Upper Carboniferous to Lower Permian volcanic successions of the Carroll-Nandewar region, northern Tamworth Belt, southern New England Orogen, Australia

Abstract

Geological mapping in the Carroll-Nandewar region near the northwestern margin of the Tamworth Belt has identified an Upper Carboniferous to Lower Permian succession, the Willuri Formation, containing coarse volcaniclastic sediments and interbeaded dacitic to rhyolitic pyroclastics, lavas and a possible dome or coulée. The Currangandi Group (new) accommodates Upper Carboniferous volcaniclastic formations in the northern Tamworth Belt, including the Willuri Formation. Volcanic rocks in the Willuri Formation are distributed in four stratigraphically distinct, intertonguing or overlapping packages: the Kaputar, Piney Range, Tulcumba and Gunnan packages. According to SHRIMP (AS3) dating most of the succession ranges in age from ca 320 to ca 308 Ma (Namurian-Westphalian). Dacific and rhyolitic lavas, apparently in sequence with the succession on the northwestern part of Tulcumba Ridge, are 297-287 Ma or younger (Early Permian). They appear to disconformably overlie the Carboniferous succession and could be either part of the Willuri Formation or related to the Boggabri Volcanics. Volcanic centres near Maules Creek (Kaputar centre) and Wean (Wean centre) appear to have been the sources for volcanics in the Kaputar package and most parts of the Rocky Creek region to the northeast, and the Tulcumba and probably the Piney Range packages, respectively. In the Gunnan package a single major ignimbrite was derived from a volcanic centre in the Werrie pyroclastic field, but the provenance of other pyroclastics is unknown. Correlations based on SHRIMP ages and the distribution of pyroclastics indicate that the Willuri Formation is equivalent to most of the Currabubula Formation in the Werrie Syncline, and to the Rocky Creek Conglomerate and Lark Hill Formation in the Rocky Creek region. Boundaries of the Werrie and Rocky Creek pyroclastic fields are adjusted to incorporate a new pyroclastic field based on the Wean volcanic centre and covering the Tulcumba and Piney Range packages of the Willuri Formation.