STRUCTURAL STYLE AND CRUSTAL ARCHITECTURE OF THE TASMANIDES OF EASTERN AUSTRALIA: EXAMPLE OF A COMPOSITE ACCRETIONARY OROGEN

Abstract

Deformation in accretionary orogens, such as the eastern Australian Tasmanides, is clearly partitioned either as thin-skinned thrusting or thick-skinned faulting, with structural style dependent on the nature and stratal thicknesses of the sequences involved. The thin-skinned thrust systems consist of either detachment-related folds and thrust sheets within attenuated passive margin sequences or thrust sheets of chevron-folded turbidites with leading imbricate-fan geometry that are developed within former submarine fans overlying back-arc basin oceanic lithosphere. Thickskinned belts consist of major thrust faults that root into the seismic reflection Moho with no apparent common décollement and cause crustal-scale imbrication of former arc, forearc, submarine fan, and accretionary complex elements. The Tasmanides are a composite orogenic system made up of three distinct orogenic belts whose character and structural style have resulted from the deformation of different tectonic components; the former rifted passive margin to make the Delamerian Orogen, a turbidite fan system(s) in a back-arc setting to make the Lachlan Orogen, and an arc-subduction complex that includes some older accreted components to make the New England Orogen. The inboard Delamerian Orogen consists of an external, craton-vergent thrust belt with foreland-style, detachment-related folds and thrusts linked to a high-T/low-P metamorphic complex. The centrally located Lachlan Orogen is made up of three separate thrust systems largely developed in submarine turbidite fans and incorporates a shear-zone-bounded high-T/low-P metamorphic belt. The outermost New England Orogen is constructed from craton-vergent, fore-arc and magmatic arc sequences, subduction complexes, and ophiolite fragments. © 2006 Geological Society of America.