Dataset Information

Magnetite Authigenesis and the Warming of Early Mars.

ABSTRACT: The Curiosity rover has documented lacustrine sediments at Gale Crater, but how liquid water became physically stable on the early Martian surface is a matter of significant debate. To constrain the composition of the early Martian atmosphere during sediment deposition, we experimentally investigated the nucleation and growth kinetics of authigenic Fe-minerals in Gale Crater mudstones. Experiments show that pH variations within anoxic basaltic waters trigger a series of mineral transformations that rapidly generate magnetite and H2(aq). Magnetite continues to form through this mechanism despite high PCO2 and supersaturation with respect to Fe-carbonate minerals. Reactive transport simulations that incorporate these experimental data show that groundwater infiltration into a lake equilibrated with a CO2-rich atmosphere can trigger the production of both magnetite and H2(aq) in the mudstones. H2(aq), generated at concentrations that would readily exsolve from solution, is capable of increasing annual mean surface temperatures above freezing in CO2-dominated atmospheres. We therefore suggest that magnetite authigenesis could have provided a short-term feedback for stabilizing liquid water, as well as a principal feedstock for biologically relevant chemical reactions, at the early Martian surface.

SUBMITTER: Tosca NJ

PROVIDER: S-EPMC6092749 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Magnetite Authigenesis and the Warming of Early Mars.

Tosca Nicholas J NJ Ahmed Imad A M IAM Tutolo Benjamin M BM Ashpitel Alice A Hurowitz Joel A JA

Nature geoscience 20180806 9

The <i>Curiosity</i> rover has documented lacustrine sediments at Gale Crater, but how liquid water became physically stable on the early Martian surface is a matter of significant debate. To constrain the composition of the early Martian atmosphere during sediment deposition, we experimentally investigated the nucleation and growth kinetics of authigenic Fe-minerals in Gale Crater mudstones. Experiments show that pH variations within anoxic basaltic waters trigger a series of mineral transforma ...[more]

PMID: 30123317

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Project description:Refined calibrations of CRISM images are enabling identification of smaller deposits of unique aqueous materials on Mars that reveal changing environmental conditions at the region surrounding Mawrth Vallis. Through characterization of these clay-sulfate assemblages and their association with the layered, phyllosilicate units of this region, more details of the aqueous geochemical history can be gleaned. A stratigraphy including five distinct mineral horizons is mapped using compositional data from CRISM over CTX and HRSC imagery across 100s of km and from CRISM over HiRISE imagery across 100s of meters. Transitions in mineralogic units were characterized using visible/near-infrared (VNIR) spectral properties and surface morphology. We identified and characterized complex "doublet" type spectral signatures with two bands between 2.2 and 2.3 μm at one stratigraphic horizon. Based on comparisons with terrestrial sites, the spectral "doublet" unit described here may reflect the remnants of a salty, evaporative period that existed on Mars during the transition from formation of Fe-rich phyllosilicates to Al-rich phyllosilicates. Layered outcrops observed at Mawrth Vallis are thicker than in other altered regions of Mars, but may represent processes that were more widespread in wet regions of the planet during its early history. The aqueous geochemical environments supporting the outcrops observed here include: (i) the formation of Fe3+-rich smectites in a warm and wet environment, (ii) overlain by a thin ferrous-bearing clay unit that could be associated with heating or reducing conditions, (iii) followed by a transition to salty and/or acidic alteration phases and sulfates (characterized by the spectral "doublet" shape) in an evaporative setting, (iv) formation of Al-rich phyllosilicates through pedogenesis or acid leaching, and (v) finally persistence of poorly crystalline aluminosilicates marking the end of the warm climate on early Mars. The "doublet" type units described here are likely composed of clay-sulfate assemblages formed in saline, acidic evaporative environments similar to those found in Western Australia and the Atacama desert. Despite the chemically extreme and variable waters present at these terrestrial, saline lake environments, active ecosystems are present; thus, these "doublet" type units may mark exciting areas for continued exploration important to astrobiology on Mars.

Dataset Information

Magnetite Authigenesis and the Warming of Early Mars.

Publications

Magnetite Authigenesis and the Warming of Early Mars.

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