Early cleavage development in the Late Ordovician of northeast Victoria, Australia

Abstract

A pervasive cleavage, S ∗ , that subparallels bedding in the Upper Ordovician rocks of northeast Victoria can be related to an incremental strain distribution, in a shear environment, during the establishment of the first set of regional tectonic folds and faults. The cleavage is a strong, preferred orientation of phyllosilicates which overprints sedimentary features, is contemporaneous with early-formed extension fractures and postdates the formation of clastic dykes. The cleavage is attributed to tectonic and metamorphic processes rather than a static mimetic recrystallization of clay minerals during burial metamorphism. There is little evidence to suggest that this is an early deformation originating during imbricate stacking of an Ordovician accretionary prism.