Oxygen isotope fractionation study of quartz - alkali feldspar pairs

Abstract

Oxygen isotope exchange experiments with quartz, alkali feldspar, and various aqueous solutions have been performed at 600°C at a water pressure of 2 kilobars. Those experiments involving water as the aqueous phase have yielded the most reliable results and a value for Δ quartz-alkali feldspar of 1.6±0.4‰ has been obtained. Observations made during the course of this work suggest that factors which affect the rate of oxygen isotope exchange include: nature of exchange solution, grain size of starting materials, water pressure, the size of the opening to the exchange tubes, and the formation of keatite as an intermediate phase between silica gel and quartz. As a comparison, several coexisting quartz and feldspar samples from the Charleston Pegmatite and Gneiss have been analyzed for oxygen isotope ratio and temperatures have been assigned to them.