Geology of the Mt Windsor subprovince—a lower Palaeozoic volcano‐sedimentary terrane in the northern Tasman orogenic zone

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Abstract
The Mt Windsor Subprovince encompasses the dismembered remnants of a thick volcanic and sedimentary succession predominantly of Late Cambrian and Early Ordovician age located within the northern part of the Tasman Orogenic Zone. The succession is divided into four formations which together comprise the Seventy Mile Range Group. Its lower part, Puddler Creek Formation, comprises immature terrigenous clastic strata lacking in volcanics but hosting numerous penecontemporaneous dolerite sills and dykes. Its upper part, Mt Windsor Volcanics, Trooper Creek Formation and Rollston Range Formation, is dominated by acid and intermediate volcanics and volcaniclastics. The group has been dismembered, deformed and in part metamorphosed by emplacement of the Middle Ordovician Ravenswood Granodiorite Complex which is regarded as having been diapirically emplaced. Stratigraphic relationships and reconnaisance geochemistry suggest that the volcanics comprise a consanguineous series ranging from basaltic andesite to rhyolite with the silicic varieties volumetrically predominant. The volcanics are calc‐alkaline in type, typical of active continental margins. Silicic stocks and dykes intruding the Puddler Creek Formation are regarded as hypabyssal equivalents of the volcanic series. Facies relationships and thickness variations suggest that the source of the volcanics was generally from the east. The Seventy Mile Range Group is regarded as having been deposited in a back‐arc basin floored with continental crust and broadly of north to south orientation. The Mt Windsor Subprovince is thought to be a remnant of an active margin terrane which extended the entire length of eastern Australia and represents the earliest developmental stage of the Tasman Orogenic Zone. The concept of a discrete Early Palaeozoic Thomson Orogen in north‐eastern Australia is rejected.