Experimental Studies on Rocks from the Deboullie Stock, Northern Maine, including Melting Relations in the Water-Deficient Environment

Abstract

Two syenites, a syenodiorite, and a granodiorite from the Deboullie Stock were melted in the presence of excess water. In addition, the two syenites-similar in chemical composition but contrasting in the modal amounts of hydrous minerals-were melted with a series of water contents from 0 to 10 wt %. Results from the water-excess experiments are similar to those for other calc-alkaline rocks with the following differences: (1) a clinopyroxene was present through the melting interval for the syenites and syenodiorite and for only part of the interval for granodiorite; (2) at 2 kbar, the quartz-absent syenodiorite began melting at 775°C while the other three rocks began melting below 700°C; and (3) two feldspars from the syenites coexisted through an interval of 100°-150°C above the solidus at 2 kbar. Results from the water-deficient runs were difficult to interpret because of disequilibrium within runs lasting 180-330 days. In the vapor-absent region, quartz and feldspars coexist with liquid at temperatures much higher than in the vapor-present experiments. Their upper stability limits are strongly dependent on the water content increasing by about 100° C for 1 wt % decrease in water content.