REDOX CONDITIONS AS A FACTOR IN THE DIFFERENTIATION OF ALKALIC BASALTS TO FORM NORMATIVE-QUARTZ MAGMAS OF VOLCANIC SERIES

Abstract

The authors with alkali basalts of two different compositions, representing different degrees of differentiation, from the same basalt-rhyolite series of Iceland. The experiments were performed in an apparatus in which the fugacity of oxygen could be regulated at temperatures between 1090° and 1300°C and which three types of variation of f02 with temperature could be created; the 'reducing' case, the 'intermediate' case. And the 'oxidizing' case. In the last-mentioned case, the oxygen fugacity was close to that of the hematite-magnetite buffer. The compositions of the mineral phases and melts (quenched glasses) were determined with a Camebax-Microbeam probe.