Metamorphic study of metasediment from the Kangilinaaq Peninsula, West Greenland

University essay from Lunds universitet/Geologiska institutionen

Abstract: The Nagssugtoqidian Orogen is represented by an approximately 300 km wide Palaeoproterozoic deformation and metamorphic belt that stretch through the southern and middle parts of west Greenland. The Orogen is characterized and dominated by metamorphosed Archaean orthogneisses with minor supracrustal sequences. Despite its small extent the supracrustal sequences are an important factor in the interpretation of the tectonic evolution of the orogen because these rocks develop a wide range of distinctive mineral assemblages that characterise specific metamorphic zones, and can tell us about the rocks P-T history. On the Kangilinaaq Peninsula southeast of Christianshaab/Qasigiannquit in the northern part of the Nagssugtoqidian Orogen, West Greenland a relatively small belt of supracrustal rocks is situated. The geology of the area is known from earlier mapping but no detailed mapping or microstructural work is documented. Through the area, a marble layer stretches with metasedimentary sequences on either side. The behaviour of the marble during deformation and the composition, deformation and metamorphic history of the metasediments were of specific interest in this study. A clear difference in metamorphic history of the metasediments on either side of the marble could indicate that the marble acted as a tectonic boundary (thrust) between two metasedimentary sequences of different origin. The study showed that the rocks are of pelitic composition and have been metamorphosed in the upper amphibolite facies. No evidence was found indicating that the rocks have been at a higher metamorphic grad. The metapelitic rocks sampled for this study showed similar mineral assemblages and metamorphic structures on either side of the marble. Therefore no evidence was found that indicates that the marble was the site of a thrust. Since the supracrustal rocks are important for the understanding of the tectonic evolution of West Greenland, are correlations between these areas are of great interest. Metasediments from the Kangilinaaq Peninsula show lithological and mineralogical similarities to the metasediments described from the Naternaq and Ikamiut areas and a continuation of the sediments between these areas can therefore not be excluded. Four deformation phases (D1-D4), large scale structures, are known from the Nagssugtoqidian Orogen. At least three deformation phases, with F2 as the dominating structure, have been identified in the metapelites from the studied area. If the sediments from the Kangilinaaq Peninsula can be correlated with other sediment belts in the NNO, the dominating local foliation (F2) probably were formed during regional D3.

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