Late Archean Prograde Amphibolite- to Granulite-Facies Relations in the Fiskenæsset Region, Southern West Greenland

Abstract

The Tasiusarsuaq terrane in the Fiskenæsset-Nuuk region of southern West Greenland is interpreted as a late Archean tilted crustal section modified by deformation. The northern part of the terrane was affected by granulite-facies metamorphism at about 2810 Ma, but large areas were subsequently retrogressed to amphibolite facies. In the prograde amphibolite- to granulite-facies transition in inner Bjørnesund a relatively sharp, but highly irregular front that crosses structures and lithological boundaries on outcrop scale separates orthopyroxene-free from orthopyroxene-bearing rocks. Outcrop relations resemble in some ways examples of "arrested charnockite formation" described from high-grade regions in southern India and Sri Lanka. Relations in the transition zone in Bjornesund appear to be the result of late, local influx of a fluid, presumably rich in $$CO_{2}$$, that permitted orthopyroxene to grow at the expense of hornblende. Regional considerations suggest a genetic connection between granulite-facies metamorphism in the Tasiusarsuaq terrane and generation of the Ilivertalik granite-diorite suite, both perhaps caused by underplating of newly accreted continental crust by basic magmas.