--> Abstract: Grenvillian and Sveconorwegian Crust Beneath the Continental Shelves of the North Atlantic and Barents Sea, by David Gee; #90177 (2013)

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Grenvillian and Sveconorwegian Crust Beneath the Continental Shelves of the North Atlantic and Barents Sea

David Gee

There is a generally accepted interpretation that the Grenville-Sveconorwegian Orogen (G-SO) in the North Atlantic region is restricted to type areas in southeastern CA and southwestern Scandinavia. This hypothesis is based on the lack (or paucity) of outcrops and/or other direct evidence of G-SO rocks north of c. 63°N. However, unambiguous evidence of late Grenvillian orogeny has long been recognized in the upper allochthons of the East Greenland and Svalbard Caledonides. These early Neoproterozoic Renlandian (Greenland) and Nordaustlandet (Svalbard) orogenies were interpreted by some as related to an orogen (Valhalla) 'external' to the main G-SO orogen; by others, as terranes moved northwards (present day coordinates) thousands of kilometres from the type areas. It is proposed here that these occurrences are essential components of a G-SO that continued into the high Arctic. The apparent lack of Sveconorwegian rocks in the Arctic is largely the result of the removal of most of them during subsequent Caledonian Orogeny. The Scandinavian Caledonides (like the Himalayas) are characterized by vast underthrusting of one continent (Laurentia) by another (Baltica). Laurentian continental margin assemblages were emplaced on Baltica and preserved as the Uppermost Allochthon in the Scandes. Most of the highly extended Sveconorwegian crust that is inferred to have existed along the outer Baltoscandian margin of continent Baltica during the Neoproterozoic and Cambrian, covered by thick sedimentary successions in rift basins and on the passive margin, has been lost during Caledonian underthrusting. The evidence of the previous presence of Sveconorwegian crust is provided by the detrital zircon signatures of the Caledonian allochthons, mainly metasedimentary rocks, now emplaced on the Baltoscandian platform. These Neoproterozoic and Early Paleozoic successions of Baltoscandian outer margin affinities (Lower and Middle allochthons), including fluvial and shallow marine feldspathic sandstones, quartzites and foreland basin turbidites, all show clear Sveconorwegian age signatures. This is also the case for late Ordovician quartzites in the Iapetus margin Virisen Terrane of the lower Köli Nappe Complex (Upper Allochthon). Even in the Silurian and Devonian successions of the high Arctic on Novaya Zemlya, there is a total dominance (>90%) of earliest Neoproterozoic to latest Paleoproterozoic zircons inferred to be derived from proximal G-SO sources in the Arctic Caledonides. We suggest reassessment of the existing hypotheses for the crustal evolution of (proto-)Baltica and Laurentia from the late Mesoproterozoic to the mid Paleozoic in the light of the evidence that Iapetus Ocean opening and Caledonian orogeny were primarily controlled by the crustal rheology of the collapsed Grenville-Sveconorwegian Orogen.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013