Rates of postglacial rock weathering on glacially scoured outcrops (Abisko-Riksgransen area, 68°N)

Ice-polished quartz veins, feldspar phenocrysts and quartzite layers were used as reference surfaces to assess the impact of Postglacial rock weathering in Lapland (68degreesN). Over 3200 measurements were carried out on roches nioutonnees and glaciofluvially scoured outcrops distributed within three study areas covering 8 km(2). Inferred weathering rates demonstrate that 10 000 years of Holocene weathering did not significantly modify the geometry of Weichselian rock surfaces. However, rates of general surface lowering range from I to 25, depending on the rock type, with average values at 0.2 mm ka(-1) for homogeneous crystalline rocks (irrespective of their acidity and grain size), 1 mm ka(-1) for biotite-rich crystalline rocks, and 5 mm, ka(-1) for carbonate sedimentary rocks. Accelerated rates were recorded in weathering pits and along joints with values up to ten times higher than on the rest of the rock surface. Comparisons with cold and temperate areas suggest that solution rates of carbonate rocks are highly dependent on climate conditions, whilst granular disintegration of crystalline rocks operates at the same rate whatever the environment. It probably means that microgelivation is not efficient on ice-polished crystalline outcrops even under harsh climate conditions, and that granular disintegration proceeds under various climates from the same ubiquitous combination of biochemical processes. Last, the weathering state of Late-Weichselian roches moutonnees can be usefully compared to that of Preglacial tors of the nearby Kiruna area.