The Glarus thrust accommodated at least 30 km of northward displacement str
ongly localized within a 1-m layer of 'Lochseiten' (LK) calc-mylonite. This
layer displays veins in various states of plastic deformation and a wildly
refolded foliated gouge texture. Lattice- and shape-preferred orientations
are observed within the fine-grained, recrystallized matrix. These feature
s indicate the alternate activity of brittle and ductile deformation mechan
isms. In contrast to the classical view that grain boundary sliding (superp
lasticity) is the dominant deformation mechanism, it is advocated that flui
ds, derived from the footwall and expelled along the thrust, are responsibl
e for hydrofracturing and cataclastic deformation. In periods between fract
ure events, deformation was ductile. In this new interpretation, a substant
ial amount of the total thrust displacement was accommodated by numerous sh
ort-lived and strongly localized fracture events at the base of the Verruca
no thrust sheet, rather than a permanently weak decollement lithology.