长白山火山区高精度Rayleigh面波相速度结构与岩浆系统

High-resolution Rayleigh-wave phase velocity structure beneath the Changbaishan volcanic field associated with its magmatic system

近年来,有关长白山火山是否存在潜在喷发危险的讨论引起了国内外地学研究者的广泛关注,但人们目前对其壳幔岩浆系统的了解却十分不足,已有的研究对长白山火山壳内岩浆房存在的深度位置、形态规模及其部分熔融程度的认识仍存在较大分歧。本研究通过汇集长白山火山及邻区(包括朝鲜境内)多个密集流动地震台阵和区域固定地震台网的观测资料,采用背景噪声成像方法获得了长白山火山区高精度的Rayleigh面波相速度模型。成像结果表明:长白山火山中-下地壳深度位置存在显著低波速异常,可能指示了岩浆房的存在。上地壳局部低速区可能反映了壳内深部岩浆向上运移的通道或者是区域小尺度的岩浆聚集体。长白山火山上地幔顶部的低速可能揭示了软流圈热物质上涌,其减压熔融为壳内岩浆房提供了幔源岩浆补给。

Recently,a growing concern over the instability of the potentially hazardous Changbaishan volcano has drawn a lot of public attention from the geoscientific community.However,the crust and upper mantle structure related to the magmatic system underlying this volcano has not been well constrained.Previous research findings regarding the depth extent,spatial distribution and the degree of partial melting of the crustal magma chamber still remain hotly debated.In this study,we construct a high-resolution Rayleigh-wave phase velocity model via ambient noise tomography in the Changbaishan volcanic field based on the seismic data(including those from the North Korean side)recorded by several densely distributed portable networks and local permanent stations.Our model reveals that prominent middle-lower crustal low-velocity anomaly is evident beneath the Changbaishan volcano,suggesting possible existence of a crustal magma chamber.The localized low-velocity anomaly in the upper crust may reflect a magma channel sourced by the deep magma chamber or local small-scale magma bodies.The upper mantle low-velocity zone is representative of upwelling asthenosphere,which may feed the crustal magma chamber through decompression melting.