Criteria for identification of ablation debris from primitive meteoric bodies

Brownlee, D. E.; Blanchard, M. B.; Cunningham, G. C.; Beauchamp, R. H.; Fruland, R. M.

doi:10.1029/jb080i035p04917

Cited by 30 publications

(15 citation statements)

References 28 publications

(22 reference statements)

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“…In both the iron oxide and the olivine samples a distinctive texture developed, consisting of a myrmekitelike intergrowth of magnetite lamellae with glass or olivine, that was indicative of the ablation environment. These results were found to be consistent with fusion crust studies of the Allende, M urchison, and Orgueil meteorites Brownlee et al, 1975].…”

Section: Results Of the Smithsonian Institution's Program On Shortlivsupporting

confidence: 86%

Analysis of ablation debris from natural and artificial iron meteorites

Blanchard¹,

Davis²

1978

J. Geophys. Res.

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Artificial ablation studies have been performed on iron and nickel‐iron samples by using an arc‐heated plasma of ionized air. Experiment conditions simulated a meteoroid traveling about 12 km/s at an altitude of 70 km. The artificially produced fusion crusts and ablation debris show features very similar to natural fusion crusts of the iron meteorites Boguslavka, Norfork, and N'Kandhla and to magnetic spherules recovered from deep‐sea Mn nodules. X ray diffraction, electron microprobe, optical, and scanning electron microscope analyses revealed that important mineralogical, elemental, and textural changes occur during ablation. Some metal is melted and ablated. The outer margin of the melted rind is oxidized and recrystallizes as a discontinuous crust of magnetite and wüstite. Adjacent to the oxidized metallic ablation zone is an unoxidized metallic zone in which structures such as Widmannstatten bands are obliterated as the metal is transformed to unequilibrated α2 nickel‐iron. Volatile elements such as S and P are vaporized in the ablation zone. Less volatile elements such as Si and Mn undergo fractionation and are concentrated in the oxide phases, while Ni is concentrated in the metal phases. Dissimilar phases form an intimate intergrowth that persists to a submicroscopic level. Identification of meteor ablation debris in particle collections cannot be based on a single parameter; elemental and mineralogical composition as well as morphological and textural features must be considered.

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Section: Results Of the Smithsonian Institution's Program On Shortlivsupporting

confidence: 86%

Analysis of ablation debris from natural and artificial iron meteorites

Blanchard¹,

Davis²

1978

J. Geophys. Res.

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“…The spherules have a combination of magnetite and wüstite in varying percentages; however, in the nugget‐bearing spherules, magnetite content is dominantly higher and all the spherules contain a magnetite rim as well. Wüstite is a metastable iron mineral (Fe (1− x ) O), which forms under low oxygen partial pressure during atmospheric entry (Brownlee et al. 1975).…”

Section: Resultsmentioning

confidence: 99%

Micrometer‐ and nanometer‐sized platinum group nuggets in micrometeorites from deep‐sea sediments of the Indian Ocean

Rudraswami

Parashar

Prasad³

2011

Meteorit & Planetary Scien

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Abstract-We examined 378 micrometeorites collected from deep-sea sediments of the Indian Ocean of which 175, 180, and 23 are I-type, S-type, and G-type, respectively. Of the 175 I-type spherules, 13 contained platinum group element nuggets (PGNs). The nuggets occur in two distinct sizes and have distinctly different elemental compositions: micrometer (lm)-sized nuggets that are >3 lm contain dominantly Ir, Os, and Ru (iridium-platinum group element or IPGE) and sub-lm (or nanometer)-sized (<1 lm) nuggets, which contain dominantly Pt, Rh, and Pd (palladium-PGE or PPGE). The lm-sized nuggets are found only one per spherule in the cross section observed and are usually found at the edge of the spherule. By contrast, there are hundreds of nanometer-sized nuggets distributed dominantly in the magnetite phases of the spherules, and rarely in the wu¨stite phases. Both the nugget types are found as separate entities in the same spherule and apparently, nugget formation is a common phenomenon among I-type micrometeorites. However, the lm-sized nuggets are seen in fewer specimens (2.5% of the observed I-type spherules). In all, we analyzed four nuggets of lm size and 213 nanometer-sized nuggets from 13 I-type spherules for platinum group elements. Chemically, the lm-sized PGNs contain chondritic ratios of Os ⁄ Ir, but are depleted in the more volatile PGE (Pt, Rh, and Pd) relative to chondritic ratios. On the other hand, the nanometer-sized nuggets contain dominantly Pt and Rh. Importantly, the refractory PGEs are conspicuous by their absence in these nanometer nuggets. Palladium, the most volatile PGE is highly depleted (<1.1%) with respect to chondritic ratios in the lm-sized PGNs, and is observed in only 17 of 213 nanometer nuggets with concentrations that are just above the detection limit ( ‡0.2%). Distinct fractionation of the PGE into IPGE (Ir, Os, Ru) and PPGE seems to take place during the short span of atmospheric entry. These observations suggest several implications: (1) The observation of fractionated PGE in an Fe-Ni system gives rise to the possibility that Earth's core could contain fractionated PGE. (2) The present data support the processes suggested for the fractionated PGE patterns observed in the ejecta of ancient meteorite impacts. (3) Meteoric metals released in the troposphere could contain fractionated PGNs in large numbers.

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“…The absence of wüstite, a metastable phase typical in micrometeorites and in microspherules resulting from experiments simulating high-altitude ablation (e.g. Blanchard 1972;Brownlee et al 1975), precludes the origin of the hollow microspherules from the BWD-1 site as a part of the background cosmic dust population, which melts at high altitudes (mostly above 80 km; Vondrak et al 2008). Instead, the dominance of magnetite is consistent with formation in an environment with a high partial pressure of oxygen (see section below "Possible mechanisms .…”

Section: Mms#1mentioning

confidence: 99%

Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (new mexico, usa)

Andronikov

Andronikova

Loehn

et al. 2016

Geografiska Annaler: Series A, Physical Geography

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Hollow magnetic microspherules from along the lower Younger Dryas boundary (c. 12.9 ka bp) in New Mexico (USA) were studied using scanning electron microscopy, electron probe microanalysis, X‐ray diffraction, and laser‐ablation inductively coupled‐plasma mass spectrometry methods. The shell of the microspherules (10–15% of the spherule's diameter) displays dendritic surface textures, which are likely due to quenching during rapid cooling of molten material. Structurally, multiple single‐magnetite crystals attached together form the bulk of the microspherules. Iron dominates the microspherules’ composition (∼90% FeOtot), Mn is the second most abundant element (up to 0.4% MnO), Al is detected in low concentrations (<0.30% of Al2O3). Among the trace elements, the rare earth elements display slightly fractionated patterns with concentrations of 0.1–1.0× CI chondrite. The microspherules contain elevated concentrations of Ni relative to detrital magnetite (up to 435 ppm) and very low concentrations of Ti (down to 5 ppm). Chemical, structural and mineralogical features of the microspherules do not contradict the existing models of the formation during ablation while a meteoroid goes through the Earth's atmosphere. Elevated concentrations of the magnetic microspherules in sediments can be a stratigraphic marker for the lower Younger Dryas boundary in North America.

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Criteria for identification of ablation debris from primitive meteoric bodies

Cited by 30 publications

References 28 publications

Analysis of ablation debris from natural and artificial iron meteorites

Analysis of ablation debris from natural and artificial iron meteorites

Micrometer‐ and nanometer‐sized platinum group nuggets in micrometeorites from deep‐sea sediments of the Indian Ocean

Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (new mexico, usa)

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