太行山构造带壳幔结构分段性特征

分别利用纯S波波形反演和T函数法计算了太行山构造带及其邻近地区100km以上的壳幔剪切波速度结构,结果显示太行山构造带在南、中、北段的壳幔结构存在明显差异。南段邢台邯郸地区地壳中比较突出的特点是下地壳存在一个厚度近10km的低速层;中段石家庄—保定地区靠近山脉的各台地壳结构相对比较稳定,越向盆地区发展,结构愈加复杂化;北段到达北京地区,由于该区是太行山与燕山构造带的交汇地区,中下地壳出现薄高低速转换层位,呈现不稳定状态。沿太行山构造带东缘是地震活动带-河北平原地震带,通过对比速度结构与地震空间分布,发现不同区段小震分布特点与地下低速或不稳定结构关系密切。结合该区域上地幔速度结构特征,认为太行山中段与华北地区中新生代以来的岩石圈大规模减薄运动关系密切,而南北两段当前地幔物质比较活跃,构造运动相对更为强烈。

The segmental feature of crustal and mantle velocity structures beneath Taihang Mountain tectonic zone

The crustal and mantle shear wave velocity structures 100km beneath Taihang Mountain and its neighboring areas were calculated with pure S wave inversion and T function method.The results show that there is obvious difference in the crust and mantle structures at the southern,middle and northern part of Taihang tectonic zone.In the southern segment,Xingtai and Handan region,there is a 10km low velocity layer in the lower crust.In the middle segment,Shijiazhuang to Baoding region,the crustal structures near the mountain is relatively steady,but it becomes complicated toward to the basin.The northern segment,Beijing area,which is the crossing region of Taihang and Yanshan tectonic belt,shows an unstable state.Some alternated layers with high and low velocity appear in the middle and lower crust of the segment.The eastern boundary of Taihang tectonic belt is the seismically active belt-Hebei plain seismic belt.Compared the velocity structures with the distribution of earthquakes,it is found that the characteristic in the distribution of small earthquakes on different segment is closely related to the low velocity layer or unstable structures.Combined with upper mantle velocity structures beneath this area,it is thought that,the middle segment of Taihang Mountain may be correlated to the large scale lithospheric thinning activity in North China since Mesozoic and Cenozoic,while beneath the southern and northern segments,the mantle media is active at present time,and tectonic activity is stronger.