of Longmen intracontinent composite orogen refers to the extension of the northeast part, bounded to Beichuan、An’xian, with the main features exposing Jiaoziding complex rock and Tangwangzhai syncline. The overall characteristics are complex thrust-nappe structure. Through detailed field survey on the surface structure, survey on the distribution of the surface bitumen, re-interpretation of the regional seismic profiles, etc, the present paper has conducted a detail study on the surface structural characteristics, the underground structural characteristics, the process of formation and evolution, distribution characteristics of the surface bitumen and prospects for oil and gas exploration in the area. The northern segment of Longmen Mountains has three main faults:Qingchuan-Yangpingguan fault, Liangshui-Lin’ansi fault and Majiaoba-Zhuyuanba fault. The three faults have multiple phases of deformation at different times with different movement characters. The first two are mainly ductile deformation in early stage and brittle deformation in late time, and the Majiaoba-Zhuyuanba fault is mainly dominated brittle deformation. Based on the three main faults, the northern segment of Longmen Mountains and it’s near area are divide into four structure units. They are Bikou micro-block, back-Longmen intracontinent orogen, pre-Longmen intracontinent orogen and the northern sichuan composite foreland basin. Tectonic deformation of the every tectonic unit is significantly different. From northwest to southeast tand from the orogen to the basin, the deformation-metamorphism reduced significantly.The northern segment of Longmen Mountains can be divided into upper, middle and lower layer-structure in vertical direction according to the interpretation of seismic profiles. The upper structural layer is composed of imbricate thrust sheet by Silurian, Ordovician and Cambrian. The middle structural layer is composed of relatively flat structural layer by Permian, Devonian, Silurian, Ordovician and Cambrian. The under-structural layer is made up of Sinian and basement.The northern segment of Longmen Mountains developed a wide range structural styles, who mainly includes imbricate thrust structure, duplex, fault-related fold, and klippen etc.The basic shape of the northern segment of Longmen Mountains has been deformed in Indo-Chinese epoch, experienced Yanshan and Himalayan movements. Regression; general uplift and weak folding are in early Indo-Chinese epoch.Strong folding and thrusting happened in late Indo-Chinese epoch. Uneven uplifting took place and alluvial fan developed in Yanshan movement. The fault-folding enhanced and strong thrusting happened in the Himalayan movement.Beacause of the strong structure movements in the northern segment of Longmen Mountains, the early ancient reservoir has be destroyed and a large number of bitumen exposed on surface. The ancient reservoir of Dengying series in Ningqiang Shanxi province is subjected to uplifting and denudating, and bitumen dispersely distributed in the Dengying reservoir. The Kuangshanliang area in Guanyuan the bitumen is vein and mainly along the fracture distribution. It showed the ancient reservoir under the area has been destroyed on some extent because of the fault devlopment, and even maybe completely destroyed. The gravel-like bitumen of Lower Cambrian in Qingchuan area indicated that there was oil and gas generation and gathering at late Sinian. The three different bitumen have the same source rock of the upper Sinian Doushantuo formation.The northern segment of Longmen Mountains has original favorable conditions of oil and gas accumulation, but later the trap’s storage conditions deteriorated because of strong structure movements. The hydrocarbon accumulation of the northern segment Longmen Mountains was mainly controlled by the late tectonics. And the hydrocarbon accumulation of the northern Sichuan foreland basin mainly was controlled by the later structural trap and fracture system. Some small and medium-sized oil and gas field can be found in the front range of the northern segment of Longmen Mountains, and it’s front area has a good exploration prospects especially the western ramp region of Zitong depression because of adequate oil and gas source and late weak deformation.更多还原