【作者】 李佐臣；

【导师】 裴先治；

【作者基本信息】 长安大学 ， 构造地质学， 2009， 博士

【摘要】 龙门山陆内复合造山带位于扬子地块西北缘,是一个北东向展布的陆内造山带,夹持于碧口地块、南秦岭造山带、松潘-甘孜造山带、川西前陆盆地和汉南-米仓山构造带之间,也是青藏高原东部边缘地带,是诸多地块和不同类型造山带以不同方式、不同方向汇聚交接地区,具有复杂的构造图象和拼合历史。本文通过构造地质学、岩石学、岩石地球化学、同位素地质年代学及地球物理学研究相结合的方法,主要对扬子地块西北缘后龙门山造山带的物质组成、形成时代、形成环境、变形特征和变形序列进行了综合研究,取得了以下主要新进展和初步认识：1、后龙门山造山带物质组成研究新元古代早中-期的基底形成阶段主要以火山喷发和随后的岩浆侵入为特征,其中通木梁群岛弧型火山岩是Rodinia超大陆汇聚的产物,而刘家坪群裂谷型火山岩、轿子顶花岗岩和大滩花岗岩是Rodinia超大陆初始裂解阶段产物；南华纪-早古生代伸展裂陷-晚古生代-中三叠世被动大陆边缘演化阶段主要以海相沉积环境为主,其沉积环境可划分南华纪-震旦纪阶段的裂解-稳定沉积体系、寒武纪-志留纪阶段的伸展裂陷沉积体系、泥盆纪-中三叠世阶段被动大陆边缘沉积体系,包含少量的早奥陶世毛塔子陆内裂谷火山岩系；晚三叠世-新生代陆内造山演化阶段在其北侧碧口地块中形成了具有后碰撞特征的花岗岩,在其南侧前龙门山构造带以及碧口地块南缘局部则以陆相沉积岩系为主。因此,后龙门山造山带是在陆内俯冲造山基础上,后期经历了伸展滑脱、逆冲推覆以及走滑剪切形成的造山带。2、后龙门山造山带构造特征研究后龙门山造山带自晚印支期以来经历了多期次多类型的构造变形和构造叠加,通过详细的构造解析,认为可以将其构造变形分为晚三叠世挤压-收缩体制下陆内俯冲变形,早中侏罗世伸展构造体制下滑脱变形和顺层韧性剪切变形,晚侏罗世-早白垩世挤压-收缩体制下逆冲推覆变形,晚白垩世-早中新生代左行走滑韧性剪切变形,以及中-晚新生代右行走滑剪切变形五期变形。其中,伸展滑脱变形在后龙门山造山带轿子顶穹窿和碧口地块南缘蜈蚣口一带较为明显,向东逐渐减弱。对伸展滑脱构造带中变形岩石的年代学研究表明,该期伸展滑脱形成于193-165Ma,是在陆内俯冲造山后地壳均衡作用影响之下的伸展背景下形成的。3、后龙门山造山带形成演化研究后龙门山造山带自新元古代以来主要经历了新元古代早中期基底形成,南华纪-早古生代伸展裂陷-晚古生代-中三叠世被动大陆边缘演化,晚三叠世-新生代陆内造山演化三个大的阶段。其中晚三叠世-新生代陆内造山过程可划分为晚三叠世陆内俯冲造山、早-中侏罗世伸展滑脱、晚侏罗世-早白垩世逆冲推覆、晚白垩世-早中新生代左行走滑、中-晚新生代右行走滑五个阶段。可以看出认为龙门山造山带是一个陆内复合造山带,与其南北两侧的构造单元的构造演化息息相关,主要受控于秦岭造山带、扬子地块和松潘-甘孜造山带的共同作用,构造运动复杂。更多还原

