Crustal and Basin Evolution of the Southwestern Barents Sea: From Caledonian Orogen to Continental Breakup

Laurent Gernigon

A new generation of aeromagnetic data documents the post-Caledonide tectonic evolution of the southwestern Barents Sea (SBS) up to the continent-ocean transition. Clear evidence of reactivation of Caledonian structures controlling both Late Palaeozoic and Mesozoic basins can be observed at the edge of the Hammerfest and Nordkapp basins where low-angle reactivated detachments are observed on seismics. Our new aeromagnetic surveys confirm most of the previous structural elements but new features appear and illustrate the complexity of the pre-Permian and underlying basement architecture. We propose an updated tectonic scenario of the SBS in which the Caledonian nappes and thrust sheets, well constrained onshore, swing from a NE-SW trend close to the Varanger Peninsula to NW-SE across the Nordkapp Basin and the Bjarmeland Platform. On the Bjarmeland Platform, the dominant magnetic grain is clearly NNW-SSE. We show that this pattern reflects a regional pre-Permian system involving several Caledonian thrust sheets that possibly collapsed and controlled the post-Caledonian Late Palaeozoic rift development of the SBS. We also consider that this model can explain the later development of the SBS. Specific features are the Loppa and Stappen highs, which are interpreted as a series of rigid continental blocks (ribbons) poorly thinned as compared to the adjacent Hammerfest and Bjørnøya basins and the basins of the Vestbakken volcanic province that developed to the west as part of the sheared margin preceding the continental breakup. As part of this extensive complex system, the Bjørnøya Basin is interpreted as a very thinned and propagating system that aborted in Late Mesozoic time. This thick, Cretaceous, sag basin is characterised by a deep high-density body, interpreted as a combination of exhumed lower crust and/or potential serpentinised mantle as suggested by potential field modelling. The abortion of this propagating (aulacogen-type) basin may be partly explained by its trend oblique to the regional, inherited, structural grain revealed by the new aeromagnetic compilation. This abortion coincides with a migration and complete reorganisation of the crustal extension towards the western volcanic sheared margin and proto-breakup axis.

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