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贝加尔裂谷是世界上地震活动最强烈的裂谷带,其动力学成因机制是地球科学界关注的热点课题之一.我们利用全球地震台网长期运行台站TLY和ULN的远震资料,分别计算了P波接收函数(1748条),并在一定角度范围内分区域叠加,获得了研究区下方的410km和660km间断面以及地幔过渡带(MTZ)的厚度.结果表明在研究区的东南部即蒙古地区地幔过渡带厚度基本正常(250km);贝加尔裂谷地区地幔过渡带明显增厚(292km);裂谷下方存在小幅度的减薄现象(230km).综合分析推测,大范围的MTZ增厚,可能原因是中生代的蒙古华北板块(Mongolia-North China Block)与西伯利亚高原碰撞,或者地幔岩浆物质侵入到下地壳,使地壳和岩石圈增厚,致使下地壳产生榴辉岩化,导致重力不稳发生拆沉作用,拆离的部分落入地幔过渡带.拆沉作用诱发软流圈上涌,且拆离部分携带的水分加剧了上地幔熔融程度,使地幔对流速率加快,有利于裂谷的发育.我们初步研究结果认为拆沉的破坏作用及其引发一系列活动对裂谷的发育具有重要的影响,裂谷下方局部MTZ减薄所指示的热物质上涌对岩石圈的破坏可能进一步促进了裂谷的发育.
The Baikal rift is the most active rift zone in the world, and its dynamical genesis mechanism is one of the hot topics that geosciences pay close attention to.We use teleseismic data of long-run stations TLY and ULN from global seismograph stations The P wave reception function (1748) was calculated and subregionally superposed within a certain angle range, and the thickness of 410km and 660km and the MTZ of the study area were obtained.The results show that in the southeastern part of the study area That is, the mantle transitional zone in Mongolia is basically normal (250km in thickness); the mantle transitional zone in the Baikal rift area is obviously thickened (292km); there is a slight thinning phenomenon (230km) below the rift. It is probably because of the collision of the Mesozoic Mongolia-North China Block with the Siberia Plateau or the mantle magma intrusion into the lower crust, which thickens the crust and lithosphere, resulting in eclogite formation of the lower crust, resulting in gravitational Unsteady delamination, detachment of the part of the transition zone into the mantle .Deposition Shen induced asthenospheric upwelling, and detachment of some of the carrying water exacerbated the upper mantle melting degree, so that the mantle on Speeding up is conducive to the development of the rift.Our preliminary results suggest that the destructive effect of detachment and its initiation of a series of activities have an important impact on the development of the rift.The thermal mass indicated by the local MTZ thinning below the rift rises The destruction of the lithosphere may further promote the development of the rift.