Crustal Velocity Structure beneath the Site of Chinese Continental Scientific Drilling Site
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摘要: 为了深入研究大别—苏鲁超高压变质带的深部结构及空间展布特征, 进一步揭示该超高压变质形成的动力学过程, 在中国大陆科学钻探场址区进行了广角反射/折射地震测深调查.根据广角反射/折射地震测深的资料研究, 建立了中国大陆科学钻探场址区的地壳纵波速度结构.从纵向上来看, 研究区域的地壳结构可划分为上、中、下3层: 上地壳的速度小于6.2 0km/s, 厚10余km; 中地壳的速度为6.4 0km/s, 厚亦为10km左右; 下地壳的速度为6.6 0km/s.地壳厚度为31km左右, 且其地壳的平均速度为6.30km/s.上地壳中的速度倒转指示了超高压变质体在地壳内部的空间分布, 且超高压变质体在大陆科学钻探场址及其附近的下部呈现为一隆起形态.Abstract: In order to study the deep structure, spatial tectonic characteristics and the dynamic process for the Dabie-Sulu ultral-high metamorphic belt, a wide-angle reflection/refraction seismic survey was conducted in the Chinese Continental Scientific Drilling (CCSD) site. The crustal velocity structure beneath the CCSD site has been established based on wide-angle seismic reflection/refraction data acquired at the site. According to the results, the crust beneath CCSD is composed of three layers: the upper, middle and lower crust, with velocities of < 6.20 km/s, 6.40 km/s, and 6.60 km/s, and a thickness of ~10 km, ~10 km, and ~12 km respectively. The crust thickness is 31 km around with an average velocity of 6.30 km/s. However, the reversed velocity in the upper crust implies an ultrahigh-pressure metamorphic (UHPM) layer (body) with a shape of uplift beneath or near the CCSD site.
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Key words:
- CCSD /
- deep seismic sounding /
- crustal velocity structure /
- UHPM zone
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图 1 中国大陆科学钻探场址及其周边地区地质构造略图及地震测线位置
1.超高压变质带; 2.高压变质带; 3.中、新生代沉积; 4.花岗岩; 5.断裂; 6.地震剖面及炮点; WYF.五莲-烟台断裂; JXF.嘉山-响水断裂; TLF.郯城-庐江断裂; XGF.新沂-赣渝断裂
Fig. 1. Tectonic sketch map and seismic profiles in the CCSD site and its adjacent area
图 2 测线Ⅰ上W07炮的P波地震记录截面
综合速度vr为6.00 km/s, 下同
Fig. 2. Seismic record section from shotpoint W07 in Profile Ⅰ
图 6 测线Ⅰ上E10炮的P波合成地震记录截面
Fig. 6. Synthetic seismic record section from shotpoint E10 in Profile Ⅰ
图 7 测线Ⅱ上N13炮的P波资料的模拟结果
a.地震记录及理论计算走时; b.地壳速度模型其射线路径
Fig. 7. Modeling results from shotpoint N13 in Profile Ⅱ
图 8 中国大陆科学钻探场址区的地壳纵波速度结构
Fig. 8. Crustal velocity structure beneath the CCSD site and its adjacent area
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