The Nagssugtoqidian Orogen of West Greenland represents a belt of Palaeoproterozoic deformation and metamorphism between the North Atlantic Craton of South Greenland and a northern, lesser known continental segment that includes the Rinkian Orogen. First-order observations are interpreted to support a cycle of separation, convergence, and eventual collision of two continental masses. The emplacement of the Kangâmiut dyke swarm marked the onset of continental breakup at ca. 2040 Ma, and sedimentary basins formed between ca. 1950 and 1920 Ma. Subsequent convergence and consumption of an oceanic plate caused arc magmatism at 1920–1870 Ma. Granulite-facies peak metamorphism at 1860–1840 Ma in the centre of the orogen is related to crustal thickening by WNW-directed thrusting. Large-scale, upright folding with an east–west trend was ongoing by 1825 Ma. Sinistral strike-slip movement was concentrated along steeply dipping limbs of these large-scale folds and formed orogen-scale steep belts at ca. 1775 Ma. Close similarities between the northern and southern foreland suggest that the two cratons likely originated from one continuous continental block. Temporal and kinematic correlation of these events with adjoining orogens in Canada and Greenland shows close genetic links. The Nagssugtoqidian Orogen of West Greenland continues eastwards beneath the Greenland Ice cap to the Eastern Nagssugtoqidian belt of East Greenland (a.k.a. the Ammassalik belt). The Torngat Orogen of eastern Canada developed simultaneous with the Nagssugtoqidian Orogen with a kinematic compatibility suggesting that the two orogens formed on the west and north flanks, respectively, of a curved leading continental margin of an indenting North Atlantic Craton.

Terra Nova, 25, 30–37, 2013 Abstract The late Mesoproterozoic Sveconorwegian orogen in southwest Baltica is traditionally interpreted as the eastward continuation of the Grenville orogen in Canada, resulting from collision with Amazonia, forming a central part in the assembly of the Rodinia supercontinent. We challenge this conventional view based on results from recent work in southwest Norway demonstrating voluminous subduction‐related magmatism in the period 1050–1020 Ma, followed by geographically restricted high‐T/medium‐P metamorphism between 1035 and 970 Ma, succeeded by ferroan magmatism over large parts of south Norway in the period 990–920 Ma. This magmatic and metamorphic evolution may be better understood as reflecting a long‐lived accretionary margin, undergoing periodic compression and extension, than continent–continent collision. This study has implications for Grenville–Sveconorwegian correlations, comparisons with modern continental margins, Rodinia reconstructions and how we recognize geodynamic settings in ancient orogens.

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The Hardangervidda-Rogaland Block within southwest Norway is host to ~1.52-1.48 Ga continental building, and variable reworking during the ~1.1-0.9 Ga Sveconorwegian orogeny. Due to the lack of geochronological and geochemical data, the timing and tectonic setting of early Mesoproterozoic magmatism has long been ambiguous. This paper presents zircon U-Pb-Hf-O isotope data combined with whole-rock geochemistry to address the age and petrogenesis of basement units within the Suldal region, located in the centre of the Hardangervidda-Rogaland Block. The basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies.U-Pb ages confirm that magmatism occurred from ~1521 to 1485 Ma, and conspicuously lack any xenocrystic inheritance of distinctly older crust. Hafnium isotope data range from εHf (initial) +1 to +11, suggesting a rather juvenile magmatic source, but with possible involvement of late Palaeoproterozoic crust. Oxygen isotope data range from mantle-like (δ 18 O ~5‰) to elevated (~10‰) suggesting involvement of low-temperature altered material (e.g. supracrustal rocks) in the magma source. The Hf-O isotope array is compatible with mixing between mantle-derived material with young low-temperature altered material (oceanic crust/sediments) and older low-temperature altered material (continent-derived sediments). This, combined with a lack of xenoliths and xenocrysts, exposed older crust, AFC trends and S-type geochemistry, all point to mixing within a deep-crustal magma-generation zone. A proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre-existing continental margin, underthrusting to the magma generation zone, and remobilisation during arc magmatism. The geodynamic setting for this arc magmatism is comparable to that seen in the Phanerozoic (e.g. the Sierra Nevada and Coast ranges batholiths), with compositions in the Suldal Sector reaching those of average upper continental crust. As within these younger examples, factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions, and delamination of cumulate material. Underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognized. Finally, the Suldal Arc magmatism represents a significant juvenile crustal addition to SW Fennoscandia.