Lava--substrate heat transfer: implications for the preservation of volatiles in the lunar regolith

Abstract

This dissertation examines the preservation potential of exogenous particles in the lunar regolith through numerical models, laboratory experiments, remote sensing studies, and field investigations. Numerical models were used to determine the depths to which pertinent volatiles will be baked out of paleoregoliths on the Moon. Ancient regolith deposits containing exogenous particles may have been protected from the space environment by an overlying lava flow provided the lava flow did not heat the entire deposit, destroying the particle record. The inclusion of latent heat release and temperature-and depth-dependent thermophysical properties of materials is imperative to the accuracy of lava-substrate heat transfer models. Simulations revealed that implanted volatiles would be fully preserved at depths of 20 cm beneath a 1 m thick lava flow on the lunar surface. Laboratory experiments allowed the in situ measurements of heat flow from molten basalt from Kīlauea Volcano, Hawaiʻi into GSC-1, a lunar regolith simulant. Melt layers 8--10 cm thick heated simulant to particle-volatilizing temperatures to maximum depths of 5.6--7.2 cm. These depths represent the maximum depths to which exogenous particles will be volatilized on the Moon. Numerical simulations of experiments constrained the temperature-dependency of the effective thermal conductivity of GSC-1 to vary from 0.35--0.45 W m-1 K-1 at 23 °C and 0.65--0.80 W m-1 K-1 at 1227 °C. Ground-truthing of remote sensing identifications of layered lava sequences in valley walls on O'ahu, Hawaiʻi reveal that lava flow thicknesses are overestimated in image interpretations. The study of eight transects at three locations on O'ahu determined that layer thicknesses derived from image interpretations were up to 6.3 times larger than mean flow thicknesses measured in the field. Misinterpretations are primarily caused by outcrops that contain more than one lava flow unit but appear as a single layer in satellite imagery. Lava layers were also identified in Lunar Reconnaissance Orbiter Camera images. Measured average flow thicknesses of mare basalts, found to be 1.2--29.5 m, are representative of the maximum thickness of the flows identified, as image resolution does not allow for confirmation of the number of flows in visible outcrops.