Mesoproterozoic Albany – Fraser Orogen-related deformation along the southeastern margin of the Yilgarn Craton

Abstract

Deformation associated with the Mesoproterozoic Albany – Fraser Orogen of Western Australia extends up to 50 km into the Archaean rocks along the southeastern margin of the Yilgarn Craton. The Albany – Fraser Orogeny represents the Mesoproterozoic continent – continent collision of the Yilgarn Craton and the combined East Antarctic and South Australian Cratons. Albany – Fraser Orogen-related deformation (D5a – d) overprints regional D1 – D4 structures in the Archaean rocks and the onset of this Proterozoic deformation is marked by open northeast – southwest-plunging folds that formed as a result of northwest – southeast compression during D5a. A large drag fold developed during D5b immediately northwest of the Cundeelee Fault, which is the boundary between rocks of Archaean and Proterozoic origin. This fold is associated with the clockwise rotation of D1 – D5a structures from the regional north-northwest Archaean structural trend to a local boundary-parallel northeast trend. Continued Proterozoic convergence resulted in the development of an intense boundary-parallel fabric in the Archaean rocks (S5c). Late cross-cutting conjugate northwest – northeast-striking D5d structures mark the final stage of Albany – Fraser Orogen-related deformation in the Archaean rocks. A gradual increase in the metamorphic grade of Archaean rocks towards the Yilgarn Craton margin, from greenschist to amphibolite facies, may indicate that uplift of the Yilgarn Craton was associated with the collision, with exposure of deeper crustal material adjacent to the Cundeelee Fault. The clockwise rotation of Archaean rocks adjacent to the boundary indicates that a large component of dextral shear was associated with the Mesoproterozoic collision event. This is consistent with dextral shear-sense indicators in gneisses of the Albany – Fraser Orogen in the Fraser Range.