Implications of Middle Devonian deformation of the eastern part of the Hill End Trough, Lachlan Orogen, New South Wales

Abstract

The Hill End Trough is a mid‐Silurian to Early Devonian sedimentary basin that formed during middle Palaeozoic regional extension in the Eastern Belt of the Lachlan Orogen. Recent mapping suggests that in the Sofala area, the Hill End Trough extends east of the Wiagdon Thrust towards Sunny Corner and Portland. This means that the eastern part of the trough is bounded to the north by Lower‐Middle Ordovician turbidites and Upper Ordovician volcanics. Ordovician basement and fill of the Hill End Trough are juxtaposed across a west‐northwest‐trending fault system that can be traced for 35 km along strike. This fault system, the Wattle Flat‐Portland Fault System, is interpreted to be a Middle Devonian north‐dipping thrust that carried Ordovician rocks southwards over Lower Devonian rocks of the Hill End Trough during the first phase of basin deformation. Subsequent east‐west folding and partial reactivation of this fault system followed, either in the Middle Devonian during regional east‐west shortening or in the Carboniferous Kanimblan deformation, after these structurally juxtaposed units had been eroded down to sea‐level and before deposition of the unconformably overlying Upper Devonian Hervey Group. On a wider scale, there is now accumulating evidence that the Middle Devonian Tabberabberan deformation affected a large part of the Lachlan Orogen.