大别造山带南缘构造带构造几何学特征与形成演化

【作者】 钱存超；

【导师】 张国伟；

【作者基本信息】 西北大学 ， 构造地质学， 2006， 博士

【摘要】 通过构造地质学、岩石学和地球化学及地球物理研究相结合的方法，本文对大别南缘构造带的结构、物质组成和形成演化进行了综合研究，取得了以下主要进展：1、确定了大别南缘构造带是一个复杂多期演化的复合构造带，尤其是中新生代以来在先期洋陆相互作用碰撞构造带基础上叠加强烈的陆内构造而形成的巨大多层次逆冲推覆构造系。其构造几何学结构主要特点为：(1)平面呈线性弧形波状延伸；(2)剖面上呈现造山带以多种类型和不同深度层次规模的推覆构造形式，向外推置在扬子地块之上，构成陆内地壳大规模收缩推覆叠置的几何学结构；(3)现今结构垂向上从上部以近东西走向构造为主，经中深部水平流变过渡层到深部地幔南北向结构与状态，使壳幔上下呈近于直交或斜交的构造非耦合关系，总体构成具流变学分层的壳幔三维结构几何学模型。2、厘定大别南缘构造带中肢解的蛇绿混杂岩和残留岛弧火山岩的存在，讨论了勉略带的东延。肢解的蛇绿混杂岩和残留的岛弧火山岩共同存在，表明大别山南缘地区曾存在洋内岛弧至活动的大陆边缘岛弧构造背景，与秦岭构造带勉略带不同地段残存的蛇绿岩和火山岩等从区域构造与构造部位、岩石学、地球化学等综合特征可以对比。但因受到印支期陆—陆深俯冲碰撞和UHP的快速折返以及燕山期陆内构造作用的强烈改造而呈残存状态，杂乱分布。它们现今裸露在造山带根带前寒武纪古老岩石中，而中上部浅层岩石，包括类似勉略带在内的岩石可能大多已被剥蚀，或因大别山南缘的巨大推覆而被掩埋。因此，在大别山南缘构造带抬升的古老基底根带岩石中，目前尚可见到老的蛇绿岩和岛弧火山岩块的保存，而新的尚未发现或保存。3、探讨了大别南缘构造带的形成演化对于大别造山带和大别HP、UHP变质岩石形成与折返的作用和意义及其大陆动力学意义。大别南缘构造带经历了变质基底岩系原岩形成阶段、扬子地块北缘震旦纪—中三叠世被动大陆边缘沉积阶段、印支期深俯冲与碰撞造山阶段、晚印支—燕山期逆冲推覆构造与UHP折返阶段、中新生代陆内构造阶段等5个长期复杂的构造演化阶段。大别山南缘俯冲消减带与构造带的存在，造成大别南、北的双层俯冲，而南缘扬子岩石圈俯冲促进和加速了大别北缘陆壳快速的深俯冲，致使其形成UHP岩石。其中所要强调的是在扬子与华北两大板块区域汇聚和大别南、北陆壳双层俯冲中，南缘的俯冲碰撞加强了北缘的深俯冲与折返作用。这也是本文研究大别南缘构造带的主要原因和意义，也是本文提出的重要新认识。4、研究与厘定大别山前陆褶冲带的变形特征。前陆褶冲带和大别南缘带经历了相同构造变形期次，即至少三期的构造变形，早期表现为扬子陆块向北的俯冲碰撞，主期表现为超高压岩石的折返，形成前陆褶冲带，晚期表现大别山隆起时向南的逆冲推覆构造格局。更多还原

【Abstract】 Based on structural geology, petrology, geochemistry and geophysics, the structure, composition and evolution of the south marginal structural belt of the Dabie orogen has been comprehensively studied. Major progresses of this work are as follows:1. This study ascertained that the southern margin tectonic belt of the Dabieshan is experienced Iong,complicated evolvement,especially the intracontinental overthrust structure formed by collision and congruence of ocean-continent since Meso-Cenozoic.The main characteristics of tectonic geometry are as follows:(1)The tectonic belts extends in linear or arc shape. (2) In a profile, orogen thrusted outward onto the Yangtze block in the way of nappe structures in various types and different depth, which is composed of large—scale thrusted and superimposed geometry structures of the intercontinental crust. (3) Now the southern border tectonic belt of the Dabieshan is formed in the three-dimensional of geometric model, which mostly trending EW on the top , throughing the aclinic beds of passage intermediately to the gradient or erect flow structure at the bottom.2. The existence of dismembered ophiolitic melange and the preserve of the island arc volcanic rocks in the south structural belt of the Dabie orogen have been determined. This shows that the Mianlue belt should be extended eastward to the south part of the Dabie orogen.The same occurrence of the dismembered ophiolitic melange belt and the relics of island arc volcanic rocks show that the south of the Dabie orogen had undergone tectonic processes from the oceanic island arc to the continental margin island arc. Compared with the remained ophiolite and volcanic rocks in different section of the Mianlue suture of the Qinling tectonic belt, it shows that the Mianlue suture of the Qinling tectonic belt, which is eastwardly through Huashan to south area of the Dabie orogen.The ophiolite blockes and island-arc volcanic rock in southern border tectonic belt of the Dabieshan are presented survival state and distributed promisecuously, because of the deep subduction-collision between lands and frequently uplift of UHP in Indosinian epoch, and intense intracontinental tectonic effect in yanshannian. They are bared in the rock of orogenic belt root and in the old rock of Cambrian period, in the middle or under the middle including the rock of Mianlue suture zone are eroded, or be buried by the forcing of Dabieshan. So, in southern border tectonic belt of the Dabieshan,the old ophiolite and island-arc volcanic rock are existent and the new are not.3. The paper has discussed the formation and uplift significance, effect and its continental dynamical significance of the formation and evolution of the southern border tectonic zone of the Dabieshan to the Dabie orogenic belt and the Dabie high-pressure and ultrahigh-pressure metamorphic belt.The southern border tectonic belt of the Dabieshan went through five long and intricate evolvements, including that the formation of source rokes in metamorphic basement rock series , continetal margin of Yangtze platform in Sinian Period-Middle Triassic deposited passively, the collision-orogenic and deep subduction period in Indosinian epoch, trust tectonics and uplift of UHP in late Indosinian- Yanshanian, and intracontinental tectonic stage in Meso-Cenozoic.The existence of subduction zone of the southern margin of Dabieshan maked the cceleration of the subduction of Yantze Platform to the depth of the Mantle, forming the UHP rocks, we need to emphasize the regional convergence of the Yangtze plate and North China plate and double-plate subduction of southen and northen Dabieshan. The subduction of the sorthen margin improved the northen deep subduction and exhumation.This is the main reason and meaning by which we do the research in this paper,also,it is important new cognition in this paper.4. Deformation of the foreland fold and thrust belt of Dabie orogen are studiedThe foreland fold and thrust belt are product of the collision between the Dabie orogen and the lower Yangtze block in Indosinian age, which underwent at least three—stage deformation. The earlier deformation resulted from the northward subduction of the Yangtze block. The main deformation is from the ultra high—pressure returning processes, and the last one is southward thrusting and napping.更多还原