A Spectroscopic Analysis of the Humuula Saddle, Hawaii Drill Core as an Analogue for Mars

Abstract:

The Martian surface is made up of volcanic material that has experienced widespread alteration at various points in its geologic history. The oldest of the geologic records, Noachian terrains, are characterized by low Ca-pyroxenes and widespread Fe/Mg clays. Alteration in these regions may be linked to weathering, hydrothermal, and/or diagenetic alteration. A key finding in the last decade has been that phyllosilicates are found in nearly every exposure of Noachian crust. These minerals may have been formed either in groundwater aquifers, been altered at the surface then buried, or an indication of impact driven hydrothermal activity.

The subsurface of Hawaii provides an analog for these various environments. In 2013 and 2015, two drill cores were made in the Humu’ula Saddle region that traverse various sub aerial lava flows, representing the shield-building phase of the island. The lithology is dominantly basalt with varying amounts of plagioclase and olivine phenocrysts. Our work includes measuring visible, short-wave, and long-wave reflection spectra on the core and cut samples, wavelengths relevant to interpret remote sensing spectral data from Mars. We seek to understand the characteristics of mineral mixtures and how they vary with depth and use the minerals identified to better understand alteration of basaltic material on Mars.

The use of linear mixing models predicts the contribution of minerals to the reflectance spectra collected from the drill core. Our results show that drill core samples are dominated by with Mg/Fe rich pyroxenes including augite and pigeonite, and Mg rich endmembers of olivine (forsterite) with alteration to Mg phyllosilicates and zeolites. We will present the results of our analysis on the chemical and mineralogical diversity of these samples. By understanding the characteristics of the drill core, we hope to help illuminate the environment and mechanisms of formation that led to the spectral diversity observed in Noachian terrains