Study of Magmatic and Hydrothermal Processes in an Ultramafic Setting (Rainbow, Mid-Atlantic Ridge) Using Advanced Seismic Modeling and Imaging

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The ocean crust is created at Mid-Ocean Ridges as magmas rise from the mantle and cool. In order to cool this melt, seawater penetrates the ocean crust, resulting in many chemical changes of both the rocks of the crust as well as the oceans. Thus, “hydrothermal” fluid flow is a primary mechanism for mass and heat transfer between the deep Earth and the oceans, accounting for approximately one third of the global yearly heat loss. Of particular interest are hydrothermal systems hosted in rocks that were brought up from the deeper mantle, so-called “ultramafic” rocks due to their composition. This is because: (1) the mechanisms that produce such mantle exposures are not fully understood; (2) there is potential for these ultramafic rocks to sequester CO2 sequestration; and (3) the fluids resulting from hydration of ultramafic rocks can create unique chemical environments that are important for biology on earth. This project will use an existing dataset acquired in 2013 that probes the subsurface of such an ultramafic exposure beneath an active hydrothermal system along the Mid-Atlantic Ridge. This project will serve the national interest by promoting the progress of science, in particular by investigating the linkages and interactions between mantle rocks, fluids, and (sub)surface ecosystems. This is a major scientific goal of the geoscience community and its importance has been highlighted in science plans providing guidance to scientists, funding agencies and policy makers, such as the IODP Science Plan for 2013-2023 or The National Academy of Sciences Sea Change 2015-2025 Decadal Survey of Ocean Sciences Report. This project will support a postdoctoral investigator, providing an opportunity for developing the early career of an independent scientist, and contributing to the new generation of geoscientists with expertise in advanced seismic imaging techniques. Such expertise is of great importance for the US industries in the field of exploration and production of natural resources. By making use of existing seismic datasets, this project will also leverage previous NSF investments in marine seismic acquisition. This project will conduct a multi-scale advanced seismic modeling and imaging study of a subset of a seismic data collected in 2013. These data were collected as part of the NSF-funded MARINER experiment in the Rainbow massif of the Mid-Atlantic Ridge. The dataset includes active-source long-streamer seismic reflection data, ocean bottom seismometer wide-angle data, and a microseismicity catalog. The approach will consist of (1) downward continuation and travel-time tomography, yielding intermediate resolution models of the P-wave velocity structure; (2) elastic full waveform inversion, yielding high-resolution models of the P-wave velocity structure; (3) reverse time migration, yielding geometrically accurate, high fidelity seismic reflection images; and (4) micro-earthquake tomography, yielding a km-scale regional 3-D model of the S-wave velocity structure. These models and images will be used to investigate the physical properties of magmatic rocks within the oceanic crust. They will help to quantify their partially molten or solidified state, and how they are linked to active and inactive hydrothermal fields. Furthermore, the models and images will illuminate fluid pathways and small-scale faulting, potential connecting the seafloor hydrothermal fields to the magmatic system at depth. The results, when jointly interpreted with existing seafloor geology observations, seafloor sampling and near-bottom imagery from previous studies will provide a comprehensive understanding of the role of magmatism and other geological controls on hydrothermal activity in regions of mantle exposures along mid-ocean ridges.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.