Formation of refractory metal nuggets and their link to the history of CAIs

D. Schwander, L. Kööp, T. Berg, G. Schönhense, P. R. Heck, A. M. Davis, U. Ott

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Ca, Al-rich inclusions (CAIs) often contain numerous refractory metal nuggets (RMNs), consisting of elements like Os, Ir, Mo, Pt and Ru. The nuggets are usually thought to have formed by equilibrium condensation from a gas of solar composition, simultaneously with or prior to oxide and silicate minerals. However, the exact mechanisms responsible for their extremely variable compositions, small sizes and associations with CAI minerals remain puzzling. Expanding on previous work on chemically separated RMNs, we have studied a large number of RMNs within their host CAIs from three different meteorite types, i.e., the highly primitive chondrite Acfer 094 (C2-ungrouped), Allende (CV3ox) and Murchison (CM2). Our results show several inconsistencies between the observed features and a direct condensation origin, including a lack of correlated abundance variations in the refractory metals that are expected from variations in condensation temperature. Instead, we show that most RMN features are consistent with RMN formation by precipitation from a CAI liquid enriched in refractory metals. This scenario is additionally supported by the common occurrence of RMNs in CAIs with clear melt crystallization textures as well as the occurrence of synthetic RMNs with highly variable compositions in run products from Schwander et al. (2015). In some cases, the sizes of meteoritic RMNs correlate with the sizes of their host minerals in CAIs, which indicates common cooling rates.

Original languageEnglish
Pages (from-to)70-87
Number of pages18
JournalGeochimica et Cosmochimica Acta
Volume168
DOIs
Publication statusPublished - Nov 1 2015

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Refractory metals
metal
history
condensation
Condensation
Minerals
Chemical analysis
Oxide minerals
Silicate minerals
Meteorites
silicate mineral
mineral
Crystallization
chondrite
meteorite
crystallization
Textures
Gases
texture
melt

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Formation of refractory metal nuggets and their link to the history of CAIs. / Schwander, D.; Kööp, L.; Berg, T.; Schönhense, G.; Heck, P. R.; Davis, A. M.; Ott, U.

In: Geochimica et Cosmochimica Acta, Vol. 168, 01.11.2015, p. 70-87.

Research output: Contribution to journalArticle

Schwander, D. ; Kööp, L. ; Berg, T. ; Schönhense, G. ; Heck, P. R. ; Davis, A. M. ; Ott, U. / Formation of refractory metal nuggets and their link to the history of CAIs. In: Geochimica et Cosmochimica Acta. 2015 ; Vol. 168. pp. 70-87.
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