Collaborative Research: NorthEast China Extended seiSmic Array (NECESS Array): Deep Subduction, Mantle Dynamics, and Lithospheric Evolution beneath Northeast China

沿着中国东北的东部边界，俯冲的太平洋板块深达600公里。中国东北部地表是板内大陆岩浆活动和伸展活动的区域。中国东北部的基岩是由太古宙克拉通与古生代褶皱带并列而成。东北中国扩展地震台阵(NECESS阵列)项目是一项多国合作的地震实验，在东北中国地区部署了280台宽带地震仪，以研究地幔过渡带的板片行为，板内大陆岩浆活动和构造的原因，以及经历了实质性修改的古太古代岩石圈的演化。这项实验将与来自日本中国地震局、东京大学地震研究所、日本东北大学地震和火山喷发预测研究中心的科学家以及美国这项提议的PI合作进行。总体而言，中国将提供140台宽带地震仪的数据，日本将提供40台，我们正在申请资金部署100台仪器。该阵列中仪器的最大间距约为80公里，口径约为1000公里乘1200公里，部署期限为两年。通过我们的合作，我们将把所有可用的地震成像技术应用于我们收集的数据，以开发出从地壳到1000公里量级的东北中国地幔的地震图像。地壳和地幔的地震图像将包括比例尺长度约为50公里的三维P和S速度模型、反射率剖面和各向异性图。地震结果将被用来回答一些问题，包括：1)俯冲的太平洋板块在660公里的边界上是平的吗？2)如果板块是平的，它在过渡带内中国东北下方向西延伸了多远？3)板块在某一时刻是否下沉到下地幔，如果是，它是如何下沉的？4)像在其他俯冲带中观察到的那样，中国东北下方的下地幔顶部是否有反射体，如果是这样的话，它们在矿物学和化学方面与俯冲板块有何关系？5)是否有迹象表明下地幔顶部存在阻碍板块流动的屏障？6)俯冲板块上方的地幔流动与东北中国的活动构造有什么关系(朝鲜-中国边界的岩浆活动，蒙古-中国边界的岩浆活动和隆起，7)太古代地幔岩石圈经历了怎样的俯冲和碰撞历史？8)太古代地幔岩石圈是真的被拆离了还是只是被改造和水平位移了？这个必要的项目是地震学的，但我们的结果应该对地幔过渡带中涉及的俯冲过程提供约束。这反过来将为矿物物理学家和地球动力学家研究地幔对流及其矿物学和化学成分提供基本限制。对于如此大的区域，浅地幔的地震图像将达到前所未有的分辨率，并将包括正在经历活动构造过程的地区以及经历了修改的太古宙岩石圈。因此，我们的结果将对地球化学家理解古老的岩石圈改造作用具有重要意义，并有助于更好地理解通过研究捕虏体和地震观测数据进行的岩石测量之间的关系以及板内构造的原因。

Along the eastern boundary of Northeast China the subducting Pacific plate approaches depths of 600 km. The surface of Northeast China is a region of active intraplate continental magmatism and extension. The basement rock of Northeast China is composed of an Archean craton juxtaposed with a Paleozoic foldbelt. The NorthEast China Extended SeiSmic Array (NECESSArray) project is a multi-national collaborative seismic experiment to deploy 280 broadband seismometers across Northeast China to study slab behavior in the mantle transition zone, the cause of intraplate continental magmatism and tectonics, and the evolution of ancient Archean lithosphere that has undergone substantial modification. The experiment will be done in collaboration with scientists from the China Earthquake Administration (CEA), the Earthquake Research Institute (ERI) of Tokyo University and the Research Center for Prediction of Earthquakes and Volcanic Eruptions of Tohoku Univeristy, in Japan and the PI's of this proposal from the United States. In total, the Chinese will provide data from 140 broadband seismometers, the Japanese 40, and we are requesting funding to deploy 100 instruments. The maximum spacing of instruments in the array will be about 80 km with an aperture of roughly 1000 km by 1200 km and a duration of deployment of two years. Through our collaborations we will apply all available seismic imaging techniques to the data we collect to develop a seismic image of the mantle beneath Northeast China from the crust to depths on the order of 1000 km. The seismic image of the crust and mantle will include a three-dimensional P and S velocity model with scale lengths of roughly 50 km, a reflectivity profile, and a map of anisotropy. The seismic results will be used to answer a number of questions including:1) Does the subducted Pacific plate lie flat on the 660 km boundary?2) If the plate is flat, how far does it extend to the west beneath Northeast China within the transition zone?3) Does the plate at some point sink into the lower mantle and if so how does it do this?4) Are there reflectors in the top of the lower mantle beneath Northeast China as observed in other subduction zones, and if so how are they related to subducted slab in terms of mineralogy and chemistry?5) Is there any indication of a barrier to slab flow within the top of the lower mantle?6) What is the relationship of mantle flow above the subducted slab to the active tectonics of Northeast China ( magmatism along the North Korea-China border, magmatism and uplift along the Mongolian-China border, and extension within the Songliao basin)? 7) How has the Archean mantle lithosphere been modified and deformed due to the subduction and collision history it has experienced?8) Has Archean mantle lithosphere truly been delaminated or has it only been modified and displaced horizontally?The NECESS project is seismological but our results should provide constraints on the processes involved in subduction in the mantle transition zone. This in turn will provide fundamental constraints for mineral physicists and geodynamicists studying convection in the mantle as well as its mineralogy and chemical composition. The seismic images of the shallow mantle will be at an unprecedented resolution for such a large area and will include regions undergoing active tectonic processes as well as Archean lithosphere that has undergone modification. Thus our results will be important for geochemists understanding of old lithosphere modification and lead to a better understanding of the relationship between rock measurements made through studies of xenoliths and seismic observables as well as the cause of intraplate tectonics.