腾冲火山区的地壳厚度和平均泊松比研究  

Crustal thickness and Poisson's ratio of the Tengchong volcanic area in southwestern China

作　　者：胥颐[1] 李雪垒 汪晟[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院油气资源研究重点实验室,北京100029 [2]中国科学院大学,北京100049

出　　处：《地球物理学报》2017年第6期2256-2264,共9页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41374066)资助

摘　　要：腾冲是青藏高原东南缘重要的第四纪火山活动区域,全新世以来的火山主要集中在腾冲盆地的中央,由北向南形成一个串珠状的火山链.为了深入探索这一火山区的深部结构和岩浆活动特征,我们在腾冲北部开展了为期一年的流动地震观测,利用接收函数方法计算了台站下方的地壳厚度、平均波速比和泊松比,研究结果揭示出测线下方地壳结构与岩浆活动及火山分布的对应关系.测线北部7个台站的地壳厚度在35.4~37.6 km之间,平均波速比为1.82~1.92、泊松比为0.28~0.31,其中马站附近莫霍面抬升幅度最大,与相邻地区莫霍面深度相差1~2 km,平均波速比和泊松比也达到最大值.相比之下,测线南端两个台站的地壳厚度接近40 km,平均波速比和泊松比仅为1.61~1.64和0.18~0.20,与测线北部7个台站的地壳结构相差甚大.分析表明地幔上涌对火山区莫霍面的局部抬升产生了一定影响,火山湖、黑空山、大-小空山和打鹰山下方应该存在一个相互联通的壳内岩浆囊.该岩浆囊在南北方向上的尺度约为20 km,热流活动以及幔源物质的侵入是地壳平均波速比和泊松比偏高的主要原因,它与热海附近的地温异常区分属两个不同的壳内岩浆存储系统.Tengchong is a Cenozoic volcanic area in the southeastern margin of the Tibetan plateau. Holocene volcanoes are mostly concentrated in the center of the Tengchong basin, showing a string-like volcanic cluster from north to south. In order to study the fine crustal structure and its relation with the magma activity of the volcanic area, we deployed a temporary earthquake observation across the major volcanoes in the Tengchong basin from May 2015 to July 2016. We used the teleseismic receiver function technique to determine the crustal thickness, VP/VS and Poisson＇s ratios of nine temporary stations. Results show a clear correlation of the crustal structure with volcano locations and evidence of the magma activity in the crust. For seven stations in the northern part of the profile, the crustal thickness varies between 35.3-37.6 km, with average VP/VS and Poisson＇s ratios between 1.82-1.92 and 0.28-0.31, respectively. Among them, the Moho interface beneath the MZT station is elevated by 1-2 km at depth, which is also characterized by the maximal VP/VS and Poisson＇ ratios, While the crustal thickness of the two stations in the southernmost part of the profile reaches 40 km, with average VP/VS and Poisson＇ ratios of only 1.61-1.64 and 0.18-0.20, respectively, much less than the results of other stations in the profile. Our analysis indicates that the mantle upwelling has significant effects on the local elevation of the Moho in the volcanic area. We speculate that the Crater Lake, Heikongshan, Dakongshan and Dayingshan volcanoes have an interconnected magma storage system within the crust. It has a size of about 20 km from north to south and isolates from the magma chamber beneath the Rehai geothermal field south of Tengchong. Undoubtedly, the heat flow activity and mantle intrusion should be responsible for the higher VP/VS and Poisson＇ ratios in the volcanic area.

关 键 词：腾冲火山区 接收函数 地壳厚度 波速比 泊松比 

分 类 号：P315[天文地球—地震学]