Geological Society of America

T262 Alkaline Lakes on Earth and Beyond: Mineralogy, Geochemistry, and Habitability (Posters)

Wednesday, 25 September 2024
8:00 AM - 5:30 PM
Hall D

NEAR-SURFACE AQUEOUS CONDITIONS INFERRED FROM THE COMPOSITION OF MAGNESITES FROM CENTRAL QUEENSLAND, AUSTRALIA: A JEZERO CRATER ANALOG

Paper number: T262-3
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Carl Swindle Presenting Author
University of California, Los Angeles, Los Angeles, CA
Paulo M. Vasconcelos
California Institute of Technology, Pasadena, CA
Zoe Dimarco
The University of Queensland, St Lucia, QLD
Nathan Dalleska
California Institute of Technology, Pasadena, CA
Emily Cardarelli
University of California, Los Angeles, Los Angeles, CA
Surjyendu Bhattacharjee
California Institute of Technology, Pasadena, CA
Kenneth A. Farley
California Institute of Technology, Pasadena, CA
Theodore Present
California Institute of Technology, Pasadena, CA

Abstract

The Marlborough Terrane in QLD, AUS contains ultramafic serpentinite highlands surrounding low-lying sedimentary basins that both contain magnesite. Near surface aqueous alteration of the deposits is broadly analogous to carbonated ultramafic highlands and sedimentary lowlands in Jezero Crater, Mars. This study develops methods to determine aqueous alteration conditions that produce magnesite using trace element compositions. Pit mines near Marlborough provide exposures of serpentinite- and sedimentary-associated magnesite. In the serpentinite highlands, the Gumigil mine contains weathered serpentinite with syn-tectonic metasomatic magnesite veins. In the sedimentary lowlands, the Kunwarara and Yaamba mines contain magnesite nodules forming within unlithified alluvial sediments by reaction of magnesium-rich groundwater with arkosic sands and soils.

An ICP-MS protocol is developed to measure trace elements in Mg-carbonate samples, while minimizing influences of non-carbonate phases and adsorbed ions. Bulk rock compositions of serpentinite and sedimentary matrix materials were characterized by traditional methods.

Composition of Gumigil magnesite veins retain geochemical signatures typical of depleted mantle rocks, but Ce and Y anomalies record surficial alteration. In sedimentary deposits at Yaamba and Kunwarara, magnesite compositions are influenced by aqueous interactions with arkosic sediments and chemically evolved during multiple phases of diagenetic alteration by groundwater and soil waters. Zoned magnesite nodules at Yaamba contain Ce anomalies that correlate with increasing Mn from core to rim. Zoning captures redox shifts in fluids where magnesite nodules formed. At Kunwarara, Ce anomalies in magnesite diminish with depth coincident with decreasing abundance of authigenic Fe/Mn-oxides/hydroxides in the host sediments.

Results reveal that Mg-carbonates may replace host sediments in the subsurface along redox gradients in the capillary zone near the water table. These findings imply that Ce anomalies in Mg-carbonates can be used to trace paleoredox conditions of the ancient Martian surface. Ce anomalies calculated from published trace element data collected on Mg-carbonates in Martian meteorite ALH84001 suggest that Noachian Martian atmosphere could have been more oxidizing than the early Earth.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403540

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.