【作者】 陈虹；

【导师】 胡健民； 施炜；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2010， 博士

【摘要】 扬子地块周缘西南缘金沙江—哀牢山缝合带、昌宁—孟连缝合带和甘孜—理塘缝合带、北缘的阿尼玛卿—勉略缝合带的研究,已经刻画出一个比较清晰的古特提斯洋由打开-扩张-俯冲-消亡的演化过程。本文通过对扬子北缘和西缘及邻区构造格架、变形过程和构造年代学研究,探讨扬子地块周缘构造带陆块碰撞-陆内变形阶段的构造过程。由于古特提斯洋的俯冲碰撞,扬子地块周缘在早中生代时期经历了强烈的挤压缩短构造变形过程。扬子北缘碰撞主要发生在早-中三叠世,主碰撞早期主要表现为由北往南的逆冲推覆,形成叠瓦状逆冲推覆构造格局。主碰撞之后叠加了强烈的韧性和脆性走滑变形。勉略缝合带内左行韧性剪切变形带中形成拉伸线理的白云母的Ar-Ar年龄为223 Ma,与南秦岭造山带内大量晚三叠世时期侵入的向伸展环境转换的花岗岩时代相吻合,表明扬子地块北缘在晚三叠世早期就已经进入陆内变形阶段,变形方式是以顺造山带的走滑变形为主。晚中生代期间,扬子地块北缘南秦岭构造带发育两条重要的韧性-韧脆性走滑剪切变形带,即宁陕左行韧性走滑剪切带(宁陕断裂)和安康右行韧性走滑剪切带(安康断裂),同变形矿物的40Ar-39Ar定年(160-173 Ma)和侵入变形岩石的花岗岩锆石定年(186 Ma)等研究显示其变形时代为早-中侏罗世。相反的运动学指向表明,扬子北缘南秦岭构造带在早-中侏罗世的构造效应为顺造山带的向东挤出。扬子地块西缘龙门山、安宁河、金沙江一带，由于新生代构造变形的强烈叠加,新生代之前与扬子周缘碰撞相关的构造变形难于识别。在复杂的新生代构造变形格局中,本文通过一些中生代盆地古水流方向的研究,发现它们的形成与扬子地块西缘发育的一系列北西-北北西向左行走滑断裂的形成密切相关。这个左行走滑构造变形带很可能是扬子地块西缘对北缘秦岭主碰撞以及西侧甘孜—理塘带碰撞的构造响应,时代发生在晚三叠世。大体与此同时,相邻的松潘-甘孜地体内也发生由西往东的逆冲推覆和褶皱加厚等构造变形。这些走滑断层面上的擦痕显示,走滑之前曾经发生过由南西向北东方向的逆冲,由于没有产生相关的变质变形矿物和岩浆作用,这次逆冲变形的时代难于准确的限定。根据断层与所控制沉积盆地的关系及区域构造背景,推测应该发生在晚三叠世-早侏罗世。根据受这些左行走滑断裂控制的甘洛盆地和九襄盆地地层发育特征判断,扬子西缘的左行走滑剪切变形从晚三叠世一直持续到侏罗纪结束。初步估算,这个时期扬子西缘走滑位移量至少达到了27 km。古地磁研究已经证明扬子地块在中生代时期发生过30°左右的顺时针旋转,扬子地块周缘已经鉴别出来的一系列左行走滑断裂,如龙门山左行压剪性断裂、扬子西缘左行走滑断裂系、紫罗断裂、华蓥山断裂等,很可能与这种旋转有关。扬子地块北缘由于牵扯到我国南北大陆的碰撞拼贴,情况相对复杂。在特提斯洋俯冲关闭之后的主碰撞阶段,首先是垂直于造山带的高角度逆冲,并导致叠瓦状堆垛的冲断推覆构造格局,此后很快进入陆内变形阶段,发生强烈的顺造山带的走滑或侧向挤出,同时叠加了由扬子地块顺时针旋转所造成的左行走滑变形。因此,中生代期间,扬子地块周缘的构造变形,揭示出古特提斯构造域中一个非常独特的大陆碰撞过程,即位于碰撞带南侧的扬子地块在顺时针旋转过程中向北俯冲碰撞。更多还原

