中国东北地区太平洋板块精细俯冲特征

Subducting Characteristic of the Pacific Slab Beneath Northeast China

中国东北地区的火山较为活跃。一些学者认为这些火山的起源与西太平洋板块的俯冲和软流圈物质的上涌存在密切联系。尽管天然地震层析成像结果明显地显示出火山区下方存在着太平洋板块,但板块的厚度、存在范围等俯冲特征仍然不是特别清晰。为此,采用远震层析成像和走时拟合相结合的方法深入研究了中国东北地区的壳幔速度结构,特别是太平洋俯冲板块的精细结构。研究结果表明:(1)板块的平均厚度和速度异常分别为85 km和1%,而且与日本海地区结果进行对比可推测板块并未增厚;(2)板块以低角度俯冲进入地幔过渡带,到达过渡带底部后弯曲成水平状,向西延伸至东经127°而停止;(3)水平延伸的板块恰好位于火山区的下方。这些俯冲特征有助于人们更好地理解陆内火山的起源及地球深部动力学过程。

The volcanoes locating in northeast China are very active.Some researchers consider that the origin of volcanoes is closely related to the subducting western Pacific plate and the upwelling asthenosphere.The thickness and the existing range of the subducted plate are not clear as far although the seismic tomography results obviously show that the Pacific plate exists below the volcano region.Therefore,in this study,we adopted the method combining the teleseismic tomography with travel time forward modeling to further study the velocity structure beneath northeast China,especially the precise model of subducted Pacific plate.Our results show that（1） the average thickness and velocity perturbation of slab are 85 km and 1%,respectively,and the slab has not been thickened compared with the previous result of the Japan Sea;（2） the Pacific plate subducted into the mantle transition zone with a shallow dip angle,and changed horizontally when it touched the bottom of mantle transition zone,and extended westward to Longitude 127°E and then stops over there;（3） the horizontal slab locates right below the volcano region.These above features help people understand the origin of intraplate volcanoes and the geodynamical process better.