NSFGEO-NERC: Data Mining the Deep: Combining Geochemistry and Imaging Spectroscopy to Quantify Deep Hydrothermal Circulation at Mid-Ocean Ridges

Ocean crust is formed at mid-ocean ridge spreading ridges and covers more than 60% of the surface of Earth. Because of the plate tectonic cycle and subduction, the ocean crust is geologically young, on average less than 70 million years old and all is less than 200 million years; much younger than the old rocks that make up the continents. Heated seawater circulates within the ocean crust from the ridge axes until it gets consumed in subduction zones. During this circulation, these seawater-derived fluids react with the rocks forming new minerals, and key elements and molecules such as water, CO2, K, Mg are exchanged between seawater and the ocean crust. These interactions between fluids and the rock are a major - but not yet quantified - contributor to seawater chemistry, and through subduction the composition of the interior of Earth.

A key challenge is that ocean drilling has not sampled the deepest ocean crust many kilometers below the seafloor. However, in the past few years, the International Continental Scientific Drilling Program's Oman Drilling Project has drilled a few kilometers of oceanic crust and the uppermost mantle in Oman, where tectonics have pushed this critical portion of Earth's crust onto the continent. In this project, scientists at Caltech will work with colleagues at the Universities of Southampton and Plymouth in the UK to investigate these drill core to work out how much exchange there has been between seawater and the deep ocean crust. We will take an innovative approach that combines detailed but traditional laboratory analyses with a novel technique, micro-imaging spectroscopy, which allows us to use the reflectance of infrared light to determine the mineralogy of the entire drill core at a spatial resolution of less than one millimeter. This research will achieve major advances in our understanding of deep circulation of fluids within the ocean crust through objective characterization at a scale and sampling completeness previously impossible. It will yield insights into the contribution of fluid-rock reactions to global geochemical cycling and seawater chemistry as well as constraining the role of deep fluid circulation in cooling and alteration of the lower oceanic crust. We will build a website with a core viewer to disseminate mineral maps of the drill cores to the broader scientific community and for educational use in classes.