摘要
利用在华北克拉通西部完成的两条高分辨折射探测剖面获得的21炮Pg波资料,在对不同构造区Pg波的运动学与动力学特征分析对比的基础上、采用有限差分反演方法构建了两剖面的基底结构模型.研究结果不仅清晰地标定了主要断裂的位置及形态,还反映出不同构造区基底埋深和速度结构的差异.鄂尔多斯地块的基底埋深在4.5~5.5 km间、起伏变化不大,且速度梯度横向变化不甚明显,结合Pg波走时平稳、追踪远等地震学现象,揭示出鄂尔多斯地块浅表沉积和基底结构比较稳定;贺兰山和银川盆地两者不仅在地形地貌上差异显著,其基底埋深从2.0~4.0 km的较大变化以及速度结构显著的横向非均匀性足以表明两者之间垂直差异运动及变形的强烈程度.银川盆地Pg波走时趋势与速度结构图像基本反映了基底局部坳陷的形态特征和新生代沉积厚、速度低的客观现象;弧形构造区地处祁连、阿拉善、鄂尔多斯三者相互作用的复杂构造环境之中,基底埋深6.0 km的巨厚坳陷与相邻仅2.0 km厚的基底隆起形成较大反差,这与印度板块和欧亚板块强烈的碰撞推挤致使在青藏高原东北缘多个构造块体交汇复合部位呈现变形强烈、极度不稳定的基底结构密切相关.鄂尔多斯块体基底呈现西深东浅特征及周缘基底强烈的横向不均匀性、挤压褶皱变形及断裂带的发育,均反映了青藏高原NE向的持续挤压运动遭到了鄂尔多斯块体的阻挡.
Two 1420 km-long,high-resolution wide-angle reflection/refraction profiles were produced for the western part of the North China Craton.Twenty-one shots were fired along the two profiles and seismic data was collected by 700 portable three-component digital seismographers.The crust-mantle structure was investigated in different regions,including the Ordos Block,Haiyuan arcuate tectonic region,Alashan Block,and Yinchuan Basin.First-arrival Pg waves were analyzed using the finite-difference method of first-arrival traveltime tomography to construct the 2 D interface morphology and velocity structure of the crystalline basement.The study identified the location and shape of major faults,and notable variations in basement depth and velocity structure in different regions.The crystalline basement in the Ordos Block is typically stable with a depth of 4.5–5.5 km and exhibits only minor fluctuations in the lateral velocity gradient.This is evidenced by Pg wave features,including stable travel time,long tracing distance and high velocity.Between the Helan Mountains and the Yinchuan Basin,notable variations in topography,basement depth,and velocity structure were identified,indicating strong divergence in vertical movement and deformation.In the Yinchuan Basin,the Pg wave traveltime curve revealed the complex structure of the crystalline basement and variations in the velocity gradient.Since the Cenozoic Era,the western North China Craton has experienced strong and frequent tectonic activity causing strong deformation on the periphery of the Alashan Block.The presence of small,low-velocity,near-surface basins,and variations in the crystalline basement interface and velocity isolines provides evidence of strong tectonic deformation of the basement near Bayan Ura Hill,on the eastern margin of the Alashan Block.The Haiyuan arcuate tectonic region is complex and interacts with the Qilian Mountains,Alashan Block,and Ordos Block.Basement depth extends to 6.0 km and varies considerably from the adjacent uplift zone,which has a depth of 2.0 km.The highly deformed and unstable basement structure at the northeastern margin of the Tibetan Plateau is probably related to the collision and squeezing of the Indian Plate and the Eurasian Plate.Seismology data indicates differences between the crystalline basement interface and the velocity structure,as well as strong transverse inhomogeneity.Differences in basement depth in the Ordos Block,together with significant lateral heterogeneity,compressional fold deformation,and the presence of fault zones in the marginal basement,block the continuous compressive movement of the Tibetan Plateau in a northeast direction.
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第36期4294-4306,共13页
Chinese Science Bulletin
基金
国家自然科学基金(41474077
91214205
41474076)
中国地震活动断层探察-南北地震带北段项目(201408023)资助
关键词
华北克拉通西部
基底结构
鄂尔多斯块体
银川盆地
宽角反射/折射剖面
Pg波震相
速度结构
western North China Craton, basement structure, Ordos Block, Yinchuan Basin, wide-angle reflection/refraction profiles, Pg wave, velocity structure
