CSEDI Collaborative Research: Understanding the origins of MORB geochemical heterogeneity using constraints from seismic tomography and geodynamic modeling

University Of California-Davis, Davis CA

Investigators

Abstract

The chemical composition of lavas erupted under the water at mid ocean ridges, where new seafloor is created as tectonic plates spread apart, is influenced by the temperature and composition of the underlying mantle from which these melts are generated. The proposed work examines correlations between mid ocean ridge basalt (MORB) chemistry and images of Earth's interior produced using seismic tomography. It uses large-scale numerical models of mantle flow to connect surface observations with past and present mantle structure. The proposed work has three components. First, it examines the distributions of helium isotopes and other geochemical indicators of mantle temperature at spreading centers and how these are related to temperature and compositional variations in the sub-oceanic mantle. Second, it explores the flow history of mantle material that is sampled at spreading centers. Third, it addresses how the mid ocean ridges in different ocean basins have sampled the mantle since the breakup of the supercontinent Pangea. The project will provide new information about how variations in seismic velocity beneath the ocean basins are related to the variations in chemical composition of MORB, and how upper mantle variations in composition and temperature are related to deeper mantle structure. Different disciplines make distinct contributions to our understanding of the dynamics of Earth's mantle. In particular, relating the distribution of geochemical and seismological heterogeneity at the global scale has been a challenge because of the different wavelengths sampled in these two types of approaches: local, for geochemistry, long wavelength, for seismology. Recently, progress has been made in both fields, with resolution reaching sub-1000 km scale in global seismic tomography, and a more complete geochemical sampling along mid-ocean ridges, allowing the investigation of patterns at wavelengths commensurate with the seismic imaging. Concurrently, progress has been made in developing methodologies for realistic geodynamic modeling of mantle circulation in 3D, incorporating constraints from seismology and surface observables (e.g. plate motions, topography, and the geoid). Tying these elements together to better constrain the flow history of material sampled at ridges is becoming feasible at the present time. The proposed work will produce new geochemical datasets, tomographic models, and results from geodynamic models that will be distributed to the broader geoscience community for further analysis and in a format that permits immersive 3D visualization. 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.