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

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+pyrrhotitefapatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO(2)>71%). QUILF temperature calculations for the trachytes range from 709 to 793 degrees C and for the pantellerites 668-708 degrees 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 (Delta FMQ + 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. (C) 2006 Elsevier B.V All rights reserved.