大别山超高压变质带层析地震调查

Seismic Tomography Investigation on UHP in the Dabie Mountains

1997年3月中德合作进行了大别山科学钻探选址区层析地震调查,研究结果揭示出大别山超高压变质带(UHP)地壳精细结构。郯庐断裂带近垂直延伸至Moho界面(可能更深),在Moho界面以上郯庐断裂带西侧大别山地壳物质没有迁移进入其东侧。在主测线(横中至潜山镇)20km深度发现一个由西向东倾斜的强反射层,推测可能是一个大的滑脱层。超高压变质岩石(或地幔物质)可能由地幔深处通过郯庐断裂带再沿此滑脱层折返到地壳上部,经后期剥蚀出露地表。

In the spring of 1997, scientists from the Chinese Academy of Geological Sciences and Geo-ForschungsZentrum Potsdam jointly collected seismic reflection data along a line in the Dabie Mountains. The seismic line , about 20 km long, begins west of the Town of Qianshan, crossing the Tancheng-Lujiang Tancheng-Lujiang Fault, and ends up in the ultra-high pressure meta-morphic block in the Dabie Mountains area. The experiment mainly explored layered structure of the upper, middle and lower crust. To study the crustal reflectivity, the standard common-depth-point (CDP) experiment was carried out. The tomographic method was applied to provide velocity information for the shallow (≤5km) structure, and the companion wide-angle shots gave control on the velocity structure of the deeper reflectors. The conventional CDP processing resulting in a stacked time section shows a very detailed structure with different reflectors down to 11s two-way time (TWT). The reflectors generally dip to the east in the middle and lower crust, while to the west in the upper crust, indicating complex evolution of this area. The Moho appears throughout the profile, generally at about lls TWT. The result from the seismic tomographic image shows that the high velocity bodies might be positioned at a depth of only about 1. 5 km below sea level within the Dabie ultra-high pressure metamorphic belt.