| Summary: | The Skellefte district in northern Sweden is a Palaeoproterozoic volcanic arc hosting abundant volcanogenic massive sulphide (VMS) deposits. The dominating rocks in the district are submarine volcanic and volcaniclastic rocks of the Skellefte Group deposited in an extensional regime at 1.89–1.88 Ga. Structural analysis and facies analysis combined with reflection seismic investigations in the central part of the Skellefte district revealed a pronounced pattern of WNW–ESE-striking normal faults and NE–SW-striking transfer faults that developed synchronously with volcanic activity. Dextral strike-slip movement along regional-scale NE-SW-striking faults favoured the opening of a pull-apart system. VMS deposits formed as sub-seafloor replacement and partly exhalative deposits mainly in the uppermost parts of Skellefte Group but also in the lowermost parts of the overlying Vargfors Group. Furthermore, the VMS deposits show a close spatial relationship to faults indicating that the ore-forming hydrothermal fluids utilized the synextensional faults as fluid conduits. The Vargfors Group sedimentary rocks form a distinct sub-basin in the central Skellefte district, the so called Vargfors basin or Vargfors syncline. Syn-extensional faulting created fault-bound compartments within the Vargfors basin. Syn-tectonic sedimentation of the Vargfors Group within the sub-basin is responsible for changes in stratigraphy between the individual compartments. Progressive opening of the sub-basin from the centre towards north-west and south-east is evident from the change of sedimentary facies associations. The onset of Vargfors Group deposition is characterized by turbiditic sedimentation with intercalated sandstones and monomict conglomerates derived from eroded and/or reworked Skellefte Group volcanic rocks. These facies associations are unconformably overlain by polymict conglomerates of alluvial fan and braided systems caused by the uplift of the Jörn intrusive complex and the subsequent formation of the Arvidsjaur volcanic arc, ...
|
|---|