【摘要】 受俯冲残留体影响的410km间断面起伏形态的研究对于确定地球内部物质构成及地球动力学过程具有重要作用.帕米尔—兴都库什俯冲区域拥有全球少有的中、深源地震,为研究410km间断面起伏提供了良好的资源.利用日本Hi-net地震台网和美国TA台阵记录的帕米尔—兴都库什俯冲区域的6个震源深度为154.0~220.9km、震级为Mb5.6~6.4的中、深源地震的短周期/宽频带波形资料,经过4次根倾斜叠加处理,获得了36组Hi-net子台网和TA记录资料的倾斜叠加灰度图,从中提取了与410km间断面相关的次生转换震相SdP,发现受俯冲残留体影响下的410km间断面的深度位于372~398km.较之持续俯冲的西太平洋地区海洋岩石圈,研究区域俯冲滞留体对于410km间断面的相变线的影响要小得多.更多还原

【Abstract】 The effects of stagnant slabs on the topography of the 410 km discontinuity is helpful in determining the composition of Earth′s interior and understanding the related geodynamical process.The different stages of subduction can introduce different temperature and material anomalies on mantle discontinuities.Comparing with the subducting slabs around the western Pacific regions,the subducted oceanic lithosphere beneath the Pamir-Hindu Kush should have less effects on the phase transition of mantle discontinuities.Pamir-Hindu Kush is a rare subduction region with a lot of mid-deep earthquakes.Broadband/short period waveform data of6 earthquakes in the subducted slabs beneath Pamir-Hindu Kush,whose focal depths are between154.0~220.9km and magnitudes are between Mb5.6~6.4,recorded by Hi-net seismic network,Japan,and one event among them by the TA seismic array,USA,were processed with the 4-th root slant stack method.36 vespegrams deduced from the observed waveform data from Hi-net subnetworks and the TA array were used to obtain the conversion phase SdP,then the conversion depths around 410 km were determined based on IASP91.For the Ev.4,the conversion points picked from the vespegrams of Hi-net at the epicentral distances of 40°~50°and the TA at about 95°respectively show almost the same conversion depths at 390 km and which means that the conversion depths from different sub-networks of Hinet and TA array are consistent.Based on the distribution of 36 conversion points around the depth of 410 km related to picked SdP phases,the 410 km discontinuity is uplifted to the depths between 372~398km and has relatively complicated structure.Assuming the Clapeyron slope as-2.9 MPa/K(Bina and Helffrich,1994),the subducted slabs cause a low temperature anomaly about 250 to 360K.Combining with geological and geochemical results,the continent-continent collision of Pamir-Hindu Kush happened at 102~85 Ma(Ali et al.,2002),so the stagnant materials of subducted slabs have been warmed up since then.The stagnant materials including the garnet and pyroxene,and some volatiles make the 410 km discontinuity structure complicated.Because of long-period warming-up process of the subducted slabs beneath Pamir-Hindu Kush,the stagnant materials have less impacts on the 410 km discontinuity than those from subducting slabs around the western Pacific region where the discontinuity is up-lifted by 60~70km(e.g.,Collier and Helffrich,1997;Collier et al.,2001).36 vespegrams deduced from the observed waveform data of Hi-net sub-networks and the TA array of 6 mid-deep events beneath PamirHindu Kush were used to retrieve the conversion phases SdP caused by the 410 km discontinuity.The conversion depths around 410 km were determined based on IASP91.From the distribution of conversion points,the 410 km discontinuity is up-lifted to the depths around 372~398km caused by the long-period warming-up stagnant materials from the subducted oceanic lithosphere.Comparing with the western Pacific subducting slabs,the subducted stagnancy has less impacts on the topography of the 410 discontinuity.更多还原