Role of water in pantellerite genesis

Abstract

Sub-solidus, mass transfer experiments along a temperature gradient, in which water reacted with alkali olivine basalt, trachybasalt, and peridotite, have yielded acidic extracts directly from basic material. It is proposed that the process may also occur under magmatic conditions by progressive and efficient enrichment of the upper portions of a magma reservoir in the constituents of petrogeny’s residua via an aqueous fluid. This hypothesis could explain the production of silica-oversaturated rocks from nepheline-normative parent material, and their association with basalts of alkaline affinity but without volumetrically significant compositional intermediates. In the case of the trachybasalt experiment the transfer products were also peralkaline and the hypothesis may thus be extended to peralkaline oversaturated rocks.