Petrographic examination of Norwegian glaciofluvial aggregates: interpretation of mechanisms leading to high contents of cataclastic rocks

Abstract

Endel av artikkelen omhandler Verran og Mosvik i Nord-Trøndelag, kartblad 1622-I, Verran. Norwegian glaciofluvial aggregates have been examined microscopically and classified according to a newly established petrographic method. The results of this study and previous data show that there are high amounts of particles of cataclastic rocks in many Norwegian glaciofluvial aggregates. These rocks are unsuitable because of the expansive effects of suck rock-types in concrete, due to alkali-aggregate reactions (AAR). Some interpretations and reasons are put forward to account for the more extensive occurrence of cataclastic rocks in certain areas. Regional examination of glaciofluvial aggregates shows that cataclastic rocks can resist erosion over relatively long transport distances, and that particles within specific size ranges show higher enrichment in these rock-types. It is recognised that the concentration of cataclastic rocks within particular particle fractions is governed by the provenance, distance from the source rock, and the mechanical properties of specific types of cataclastic rocks.