Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments

K. T. Howard, C. M.O.D. Alexander, Devin Schrader, K. A. Dyl

Research output: Contribution to journalArticle

75 Citations (Scopus)

Abstract

The relative differences in the degree of hydration should be reflected in any classification scheme for aqueously altered meteorites. Here we report the bulk mineralogies and degree of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.%) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (total phyllosilicate/total anhydrous silicate+total phyllosilicate). Samples are linearly ranked from type 3.0 - corresponding to a phyllosilicate fraction of <0.05, to type 1.0 - corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7-1.2. The primary manifestation of aqueous alteration is the production of phyllosilicate, which ceased when the fluid supply was exhausted, leading to the preservation of anhydrous silicates in all samples. The variability in hydration indicates that either accretion of ices was heterogeneous or fluid was mobilized. From the bulk mineral abundances of the most hydrated samples, we infer that the initial mass fraction of H2O inside of their parent body(ies) asteroids was <20wt.%. Bulk carbonaceous chondrite mineralogy evolved towards increasingly oxidizing assemblages as the extent of bulk hydration increased. This is consistent with the escape of reducing H2 gas that is predicted to have been produced from water during hydration reactions.

Original languageEnglish (US)
Pages (from-to)206-222
Number of pages17
JournalGeochimica et Cosmochimica Acta
Volume149
DOIs
StatePublished - Nov 4 2014
Externally publishedYes

Fingerprint

Meteorites
Mineralogy
planetesimal
phyllosilicate
hydration
chondrite
Hydration
meteorite
mineralogy
X-ray diffraction
carbonaceous chondrite
Detectors
X ray diffraction
Silicates
Minerals
silicate
Asteroids
Fluids
fluid
parent body

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction : PSD-XRD modal mineralogy and planetesimal environments. / Howard, K. T.; Alexander, C. M.O.D.; Schrader, Devin; Dyl, K. A.

In: Geochimica et Cosmochimica Acta, Vol. 149, 04.11.2014, p. 206-222.

Research output: Contribution to journalArticle

@article{da3e212524274aa3a5677075601dbb9b,
title = "Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments",
abstract = "The relative differences in the degree of hydration should be reflected in any classification scheme for aqueously altered meteorites. Here we report the bulk mineralogies and degree of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.{\%}) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (total phyllosilicate/total anhydrous silicate+total phyllosilicate). Samples are linearly ranked from type 3.0 - corresponding to a phyllosilicate fraction of <0.05, to type 1.0 - corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7-1.2. The primary manifestation of aqueous alteration is the production of phyllosilicate, which ceased when the fluid supply was exhausted, leading to the preservation of anhydrous silicates in all samples. The variability in hydration indicates that either accretion of ices was heterogeneous or fluid was mobilized. From the bulk mineral abundances of the most hydrated samples, we infer that the initial mass fraction of H2O inside of their parent body(ies) asteroids was <20wt.{\%}. Bulk carbonaceous chondrite mineralogy evolved towards increasingly oxidizing assemblages as the extent of bulk hydration increased. This is consistent with the escape of reducing H2 gas that is predicted to have been produced from water during hydration reactions.",
author = "Howard, {K. T.} and Alexander, {C. M.O.D.} and Devin Schrader and Dyl, {K. A.}",
year = "2014",
month = "11",
day = "4",
doi = "10.1016/j.gca.2014.10.025",
language = "English (US)",
volume = "149",
pages = "206--222",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",

}

TY - JOUR

T1 - Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction

T2 - PSD-XRD modal mineralogy and planetesimal environments

AU - Howard, K. T.

AU - Alexander, C. M.O.D.

AU - Schrader, Devin

AU - Dyl, K. A.

PY - 2014/11/4

Y1 - 2014/11/4

N2 - The relative differences in the degree of hydration should be reflected in any classification scheme for aqueously altered meteorites. Here we report the bulk mineralogies and degree of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.%) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (total phyllosilicate/total anhydrous silicate+total phyllosilicate). Samples are linearly ranked from type 3.0 - corresponding to a phyllosilicate fraction of <0.05, to type 1.0 - corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7-1.2. The primary manifestation of aqueous alteration is the production of phyllosilicate, which ceased when the fluid supply was exhausted, leading to the preservation of anhydrous silicates in all samples. The variability in hydration indicates that either accretion of ices was heterogeneous or fluid was mobilized. From the bulk mineral abundances of the most hydrated samples, we infer that the initial mass fraction of H2O inside of their parent body(ies) asteroids was <20wt.%. Bulk carbonaceous chondrite mineralogy evolved towards increasingly oxidizing assemblages as the extent of bulk hydration increased. This is consistent with the escape of reducing H2 gas that is predicted to have been produced from water during hydration reactions.

AB - The relative differences in the degree of hydration should be reflected in any classification scheme for aqueously altered meteorites. Here we report the bulk mineralogies and degree of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.%) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (total phyllosilicate/total anhydrous silicate+total phyllosilicate). Samples are linearly ranked from type 3.0 - corresponding to a phyllosilicate fraction of <0.05, to type 1.0 - corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7-1.2. The primary manifestation of aqueous alteration is the production of phyllosilicate, which ceased when the fluid supply was exhausted, leading to the preservation of anhydrous silicates in all samples. The variability in hydration indicates that either accretion of ices was heterogeneous or fluid was mobilized. From the bulk mineral abundances of the most hydrated samples, we infer that the initial mass fraction of H2O inside of their parent body(ies) asteroids was <20wt.%. Bulk carbonaceous chondrite mineralogy evolved towards increasingly oxidizing assemblages as the extent of bulk hydration increased. This is consistent with the escape of reducing H2 gas that is predicted to have been produced from water during hydration reactions.

UR - http://www.scopus.com/inward/record.url?scp=84922821308&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84922821308&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2014.10.025

DO - 10.1016/j.gca.2014.10.025

M3 - Article

AN - SCOPUS:84922821308

VL - 149

SP - 206

EP - 222

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

ER -