Devonian – Carboniferous structure and tectonics at Maccullochs Range, and the recognition of the Darling Basin Conjugate Fault System showing switching of the directions of principal horizontal stress

Abstract

South of the east – northeast (055°)-trending Darling River Lineament at Maccullochs Range there are > 2.5 km-thick Lower Devonian synorogenic, alluvial fan-deposited strata of the Winduck Group. These strata are cut by five faults that are parallel to the Darling River Lineament: Mountain Bore (in the north), Yards, Rest Area, Coolabah Bore, and Wild Dog (in the south). Several blocks between these faults show fold trends consistent with sinistral and/or dextral faulting. Folds lying between the Rest Area and Coolabah Bore Faults indicate formation during sinistral tectonics followed later by dextral tectonics, and there was a prior period when there was north-northwest compression. It is inferred that the tectonics occurring in the range were like those in the unexposed Palaeozoic strata lying along the Darling River Lineament. During ?Late Silurian to Early Carboniferous time the structure/tectonics of the Darling Basin was dominated by the Lake Wintlow – Koonenberry Faults and the Darling River Lineament. These intersecting faults form the Darling Basin Conjugate Fault System in which the acute sectors of the Darling Basin Conjugate Fault System lie southwest – northeast and the obtuse sectors lie south-southeast – north-northwest. Compression and uplift and extension and subsidence within the sectors of the Darling Basin Conjugate Fault System alternated (shown by alternating dextral and sinistral activity on the Koonenberry Fault and by inference from tectonics at the Maccullochs Range, on the Darling River Lineament). There has been little/no long-term horizontal displacement along the Darling River Lineament or along the Lake Wintlow-Koonenberry Faults. These phenomena are consistent with two forces deforming the basin and much of eastern Australia, during Late Silurian to Early Carboniferous time: (i) dominant east – west compression generated in the subduction zone which lay far to the east in coastal New South Wales (two phases); and (ii) dominant northward compression, (shown by three compression phases) due to the collision of Gondwana, which lay in the south, with Laurasia, which lay to the north.