Reconnaissance P,T studies of Proterozoic crustal evolution of the Ammassalik area, East Greenland

Abstract

The Ammassalik area of East Greenland lies in the centre of a 300 km wide early Proterozoic mobile belt, dominated by Archaean gneisses and early Proterozoic metasediments. Regional Proterozoic synkinematic metamorphism was associated with crustal thickening by southerly-directed thrusting and isoclinal folding. Maximum P, T conditions recorded during the regional metamorphism are found in the northern half of the mobile belt and are 9.5 kbar (equivalent to 30 km burial) and c. 700°C. Following some erosion and uplift, the late kinematic 1885 Ma Ammassalik Intrusive Complex (AIC) was intruded at pressures of c. 7 kbar (equivalent to a depth of 20 km). Temperatures in the metamorphic aureole of the AIC reached 800°C. Following further erosion and uplift, post kinematic, c. 1575 Ma granite-diorite-gabbro complexes were intruded, under pressures of 2.5 kbar (equivalent to a depth of 8 km).