Iron Mobility During Diagenesis at Vera Rubin Ridge, Gale Crater, Mars
Abstract
The Curiosity rover investigated a topographic structure known as Vera Rubin ridge, associated with a hematite signature in orbital spectra. There, Curiosity encountered mudstones interpreted as lacustrine deposits, in continuity with the 300 m-thick underlying sedimentary rocks of the Murray formation at the base of Mount Sharp. While the presence of hematite (-Fe2O3) was confirmed insitu by both Mastcam and ChemCam spectral observations and by the CheMin instrument, neither ChemCam nor APXS observed any significant increase in FeO (total iron oxide) abundances compared to the Murray formation. Instead, Curiosity discovered dark-toned diagenetic features displaying anomalously high FeO abundances, commonly observed in association with light-toned Ca-sulfate veins but also as crystal pseudomorphs in the host rock. These iron-rich diagenetic features are predominantly observed in "grey" outcrops on the upper part of the ridge, which lack the telltale ferric signature of other Vera Rubin ridge outcrops. Their composition is consistent with anhydrous Fe-oxide, as the enrichment in iron is not associated with enrichment in any other elements, nor with detections of volatiles. The lack of ferric absorption features in the ChemCam reflectance spectra and the hexagonal crystalline structure associated with dark-toned crystals points toward coarse "grey" hematite. In addition, the host rock adjacent to these features appears bleached and show low-FeO content as well as depletion in Mn, indicating mobilization of these redox-sensitive elements during diagenesis. Thus, groundwater fluid circulations could account for the remobilization of iron and recrystallization as crystalline hematite during diagenesis as well as color variations observed in the Vera Rubin ridge outcrops.
Cite
@article{arxiv.2101.03767,
title = {Iron Mobility During Diagenesis at Vera Rubin Ridge, Gale Crater, Mars},
author = {J l'Haridon and N Mangold and A Fraeman and J Johnson and A Cousin and W Rapin and G David and E Dehouck and V Sun and J Frydenvang and O Gasnault and P Gasda and N Lanza and O Forni and P. -Y Meslin and S Schwenzer and J Bridges and B Horgan and C House and S Maurice and R Wiens},
journal= {arXiv preprint arXiv:2101.03767},
year = {2021}
}