【作者】 孙东；

【导师】 刘树根；

【作者基本信息】 成都理工大学 ， 构造地质学， 2011， 博士

【摘要】 造山带与沉积盆地的耦合过程是21世纪以来构造地质学研究的一个热点。盆山耦合研究是建立在冲断带和沉积盆地动态演化基础之上,并结合二者之间的物质能量交换过程而展开的全方位研究工作。论文选择扬子北缘的米仓山构造带及毗邻的沉积盆地为研究对象,以板块构造理论为纲,以活动论和大陆动力学为指导思想,从构造解析角度出发,综合运用构造地质学、沉积学、构造年代学、地震地质学、成盆动力学和盆-山耦合的理论,通过地表地质调查,并结合钻井、地震资料,对米仓山构造带的几何学、运动学、变形学特征及盆地充填序列、沉降历史等展开讨论。在此基础上,重点讨论了米仓山构造带的构造期次,盆山转换过程及中-新生代构造演化史,并对其形成机制进行了探索。位于扬子板块北缘的米仓山构造带,西邻龙门山陆内复合造山带,北侧为秦岭造山带和汉南隆起,东与大巴山前陆冲断带相接,南与四川盆地毗邻。野外的地质调查表明,米仓山构造带为典型的复合叠加构造。早期的走向近东西的褶皱构造和冲断作用受控于扬子板块和华北板块的碰撞作用;后期的北东走向的断裂构造受控于扬子板块向秦岭造山带的楔入作用。且晚期构造复合叠加于早期的构造之上,表现为后期构造迁就利用和切割早期构造。地震资料和地表调查研究表明,米仓山构造带发育典型基底卷入式厚皮构造,同时发育以中下三叠统滑脱面为顶板反冲断层、以基底岩系内20km±深度的滑脱面为底板断层的被动顶板双重构造,其整体的构造样式类似于阿尔伯达型构造三角带。古应力分析表明米仓山地区经历了包括两期南北向、一期北西-南东向、一期北东-南西向、一期东西向在内的至少5期应力场。显微构造及有限应变测量表明米仓山构造带应变样式多为拉长型。同时,多重热年代学分析结果表明米仓山构造带与汉南隆起具有不同步的隆升过程,米仓山快速隆升大致开始于138Ma,比汉南隆起晚约22Ma。通过米仓山前缘地层接触关系、盆地充填序列、物源分析等表明米仓山南缘盆地不具有典型的前陆盆地特征。且该盆地在中生代以来与米仓山构造带不具有横向上物质交换的耦合过程。相反,与米仓山构造带以北的秦岭造山带和汉南隆起具有较好的耦合过程。通过对扬子板块北缘和西缘的龙门山陆内复合造山带、米仓山构造带、大巴山前陆冲断带的对比研究,表明这三大造山带是在扬子板块向北俯冲至华北板块之下,并顺时针旋转的统一板块运动背景下,不规则板块几何边界所控制而产生的不同方向的造山带。由于板块的穿时碰撞和陆内变形的不等时性,米仓山构造带构造一方面对两侧的造山带起限制作用,另一方面,两侧造山带构造对米仓山构造带构造产生叠加改造。通过沉积学、构造年代学、构造交切关系、古应力场综合分析,重建了米仓山构造带中—新生代构造演化史。可以概括为6个主要的阶段:①前碰撞期,晚三叠世之前,米仓山构造带地区为特提斯南秦岭洋南侧的扬子板块北部的被动大陆边缘;②同碰撞阶段,晚三叠世至早侏罗世,由于扬子板块与华北板块由东向西的穿时碰撞,米仓山北侧的汉南及秦岭造山带构造活动强烈,而米仓山地区构造作用微弱,表现为轻微的水下隆起特征,仍继续接受沉积;③构造平静期,中侏罗世—早白垩世早期,米仓山地区构造作用微弱,表现为轻微的由北而南的掀斜过程;④陆内变形阶段,白垩纪期间,伴随着扬子板块向秦岭造山带的楔入作用,米仓山构造带发生强烈的陆内变形,首先形成了东西向由北而南的冲断构造级褶皱构造,随后形成北东向走滑构造,并左旋错断前期的东西向构造体系,此时米仓山主体构造基本定型;⑤叠加构造变形阶段,古新世至始新世早期,米仓山构造带两侧的构造带向盆内的扩展变形作用复合叠加于米仓山构造带周缘的沉积盖层区的前期构造之上;⑥整体隆升阶段,始新世晚期以来,受青藏高原隆升的影响,米仓山构造带及毗邻盆地整体性由西向东隆升,遭受剥蚀。更多还原

