Brittle-ductile transition: semi-brittle behavior

In central British Columbia mesoscopic and microscopic deformation mechanisms within metamorphic rocks ranging from greenschist facies through upper amphibolite facies have been examined to evaluate the applicability of single mechanism flow laws at different crustal levels. Throughout the entire sequence, regardless of metamorphic grade, the processes of regional strain accommodation were dominantly semi-brittle in the presence of an aqueous fluid phase. No sign was found of abrupt brittle-ductile transition and caution against calculating such a transition through the intersection of single mechanism flow “laws” with friction law(s) that, on the regional and local scales, do not appear to describe the mechanisms whereby regional strain is accommodated, is advised.