RII Track-4: Investigating the Effects of Faulting on Chemical Exchange Between Seawater and Earth’s Mantle at Slow Mid-Ocean Ridges

The mid-ocean ridge system is a 65,000 km-long mountain range that wraps around the Earth at the center of each ocean basin. New tectonic plate is continuously generated along the ridges at rates of one to 20 cm per year. Global seawater composition, and thus Earth’s climate, is maintained over geologic timescales by a balance between chemical-exchange reactions that occur when seawater infiltrates into hot rock at mid-ocean ridges, and salts flowing into the ocean from continental rivers systems.

Mantle rock has a radically different chemical and mineral composition than crustal rock, and the nature of its chemical interactions with seawater, along with the larger implications for seawater composition, are poorly understood. The goal of this proposal is to build understanding of the processes by which seafloor mantle-rock exposures are fractured to permit seawater infiltration, and thus facilitate water-rock chemical exchange on roughly half of the global mid-ocean ridge system.

Results from this study will be integrated in the undergraduate Earth Science courses and independent research projects for undergraduate students at Bennington College, a small liberal arts institution.

The goals of this project are to understand how pre-existing ductile deformation fabrics and the tectonic environment of mantle peridotite exposures control the process by which rock permeability is generated during brittle fracturing. Rock samples collected from three mantle peridotite exposures along the Mid-Atlantic Ridge (MAR) that formed by very different types of fault zones will be examined using several distinct microanalysis and imaging techniques: 1) micro-computed tomography and scanning electron microscope imaging will be used to characterize the micro-scale geometry of fracture networks, 2) thermogravimetric analysis and helium gas pycnometry will be used to quantify the degree of hydrothermal alteration and 3) confocal Raman spectroscopy will be used to place additional constraints on the nature of hydrothermal exchange with micro-analysis of alteration minerals and trapped fluids.

Rock samples will be obtained from collections at Woods Hole Oceanographic Institution and from the Bremen Core Repository in Bremen, Germany. The outcomes of this research will have broad applications to understanding the deep biosphere, and potential origins of life on Earth as well as potential hosts for life on other planets.

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.