Stoichiometric Minerals in PIXL Data from the Mars 2020 Mission

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part I

Presenting Author:

Eleanor Moreland

Authors:

Moreland, Eleanor¹, Siebach, Kirsten², Costin, Gelu³, Tice, Michael⁴, Hurowitz, Joel⁵, Treiman, Allan⁶, Simon, Justin⁷, Liu, Yang⁸, Jiang, Yueyang⁹

(1) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (2) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (3) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (4) Geology & Geophysics, Texas A&M University, College Station, TX, USA, (5) Earth & Space Sciences, Stony Brook University, Stony Brook, NY, USA, (6) Lunar and Planetary Institute, Houston, TX, USA, (7) NASA Johnson Space Center, Houston, TX, USA, (8) California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA, USA, (9) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA,

Abstract:

Tracking mineralogy across Gale crater's stratigraphy with the Chemistry & Mineralogy (CheMin) instrument has been crucial for the Curiosity rover's understanding of distinct environments through time. In Jezero crater, the Perseverance rover is exploring a different period and place on Mars. Perseverance lacks an X-ray diffraction instrument like CheMin; however, the Planetary Instrument for X-ray Lithochemistry (PIXL) instrument provides geochemical analyses of spots ~125 microns in diameter. The beam size is small enough to make diagnostic observations on individual fine-sand-sized mineral grains and even finer-grained monomineralic surfaces, providing a unique opportunity to retrieve crystal chemistry. We apply the Mineral Identification by Stoichiometry (MIST) algorithm to identify all PIXL observation spots with compositions consistent with the stoichiometry of known mineral species. This capability permits tracking of mineralogy along Perseverance’s traverse in Jezero, enabling comparison with the determined mineralogy in Gale crater.

 

In Jezero, we find broadly (ultra)mafic parent lithologies affected by at least three temporally distinct episodes of aqueous alteration: 1) hot acidic fluid, only in the crater floor, indicated by minerals greenalite/hisingerite and ferro/aluminoceladonite; 2) warm and circumneutral fluid, which affected more facies, based on minnesotaite and clinoptilolite; 3) widespread, near ambient temperature and alkaline fluid, recorded by the presence of sepiolite. These minerals allow us to rebuild pieces of Jezero’s history and compare them to those in Gale crater. For example, CheMin discovered intriguing minnesotaite interlayered with greenalite, and MIST has identified minnesotaite in PIXL data. Originally discovered in the Duluth complex in Minnesota, this mineral has important implications for the conditions and products of serpentinization, suggesting Mars may have experienced more pervasive, lower-temperature, Fe-serpentinization in its past compared to the dominant Mg-serpentinization on Earth.