| 青藏高原东部晚新生代重大构造事件与挤出造山构造体系 |
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| 引用本文： | 张岳桥,李海龙.青藏高原东部晚新生代重大构造事件与挤出造山构造体系[J].中国地质,2016(6):1829-1852. |
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| 作者姓名： | 张岳桥 李海龙 |
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| 作者单位： | 南京大学地球科学与工程学院, 江苏 南京 210023,中国地质科学院地质力学研究所, 北京 100081 |
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| 基金项目： | 国家自然科学基金（41472178）和中国地质调查局地质调查项目（1212011120167，12120114002211）联合资助。 |
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| 摘 要： | 文章系统梳理了青藏高原东部地区晚新生代重大构造事件的沉积记录、岩浆记录和构造变形响应,重新厘定了青藏运动或横断事件的起始时限,建立了青藏高原东部晚新生代构造演化序列与挤出造山构造体系。研究认为,发生在上新世之前的青藏运动是青藏高原东部最重要的构造作用阶段,起始于距今12~8 Ma,并持续到上新世早期,持续时间达6~8 Ma。在这个构造运动阶段,青藏高原东部地块(川滇地块、川青地块、西秦岭构造带和陇中地块等)有序地向东挤出,受到鲜水河、东昆仑、海原等WNW-ESE向大型断裂左旋走滑运动调节,构造挤出同时伴随地块内部逆冲褶皱变形,导致地壳增厚和高原东缘山脉快速崛起;构造挤出也超越了现今东缘地貌边界,向东扩展导致扬子地块盖层滑脱褶皱,形成龙泉山、大凉山等褶皱构造带。上新世出现的砾石层(东缘前陆地带的大邑砾石层、临夏盆地的积石砾石层、兰州盆地的五泉砾石层等)标志了青藏高原东部差异性构造地貌的形成。上新世晚期至早更新世时期(3.6~1.0 Ma)对应一个构造松弛阶段,青藏高原东部整体进入冰冻时期,沿其东缘发育一系列受正断层控制的南北向伸展断陷盆地,如安宁河谷地、元谋盆地、盐源盆地、滇西北盆地群等,其中加积了以昔格达组为代表的稳定河湖相沉积。发生在早、中更新世之交(距今1.0~0.6 Ma)的昆—黄运动或元谋事件使青藏高原东部地块进一步向东挤出、东缘地壳逆冲增厚和年轻山系加速隆升。晚更新世以来的构造运动称为共和运动或最新构造变动阶段,起始于距今约120 ka,青藏高原东缘构造变形系统出现重大分化,南段川滇菱形地块发生绕喜玛拉雅东构造结的顺时针旋转运动,形成川滇双弧形旋扭构造体系;而中段川青地块的挤出伴随东缘龙门山断裂带的右旋走滑运动和秦岭山系的向东挤出。在这个最新构造变动阶段,青藏高原东部下地壳通道流可能是重要的深部构造驱动因素。
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| 关 键 词： | 青藏高原东部 晚新生代 青藏运动 横断事件 昆黄或元谋事件 共和运动 构造挤出造山作用 下地壳通道流 |
| 收稿时间： | 2016/7/8 0:00:00 |
| 修稿时间： | 2016/9/30 0:00:00 |
Late Cenozoic tectonic events in east Tibetan Plateau and extrusion-related orogenic system |
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| ZHANG Yue-qiao and LI Hai-long.Late Cenozoic tectonic events in east Tibetan Plateau and extrusion-related orogenic system[J].Chinese Geology,2016(6):1829-1852. |
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| Authors: | ZHANG Yue-qiao and LI Hai-long |
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| Institution: | School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, Jiangsu, China and Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, 100081, China |
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| Abstract: | This paper revised the chronology of major late Cenozoic tectonic events in east Tibetan Plateau, mostly based on records of stratigraphy in the basins and magmatism and deformation along active fault zones, with the purpose of establishing an evolution history of extrusion-related orogenic system. It is shown that the most important event, as previously named the Qingzang movement, was initiated at 12-8 Ma and lasted to early Pliocene, with a duration of 6-8 Ma. The crustal fragments in east Tibet, such as the Chuan-Dian, Chuan-Qing, Longzhong blocks, were orderly extruded eastward accommodated by large-scale sinistral strike-slip faults like the Xianshuihe, East Kunlun and Haiyuan faults. This eastward extrusion was concomitant with thrusting, which resulted in fast uplift of the ranges along its eastern edges, and went beyond this margin through decollement, generating folds of the cover rocks like the Longquanshan, Daliangshan in the Yangze craton. The deposition of late Pliocene conglomeratic layer, namely the Dayi conglomerates along the eastern foreland zone, the Jishi conglomerates and the Wuquan conglomerates at the northeast corner of Tibet, marked the emergence of contrast geomorphology in this region. Late Pliocene to early Pleistocene (3.6-1Ma) corresponds to a period of tectonically quiescence or relaxation, during which a set of N-S trending rift basins, such as Yuanmu, Yanyuan, and Anninghe, were developed along the eastern margin, and accumulated a series of fluviao-lacustrine facies deposits in these basins. This relaxation stage was followed in Early-Middle Pleistocene (1.0-0.6 Ma) by an important compressional event named the Kun-Huang or Yuanmu event, which caused further uplift of east Tibet. Active faulting pattern in east Tibet has been changed greatly since the late Pleistocene (about 120 Ka), featured along its southwest part by clockwise rotation around the east Himalaya syntax of two sinistral strike-slip fault zones, and along its central north part by a counter clockwise rotation accommodated by dextral strike-slip motion in the Longmenshan fault zone and eastward push of the Qinling range. The lower crustal flow could be a major driven mechanism for the deformation of this most recent stage. |
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| Keywords: | eastern margin of Tibet late Cenozoic Qingzang movement Hengduan event Kun-Huang or Yuanmu event Gonghe event extrusion-related orogeny lower crustal flow |
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