Determination of the Modal Abundance of Nano-Scale Amorphous Phases Using Selected Area Electron Diffraction Mapping

Gregorio, Bradley De; Stroud, R. M.; Abreu, N. M.; Howard, K. T.

doi:10.1017/s1431927616009776

Cited by 2 publications

(3 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous studies of ALH 77307 indicate that the amorphous component of its matrix is an iron-bearing silicate (Brearley, 1993;De Gregorio et al, 2016). Spectroscopically, the amorphous materials in least-processed CO matrices behave like other amorphous silicates, including impact and volcanic glasses, due to their structural similarity.…”

Section: Introductionmentioning

confidence: 93%

“…Amorphous silicates in chondrules (mesostases) tend to have low iron contents and will only contribute weakly to the X-ray residuals (Howard et al, 2015;Kurahashi et al, 2008). Sections of least-processed CO meteorites studied using TEM methods, including ALH 77307 and Acfer 094, confirm the presence of abundant and amorphous Fe-rich silicate in the matrices of these samples (Brearley, 1993, Greshake, 1997, De Gregorio et al, 2016. Previous studies have used bulk compositions and petrography to demonstrate that most amorphous material identified by PSD-XRD in primitive CR 3.0 samples is also Fe-rich silicate in matrix (e.g., Howard et al, 2015a).…”

Section: Modal Mineralogy Of Selected Samplesmentioning

confidence: 99%

“…The amorphous-rich matrices of these least-processed COs have been extensively studied in certain CO samples (e.g., Brearley, 1993) and other low-metamorphic grade carbonaceous chondrites (e.g., Abreu and Brearley, 2010;Greshake, 1997;Le Guillou and Brearley, 2014;Abreu, 2016). The matrices of least-processed carbonaceous chondrites are dominated by truly amorphous material with little or no long range ordering, but do include some crystalline silicate grains (Brearley, 1993;De Gregorio et al, 2016). The matrix in ALH 77307 also contains highly 6 localized 'proto-phyllosilicates' regions with some ordering, but these regions could be the result of terrestrial weathering (Brearley, 1993).…”

Section: The Least-altered Co Meteoritesmentioning

confidence: 99%

See 2 more Smart Citations

Spectral evidence for amorphous silicates in least-processed CO meteorites and their parent bodies

McAdam

Sunshine

Howard

et al. 2018

Icarus

View full text Add to dashboard Cite

Least-processed carbonaceous chondrites (carbonaceous chondrites that have experienced minimal aqueous alteration and thermal metamorphism) are characterized by their predominately amorphous iron-rich silicate interchondrule matrices and chondrule rims. This material is highly susceptible to destruction by the parent body processes of thermal metamorphism or aqueous alteration. The presence of abundant amorphous material in a meteorite indicates that the parent body, or at least a region of the parent body, experienced minimal processing since the time of accretion. The CO chemical group of carbonaceous chondrites has a significant number of these least-processed samples. We present visible/nearinfrared and mid-infrared spectra of eight least-processed CO meteorites (petrologic type 3.0-3.1). In the visible/near-infrared, these COs are characterized by a broad weak feature that was first observed by Cloutis et al. (2012) to be at 1.3-µm and attributed to iron-rich amorphous silicate matrix materials. This feature is observed to be centered at 1.4-µm for terrestrially unweathered, least-processed CO meteorites. At mid-infrared wavelengths, a 21-µm feature, consistent with Si-O vibrations of amorphous materials and glasses, is also present. The spectral 2 features of iron-rich amorphous silicate matrix are absent in both the near-and mid-infrared spectra of higher metamorphic grade COs because this material has recrystallized as crystalline olivine. Furthermore, spectra of least-processed primitive meteorites from other chemical groups (CRs, MET 00426 and QUE 99177, and C2-ungrouped Acfer 094), also exhibit a 21-µm feature.Thus, we conclude that the 1.4-and 21-µm features are characteristic of primitive least-processed meteorites from all chemical groups of carbonaceous chondrites. Finally, we present an IRTF+SPeX observation of asteroid (93) Minerva that has spectral similarities in the visible/near-infrared to the least-processed CO carbonaceous chondrites. While Minerva is not the only CO-like asteroid (e.g., Burbine et al., 2001), Minerva is likely the least-processed COlike asteroid observed to date.

show abstract

Section: Introductionmentioning

confidence: 93%