Askival: An altered feldspathic cumulate sample in Gale crater

D L Bowden (1) , John Bridges (1) , Agnès Cousin (2) , William Rapin (2) , J Semprich (3) , Olivier Gasnault (2) , Olivier Forni (2) , Patrick J Gasda (4) , D Das (5) , V Payré (6) , V. Sautter (7) , Candice C Bedford (8, 9) , Roger C Wiens (4) , P. Pinet (2) , Jens Frydenvang (10)

1 School of Physics and Astronomy [Leicester]
2 IRAP - Institut de recherche en astrophysique et planétologie
3 OU - The Open University [Milton Keynes]
4 LANL - Los Alamos National Laboratory
5 EPS - Department of Earth and Planetary Sciences [Montréal]
6 Department of Earth and Environmental Sciences [Iowa City]
7 MNHN - Muséum national d'Histoire naturelle
8 LPI - Lunar and Planetary Institute [Houston]
9 ARES - Astromaterials Research and Exploration Science
10 UCPH - University of Copenhagen = Københavns Universitet

Askival is a light toned, coarsely crystalline float rock, which was identified near the base of Vera Rubin Ridge in Gale Crater. We have studied Askival, principally with the ChemCam instrument but also using APXS compositional data and MAHLI images. Askival and an earlier identified sample, Bindi, represent two rare examples of feldspathic cumulate float rocks in Gale crater with >65% relict plagioclase. Bindi appears unaltered whereas Askival shows textural and compositional signatures of silicification, along with alkali remobilization and hydration. Askival likely experienced multiple stages of alteration, occurring first through acidic hydrolysis of metal cations, followed by deposition of silica and possible phyllosilicates at low T and neutral-34 alkaline pH. Through LIBS compositional analyses and normative calculations, we suggest that an assemblage of Fe-Mg silicates including amphibole and pyroxene, Fe phases and possibly Mg-rich phyllosilicate are present. Thermodynamic modelling of the more pristine Bindi composition predicts that amphibole and feldspar are stable within an upper crustal setting. This is consistent with the presence of amphibole in the parent igneous rocks of Askival and suggests that the paucity of amphiboles in other known Martian samples reflects the lack of representative samples of the Martian crust rather than their absence on Mars.

Domaines: Planétologie

D L Bowden, John Bridges, Agnès Cousin, William Rapin, J Semprich, et al.. Askival: An altered feldspathic cumulate sample in Gale crater. Meteoritics and Planetary Science, 2023, 58 (1), pp.41-62. ⟨10.1111/maps.13933⟩. ⟨insu-03870938⟩