华北新构造：印欧碰撞远场效应与太平洋俯冲地幔上涌之间的相互作用

作为大陆内部典型的伸展断陷区和强震活动区,华北地区处于东部太平洋板块俯冲构造和西部印欧大陆碰撞构造的双重大地构造背景之下,其新构造运动相当复杂:西部沿鄂尔多斯地块周缘两个地堑盆地系引张伸展断陷作用、中部太行山块体的局部断陷和整体隆升、东部华北平原区和渤海湾海域区的区域沉降,南缘沿秦岭构造带的左旋走滑拉张活动,东缘沿郯庐断裂带的右旋挤压走滑活动。这些不同类型的断裂构造在晚新生代的阶段性活动,产生了复杂的构造地貌组合特征。综合研究发现,华北晚新生代经历了3期伸展断陷-挤压隆升演化阶段:新近纪晚期(10～2.5 Ma)、早中更新世和晚更新世以来。地壳引张应力方向或NW-SE、或NE-SW向;地块隆升导致湖盆的消亡,挤压应力方向为NE-SW至W-E向。研究认为,华北地区新构造受两个岩石圈构造过程的相互影响:印欧碰撞产生的远程效应和东部岩石圈地幔的上涌。一方面,青藏高原东北缘地块的持续推挤及其构造应力向东的传递导致鄂尔多斯地块反时针旋转和秦岭山地的向东挤出逃逸,这个挤出构造动力学统治了华北地区晚新生代的引张伸展、斜张走滑和挤压变形。尤其是,新近纪晚期强烈的NW-SE向地壳伸展变形与青藏东缘挤出造山作用同步(10～9 Ma至4.2 Ma);上新世末期(约2.5 Ma)、晚更新世早期(约200～70 ka)和晚更新世晚期—全新世(约20 ka以来)3次构造挤压事件与青藏高原东缘构造事件基本对应。另一方面,岩石圈地幔上涌主导了华北东部平原区的区域地壳沉降,同时伴随着早、中更新世的5期幔源火山活动。这两个岩石圈构造作用力此消彼长,深刻统治着华北地区新构造与现今活动构造以及地震构造。

Neotectonics of North China: interplay between far- field effect of India- Eurasia collision and Pacific subduction related deep- seated mantle upwelling

North China is a seismically active region, where large- to- moderate historic earthquakes shocked frequently, and become a locus of natural laboratory for study of intraplateneotectonics. Neotectonics of North China is characterized by a rather complex pattern: normal faulting along the two graben systems surrounding the Ordos block in the west, regional uplift of the Taihang Shan Highland in the center and subsidence of the North China- Bohai Bay Plain in the east, sinistral transtensional faulting along its southern Qinling range and dextral transpressional faulting along the NNE- striking Tan- Lu Fault zone. These types of faulting occurred episodically during late Cenozoic, giving rise to a complex morpho- tectonic features. Neotectonics in North China was operated through three episodes of crustal extension- compression, respectively occurring in late Neogene (9~2.5 Ma), Early- Late Pleistocene and late Pleistocene. Crustal extension derived from fault kinematics inversion oriented either in NW- SE or in NE- SW, and crustal compression determined from focal solutions of earthquakes oriented in NE- SW to W- E. It is thought that episodic development of Neotectonics in North China has been orchestrated by the interplay of two tectonic processes: far- field effect of India- Eurasia collision and subduction- related deep- seated upwelling of lithospheric mantle. In one hand, the eastward push of the crustal fragments in NE Tibet resulted in counterclockwise rotation of the Ordos block and eastward extrusion of Qinling Range, the process of which has profoundly governed late Cenozoic extensional, transtensional and compressional deformation in North China. Specifically the late Neogene NW- SE crustal extension around the Ordos block ((10~9 Ma)~(4.2 Ma)) was concomitant with the extrusion- related orogeny along the eastern Tibetan margin, and three compressional tectonic events occurring at latest Pliocene(before 2.5 Ma), early Late Pleistocene(~200~70 ka)and since latest Pleistocene (~20 ka) are fairly coeval with those occurred along the eastern Tibetan margin. On the other hand, lithospheric mantle upwelling responsible for regional subsidence of the Bohai Bay basin in the plain region east of Mt. Taihangshan, was manifested by five episodes of mantle- derived volcanism particularly active in Early- Late Pleistocene. These two tectonic processes have been spatio- temporally interacted with each other, which has profoundly dominated Neotectonics and seismo- tectonics of North China.