Characterizing olivine-carbonate rocks on Mars with rover datasets and numerical modeling

Abstract

The Perseverance rover landed in Jezero crater in 2021, in an area of Mars rich in olivine- and carbonate-bearing rocks. Olivine-rich rocks on Mars are of interest for understanding magmatic and igneous processes, in addition to the extent of past surface water, given that olivine is readily altered by water on geologic timescales. Carbonate-rich rocks are also a key target for exploration on Mars given that carbonate typically requires water to form, and has high biosignature preservation potential. Therefore, this dissertation was motivated by a desire to understand the origin of these rocks and to provide context to the Perseverance rover’s exploration of Jezero crater. In Chapter 2 I use numerical modeling to investigate the settling of ash particles from mafic explosive volcanic eruptions on Mars, and to assess the plausibility of a pyroclastic origin previously proposed for the Nili Fossae olivine-carbonate unit based on analyses of orbital data. My results show that ash from pyroclastic fall eruptions was likely less widely dispersed than previously proposed on Mars. Additionally, my results also show that if the Nili Fossae olivine-carbonate unit originated as a primary pyroclastic fall deposit, then multiple, currently unidentified sources, potentially combined with a higher-pressure atmosphere, are needed to account for the unit’s spatial extent. In Chapter 3, I use Perseverance Mastcam-Z red-green-blue (RGB) and multispectral images to examine the formation and alteration of olivine- and carbonate-bearing rocks within Jezero crater, and their potential relation to the regional olivine-carbonate unit. My results demonstrate that olivine-rich rocks on the crater floor known as the Séítah formation and previously interpreted to be layered cumulates, are distinct from the olivine- and carbonate-rich rocks of the Margin unit, but may share a genetic link, and that the extent of carbonate formation may be related to the presence of the Jezero paleolake. In Chapter 4, I use a combination of Mastcam-Z RGB and multispectral images, as well as SuperCam Remote-Micro-Imager images and visible-infrared spectra, to characterize olivine-bearing rocks across the Jezero crater rim and discuss their formation and alteration history. My findings show that these rocks may have originated as igneous intrusions or lava flows, and that olivine-bearing rocks on the crater rim experienced a distinct alteration history dominated by phyllosilicate formation, in contrast to the carbonated rocks found below proposed past stable lake levels within the crater. The results taken together suggest that intrusive igneous rather than pyroclastic processes played an important role in the formation of rocks within the Jezero crater region of Mars.