基于地下电性结构探讨中国东北活动火山形成机制

Study of the formation mechanism for volcanism in Northeast China based on deep electric structure.

东北地区是我国现代火山活动最强烈的地区之一,也是许多学者十分关注的地区。本文回顾了前人提出的关于该地区火山成因的研究成果;通过分析在东北活动火山区大地电磁观测研究的地壳上地幔结构和采用大地电磁网观测研究的地幔1000km以上的电性结构成果,发现长白山天池火山区存在地壳岩浆囊,其它活动火山没有发现地壳岩浆囊,但都存在通往地幔的岩浆通道;东北地区在80～120km左右和200～250km可能存在与地幔岩浆囊相关的地幔高温流体。基于电性结构的研究成果,作者提出了一种东北地区可能的活动火山成因假说。认为东北火山的成因可能与西太平洋板块俯冲到中国东北地区的地幔过渡带后产生脱水有密切关系。这种水以矿物组分或流体方式向上运移,在地幔200～250km和80～120km左右聚集,80～120km的聚集区可能是火山喷发的物质来源。

Northeast China is one of the regions with most active volcanic activity in the country, which attracts much attention of researchers. This paper reviews previous studies on the formation mechanism of volcanoes in this region. Then the electric structures down to depth 1000km beneath the volcanic areas in Northeast China are analyzed based on measurements of MT and Netwoek-MT survey. It is found that the Tianchi volcanic area in the Changbaishan Mountains is the unique place beneath which exist magmatic chambers featured by low resistivity in the crust, where all volcanoes has their magmatic conduits toward the mantle. While there are probably high-temperature fluids associated with low resistivity at depths 80-120km and 200-250km in the mantle in Northeast China. Based on the study of the electric structure, we propose a hypothesis for the cause of active volcanoes in Northeast China. It is suggested that these volcanoes are likely related with dehydration that occurred when the West Pacific plate subducted down to the transition zone of the upper mantle below North China. The water produced by this dehydration moved upward in form of mineral components or fluids, accumulating at depths 200-250km and 80-120km, respectively. The accumulation area at the depth 80-120km is a possible material source for volcanoes in Northeast China.