Characterization of the regional, crustal, and global distribution and abundance of the heat producing elements and their geoneutrino flux

Abstract

The amount and distribution of radiogenic power generation from the heat producing elements (HPE) U, Th, and K in the Earth is not well constrained. Compositional estimates of these elements vary by a factor of three in the bulk-Earth and 30 in the mantle after removal of the continental crust contribution. Understanding the total power derived from these elements is critical to understanding the power driving the Earth as they supply fuel to the geodynamo and mantle convection. The decay of HPE's produce particles called geoneutrinos and the measurement of the geoneutrino flux reveals the frequency of decay and the abundances of these elements in the Earth. The total geoneutrino flux can be categorized into three major contributors: the dominant component from the nearest 500 km of continental crust surrounding the detector and slightly smaller sub-equal contributions from the remaining global continental crust and the mantle. The negligible amount of HPE's within the core was tested by a mass-balance of the Th/U derived from Pb isotopes (κ_Pb). Each Earth layer was attributed a κ_Pb from representative samples with associated weighting factor from the estimated mass of U in each reservoir. The radiogenic power in the core from U and Th was constrained to ~0.03 terra-watts (median), emphasizing the core's negligible geoneutrino luminosity. To unravel the contribution from the inaccessible mantle to the signal at a detector one must build a physical and chemical description of the local and global crust. The 50x50 km regional geoneutrino flux surrounding the SNO+ detector (Sudbury, Canada) was modeled. 112 geologic samples were analyzed for their U, Th, K abundances and combined with a 3D physical model of the region. To supplement this, the methodology of Huang et al. (2013) was applied to an updated geophysical model for the bulk-crust to predict the global crustal signal at SNO+ and other detectors. Variable correlation is addressed and uncertainties from density, seismic velocity, crustal thickness, and abundances propagated. This dissertation explores the amount and distribution of HPE's within the Earth and their geoneutrino flux through geochemical and geophysical modeling on regional, crustal, and global scales. Together, the results update our understanding of the Earth's geoneutrino flux and the uncertainties still in the system.