长白山天池火山区及邻近地区壳幔结构探测研究

STUDY ON THE CRUSTAL AND UPPER MANTLESTRUCTURE IN THE TIANCHI VOLCANICREGION AND ITS ADJACENT AREA OFCHANGBAISHAN

对长白—敦化深地震测深剖面资料利用二维射线追踪程序包进行走时拟合及地震图计算 ,得到了长白山天池火山区及邻近地区地壳上地幔速度结构和深部构造 .结果表明 ,以C2 界面为标志 ,研究区地壳可分为上部地壳和下部地壳 .上部地壳厚 1 9— 2 3km ,P波速度为 6 0 0— 6 2 5km s;下部地壳厚 1 2— 1 7km ,它是由一个较均匀的速度层和一个厚 6— 9km的壳幔过渡层构成 .地壳厚度由敦化一带 31— 33km向东南逐渐增厚 ,至天池火山区最深达39km .在天池火山区地壳存在低速体 ,其速度较周围介质低约为 0 1 5km s.利用地震剖面探测、地震CT和大地电磁测深等结果显示 ,在天池火山区地壳内存在低速、低密度及低阻异常体 ,该异常体可能表明壳内岩浆囊的存在 .

In this paper 2-D ray tracing software package is used to compute synthetic seismogram and to fit travel time data of Changbai-Dunhua DSS profile. The crustal and upper mantle velocity structure and deep tectonic feature in Tianchi volcanic region and its adjacent area of Changbaishan are obtained. The results show that the crust in this region consists of the upper crust and the lower crust separated by C_2 interface. The upper crust is 19-23km thick, P wave velocity is 6.00-6.25km/s. The lower crust is 12-17km thick, which consists of a homogeneous velocity layer and a transient layer of 6-9km thick. The crustal thickness is 31-33km thick in the Dunhua, and becomes thicker gradually towards the southeast direction, reaching 39km deep in the Tianchi volcanic region. There is a low velocity body in Tianchi volcanic region, and its velocity is lower about 0.15km/s than its adjacent medium velocity. The results of the seismic prospecting, seismic tomography and magnetotelluric sounding show that there is a low velocity, low density and low resistivity abnormal body, suggesting a magma chamber in the crust of this region.