Petrogenesis and geochemistry of Archean Komatiites

Paolo A. Sossi, Stephen M. Eggins, Robert W. Nesbitt, Oliver Nebel, Janet M. Hergt, Ian H. Campbell, Hugh St C. O'Neill, Martin Van Kranendonk, D. Rhodri Davies

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Komatiites are products of decompression melting of mantle so hot that they are almost exclusively restricted to the Archean. The high degree of partial melting (F) and pressure (P) required for their generation facilitates comparison between the magma composition and its mantle source. To investigate compositional variations in Archean komatiites, a global selection of 38 Archean komatiites spanning five cratons (Kaapvaal, Zimbabwe, Yilgarn, Pilbara, Superior) were analysed for their major and trace element contents. Included are the Aluminium-Depleted (ADK, Barberton-Type) and Aluminium-Undepleted (AUK, Munro-Type) petrogenetic types that have been equated with high P/moderate F and moderate P/high F, respectively, on the basis of their Al/Ti and Gd/Yb ratios. Following calculation of the primary magma composition of each suite, we show that the absolute Al content at a specified MgO proves a more sensitive indicator of P than either of the above two ratios and hence we introduce a new classification using Al. The Mg# is a reliable proxy for F, independent of the two endmember melting styles, fractional and batch. We demonstrate that most komatiites form by batch melting, ceding to fractional melting with decreasing pressure as the density contrast between the liquid and solid grows. The Munro AUKs are the only suite to show evidence of fractional melting, with melt extraction occurring at the lowest F and P,≈ 25% melting at 5 GPa (mantle potential temperature, TP=1750°C) whereas the ADKs of Barberton segregated at the highest F and P ≈ (40%, 9 GPa, TP=1950°C). The petrogenetic type is a combination of P and F, where, at a given pressure, higher F will produce AUKs over ADKs as majorite is consumed in the source. Through numerical simulations, it is shown that both types can occur within the same mantle plume, with ADKs forming in its cooler, distal fringes whereas AUKs occur along its axis. Furthermore, and contrary to previous views, there is no temporal distinction between the two komatiite types, with both AUKs and ADKs occurring throughout the Archean. By contrast, younger, 27 Ga komatiites tend to have sources that are more depleted than those of older, 35 Ga komatiites. Komatiites are invaluable records of the mantle's chemical and physical evolution during the Archean.

Original languageEnglish
Pages (from-to)147-184
Number of pages38
JournalJournal of Petrology
Volume57
Issue number1
DOIs
Publication statusPublished - Jan 1 2016
Externally publishedYes

Fingerprint

petrogenesis
Geochemistry
geochemistry
Archean
Melting
melting
Earth mantle
mantle
Aluminum
magma
aluminum
majorite
komatiite
Zimbabwe
potential temperature
mantle plume
decompression
cratons
mantle source
chemical evolution

Keywords

  • Geochemistry
  • Komatiite
  • Mantle plume
  • Partial melting
  • Temperature
  • Thermodynamics

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Sossi, P. A., Eggins, S. M., Nesbitt, R. W., Nebel, O., Hergt, J. M., Campbell, I. H., ... Rhodri Davies, D. (2016). Petrogenesis and geochemistry of Archean Komatiites. Journal of Petrology, 57(1), 147-184. https://doi.org/10.1093/petrology/egw004

Petrogenesis and geochemistry of Archean Komatiites. / Sossi, Paolo A.; Eggins, Stephen M.; Nesbitt, Robert W.; Nebel, Oliver; Hergt, Janet M.; Campbell, Ian H.; O'Neill, Hugh St C.; Van Kranendonk, Martin; Rhodri Davies, D.

In: Journal of Petrology, Vol. 57, No. 1, 01.01.2016, p. 147-184.

Research output: Contribution to journalArticle

Sossi, PA, Eggins, SM, Nesbitt, RW, Nebel, O, Hergt, JM, Campbell, IH, O'Neill, HSC, Van Kranendonk, M & Rhodri Davies, D 2016, 'Petrogenesis and geochemistry of Archean Komatiites', Journal of Petrology, vol. 57, no. 1, pp. 147-184. https://doi.org/10.1093/petrology/egw004
Sossi PA, Eggins SM, Nesbitt RW, Nebel O, Hergt JM, Campbell IH et al. Petrogenesis and geochemistry of Archean Komatiites. Journal of Petrology. 2016 Jan 1;57(1):147-184. https://doi.org/10.1093/petrology/egw004
Sossi, Paolo A. ; Eggins, Stephen M. ; Nesbitt, Robert W. ; Nebel, Oliver ; Hergt, Janet M. ; Campbell, Ian H. ; O'Neill, Hugh St C. ; Van Kranendonk, Martin ; Rhodri Davies, D. / Petrogenesis and geochemistry of Archean Komatiites. In: Journal of Petrology. 2016 ; Vol. 57, No. 1. pp. 147-184.
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