【Abstract】 There are some Paleo-Tethys sutures around the Yangtze block, such as the Jinshajiang-Ailaoshan suture, Changning-Menglian suture and Ganzi-Litang suture at its southwest margin, and the Animaqin-Mianlue suture at its north margin. We have known the evolution of the progress of open-expand-subduction-close for Paleo-tethys. This paper mainly studied the deformation, sedimentary structure and related tectonic chorology at the northern and western Yangtze block and neighbouring area, and discussed the particular progress from continental collision to intra-continental deformation in the Tectonic belt around Yangtze block.We have known that the margin of Yangtze block has experienced the compression shortening deformation in early-Mesozoic, this deformation is related to the subduction and collision of the Paleo-Tethys ocean in this time. The collision at the northern Yangtze block is in early-mid Triassic, the Mianlue suture has experienced intense obduction-nappe structure from north to south in the early collision period, and formed imbricate thrust structural framework related. After the dominated collisional deformation, the northern Yangtze block and neighbouring orogen superimposed intense ductile and brittle slip deformation. The Ar-Ar age of the muscovite is 223 Ma in the mylonitzed green-schist experienced sinistral ductile deformation in Mianlue suture. This age consistents with the age of the granite changed to the extending environment in late-Triassic in south Qinling orogen, and indicate that the northern Yangtze block has turn into the intra-continental deformation in late-Triassic, and the deformation changing mode is lateral slip displacement along the orogenic belt. At late-Mesozoic, there are two important ductile and ductile-brittle slip shear deformation belts in south Qinling tectonic belt, named the Ningshan sinistral slip fault and Ankang dextral slip fault. The 40Ar-39Ar dating (160-173 Ma) of the syn-deformation mineral and ziron dating (186 Ma) of the granite intruded in the deformationed rock indicate the deformation time is early-mid Jurassic. The different kinematics direction indicate the tectonic effect of the south Qinling belt in early-mid Jurassic is lateral extrusion to east along the orogenic belt.he Cenozoic sinistral slip structure obviously destroyed the Mesozoic deformation framework of western Yangtze block and neighbouring area along the Longmenshan, Anninghe and Jinshajiang, so the collisional related deformation before Cenozoic around the Yangtze block is difficult to recognize. In the complex Cenozoic deformation framework, this paper discovery the development of the Mesozoic basins is related to the forming of the NW-NNW strick slip faults depend on the sedimentary character and paleo-current direction. This left-lateral slip tectonic belt must be the tectonic response for the collision in Qinling belt and Ganzi-Litang belt in western Yangtze block, and the deformation time is late-Triassic. Meanwhile, the thrust and fold thicking structure from west to east in the Songpa-Ganzi terrain is also in late-Triassic. The scrapes on the slip faults indicate that exist thrust deformation from SW to NE before the slip deformation, and the time is difficult to limit because there are no mata-deformation mineral and magma. Depended on the relationship between the faults and the basins and the tectonic sstting, we consider the thrust deformation should develope in late-Mesozoic to early-Jurassic. The sinistral shear deformation time must begin in late-Triassic and continued to Jurassic basing the strata character study of the Ganluo and Jiuxiang basins. And the displacement of slip at western Yangtze block reaches to 27 km at least by preliminary estimate.The Paleo-Geomagnetism research has evident that the Yangtze block has clockwise rotated about 30°, and there are a serious sinistral slip faults around the Yangtze block may related to the rotation, such as Longmenshan fault, Anninghe fault, Ziluo fault, Huayinshan fault, and etc. The north margin of Yangtze block is complex because of relating to collision-accretion of the Chinese continents. After the tethys ocean closed, the collision phase is dominated by the high-angle thrust vertical to orogen firstly, and formed the imbricate stow thrust-nappe framework. Then the collision quickly switches to intra-continental deformation with slip displacement or lateral extrusion along the orogen, and superimposing the sinitral slip deformation caused by the clockwise rotation of the Yangtze block at the same time. So the Mesozoic deformation around the Yangtze block shows a special continental collision process in the Paleo-Tethys field, which is the Yangtze block south of the collisional belt rotated clockwise with north direction subduction-collision.更多还原