Facies architecture of the Early Devonian Ural Volcanics, New South Wales

Abstract

The Ural Volcanics are a early Devonian, submarine, felsic lava-sill complex, exposed in the western central Lachlan Orogen, New South Wales. The Ural Volcanics and underlying Upper Silurian, deepwater, basin-fill sedimentary rocks make up the Rast Group. The Ural Range study area, centrally located in the Cargelligo 1:100 000 map sheet area, was mapped at 1:10 000 scale. Seventeen principal volcanic facies were identified in the study area, dominated by felsic coherent facies (rhyolite and dacite) and associated monomictic breccia and siltstone-matrix monomictic breccia facies. Subordinate volcaniclastic facies include the pumice-rich breccia facies association, rhyolite -dacitesiltstone breccia facies and fiamme -siltstone breccia facies. The sedimentary facies association includes mixed-provenance and non-volcanic sandstone to conglomerate, black mudstone, micaceous quartz sandstone and foliated mudstone. The succession was derived from at least two intrabasinal volcanic centres. One, in the north, was largely effusive and intrusive, building a lava -sill complex. Another, in the south, was effusive, intrusive and explosive, generating lavas and moderatevolume (*3k m 3 ) pyroclastic facies. The presence of turbidites, marine fossils, very thick massive to graded volcaniclastic units and black mudstone, and the lack of large-scale cross-beds and erosional scours, provide evidence for deposition in a submarine environment below storm wave-base. The Ural Volcanics have potential for seafloor or sub-seafloor replacement massive sulfide deposits, although no massive sulfide prospects or related altered zones have yet been defined. Sparse, disseminated sulfides occur in sericite-altered, steeply dipping shear zones.

Fiamme textures in volcanic successions: Flaming issues of definition and interpretation

“…Fiamme-bearing breccia facies in the Early Devonian, submarine Ural Volcanics, Australia (Bull and McPhie, 2006) has characteristics consistent with an origin involving water-settling of pyroclastic pumice. The Ural Volcanics are an intrabasinal, silicic volcanic succession dominated by domes and sills, but the succession includes pyroclastic facies as well.…”

“…Fiamme textures occur in the coherent facies of a rhyolite ("10ra rhyolite") from the Siluro-Devonian submarine Ural Volcanics in NSW (Bull and McPhie, 2006). The 10ra rhyolite is at least 30 m thick and exposed in a 0.4 km 2 outcrop area.…”

“…The facies occurs as 10-to 100-m-long, ≤ 80-m-thick screens within a partly extrusive, dacitic sill, and consists of 5-25%, centimetre-to metre-long, rhyolitic fiamme within diffusely to distinctly stratified, moderately sorted, volcanic siltstone to fine-grained sandstone ( Fig. 3a-c; Bull and McPhie, 2006).…”

Vesicle distribution in acidic lava flow units in the rift basins of NE China: implications for petroleum reservoir exploration

“…In contrast to basaltic lava flows, the internal structures of acidic lavas are more complex and varied. For instance, acidic lava flows have more variety in flow foliation, which includes parallel or folded foliated layers of varying crystallinity, spherulite content and vesicularity (Cas and Wright, ; Bull and Mcphie, ; Waichel et al ., ). Therefore, rhythmic vesicle layers associated with the flow foliation are more common and varied in acidic lava flows than in basaltic ones.…”

Geochemistry, geochronology and tectonic implications of Late Silurian – Early Devonian volcanic successions, Central Lachlan Orogen, New South Wales

“…Two submarine, felsic volcanic successions, the Ural Volcanics and the Mt Hope Volcanics, are associated with Siluro-Devonian, north -south-trending sedimentary basins in the western Central Lachlan Orogen, New South Wales (Cas 1983;Trigg 1987;Scheibner 1998;Colquhoun et al 2005;Bull & McPhie 2006). Each is approximately 100 km long by 10 km wide.…”