Internal structure of type I deep-sea spherules by X-ray computed microtomography

Feng, Huan; Jones, Keith; Tomov, Stanimire; Stewart, Brian W.; Herzog, G. F.; Schnabel, Christoph; Brownlee, D. E.

doi:10.1111/j.1945-5100.2005.tb00375.x

Cited by 19 publications

(17 citation statements)

References 16 publications

(29 reference statements)

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“…(1987) found them in smaller spherules as well (100–500 μm diameter range). Feng et al. (2005) reported on the presence of likely nuggets in I‐type spherules based on X‐ray computed tomographic analyses.…”

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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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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“…Considering the large uncertainty on specific gravity, we cannot infer securely that the two values exceeding pure magnetite-wustite mixtures (CS s-21 and s-30) actually contain nuggets of denser material (metallic iron or PGE, as described in Ref. [8]). However, it is a hypothesis worth considering.…”

Section: Specific Gravitymentioning

confidence: 99%

Study of a set of micrometeorites from Antarctica using magnetic and ESR methods coupled with micro-XRF

Marfaing¹,

Rochette²,

Pellerey³

et al. 2008

Journal of Magnetism and Magnetic Materials

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“…I-type spherules often contain a single large spherical void that may form by the loss of a molten metal bead from the particle. They also often exhibit an irregular void space in their centre which could result from the rapid cooling of the melt from the surface inwards (Feng et al 2005). I-type spherules are abundant in deep sea collections, as they are very resistant to weathering, but they constitute only 2% of 1600 cosmic spherules collected at the bottom of the South Pole Water Well (SPWW) (Taylor et al 2000).…”

Section: Melted Micrometeorites: Cosmic Spherulesmentioning

confidence: 99%

The classification of micrometeorites

Genge

Engrand

Gounelle

et al. 2008

Meteorit & Planetary Scien

220

375

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Abstract-Due to their small size, the mineralogical and chemical properties of micrometeorites (MMs) are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites. Identifying which groups of MM are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical, textural, and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies, albeit with minimal bias towards preconceived genetic models. Specifically, the interpretation of MMs requires a rigorous and meaningful classification scheme. At present the classification of MMs is, however, at best ambiguous. A unified petrological-chemical classification scheme is proposed in the current study and is based on observations of several thousand MMs collected from Antarctic ice.

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Internal structure of type I deep-sea spherules by X-ray computed microtomography

Cited by 19 publications

References 16 publications

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

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

Study of a set of micrometeorites from Antarctica using magnetic and ESR methods coupled with micro-XRF

The classification of micrometeorites

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