Collaborative Research: US-EAGLE (Ethiopia-Afar Grand Lithospheric Experiment): Modification of Lithospheric Structure During Continental Break- Up

0207878Keller关于大陆边缘如何形成的架构还没有被很好地理解，因为以前的大多数工作都是在裂谷完成后成功地裂解边缘。陆相(断裂主控)端元和大洋(岩浆主控)裂谷端元都得到了较好的研究，但对过渡阶段的认识还不够深入。该项目将记录这一从大陆裂谷到海洋裂谷的关键转变。PIS将进行地震实验，结合地球化学、重力和构造研究，在罕见的大陆裂谷向早期扩张过渡的地区之一-埃塞俄比亚主要裂谷(MER)-研究岩石圈结构。在MER中，向初始海底扩展的沿轴过渡提供了时间变异性的空间替代。具体目标是：1)确定过渡裂谷段上和沿线的详细地壳和地幔结构；2)了解裂谷下和裂谷内的岩浆作用。PI将获得地壳P速度剖面和S速度剖面，这些剖面可以在10度时解释埃塞俄比亚裂谷的岩性。在第一次出现活动岩浆中心的地方，并沿走向向北研究向完全岩浆裂谷的过渡。他们将根据新的地震数据解释现有的和新的重力数据，并使用地球化学数据来约束上地幔的物理状态和地壳的岩浆输入。该项目(US-EAGLE)完全与已经资助的英国-EAGLE倡议相结合。莱斯特、利兹和伦敦的科学家获得了英国的资助，以便在2003年1月对埃塞俄比亚裂谷进行单一折射剖面测量，同时进行当地地震活动研究和远程地震记录。US-Eagle PI将拍摄并记录沿轴线广角的互补正交剖面；并将向这些线阵和本地地震台网发射扇形镜头，以提供3D覆盖的测量。这些地震学实验共同构成了埃塞俄比亚裂谷和烟柱的嵌套、多尺度地震图像。地震研究将与地球化学、岩石学和重力研究(美国)以及构造、热年代学、大地电磁和其他重力研究(英国)相结合。

0207878KellerThe architecture of continental margins in terms of how they are created is not well understood because most of the previous work has been on successfully rifted margins after rifting is complete. Both continental (fault dominated) end-members and oceanic (magma dominated) rift end-members are well studied, but the transitional stage is not understood. This project will document this critical transition from continental to oceanic rifting. The PIs will carry out seismic experiments, integrated with geochemical, gravity and structural studies, to study lithospheric structure in one of the rare areas where the transition from continental rifting to incipient spreading is captured - the main Ethiopian Rift (MER). In the MER the along-axis transition to initial seafloor spreading provides a spatial proxy for temporal variability. Specific objectives are: 1) to determine detailed crust and mantle structure across and along a transitional rift segment and 2) to understand magmagenesis beneath and within the rift. The PIs will obtain crustal P-and S-velocity cross-sections that can be interpreted for lithology across the Ethiopian rift at 10 deg. N where active magmatic centers first appear, and along-strike to the north to study the transition into fully magmatic rifting. They will interpret existing and new gravity data in light of their new seismic data, and use geochemical data to constrain the physical state of the upper mantle and magmatic inputs to the crust.The project (US - EAGLE) is fully integrated with the already funded UK - EAGLE initiative. Scientists at Leicester, Leeds and London, have been awarded UK funds to carry out a single refraction profile across the Ethiopian rift in January 2003, coupled with local seismicity studies and teleseismic recording. The US - EAGLE PIs will shoot and record a complementary orthogonal along-axis wide-angle profile; and will shoot fan shots into these linear arrays and the local seismic network to provide a measure of 3D coverage. Together, these seismological experiments form a nested, multi-scale seismic image of the Ethiopian rift and plume. The seismic studies will be coupled with geochemical and petrological and gravity studies (US), and structural, thermochronological, magnetotelluric and additional gravity studies (UK).***