苏鲁超高压变质带北部地球物理调查(1)─—深反射地震

GEOPHYSICAL INVESTIGATIONS IN NORTHERN SULU UHPM BELT,PART I:DEEP SEISMIC REFLECTION

苏鲁超高压变质带是世界上研究陆一陆碰撞俯冲和壳幔作用的最佳地质场所之一．为了解超高压变质带岩石的形成、折返和相应的动力学过程，必须了解该区的地壳和浅地幔构造．本文介绍了该区北部的地质情况和进行深反射地震调查取得的成果，包括（１）在五莲─青岛断裂南侧超高压变质岩片向北倾斜，呈现叠复组构，反映岩片的折返；（２）根据地震资料推测在１４６Ｍａ前后胶南地块的隆升一伸展构造内幕；（３）超高压变质岩片厚约１２ｋｍ，由于含有大量相辉岩透镜体，地震波速高达６．８─７．３ｋｍ／ｓ；（４）莫霍面附近有许多楔形反射体，反映陆一陆碰撞；（５）石门地区７ｋｍ深处存在高波速的强反射体，可作为在该区进行大陆科学钻探的候选场址．

The Sulu high-pressure metamorphic (UHPM)belt is one of the best geological sites worldwide to study the intra-continental collision/ subduction and interactionbetween the crust and the mantle. In order to understand its formation and exhumation,as well as the related geodynamic processes,the structures of the crust and the shallow mantle should be revealed,therefore deep seismic reflection profiling has been carried out and the results from the northern Sulu are presented in this paper. Theresults include:(a)the UHPM rock slices south to the Wuliang-Qingdao fault are dipping north and stacked each other,showing exhumation in Triassic Period;(b)Seismic reflection pattern reveals the doming and extension of the Jiaonan Masiffat about l46ma,(c) the UHPM rock slices of about l2km thick contain a lot ofcoesite-bearing eclogite and have high velocity reaching 6.8 km/s;(d)many wedgereflectors exist around the Moho, showing the intra-continental collision,(f)in Shemensite the high-velocity reflector is buried from 5 7km, it could be considered as oneof candidate sites for continental deep scientific drilling. Other geophysical surveys,such as MT, have been completed in the area, the results will be presented in thepart two following this paper.