Geology of the Rinkian Orogen, central West Greenland

New geological maps at 1:100000 scale in central West Greenland allowed to constrain the tectonostratigraphic evolution of the Paleoproterozoic Karrat Group and the polyphase deformation, magmatism and metamorphism in the Rinkian orogen. Geochronology, stratigraphy, geochemistry, structural geology and economic geology data, together with 3D-photogeology, improved the understanding of the structural evolution of the region. The Karrat Group (from c. 71°00’ to 73°00’ N) formed in an intra-cratonic sag basin after c. 2000 Ma with basal quartzites unconformably overlaying Archaean gneisses of the Rae Craton. From 1950 to 1900 Ma a carbonate platform developed toward the south, while rift related alkaline volcanic rocks and syn-rift siliciclastic/volcaniclastic sediments were deposited to the north. The rifting was then succeeded by a back-arc system with transitional and tholeiitic magmatism. Arc-related granitoids intruded into and along the basal contact of the Karrat Group at c. 1900 Ma with major pulses at c. 1870 and c. 1850 Ma, concomitantly with the development of the back-arc system. During the collisional phase of the Rinkian orogen, the Karrat Group and the magmatic arc rocks underwent HT-metamorphism at c. 1830–1800 Ma. The metamorphic grade increases from greenschist facies in the south, to granulite facies in the north, where the metamorphism is associated to migmatization and emplacement of S-type leucogranites. Extensive thrust emplacement and folding characterize the Rinkian orogen south-east of the magmatic arc and its internal boundary to the west, is reworked along a top to ESE shear zone post-dating the HT-metamorphism. The ESE-ward emplacement of allochthonous thrust sheets during an early stage of thin-skinned tectonics is followed by NE-ward emplacement of basement nappes and finally by a NW-SE compression stage resulting in tectonic inversion of basin normal faults. The back-arc extension and Cordilleran-type magmatism were driven by eastward subduction of oceanic crust during the Trans-Hudson orogeny resulting from the convergence of the Superior, Meta Incognita and Rae Archean cratons between 1900–1800 Ma. The Rinkian orogen represent an example of Cordilleran-type tectonics resulting from the deformation of the Rae continental margin intruded by magmatic arc granites during subduction, followed by HT-metamorphism in the upper plate and the structuring of a back-arc fold and thrust system antithetic to the subducting plate.