【Abstract】 Longmenshan intra-continent compound orogenic belt, an inland orogenic belt with NE orientation, is located at the northwestern margin of Yangtze block and is surrounded by Bikou block, southern Qinling orogenic belt, Songpan-Ganzi orogenic belt, western Sichuan foreland basin and Hannan-Micangshan tectonic belt and constitutes the eastern margin zone of Qinghai-Tibetan plateau, which is convergent and combining zone of different blocks and kinds of orogenic belt through various mechanisms and directions and exhibits complex tectonic images and matching history. Comprehensive studies have given in this thesis on material composition, formation age, formation environment, deformation characteristics and deformation sequence of back-Longmenshan orogenic belt in the northwest margin of Yangtze block by the compound study methods of structural geology, petrology, rock geochemistry, isotopic geochronology and geophysics and a few major new developments and preliminary cognitions are acquired as follows:1.Material composition studies of back-Longmenshan orogenic beltThe basement formation in early-middle stage of Neoproterozoic is characterized by volcanic erupting and subsequent magma intruding, and in which island-arc volcanic rock of Tongmuliang Group represents the production of Rodinia super-continent’s convergence while volcanic rock of Liujiaping Group, Jiaoziding granite and Datan granite imply the primary divergence of Rodinia super-continent. The evolution process, the stage from extension and division-collapse during Nanhua period-early Paleozoic to evolution of passive continental margin during late Paleozoic-middle Triassic, is mainly of oceanic faces for sediment, which can be divided into following sediment systems:division-stable stage of Nanhua-Sinian periods, extension and division-collapse stage of Cambrian-Silurian periods, passive continental margin of Devonian period-middle Triassic epoch and a few of volcanic rocks of Maotazi intra-continent rift of early Ordovician epoch are included. The intra-continent orogenic evolution of late Triassic epoch-Cenozoic casts post-collision granites in its north of Bikou block while intra-continent sediments in its south fore-Longmenshan orogenic belt and south margin of Bikou block. Therefore, back-Longmenshan orogenic belt undertakes the process of extensional detachment, thrust nappe and strike-slip shear afterwards on the basis of intra-continent subduction previously.2.Tectonic characteristics studies of back-Longmenshan orogenic beltBack-Longmenshan orogenic belt has undertaken poly-cycle and multi-type tectonic deformation and tectonic superposition. After detailed structure analysis, it is considered that the deformations can be divided into 5 systems as follows:intra-continent subduction deformation under the mechanism of compression-contraction in Late Triassic epoch, detachment deformation and ductile shear deformation along the strata corresponding extensional effect in Early Jurassic epoch, thrust nappe deformation resulting from compression-contraction in Early-Middle Jurassic epoch, sinistral strike-slip ductile shear deformation from Late Jurassic to Late-Middle Cenozoic and dextral strike-slip shear deformation in Middle-Late Cenozoic, in which deformations extensional detachment is obvious in Jiaoziding Dome and Wugongkou of southern margin of Bikou block in Back-Longmenshan orogenic belt and is weaker to the east. Chronology studies on the deformed rocks of extension detachment orogen suggests that the extension detachment is active in about 193-165Ma, which is formed under the extensional background of Crustal balancing effect after intra-continent subduction orogenesis.3.Forming and evolution studies of Back-Longmenshan orogenic beltBack-Longmenshan orogenic belt has mainly undertaken 3 evolutional stages since Neoproterozoic, such as the basement formation of Early-Middle Neoproterozoic, from extension and division-collapse of Nanhua epoch-Early Paleozoic to passive continental margin evolution in Late Paleozoic-Middle Triassic epoch and intra-continent orogenic evolution in Late Triassic epoch-Cenozoic. The third stage can be divided into 5 secondary stage furtherly like intra-continent subduction orogenesis in Late Triassic epoch, extensional detachment in Early-Middle Jurassic epoch, thrust nappe in Late Jurassic epoch-Early Cretaceous epoch, sinistral strike-slip in Late Cretaceous epoch-Early-Middle Cenozoic and dextral strike-slip in Middle-late Cenozoic. From which it can be summarized that Longmenshan orogenic belt is an intra-continent compound orogen which has close relationship to the tectonic evolution of terranes adjacent to it both in south and north and mainly results from the interaction of Qinling orogenic belt, Yangtze block and Songpan-Ganzi orogenic belt and has complex tectonic movement.更多还原