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Application of the QUILF thermobarometer to the peralkaline trachytes and pantellerites of the Eburru volcanic complex, East African Rift, Kenya.

Research output: Contribution to journalJournal article

Published

  • Minghua Ren
  • Peter A. Omenda
  • Elizabeth A. Anthony
  • John C. White
  • Raymond MacDonald
  • D. K. Bailey
Journal publication date10/2006
JournalLithos
Journal number1-4
Volume91
Number of pages16
Pages109-124
Original languageEnglish

Abstract

The Quaternary Eburru volcanic complex in the south-central Kenya Rift consists of pantelleritic trachytes and pantellerites. The phenocryst assemblage in the trachytes is sanidine + fayalite + ferrohedenbergite + aenigmatite ± quartz ± ilmenite ± magnetite ± pyrrhotite ± pyrite. In the pantellerites, the assemblage is sanidine + quartz + ferrohedenbergite + fayalite + aenigmatite + ferrorichterite + pyrrhotite ± apatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO2 > 71%). QUILF temperature calculations for the trachytes range from 709 to 793 °C and for the pantellerites 668–708 °C, the latter temperatures being among the lowest recorded for peralkaline silicic magmas. The QUILF thermobarometer demonstrates that the Eburru magmas crystallized at relatively low oxidation states (ΔFMQ + 0.5 to − 1.6) for both trachytes and pantellerites. The trachytes and pantellerites evolved along separate liquid lines of descent, the trachytes possibly deriving from a more mafic parent by fractional crystallization and the pantellerites from extreme fractionation of comenditic magmas.