Abstract
One of the first detailed accounts of Precambrian supracrustal rocks in central West Greenland came from a small group of islands and skerries a few kilometres north-east of Aasiaat (Fig. 1). In 1948, K. Ellitsgaard-Rasmussen spent a few days on the islands and published a metamorphic study of their low-grade greenstones and aluminous clastic rocks (Ellitsgaard-Rasmussen 1954). He observed a striking dissimilarity between these supracrustal rocks and the grey gneisses found in most of the Aasiaat region, although the latter were at that time also assumed to be of supracrustal origin. He furthermore noted that the regional significance of the islands should be pursued, and that the island of Maniitsoq 4 km west of the small islands might hold a key to their interpretation. More than 50 years were to elapse before the islands were surveyed again in July 2003, during field work for the Ikamiut map sheet in the northern Nagssugtoqidian orogen (van Gool et al. 2002). The collision of two Archaean continents during the c. 1850 Ma Nagssugtoqidian orogeny caused intensive structural and thermal reworking at up to granulite facies grade in most of central West Greenland; see Connelly et al. (2000) and van Gool et al. (2002). The small islands north-east of Aasiaat are indeed regionally important, because they document a previously unrecognised low-grade, low-strain domain of presumed Archaean age that has largely escaped the Nagssugtoqidian orogeny, and as predicted by Ellitsgaard-Rasmussen (1954) a clue to their significance was found on Maniitsoq.
Highlights
One of the first detailed accounts of Precambrian supracrustal rocks in central West Greenland came from a small group of islands and skerries a few kilometres north-east of Aasiaat (Fig. 1)
Steep pencil structures in fold hinges, formed by intersection between cleavage and bedding, demonstrate that the overall deformation was constrictional with subvertical extension. Both the eastern and western islands represent the deposits of a volcanic basin dominated by basic magmatism, with associated chemical sediments found as chert, banded iron formation and calcareous rocks
Greenstones and aluminous metasediments of presumed Archaean age crop out on a few small islands north of Aasiaat and have been excellently preserved in a low-temperature and low-strain window in the northern part of the Nagssugtoqidian orogen in West Greenland. These relatively lowgrade rocks may well represent the oldest component of the region, recording a history of metamorphism and deformation during Archaean crustal growth
Summary
One of the first detailed accounts of Precambrian supracrustal rocks in central West Greenland came from a small group of islands and skerries a few kilometres north-east of Aasiaat (Fig. 1). The small islands north-east of Aasiaat are regionally important, because they document a previously unrecognised low-grade, Fig. 1. Maniitsoq and the small island west of Manertooq (A) still preserve intrusive contacts of (?) Archaean granodiorite and tonalite into the supracrustal rocks, whereas the intensity of Palaeoproterozoic (Nagssugtoqidian) strain increases greatly towards the south.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have