Documenting Dynamic Accretion in the Lower Ocean Crust: Ocean Drilling Holes U1473A and 735B, SW Indian Ridge

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The size, shape, mineralogy, and physical behavior and evolution of magma chambers beneath ocean ridges determine the geochemical, geophysical, hydrothermal, and tectonic characteristics of ocean crust, which forms over 70 percent of Earth's surface (i.e., all that occurring under the sea). To learn more about slow-spread ocean crustal structure, a major community-driven effort to drill deep bore holes into magmatic rocks on the seafloor by the International Ocean Discovery Program and involving more than 30 scientists from around the world, was carried out in 2015-2016 on the Southwest Indian Ridge at a location called the Atlantis Bank. The research that will be carried out under the auspices of this award is divided into two parts. One part consists of creating the foundational geochemical analytical data for over 300 igneous rock specimens of the 789 meter-long core, with the second part involving targeted studies of discrete core intervals to look at the origin of local features. Results of this stratigraphic work will be compared to similar data collected from an ocean drilling core taken 2.2 kilometers away a number of years ago. Broader impacts of the work include strong international collaboration with French, German, Italian, and Chinese scientists, support of a multi-national science program to understand the composition and magmatic section of the seafloor, and the training of two graduate students, one US and one Chinese, with the second being paid for by the Chinese government. Efforts will be made to transmit findings to the public via podcasts and the participation of a professional science communicator.The laboratory part of the research consists of carrying out and creating a geochemical database of whole rock and mineral major and trace element data. Each sample will be examined petrographically to determine mineral and textural relationships and discriminate between primary, secondary, and alteration phases and features. In addition, rare earth element compositions in coexisting plagioclase and pyroxene will be used as geothermometers to develop chemical zoning profiles and thermal histories of the various magmatic bodies within the stratigraphic section. These data will form the basis for the testing of the hypothesis that there is a continuity of igneous process across the Atlantis Bank, reflecting steady-state conditions of emplacement of a core complex. Results of this work can be extrapolated to help us understand other slow-spread crustal areas along the mid-ocean ridges.