Doctoral Dissertations
Date of Award
5-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Geology
Major Professor
Nicholas Dygert
Committee Members
Molly McCanta, Anna Szynkiewicz, Colin Jackson
Abstract
Solidification of a lunar magma ocean (LMO) after a giant planetary collision event formed the Moon’s gravitationally unstable juvenile mantle. Hybridization of the lunar mantle during the overturn of late-crystallized Ti- rich ilmenite-bearing cumulates (IBC) in the lunar interior is called upon to explain the variable Ti and REE abundances of melts. We experimentally investigated hybridization reactions in experiments that juxtapose an IBC glass against presynthesized dunite in a reaction couple at temperatures of 1100-1300 ºC and pressures of 0.5-2.02 GPa for 0.33-31.66 hours. We then model chemical fractionation during LMO solidification, mantle hybridization, and partial melting of hybridized and unhybridized cumulates to evaluate the formation of lunar basalts, picritic glasses, and crustal cumulates. Subsolidus experiments produce garnet in the IBC at 2 GPa. Supersolidus experiments exhibit dissolution of olivine material into the IBC melt and the formation of clinopyroxene at the IBC melt-dunite interface. Simple numerical simulations suggest that mechanical mixing may be required in addition to dissolution-precipitation reactions to produce volumetrically significant hybridized mantle sources capable of producing lunar melts over geologically relevant timescales. Geochemical models indicate that plagioclase floatation efficiency during LMO solidification and crustal formation must be >90% to explain the negative Eu anomaly demonstrated by lunar melts. Melting models demonstrate that unhybridized cumulates could produce low-Ti melts, and hybridized garnet-free sources can generate many intermediate to high-Ti melts. The Heavy Rare Earth Element depleted compositions of some high-Ti lunar melts require a ~0.25-5% garnet component in the downwelling IBC or hybridized sources. The need for garnet combined with isotope ratios of high-Ti lunar basalts indicates the cumulate overturn is likely required. Geochemical models of LMO solidification also demonstrate that the Moon likely contains90% of the lunar HPE budget should initially be concentrated in the lunar crust and upper mantle cumulates following LMO solidification.
Recommended Citation
Scholpp, Jesse, "The Chemical and Physical Impacts of Magma Ocean Solidification: Insights into Lunar Magma Ocean Solidification, Mantle Formation, and Mantle Evolution.. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/12320
Chemical Data for Chapter 1