Carbonates in Vigarano: Terrestrial, preterrestrial, or both?

Abreu, N. M.; Brearley, Adrian J.

doi:10.1111/j.1945-5100.2005.tb00966.x

Cited by 30 publications

(25 citation statements)

References 29 publications

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“…2008). Abreu and Brearley (2005) have also reported the presence of rare calcite apparently replacing melilite in a CAI in Vigarano. These data, in addition to the evidence of oxidation of Fe, Ni metal in chondrules, indicate that aqueous fluids, albeit limited compared with the oxidized CV3 chondrites, may have been present during thermal metamorphism.…”

Section: Discussionmentioning

confidence: 86%

Deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced CV3 chondrite Vigarano

Abreu

Brearley²

2011

Meteorit & Planetary Scien

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Abstract-We have conducted scanning electron microscope (SEM) and transmission electron microscope (TEM) studies of a variety of occurrences of matrix in the reduced CV3 chondrite breccia Vigarano. Matrix, which occurs as clastic interchondrule material and finer-grained rims, is dominated by morphologically variable olivines that host submicron, hercynitic spinel, and carbonaceous inclusions. Clastic matrix and fine-grained rims show significant differences in their olivine morphologies, abundance, and composition of olivine inclusions, and characteristics of the carbonaceous matter. We suggest that these differences are the result of different degrees of alteration of clastic matrix and rims and are not due to variability in their precursor materials. Textural and compositional characteristics of olivine in the matrix are consistent with formation by growth, possibly from an amorphous precursor material during asteroidal metamorphism, in the presence of limited quantities of aqueous fluids. Spinel inclusions in olivine may be nebular condensates that acted as seeds for nucleation of olivine or may have formed during metamorphism and were subsequently overgrown by olivine. Carbonaceous material occurs as nanometer-sized inclusions within olivine in both fine-grained rims and clastic matrix, but is most abundant as 100-200 nm grains, interstitial to matrix olivines. Most carbonaceous material is amorphous, but poorly graphitized carbon (PGC) also occurs as a minor component in both olivine inclusions and interstitial C. The widespread occurrence of fine-grained amorphous carbon grains in the interstitial regions between olivine grains may preserve the distribution and grain size of nebular organic material. No clear textural relationships exist between carbonaceous grains and the other mineralogical components of Vigarano matrix that could help constrain the origin of the organic grains (i.e., evidence for Fischer-Tropsch-type reactions). Finally, there are considerable differences between matrix olivines in Vigarano in comparison with those in oxidized CV3 chondrites. In particular, the mineralogy and morphology of the matrix olivines and the nature, composition, and distribution of inclusions in the olivine grains are distinct. Based on these differences, we conclude that matrix in the oxidized CV3 chondrites could not have formed by thermal processing of Vigarano-like material.

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Section: Discussionmentioning

confidence: 86%

Deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced CV3 chondrite Vigarano

Abreu

Brearley²

2011

Meteorit & Planetary Scien

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“…). For example, Abreu and Brearley () have concluded that the veins in CV3 chondrite fall Vigarano are terrestrial in origin.…”

Section: Discussionmentioning

confidence: 99%

Thermal and porosity properties of meteorites: A compilation of published data and new measurements

Soini

Kukkonen

Kohout

et al. 2020

Meteorit & Planetary Scien

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We report direct measurements of thermal diffusivity and conductivity at room temperature for 38 meteorite samples of 36 different meteorites including mostly chondrites, and thus almost triple the number of meteorites for which thermal conductivity is directly measured. Additionally, we measured porosity for 34 of these samples. Thermal properties were measured using an optical infrared scanning method on samples of cm‐sizes with a flat, sawn surface. A database compiled from our measurements and literature data suggests that thermal diffusivities and conductivities at room temperature vary largely among samples even of the same petrologic and chemical type and overlap among, for example, different ordinary chondrite classes. Measured conductivities of ordinary chondrites vary from 0.4 to 5.1 W m−1 K−1. On average, enstatite chondrites show much higher values (2.33–5.51 W m−1 K−1) and carbonaceous chondrites lower values (0.5–2.55 W m−1 K−1). Mineral composition (silicates versus iron‐nickel) and porosity control conductivity. Porosity shows (linear) negative correlation with conductivity. Variable conductivity is attributed to heterogeneity in mineral composition and porosity by intra‐ and intergranular voids and cracks, which are important in the scale of typical meteorite samples. The effect of porosity may be even more significant for thermal properties than that of the metal content in chondrites.

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“…Lee et al (1996) and Abreu and Brearley (2011) found evidence for incipient aqueous alteration in the matrix of Vigarano in the form of ferrihydrite and rare, very fine-grained saponite. Rare calcite also occurs ( Abreu and Brearley, 2005) that appears to be extraterrestrial in origin. The ubiquitous presence of these alteration products interstitial to matrix olivines led Lee et al (1996) to conclude that alteration occurred in an asteroidal environment, a conclusion that is supported by the fact that the olivine grains appear to be the product of parent body thermal metamorphism ( Abreu and Brearley, 2011).…”

Section: Carbonaceous Chondritesmentioning

confidence: 97%

Nebular Versus Parent Body Processing

Brearley

2014

Treatise on Geochemistry

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Carbonates in Vigarano: Terrestrial, preterrestrial, or both?

Cited by 30 publications

References 29 publications

Deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced CV3 chondrite Vigarano

Deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced CV3 chondrite Vigarano

Thermal and porosity properties of meteorites: A compilation of published data and new measurements

Nebular Versus Parent Body Processing

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