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

地球是一颗充满活力的行星。它的表面在洋脊和俯冲带上不断地被创造和破坏，这些海脊和俯冲带构成了巨大的构造板块的边界。这些过程造成地震和火山灾害，并产生经济资源、热能以及地球上的海洋和大气。下面是地幔的环流，主要表现为沿洋脊的上升流和地幔羽流。后者是向上流动，产生地幔热点，如夏威夷和冰岛。在大西洋的冰岛和亚速尔群岛以及印度洋的马里昂热点附近，洋脊经过地幔热点附近，洋脊的化学成分与相关的地幔热点相似。对此的标准科学解释是，火山热点是由根植于地幔深处的地幔热柱造成的，这种热柱的流动部分转移到了邻近的大洋脊，在那里成为熔岩喷发的来源。然而，海平面上升之间存在巨大差异，马里恩热点可能是由不同的过程造成的。马里恩热点位于南非东南约1000英里处，位于非洲板块和南极构造板块的交界处。由德国、美国和中国科学家领导的一个国际团队正在合作测试一个新的假设，即马里恩隆起代表着古老的超大陆冈瓦那解体期间漂浮在地球深处的一块异常地幔的融化。传统的深部地幔热柱假说预测地壳一直在上升，而重新熔融的冈瓦纳地幔预测沿海脊的地壳较薄或缺失，具有孤立的、分布广泛的局部岩浆中心，最厚的地壳位于地幔熔融异常与海脊的交汇处。该奖项支持美国参与德国-美国-中国合作巡航，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。美国科学党将指导对布维岛以北发现断裂带以西的西南印度海脊进行地球物理磁学、重力和多波束测绘调查，并将这些数据与德国科考船Sonne上的岩石疏浚和ROV采样结果结合起来，绘制出地幔直接暴露在海底的范围，并约束不暴露的地壳厚度。它们将描述海底地形和构造与东太平洋隆起和中大西洋海脊等更强大的洋脊的不同之处。在这样做的过程中，他们将直接测试和验证上述马里恩隆起起源的两个假说之一。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.