Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars

Abstract

Mineral abundances derived from the analysis of remotely sensed thermal emission data from Mars have been interpreted to indicate that the surface is composed of basalt (Surface Type 1) and andesite (Surface Type 2). The global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient, heavily cratered crust in the southern hemisphere (basalt) from younger lowland plains in the north (andesite). But the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of Mars. Here we reinterpret martian surface rock lithologies using mineral abundances from previous work and new mineralogies derived from a spectral end-member set representing minerals common in unaltered and low-temperature aqueously altered basalts. Our results continue to indicate the dominance of unaltered basalt in the southern highlands, but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite. The coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre.

Quantitative compositional analysis of martian mafic regions using the MEx/OMEGA reflectance data 1. Methodology, uncertainties and examples of application

“…The mineral abundances for the HCP and neutral components are in a proportion similar to the TES-Type I spectra found in the low albedo terrains (Wyatt and McSween, 2002;McSween et al, 2003), as well as with the regional studies of Rogers and Christensen (2007) within the uncertainties of the models. Not surprisingly, this work gives a plagioclase/pyroxene ratio of 1.25+/-0.20, which is also consistent with the values of previous works (Bandfield, 2002;Rogers and Christensen, 2007).…”

“…Some TES analyses revealed that high-silica phase(s) could be one of the significant mineral groups for many low albedo regions. Primary high-silica volcanic glasses are potentially indistinguishable from some secondary amorphous or poorly crystalline high-silica materials in the thermal infrared spectral region (Bandfield, 2002;Wyatt and McSween, 2002;Kraft et al, 2003;Michalski et al, 2003;Morris et al, 2003;Ruff, 2004;Koeppen and Hamilton, 2005), which complicates the interpretation of high-silica phase(s) detected by the TES instrument. OMEGA detects hydrated minerals including phyllosilicates in some specific geological units that are disconnected from the low albedo mafic-rich regions .…”

New evidence for a magmatic influence on the origin of Valles Marineris, Mars

“…Specifically, canonical spectral endmembers representing atmospheric contributions (Bandfield and Smith, 2003), as well as surface types and pure mineral endmembers from the Arizona State University (ASU) Spectral Library (e.g., Bandfield et al, 2000;Christensen et al, 2000;Wyatt and McSween, 2002;Bandfield and Smith, 2003;Ruff, 2003), were used for the unsupervised clustering investigation. The endmembers used in the analysis included: Type I (basaltic endmembers)-Anorthite, Augite, Bytownite, Fayalite, Forsterite, and Labradorite, and Type II (granite-granodirite endmembers)-Albite, Anorthoclase, Biotite, Microcline, Muscovite, Oligoclase, and Quartz.…”

“…During the training phase, the human experts manually (Dohm et al, 2001b) (see corresponding Table 1). The TES data was classified by applying machine learning "untrained" techniques to Type 1 and Type 2 information Wyatt and McSween, 2002;Ruff, 2003) using quality TES strips that cover part of the ancient Thaumasia highlands mountain range and younger plains-forming materials to the north and south of the mountain range. The geology has been reclassified into two types of materials: Ancient (mostly Early and Middle Noachian-stage 1 map units) and Young (Late Noachian and younger-stages 2-4 map units) based on (Dohm et al, 2001b).…”

Multispectral imaging from Mars Pathfinder

“…Based on these color characteristics, it was expected that rock surfaces would be largely dust-free and unweathered (Golombek et al, 1997a). In postlanding studies, Wyatt et al(2003) noted that the region is also intermediate between the basaltic "surface type 1" and, nominally, more andesitic and/or more weathered "surface type 2" spectral classes identified by the Mars Global Surveyor Thermal Emission Spectrometer (TES) (Bandfield et al, 2000;Wyatt and McSween, 2002).…”