Significance of brittle and plastic fabrics within the Massawippi Lake fault zone, southern Canadian Appalachians

Abstract

Brittle and plastic deformation structures are common features of many well-described brittle-ductile fault zones. These fabrics coexist in the Massawippi Lake fault zone (MLFZ), a NW-SE-oriented fault related to the La Guadeloupe fault in the Dunnage Zone of the Canadian Appalachians. Kinematic analysis of the MLFZ indicates that it is a NW-directed ramp thrust underlain by tectonic slices of mafic-ultramafic and granitic rocks. The association of brittle and plastic deformation structures is well demonstrated within the granitic rocks. Brittle fabrics include cataclasites and quartz-filled fractures and microfractures. Plastic deformation is superimposed on brittle textures. Microstructures and c-axis fabrics suggest plastic and superplastic regimes of deformation. Analysis of coexisting brittle and plastic microstructures in terms of deformation mechanism associations reveals inconsistencies between brittle- and ductile-related conditions of deformation. Combined with the regional structural and metamorphic history, this suggests that brittle fabrics are relict structures preserved within a predominantly ductile shear zone.