Date of Award

August 2024

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

Lindsay J McHenry

Committee Members

Julie A Bowles, Barry I Cameron

Keywords

Alteration, Cation Migration, High-temperature, Lava tubes, Venus

Abstract

Scientific exploration of other planetary bodies comes with many limitations, and Venus is no exception. Average surface temperatures of ∼460°C and an atmospheric pressure of ∼96 bars has severely limited the longevity of any instruments sent to the surface of Venus. Furthermore, with an atmosphere composed of ∼96.5% CO2, there are only three wavelength windows in the near infrared region that can be used to measure the mineralogical composition of the surface. Due to these constraints, our understanding of Venus’ surface mineralogy is severely limited and to date direct measurements of its geologic composition are limited to a handful of XRF measurements from short-lived Soviet-era landers. A better understanding of the surface mineralogy helps us to better constrain the primary composition, the climate history, and the geochemical reactions between the surface and atmosphere. Laboratory experiments and modeling have helped interpret spectroscopic readings of the planet’s surface. Experiments and models indicate that surface-atmosphere interactions under Venus conditions alter basaltic rock surfaces to produce secondary minerals, predominantly anhydrous sulfates and iron oxides, which may affect spectroscopic readings. This study demonstrates that using lava tubes as an analogue for the surface geology of Venus may also prove informative. Lava tubes are geologic landforms that provide high-temperature, insulated environments as they cool, and are observed to contain minerals predicted to form on the surface of Venus. Tholeiitic basalt samples were collected from the interiors of lava tubes on the Big Island of Hawai’i. X-ray diffraction (XRD) patterns reveal the mineral assemblages of the substrates and lava tube interiors. Primary minerals present in the substrate samples include augite, anorthite, ilmenite, and titanomagnetite. SEM imagery and VNIR spectroscopy of surface veneers indicate that magnesioferrite, hematite, diopside, cristobalite, and tridymite are secondary minerals produced through cation migration in a dry, high-temperature environment. While there are significant differences in temperature and atmospheric composition between lava tubes and Venus, these results are still similar to weathering experiments conducted in Venus simulated environments. Further investigation of lava tubes can better constrain the differences in weathering intensity, as well as teach us more about how lava behaves in a slow-cooling environment.

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