Textures of Archaean granites, Ivisârtoq region, southern West Greenland

Abstract

Granite textures are widely believed to reflect the effect of extensive subsolidus (i.e. postmagmatic) recrystallisation. Detailed thin section observations of Archaean granites from the Ivisartoq map sheet area, however, have revealed that subsolidus recrystallisation may by very limited. These observations apply to Qôrqut Granite Complex, 2610 Ma granites (Robertson, 1983) and Nûk granites from north-east Ivisartoq. They all contain modal quartz, plagioclase and microcline in approximately equal proportions, with variable amounts of biotite ranging up to a maximum of 12% of the total. Accessory mineral phases include zircon, apatite, allanite, sphene, ilmenite, magnetite and occasionally pyrite. Textural relations suggest that the accessory phases crystallised at an early stage in the evolution of the granites and all appear to predate biotite, the earliest of the major minerals.