云南腾冲火山区地壳及岩石圈厚度研究

Study on crustal and lithosphere thicknesses of Tengchong volcanic area in Yunnan

使用云南腾冲火山监测台网9个宽频带地震台站的远震数据,采用P波和S波接收函数的方法研究了腾冲火山区的地壳厚度、泊松比值以及岩石圈和软流圈分界面（LAB）深度.研究结果表明：1）云南腾冲火山区的地壳厚度约在33.5～38.0km之间;2）火山区的泊松比主要集中范围为0.26～0.32,其中6个台站均大于0.29,推测与地壳镁铁质成分的增加有关并且可能存有2个岩浆囊;3）火山区的岩石圈厚度在78.2～88.0km,较周边地区明显隆起且横向差异较大.腾冲火山区岩石圈的明显穹隆,由软流圈上涌（地幔热物质上升）引起岩石圈的拉张与减薄所致.

Tengchong Volcano Area（24°40′—25°30′N,98°15′—98°45′E）is one of the most famous and youngest volcano-active areas in China.It is located on the northeast side of the collision belt between the Indian and Euroasian plates.It is a part of Myanmar Arc seismic structure,belonging to the Himalayan strong-earthquake belt.There are 68 volcanoes distributed in the region of 90 km long in the north-south direction and 50 km wide in the east-west direction.Among them are 4Holocene（Q4）volcanoes,18Late-Pleistocene（Q3）volcanoes,and 38EarlyPleistocene（Q1）volcanoes.To study the geologic evolution and volcanic activity of the Tengchong Volcano Area,we need to investigate the variation of crustal thickness and the distribution of the Poisson′s ratio in the area,as well as the detailed thickness and topography of the lithosphere.We use the seismic data observed by 9digital broadband stations of Tengchong EarthquakeMonitoring Net from July 2007 through December 2011.The P receiver functions are used tostudy the crustal thickness and the Poisson′s ratio in the region,while the converted phases at the Moho and the LAB in the S receiver functions are utilized to get the depths of the Moho and the LAB.To reduce the noises and remove the effect of the heterogeneity,we stack the P and S receiver functions beneath each station,respectively,to get an averaged trace of P receiver functions and an average trace of S receiver functions.Before the stacking of the weak converted phases from the Moho and the LAB,each seismic event is moveout corrected to the reference epicentral distance of 67degree（corresponding to the ray parameter of 6.40s/deg）.Based on the IAS91 model,the receiver functions are transformed from the time domain to the depth domain.1）The crustal thickness of Tengchong Volcanic Area ranges from 33.5to 38.0km.2）The Poisson′s ratio of the area mainly varies from 0.26 to 0.32.The ratio beneath 6stations is over0.29,which is attributed to the increase of mafic component in the crust.There may exist two magma chambers.3）The thickness of the lithosphere ranges from 78.2to 88.0km.The crustal thickness of Tengchong Volcanic Area ranges from 33.5to 38.0km,with a feature of being thick at the north and south ends but thin in the middle（or the Moho is uplifted in the middle part）.The Poisson′s ratio is between 0.262 and 0.322.Six stations present high Poisson′s ratio,and the crust may be partially melted in some local areas.There probably exist two magma chambers on the east side of Mazhang and the area of Tengchong-Shaba,but their scopes need further determination.The thickness of the lithosphere ranges from 78.2to 88.0km,being thinner than that of the surrounding area.In the center of the volcano area（i.e.,the convergence between the Tengchong volcanic fault and the Yingjiang-Longchuan fault）,both the crust and the lithosphere are uplifted.The lithosphere presents a dome shape obviously,caused by the extension and thinning of the lithosphere by the upwelling of the asthenosphere（or the uplift of mantle hot materials）.