Collaborative Research: Thin Crust Over The Marion Rise: Remelting The Gondwanan Mantle II

合作研究：马里恩隆起的薄地壳：冈瓦纳地幔 II 的重熔

• 批准号: 1935863
• 负责人: Michael Cheadle
• 金额: $ 5.19万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-15 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1935863&HistoricalAwards=false
• 关键词: Collaborative; Research; Thin; Crust; Over

Earth is a dynamic planet. Its surface is being continuously created and destroyed at ocean ridges and subduction zones, which comprise the boundaries of the great tectonic plates. These processes create seismic and volcanic hazards as well as generating economic resources, thermal energy, and the planet's oceans and atmosphere. Underlying this is the circulation of the Earth's mantle, largely manifest by upwelling along ocean ridges, and mantle plumes. The latter are upward flows that produce mantle hotspots, such as Hawaii and Iceland. Where ocean ridges pass near mantle hotspots as at Iceland and the Azores Islands in the Atlantic, and at Marion Hotspot in the Indian Ocean, the ocean ridge is greatly elevated and has a chemical composition similar to the associated mantle hotspot. The standard scientific explanation for this is that the volcanic hotspot is created by a mantle plume rooted deep in the mantle, and that the flow of this plume is partially diverted to the adjacent ocean ridge, where it becomes the source of the lavas erupting there. However, there are large differences between ocean rises, and a different process may be responsible for the Marion Hotspot, a remote volcanic feature roughly 1,000 miles southeast of South Africa that sits at the boundary of the African and Antarctic tectonic plates. An international team, led by German, U.S., and Chinese scientists, is working together to test a new hypothesis that the Marion Rise represents the melting of a piece of anomalous mantle set adrift in the deep earth during the breakup of the ancient supercontinent Gondwana. The conventional deep mantle plume hypothesis predicts thickened crust all along the rise, while remelting the Gondwana mantle predicts thin or missing crust along the ridge, with isolated widely spaced local magmatic centers, with the thickest crust located at the intersection of the mantle melting anomaly with the ridge. This award supports the U.S. participation in a German-U.S.-China collaborative cruise, which is the second of a two expedition program, the first of which was led by the U.S. scientists. The U.S. Scientific Party will direct the geophysical magnetics, gravity, and multibeam mapping survey of the Southwest Indian Ridge west of the Discovery Fracture Zone north of Bouvet Island, and will use this data, in combination with the results of the rock dredging and ROV sampling on the German research vessel Sonne, to map out the extent of the mantle directly exposed on the seafloor, and constrain the crustal thickness where it is not exposed. They will characterize the differences in seafloor topography and tectonics from that seen at magmatically more robust ocean ridges such as the East Pacific Rise and Mid-Atlantic Ridge. In doing this, they will directly test and validate one of the two hypotheses for the origin of the Marion Rise described above.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球是一个充满活力的星球。它的表面在构成大板块边界的洋脊和俯冲带不断地被创造和破坏。这些过程产生了地震和火山灾害，同时也产生了经济资源、热能以及地球的海洋和大气。这背后是地幔的循环，主要表现为沿洋脊和地幔柱的上升流。后者是向上流动，产生地幔热点，如夏威夷和冰岛。在洋脊经过地幔热点附近的地方，如大西洋的冰岛和亚速尔群岛，以及印度洋的马里恩热点，洋脊被大大抬高，其化学成分与相关的地幔热点相似。对此，标准的科学解释是，火山热点是由根植于地幔深处的地幔柱形成的，而地幔柱的流动部分转向了邻近的洋脊，成为那里喷发的熔岩的来源。然而，海洋上升之间有很大的差异，马里恩热点可能是一个不同的过程造成的，马里恩热点是一个遥远的火山特征，位于南非东南约1000英里处，位于非洲和南极构造板块的边界。一个由德国、美国和中国科学家领导的国际研究小组正在共同验证一个新的假设，即马里恩隆起代表了古超大陆冈瓦纳分裂期间在地球深处漂流的一块异常地幔的融化。传统的深地幔柱假说预测沿上升的地壳会变厚，而冈瓦纳地幔的重熔预测沿山脊的地壳会变薄或消失，有孤立的大间隔的局部岩浆中心，最厚的地壳位于地幔熔化异常与山脊的交汇处。该奖项支持美国参与德美联合军事行动。这是两个探险项目中的第二个，第一个项目由美国科学家领导。美国科学小组将对Bouvet岛北部Discovery断裂带以西的西南印度洋脊进行地球物理、重力和多波束测绘调查，并将利用这些数据，结合德国研究船Sonne的岩石疏通和ROV采样结果，绘制出直接暴露在海底的地幔范围，并限制地壳厚度。他们将描绘海底地形和构造的不同之处，这些不同之处与岩浆更为活跃的洋脊（如东太平洋隆起和中大西洋洋脊）的不同之处。在此过程中，他们将直接测试并验证上述马里恩隆起起源的两个假设之一。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。