【Abstract】 The couple between orogen and sedimentary basin has been one of hotspots in tectonic geology since 21st century. It is based on the dynamic evolution processes of thrust belt and its periphery sedimentary basin, and the material-energy exchanging process between them. As a typical example, we conduct structural and sedimentary investigations on the Micang Ms. and Northern Sichuan basin located in the north Yangtze plate, guided by the theories of continental dynamics and plate tectonics. Our methods are included of fields, boreholes, seismic data, geochronology, etc. Thus, the objects of our study are focus on three points. (1) Multistage deformation. (2) The dynamic evolution processes in orogen-basin system during Meso-Cenozoic. (3) The evolutional mechanism of Micang Ms.Micang Ms. Structural Zone is located in the northern margin of Yangtze plate and Sichuan basin, connected with Longmen Ms. orogen belt to the west, Daba Ms. foreland-thrust belt to the east, and Qinling orogen belt and Hannan uplift to the north, respectively. Based on field investigation, Micang Ms. is characteristic by typical superimposed structures with obvious three-episode. The first stage is characteristic with E-W striking structures (e.g., anticlines, thrust-faults), under the control of the collision between the Yangtze and the North China plates. The second stage is characteristic with NE-strike structures controlled by the wedging process of the Yangtze plate into Qinling orogen. Furthermore, the last stage is characteristic with typical superimposed structures on the former structures, and penetratively reworked older structures.The seismic data and field investigations show that it developed typical thick-skinned structures with involved basement, duplex-thrust with roof thrust and floor thrust in the Lower Triassic and the basement with depth of ~20km, respectively. Of which the structural style is much similar to Alberta-style triangle zone. Moreover, paleostress analysis indicates there are at least 5 episodes stress field in region, including two episodes of N-S trending, one episode of NW-SE, one episode of NE-SW and one episode of E-W trending. Microstructures and finite strain measurement suggest that an elongation of triaxial-prolate ellipsoid pattern predominantly take place in Micang Ms. Meanwhile, the results of multiple thermochronology analysis prove that MiCang Ms tectonic belt and Hannan uplift process is asynchronous. The rapid uplifting time of MiCang Ms began in ca.138Ma, 22Ma later than Hannan.Sedimentology investigations (e.g., stratigraphic contacts, basin filling sequence, provenance) in Micang Ms. and its periphery suggest that the Northern Sichuan basin which located in the south edge of Micang Ms. and don’t have characters of typical forland basin. Moreover, the basin has not any exchange of material with Micang Ms. since Mesozoic in space. On the contrary, there is an obvious coupling process between Qinling orogen with Hanan uplift during the same time.According to the comparative researches among Longmen Ms., Micang Ms. and Daba Ms., it indicates that the formation of Micang Ms. is under the control both of irregular geometry boundaries in the northern margin of Yangtze plate, and diachronous collision process between the Yangtze and the North China plates. Thus, there are two significant roles of the Micang Ms., one is as a rheologically strong basement to block the deformation of its peripheral orogens, and another is a superimposed block by the multistage deformation from its peripheral orogens.By comprehensive analysis of sedimentology, geochronology, cross-cutting relations in structures and palaeostress, it suggests that the Micang Ms. has been experienced six episodes of tectonic evolution. (1) Pre-collision stage before Late Triassic, Micang Ms. was a passive continental margin of the north Yangtze plate located at the south of Qinling Paleotethys. (2) Syn-collision stage from Late Triassic to Early Jurassic, because of diachronous collision between the Yangtze and the North China plates from east to west, Hannan area and Qinling orogen underwent strong tectonism. However, Micang Ms. slightly underwent tectonism, more probably, to form an underwater uplift and partially deposit. (3) Tectonic Quiescence from Middle Jurassic to Early Cretaceous, Micang Ms. was characteristic with a faintly N-S ward tilting process. (4) Intracontinental deformation stage during Cretaceous, under the control of Yangtze plate wedging into Qinling orogen, strong intracontinental deformation took place here. Firstly, the E-W trending thrust structures formed, and then to form strike-slip structures with NE-striking that superimposed the former structures. The main structures of Micang Ms. were basically stereotyped until now. (5) Superimposed deformation stage from Paleocene to Early Eocene, the tectonic belts on both sides of Micang Ms. was expanded and deformed to within the basin, which superimposed on the earlier structures of sedimentary cap rock around its periphery. (6) Uplift stage since Late Eocene, influenced by eastward growth of the Qinghai-Tibet plateau, Micang Ms. and its periphery was entirely uplifted from west to east and suffered from denudation.更多还原