摘要
为了研究安徽及周边地区的地壳精细结构及其动力学变形机制,本文利用中国地震台网50个固定台站记录的远震波形数据,采用"水准量"反褶积法提取P波接收函数,采用H-κ叠加技术和莫霍面Ps横波分裂技术,获得了各台站下方的地壳厚度、纵横波速比和地壳各向异性信息.H-κ叠加结果显示:研究区域的地壳厚度和纵横波速比在空间分布上均存在明显的区域特征.华北地块地壳厚度较薄,平均厚度约29 km,且相对平坦,波速比较高,表明地壳中镁铁成分居多.大别造山带地壳较厚,平均为33.1 km,但波速比变化较大.造山带主体波速比约为1.75甚至更低,是长英质-中性岩石特征,与造山带中下地壳拆沉有关,而造山带北部的六安断裂带出现的高波速比与局部岩浆活动产生的基性火山岩有关.扬子地块地壳厚度介于前两者之间,平均为31.5 km,波速比局部特征明显.黄山区域波速比为1.79,反映了该区域中酸性花岗岩特征.地壳各向异性结果显示:整个研究区域的分裂时间为0.2～0.6 s.华北地块横波快波方向总体为NW-SE向,与SKS分裂方向和GPS方向一致,表明壳幔变形方向一致,再结合华北块体地壳厚度较薄和高波速比,推测华北地块在拉张应力下,上地幔物质上涌,侵蚀下地壳,导致地壳变薄和火山岩成分增多.大别造山带区域的快波方向表现为NW-SE向,这与SE向的中下地壳塑性流动或多期的拆离折返构造事件吻合.郯庐断裂带附近的快波方向为NE-SW甚至N-S向,反映了该断裂带在其东西两侧挤压作用下,近南北向拉张运动.
In this paper, we analyzed a large amount of receiver function data recorded by 50 seismic stations of China Earthquake Administration and obtained the crustal structure and crustal anisotropy information to investigate their dynamic deformation mechanism beneath the Anhui province and its surroundings through H-κ stacking method and Moho Ps shear-wave splitting technology. The crustal thickness and V_p/V_s ratio in the study region both show distinct regional characteristics. The crustal thickness in the North China block is thinner with an average thickness of 29 km and relatively flat, while the V_p/V_s ratio is obviously high, indicating that there exists more mafic rock compositions. The moderately thick crust is observed in the Dabie Orogenic belt with a Moho depth in the range of 30.1～37.2 km, which may be related with the collision between Yangtze block and North China block, subsequently causing the exhumation and upwelling of the multi-stage metamorphic belt. The V_p/V_s ratio in most of the Orogenic belt is about 1.75 even lower, which is characterized by felsic and intermediate rock compositions may connected with the middle-lower crustal delamination, while high V_p/V_s appeared in the Liu'an falt is considered as mafic volcanic rocks caused by regional magmatism. The average crustal thickness of Yangtze block is about 31 km,while V_p/V_s shows obvious region characteristics, in particular, the higher V_p/V_s ratio about 1.79 in the Huangshan area reflects the acid-intermediate granite. We also measured the crustal anisotropy used the Moho Ps conversion wave. The results show that the splitting time of the study region varies from 0.2 s to 0.6 s. The fast wave direction in the North China block is NW-SE, which is consistent with SKS splitting direction and GPS velocity filed, suggesting a crustal-mantle consistent deformation in the North China block. Further, combined with our H-κ stacking method in this area, we deduce that the upwelling material of hot upper mantle eroded the lower crust and thinning the crust based on the tensile stress, and it also increases the composition of the volcanic rocks in the crust. We also obtained the similar NW-SE fast wave direction in the Dabie Orogenic blet. It coincides with the mid-lower crustal plastic flow and multi-stage detachment and exhumation mechanism. However, the fast polarization direction is NE-SW or even to N-S beneath the Tanlu fault zone, reflecting that the fault experienced near N-S tension movement under E-W side compression environment.