Mafic dykes in the Kongsfjord Formation, Barents Sea Group, North Varanger Region, lie sub-parallel to the steeply dipping axial surfaces of NE-SW to ENE-WSW trending Fl folds formed during dextral strike-slip movement along the Trollfjorden-Komagelva Fault. Previously, it has been asserted that the dykes were broadly syntectonic with the folding. However, several lines of evidence indicate that the dykes pre-dated deformation; sediments within unbroken bridge structures are folded along atypical axial trends; atypical dyke directions (e.g. in linking dykes in bridge structures) have atypical fold axial orientations at their margins; the position of fold axes was affected by bridge structures in the dykes; thin dykes are offset by flexural-slip folding. These folds all have the typical S1 slaty cleavage. In the proposed model, dyke emplacement was caused by pure-shear extension, related to a regional late Sturtian-early Vendian reactivation of the rift systems surrounding Baltica, and predated dextral strike-slip movement. This extension may have caused a minor component of sinistral movement along the Trollfjorden-Komagelva Fault.
A. H. N. Rice* & W. Reiz, Geologisch-Paläontologisches Institut, Ruprecht-Karls Universität, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany
*Present address: Institut für Geologie, University of Vienna, Universitätsstra?e, 1010 Vienna, Austria.