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

DRS at CSIR-National Institute of Oceanography

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Title Micrometer- and nanometer-sized platinum group nuggets in micrometeorites from deep-sea sediments of the Indian Ocean
 
Creator Rudraswami, N.G.
Parashar, K.
ShyamPrasad, M.
 
Subject micrometeorites
sediments
Indian Ocean
nuggets
 
Description 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 (mu m)-sized nuggets that are >3 mu m contain dominantly Ir, Os, and Ru (iridium-platinum group element or IPGE) and sub-mu m (or nanometer)-sized (< 1 mu m) nuggets, which contain dominantly Pt, Rh, and Pd (palladium-PGE or PPGE). The mu m-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 wustite 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 mu m-sized nuggets are seen in fewer specimens (approx. 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 mu m-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 mu m-sized PGNs, and is observed in only 17 of 213 nanometer nuggets with concentrations that are just above the detection limit (greater than or equal to 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
 
Date 2011-03-24T06:52:25Z
2011-03-24T06:52:25Z
2011
 
Type Journal Article
 
Identifier Meteoritics & Planetary Science, vol.46(3); 2011; 470-491
no
http://drs.nio.org/drs/handle/2264/3825
 
Language en
 
Relation Meteor_Planet_Sci_46_470.jpg
 
Rights An edited version of this paper was published by Blackwell. Copyright [2011] The Meteoritical Society. All efforts have been made to respect the copyright to the best of our knowledge. Inadvertent omissions, if brought to our notice, stand for correction and withdrawal of document from this repository.
 
Publisher The Meteoritical Society