Granite studies II. The Precambrian Flå granite, a geological and geophysical investigation.

Abstract

The Flå granite is composed of two adjacent elliptical granite bodies, the larger northern Hedal granite and the Ådal granite. The granites are surrounded by banded granodioritic gneisses. Migmatites and augen gneisses are common just outside the granite contacts. Banded quartz-monzonitic gneisses are found on the east side. Telemark supracrustal rocks composed of interlayered quartzites and amphibolites are found on the west side and banded quartz-dioritic gneisses are found on the north side of the area. The varieties of the granite are limeted to porphyritic granite, which comprises most of the outcrops, and to fine-grained granite which comprises the center of the Hedal granite. The porphyric granite appears to be younger than the fine-grained granite; K-feldspar megacrysts in the pophyric granite are probably porphyroblasts. The composition of the granite falls within the range of quartz monzonites and corresponds fairly closely to the minimum-melting composition in the granite system.