Caledonian tectonostratigraphy in northern Scandinavia - A review and implications for models of late-stage collisional orogenesis

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Anderson, Mark۱; Steltenpohl, Mark۲; Andresen, Arild۳; Hames, Willis۲
Holding Date 05 October 2008

The Caledonides of north-central Scandinavia (Torneträsk-Troms-Ofoten) are dominated by a series of crystalline thrust sheets ("nappes") that structurally overlie autochthonous and internally imbricated pre-Caledonian crystalline basement and cover rocks of the Baltic Shield. The allochthons were emplaced during ESE-directed translation of a previously assembled nappe stack across the margin of Baltica, mainly during the Devonian. This occurred in a largely passive, piggy-back style although the recognition of major late-stage, out-of-sequence thrusts at several structural levels within the allochthon, causes regional scale repetition and truncation of tectonostratigraphy. Hanging-wall and footwall geometries and radiometric dating of shear zone fabrics indicate that the development of these late thrusts closely relates to reactivation of pre-Caledonian Baltic basement during the Devonian (400-370 Ma). East-west contraction during the upper end of this time frame is peculiar considering that this was the period of large magnitude and rapid extension in western Norway.
In this presentation we review basement-cover relationships and internal tectonostratigraphic relationships within the Caledonian crust in this area together with our ongoing research in Lofoten, aimed at attempting to tie in its unusual/ suspect (paultry Caledonian fabrics and structures, Middle Ordovician eclogites, etc.) evolution. We examine the evidence for late-stage contractional and extensional tectonics and consider the implications for regional nappe correlations and models of accretion during Caledonian collisional orogenesis.