Composition of fluid inclusions in granites and quartz syenites from the Gardar continental rift province (South Greenland)

Abstract

Fluid inclusions in quartz from granites and quartz syenites from the Precambrian Gardar province (south Greenland) vary in composition from CO2-CH4, through CO2-CH4-H2O mixtures, to aqueous saline fluids. The inclusions primarily represent fluids present during most-magmatic stages. Aqueous inclusions are the dominant type in all examined complexes. Salinities vary from 1 to 64 weight per cent, but late inclusions contain less than 40 equivalent weight per cent NaCl and have densities from 0.9 to 1.15 g/cm3. Boiling of the aqueous fluids does not appear to have played a prominent role in the generation of the higher salinity fluids. Early CO2-CH4 fluids contain less than 5 mole per cent CH4 and have densities from 0.75 to 1.0 g/cm3, but later fluids may contain up to about 80 mole per cent CH4 and have lower densities. Conditions for entrapment of most of the examined inclusion fluids at 250° to 400 °C and about 1-2 kbar are indicated.