Potassium‐rich sandstones within the Gale impact crater, Mars: The APXS perspective

Abstract

The Alpha Particle X‐ray spectrometer (APXS) on board the Curiosity rover at the Kimberley location within Gale crater, Mars, analyzed basaltic sandstones that are characterized by potassium enrichments of 2 to 8 times estimates for average Martian crust. They are the most potassic rocks sampled on Mars to date. They exhibit elevated Fe, Mg, Mn and Zn and depleted Na, Al, and Si. These compositional characteristics are common to other potassic sedimentary rocks analyzed by APXS at Gale but distinct from other landing sites and Martian meteorites. CheMin and APXS analysis of a drilled sample indicate mineralogy dominated by sanidine, Ca‐rich and Ca‐poor clinopyroxene, magnetite, olivine, and andesine. The anhydrous mineralogy of the Kimberley sample, and the normative mineralogy derived from APXS of other Bathurst class rocks, together indicate provenance from one or more potassium‐rich magmatic or impact‐generated source rocks on the rim of Gale crater or beyond. Elevated Zn, Ge, and Cu suggest that a localized area of the source region(s) experienced hydrothermal alteration, which was subsequently eroded, dispersed, and diluted throughout the unaltered sediment during transport and deposition. The identification of the basaltic, high potassium Bathurst class and other distinct rock compositional classes by the APXS, attests to the diverse chemistry of crustal rocks within and in the vicinity of Gale crater. We conclude that weathering, transport, and diagenesis of the sediment did not occur in a warm and wet environment, but instead under relatively cold and wet conditions, perhaps more fitting with processes typical of glacial/periglacial environments.

Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars

“…APXS provides the chemical compositions of rocks and soils by X‐ray fluorescence spectroscopy using a 244 Cm radioactive source to irradiate the samples and a silicon diode detector to detect fluoresced X‐rays. The MSL APXS instrument can detect and quantify the elements Na to Br (with characteristic X‐ray energies between ~0.7 and ~25 keV [ Thompson et al , ]). The initial Gobabeb APXS analysis was made of soil disturbed by the rover wheel and is considered to represent the bulk dune composition.…”

APXS‐derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average

“…The majority of rocks encountered thus far on Mars are considered to be sedimentary rocks, with an igneous provenance. This is also the case at Gale, where the sedimentary rocks and surficial sediments have retained much of their igneous signature [e.g., Vaniman et al ., ; Thompson et al , , , ; Treiman et al ., ]. Averages for each unit are in Table ; full compositional data for each soil and sand sample are available in supporting information Tables S1–S3 and archived in the Planetary Data System (http://pds.nasa.gov).…”

A rover's geologic field campaign: Exploration of the Kimberley by Curiosity

“…Through measurements of chemistry and mineralogy at the Kimberley, Curiosity expanded the range of known igneous rock diversity on Mars and provided insight into the processes that affected the sediments from their point of origin until after their deposition. ChemCam laser‐induced breakdown spectroscopy (LIBS) [ Le Deit et al ., ] and the Alpha Particle X‐ray Spectrometer [ Thompson et al ., ] yielded major and minor element chemistry measurements on multiple scales. The CheMin investigation provided mineralogy of a single drill sample from the Dillinger member [ Treiman et al ., ], the finest grained lithology readily accessible at the Kimberley and hypothesized to have a young surface exposure age [ Rice et al ., ].…”

“…The CheMin investigation provided mineralogy of a single drill sample from the Dillinger member [ Treiman et al ., ], the finest grained lithology readily accessible at the Kimberley and hypothesized to have a young surface exposure age [ Rice et al ., ]. The signature chemical characteristic of the Kimberley sediments is K enrichment, with K contents from 2 to 8 times the average Martian crustal value [ Thompson et al ., ; Le Deit et al ., ; Taylor and Mclennan , ]. Kimberley sediments also exhibit Mn enrichment and Zn enrichment, with the highest concentrations in the Dillinger member [ Lanza et al ., ; Lasue et al ., ; Le Deit et al ., ; Thompson et al ., ].…”

“…The signature chemical characteristic of the Kimberley sediments is K enrichment, with K contents from 2 to 8 times the average Martian crustal value [ Thompson et al ., ; Le Deit et al ., ; Taylor and Mclennan , ]. Kimberley sediments also exhibit Mn enrichment and Zn enrichment, with the highest concentrations in the Dillinger member [ Lanza et al ., ; Lasue et al ., ; Le Deit et al ., ; Thompson et al ., ]. CheMin analysis of the drilled target, called Windjana, revealed the carrier of K: 21% of the sample is sanidine in a strict sense, a K‐rich feldspar with extensive Al‐Si disorder [ Treiman et al ., ].…”