107 research outputs found
A new micrometeorite collection from Antarctica and its preliminary characterization by magnetic methods
The Thermal Decomposition of Fine-grained Micrometeorites, Observations from Mid-IR Spectroscopy
We analysed 44 fine-grained and scoriaceous micrometeorites. A bulk mid-IR spectrum (8–13 lm) for each grain was collected
and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption
bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via
EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive
thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth,
asymmetric spectra with a peak at 10 lm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation,
annealing and finally by the onset of partial melting. Both CI-like and CM-like micrometeorites are shown to pass
through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each
decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds
for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables
are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CIlike
grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations
and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small
population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating
and dehydroxylation have occurred. These grains may therefore represent regolith micrometeorites derived from the surface
of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance
peak at 9.0–9.5 lm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that
future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous
asteroid families
The age of the ice at the Frontier Mountain blue ice field (Antarctica) constrained by Ar-40 Ar-39 chronology of Englacial tephra
The Asco meteorite (1805): New petrographic description, chemical data, and classification
Abstract— We present magnetic measurements, chemical analyses, and petrographic observations of the poorly studied Asco historical meteorite fall (1805). These new data indicate that this meteorite has been previously misclassified as an L6 ordinary chondrite. Asco is reclassified as an H6 ordinary chondrite with shock stage S3. An interesting feature of this meteorite is the presence of chromite‐plagioclase assemblages with variable textures
The Meteoritical Bulletin, No. 92, 2007 September
Abstract— In this edition of The Meteoritical Bulletin, 1394 recognized meteorites are reported, 27 from specific locations within Africa, 133 from Northwest Africa, 1227 from Antarctica (from ANSMET, PNRA, and PRIC expeditions), and 7 from Asia. The Meteoritical Bulletin announces the approval of four new names series by the Nomenclature Committee of the Meteoritical Society, two from Africa and one from Asia, including Al Haggounia, from Al Haggounia, Morocco, which is projected to be on the order of 3 metric tons of material related to enstatite chondrites and aubrites. Approved are two falls from Africa, Bassikounou (Mauritania) and Gashua (Nigeria). Approved from areas other than Antarctica are one lunar, two Martian, 32 other achondrites, three mesosiderites, two pallasites, one CM, two CK, one CR2, two CV3, one CR2, and four R chondrites. The Nomenclature Committee of the Meteoritical Society announces 48 newly approved relict meteorites from two new name series, Österplana and Gullhögen (both from Sweden)
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