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

合作研究：中国东北扩展地震台阵（NECESS Array）：中国东北地区深俯冲、地幔动力学和岩石圈演化

• 批准号: 0635855
• 负责人: Stephen Grand
• 金额: $ 44万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635855&HistoricalAwards=false
• 关键词: Collaborative; Research; NorthEast; China; Extended

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.

沿着中国东北东部边界，太平洋板块俯冲深度接近600 km。中国东北地区地表是板内大陆岩浆活动和伸展作用活跃的地区。中国东北地区的基底岩石由太古宙克拉通和古生代褶皱带组成。中国东北扩展地震台阵（NECESSArray）项目是一项多国合作的地震实验，在中国东北地区部署280台宽频带地震仪，研究地幔过渡带板片行为、板内大陆岩浆活动和构造成因，以及经历了实质性改造的古太古代岩石圈演化。该实验将与来自中国地震局（CEA），东京大学地震研究所（ERI）和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该提案的PI合作进行。总共，中国将提供140个宽带地震仪的数据，日本将提供40个，我们正在申请资金部署100个仪器。阵列中仪器的最大间距约为80公里，孔径约为1，000公里× 1，200公里，部署期为两年。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，以开发中国东北地区从地壳到1000公里深度的地幔地震图像。地壳和地幔的地震图像将包括一个三维P和S速度模型，其标度长度约为50公里，反射率剖面图和各向异性图。地震结果将被用来回答一些问题，包括：1）俯冲的太平洋板块是否平放在660公里的边界上？2)如果板块是平的，它在过渡带内向西延伸到中国东北之下有多远？3)板块是否在某个时候沉入下地幔，如果是的话，它是如何做到的？4)东北地区下地幔顶部是否存在与其他俯冲带一样的反射层？如果存在，它们与俯冲板片在矿物学和化学方面有何关系？5)在下地幔顶部是否有板块流动的障碍物？6)俯冲板片上方的地幔流动与中国东北地区的活动构造（沿沿着中朝边界的岩浆活动、沿沿着蒙中边界的岩浆活动和隆升以及松辽盆地内部的伸展作用）有何关系？7)太古代地幔岩石圈经历了怎样的俯冲和碰撞历史，使其发生了怎样的改造和变形？8)太古宙地幔岩石圈真的发生了拆沉还是仅仅发生了改造和水平位移？NECESS项目是地震学的，但我们的研究结果应该提供的过程中所涉及的地幔过渡带俯冲的限制。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的限制。浅层地幔的地震图像对于如此大的区域来说将具有前所未有的分辨率，并将包括经历活跃构造过程的区域以及经历了修改的太古代岩石圈。因此，我们的研究结果将是重要的地球化学家了解旧的岩石圈改造，并导致更好地了解岩石测量之间的关系，通过研究捕虏体和地震观测值以及板内构造的原因。