Evidence for shock heating and constraints on Martian surface temperatures revealed by 40Ar/39Ar thermochronometry of Martian meteorites

Cassata, William S.; Shuster, David L.; Renne, Paul R.; Weiss, B. P.

doi:10.1016/j.gca.2010.08.027

Cited by 84 publications

(82 citation statements)

References 71 publications

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“…7). This shock event might also coincide with the age of resetting of radiogenic 40 Ar distribution in Nakhla clinopyroxenes at 913 -9 Ma observed by Cassata et al (2010), which records a geological event that caused extensive fracturing of clinopyroxene grains and highly localized heating. Most probably, it occurred at pressures between 20 and 40 GPa, a range that is FIG.…”

Section: Chemical Analysis and Raman Spectroscopy Of Nearby Mineral Pmentioning

confidence: 54%

“…Ar isotopic system in Nakhla clinopyroxenes, as observed by Cassata et al (2010). This shock event could have brecciated the parent rock of Nakhla, fractured its crystalline matrix, and possibly even resulted in the formation of the ovoid structure in Nakhla (i.e., as a vesicle during the quenching of its host mesostasis glass; see further discussion in Section 3.2.4.).…”

mentioning

confidence: 79%

“…Nakhla is classified as a cumulus clinopyroxenite that crystallized at about 1.3-1.4 Ga (Ganapathy and Anders, 1969;Cassata et al, 2010;Korochantseva et al, 2011) as part of a differentiated shallow intrusion (Lentz et al, 1999). A first shock event occurred at 913 -9 Ma, which resulted in a brief and localized heating of Nakhla at temperatures above the melting point of pyroxene in isolated locations (Cassata et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…A first shock event occurred at 913 -9 Ma, which resulted in a brief and localized heating of Nakhla at temperatures above the melting point of pyroxene in isolated locations (Cassata et al, 2010). The secondary aqueous alteration that affected Nakhla is estimated to have taken place on Mars at about 620 Ma (Treiman, 2005, and references therein).…”

Section: Introductionmentioning

confidence: 99%

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A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

Chatzitheodoridis

Haigh

Lyon³

2014

Astrobiology

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A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a layer of iron oxides/hydroxides. Carbonates, halite, and sulfates were deposited last within interstitial spaces and along fractures. Among three plausible competing hypotheses here, this particular abiotic scenario is considered to be the most reasonable explanation for the formation of the ovoid structure in Nakhla, and although compelling evidence for a biotic origin is lacking, it is evident that the martian subsurface contains niche environments where life could develop.

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Section: Chemical Analysis and Raman Spectroscopy Of Nearby Mineral Pmentioning

confidence: 54%

mentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

Chatzitheodoridis

Haigh

Lyon³

2014

Astrobiology

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“…Textural observations indicate that after carbonate growth, ALH84001 experienced brief, localized, shock-related heating, but natural remanent magnetization and argon thermochronometry place upper limits of approximately 40°C on the shortduration (approximately 10 min) and approximately 20-30°C on the long-duration (billions of years) thermal history of this rock (29,30).…”

mentioning

confidence: 95%

Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment

Halevy

Fischer

Eiler

2011

Proc. Natl. Acad. Sci. U.S.A.

107

121

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Despite evidence for liquid water at the surface of Mars during the Noachian epoch, the temperature of early aqueous environments has been impossible to establish, raising questions of whether the surface of Mars was ever warmer than today. We address this problem by determining the precipitation temperature of secondary carbonate minerals preserved in the oldest known sample of Mars' crust-the approximately 4.1 billion-year-old meteorite Allan Hills 84001 (ALH84001). The formation environment of these carbonates, which are constrained to be slightly younger than the crystallization age of the rock (i.e., 3.9 to 4.0 billion years), has been poorly understood, hindering insight into the hydrologic and carbon cycles of earliest Mars. Using "clumped" isotope thermometry we find that the carbonates in ALH84001 precipitated at a temperature of approximately 18°C, with water and carbon dioxide derived from the ancient Martian atmosphere. Furthermore, covarying carbonate carbon and oxygen isotope ratios are constrained to have formed at constant, low temperatures, pointing to deposition from a gradually evaporating, subsurface water body-likely a shallow aquifer (meters to tens of meters below the surface). Despite the mild temperatures, the apparently ephemeral nature of water in this environment leaves open the question of its habitability.T he extreme difficulty in achieving mild surface temperatures in early Mars climate models (1) is in disagreement with widespread geomorphological evidence for surface water runoff during the Noachian epoch (2, 3). A robust determination of the temperature at or near the surface of Noachian Mars would provide insight into this apparent paradox, but has been challenging to establish. Carbonate minerals can record and preserve information regarding the temperature and chemistry of their formation environment through aspects of their oxygen and carbon isotopic composition (δ 18 O and δ 13 C, respectively). These minerals have been observed in a range of Martian geological materials, including dust, bedrock outcrops, and several meteorites (4-9). Collectively, these observations highlight a role for carbonate formation in the global Martian carbon cycle and the evolution of its atmosphere. The oldest known carbonate from Mars, or any other planetary body, occurs as a minor constituent (approximately 1% by weight) in the meteorite Allan Hills 84001 (ALH84001), which has a crystallization age of approximately 4.1 billion years (10). The carbonate in ALH84001, geochronologically constrained to be slightly younger in age [between 3.9 and 4.0 billion years old; (11)], provides a unique window into the hydrologic cycle, carbon cycle, and climate of Noachian Mars.Texturally, the carbonates in ALH84001 occur as (i) chemically and isotopically zoned ovoid concretions, veins, and void fillings and (ii) regions of massive carbonate, variably intergrown with unweathered feldspathic glass and orthopyroxene, the latter of which makes up the bulk of the meteorite (12)(13)(14) The carbonates in ALH84...

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Further evidence for early lunar magnetism from troctolite 76535

et al. 2017

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The earliest history of the lunar dynamo is largely unknown and has important implications for the thermal state of the Moon and the physics of dynamo generation. The lunar sample with the oldest known paleomagnetic record is the 4.25 billion year old (Ga) troctolite 76535. Previous studies of unoriented subsamples of 76535 found evidence for a dynamo field with a paleointensity of several tens of microteslas. However, the lack of mutual subsample orientation prevented a demonstration that the magnetization was unidirectional, a key property of thermoremanent magnetization. Here we report further alternating field demagnetization on three mutually oriented subsamples of 76535, as well as new pressure remanent magnetization experiments to help rule out shock magnetization. We also describe new 40Ar/39Ar thermochronometry and cosmogenic neon measurements that better constrain the rock's thermal history. Although the rock is unbrecciated, unshocked, and slowly cooled, its demagnetization behavior is not ideal due to spurious remanence acquisition. Despite this limitation, all three subsamples record a high coercivity magnetization oriented in nearly the same direction, implying that they were magnetized by a unidirectional field on the Moon. We find no evidence for shock remanence, and our thermochronometry calculations show no significant reheating events since 4249 ± 12 million years ago (Ma). We infer a field paleointensity of approximately 20–40 μT, supporting the previous conclusion that a lunar dynamo existed at 4.25 Ga. The timing of this field supports an early dynamo powered by thermal or thermochemical core convection and/or a mechanical dynamo but marginally excludes a dynamo delayed by thermal blanketing from radiogenic element‐rich magma ocean cumulates.

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Evidence for shock heating and constraints on Martian surface temperatures revealed by 40Ar/39Ar thermochronometry of Martian meteorites

Cited by 84 publications

References 71 publications

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment

Further evidence for early lunar magnetism from troctolite 76535

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