Proterozoic deformation in the Duchess belt, Australia: A contribution to the BMR Mount Isa Regional Tectonic History Program

Abstract

In medium to high grade metasediments of the Proterozoic Mt. Isa Inlier, Australia, at least three regional phases of deformation can be recognized. Early events of low angle brittle faulting at low grade conditions (D1a), probably followed by localized transcurrent flow along a N-S ductile shearzone (D1b) were overprinted by a phase of intense E-W shortening and vertical extension (D2). During this phase, strain was accommodated without significant flow localization, i.e. without development of major shearzones. Important granite and gabbro intrusion occurred before and early during D2. Crustal shortening values of up to 80% have been realized during D2 leading to large-scale folding and the development of spectacular strain shadows around the major plutons. D3 is characterised by strike-slip faults and minor accomodation structures.