云南地区的地幔过渡带结构及其动力学意义  

Structure of the mantle transition zone under the Yunnan region and its geodynamic implications

作　　者：薛明[1,2] 王苏[1,2] 徐晓雅[1,2] 胡家富[1] 

机构地区：[1]云南大学地球物理系,昆明650091 [2]昆明南方地球物理技术开发有限公司,昆明650091

出　　处：《科学通报》2017年第16期1752-1765,共14页Chinese Science Bulletin

基　　金：国家自然科学基金(41374106;41304076)资助

摘　　要：计算云南及周边地区48个宽频地震台记录的8600个远震P波接收函数,并根据参考地球模型将接收函数从时间域转换到深度域.在转换深度550 km处,将1°×1°面元内的接收函数叠加成一道信号,共获得了沿纬度28°,27°,26°,25°,24°和23°N的6个共转换面元叠加剖面,其叠加深度在0~800 km之间.结果表明:(1)在26°N以北的地区,410和660 km间断面的平均深度分别为407~408和663~667 km,地幔过渡带的平均厚度处于255~259 km之间,过渡带的厚度接近全球平均厚度250 km;(2)在26°N以南的地区,410和660 km间断面的平均深度分别为412~426和675~703 km,地幔过渡带的平均厚度处于262~279 km之间,明显大于全球平均厚度250 km.云南地区410和660km间断面的加深显然与印度板块在缅甸弧下方的俯冲有关,然而,从云南地区地幔过渡带的结构来分析,本文认为印度板块沿缅甸弧向东俯冲主要发生在26°N以南地区.The mantle transition zone （MTZ） bounded by physical discontinuities at 410 and 660 km depth is believed to play a key role in controlling mantle flow. Mineral physics experiments reveal that phase changes from olivine to fl phase and y-spinel to perovskite＋magnesiowustite, at pressures equivalent to the existing at those mantle discontinuities, largely explain the variations in seismic velocity observed by the seismologists. The globally observed seismic velocity discontinuity at 660 km depth marks the bottom of the MTZ, which is the natural boundary between the upper and lower mantle. This discontinuity is considered an important mantle boundary, since it is especially associated with the mantle dynamics, the source of mantle plumes and the sinking of the subducted plates. On the other hand, temperature variations are the cause of thickening and thinning of the MTZ in correspondence with the positive and negative slopes of the Clapeyron curve at the 410 and 660 km mantle discontinuities, respectively. Receiver function analysis is a straightforward and commonly accepted method of studying the crust and upper-mantle structure through the use of teleseismic waveforms recorded at three-component seismic stations. This method requires the rotation of the ZNE displacement components to the radial and transversal components in the horizontal plane; and later the transformation of the radial and vertical components, which lie in the same vertical plane, into the L and Q components of the ground motion. By deconvolving the L component from the Q-component, both the source, far field path and instrument effects are removed. The resulting receiver function waveform is the ground＇s impulse response. The analysis of each receiver function recorded at an array station provides, after moveout correction, a detailed estimation of the depth of the interface where the P-to-S seismic phase conversion is produced. However, the converted Ps phases at the discontinuities of 410 and 660 km depth are so weak that stacking of

关 键 词：P波接收函数 面元叠加 地幔过渡带 印度板块 向东俯冲 

分 类 号：P315.2[天文地球—地震学]