Archaean orthogneisses and supracrustal rocks in eastern Nuussuaq in the southern part of the Rinkian orogen preserve much indirect evidence of Proterozoic reworking. In northern Nuussuaq, a marble occurrence which can be correlated with the Proterozoic Mârmorilik Formation of the Uummannaq district...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.540.4920 http://www.geus.dk/publications/bull-gl/nr181/nr181_p141-154.pdf |
| Summary: | Archaean orthogneisses and supracrustal rocks in eastern Nuussuaq in the southern part of the Rinkian orogen preserve much indirect evidence of Proterozoic reworking. In northern Nuussuaq, a marble occurrence which can be correlated with the Proterozoic Mârmorilik Formation of the Uummannaq district, is interleaved and intensely folded with Archaean orthogneisses. Dykes and sills of presumed Proterozoic age in southern Nuussuaq pre-date two major shear zones. Furthermore, published K-Ar and 40Ar-39Ar hornblende ages indicate that metamorphic tempera-tures of at least c. 550°C were reached in large parts of Nuussuaq during the Proterozoic. Although available data are not suffi cient to fi rmly establish the tectonic evolution of Nuussuaq, it can be shown that development of a regional fl at-lying structure was succeeded fi rst by upright folding and development of a major NW–SE-trending shear zone during crustal shortening, and subsequently by formation of an ENE–WSW-trending shear zone during crustal extension. A Rinkian detachment zone across Nuussuaq, similar to those known in the Uummannaq district, may link Proterozoic marble occurrences south of the peninsula with the marbles known in northern Nuussuaq and in the Uummannaq district. Observations suggest that geological structures and lithologies can be traced from north to south across the fjord Torsukattak, into the Ataa area which is hardly affected by Proterozoic deformation. This is used to infer that a major crustal boundary structure along the fjord (previ-ously assumed to form the northern boundary of the Burwell terrane in West Greenland) does not exist. |
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