GEMOC ARC National Key Centre

Y. H. Poudjom Djomani¹, J.D. Fairhead² and W.L. Griffin^1,3

1. GEMOC Macquarie
2. GETECH c/o Dept of Earth Sciences, University of Leeds
3. CSIRO Exploration and Mining

Fennoscandia is made up of the Baltic Shield and the Caledonian orogen of Norway and northern Sweden. The Shield is characterised by an old, thick and cold lithosphere in contrast to the Caledonides where the lithosphere is hotter and thinner. Geophysical data and information from xenoliths in volcanic rocks have been used to characterise lithosphere thickness and thermal state in different parts of the region. We have inverted gravity and topography data to determine the flexural rigidity or elastic plate thickness (Te), which is a measure of the mechanical strength of the lithosphere, across the different tectonic domains within Fennoscandia. Our results show a regional variation in elastic plate thickness from 8 km to 70 km, or equivalently, a flexural rigidity between 0.4*1022 and 3*1024 Nm. These results suggest that the lithosphere is strongest in the relatively stable Archaean Province, weaker in the regions characterised by Proterozoic crustal formation, and lowest in the tectonically reworked and deformed Caledonian belt. Within this region, there is a direct correlation between lithosphere strength, the age of the last major tectonothermal event registered in the crust and lithospheric mantle composition. These broad correlations reflect thinner and more fertile lithosphere, and higher geothermal gradients, beneath regions of progressively younger crust.