Facies in an Upper Permian volcanic succession, Emmaville Volcanics, Deepwater, northeastern New South Wales
Titel:
Facies in an Upper Permian volcanic succession, Emmaville Volcanics, Deepwater, northeastern New South Wales
Auteur:
Stewart, A. L.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 48 (2001) nr. 6 pagina's 929-942
Jaar:
2001-12
Inhoud:
The Upper Permian Emmaville Volcanics at Deepwater, northeastern New South Wales, consist of a diverse succession of calc-alkaline silicic-intermediate ignimbrites, volcaniclastics and minor lavas. This 2.5 km-thick sequence underlies and outcrops extensively along the northern margin of the Dundee Rhyodacite Outlier at Dundee. Detailed mapping and facies analysis have revealed eight locally mappable units namely; Magistrate Volcanic Member (rhyolitic ignimbrites), Wollundi Mudstone Member, Dellwood Ignimbrite Member, Marrawarra Rhyolite Member, Top-Crossing Sandstone Member, Arranmor Ignimbrite Member, Yarramundi Andesite Member (lava, breccia) and Welcome Volcanic Member (rhyolitic ignimbrites). All volcanic units are contained in two fault-bounded blocks of different lithology and structure. The volcanic succession ranges in composition from andesite to high-silica rhyolite (58.6-78% SiO2). Chemical characteristics include enrichment in K2O (>3.5%), Al2O3 and large-ion lithophile elements (LILE: Rb, K and light rare-earth elements (LREE)), and depletion in high field strength elements (HFSE: Ti, Nb and Zr). These geochemical attributes reflect a continental subduction-related signature. The facies architecture indicates that the principal volcanic features of the Late Permian palaeogeography in northeastern New South Wales was a topographically subdued depression flanked by low-angle ignimbrite sheets with rhyolitic-intermediate volcanic centres rising gently from the sloping terrain. The succession demonstrates that during the Late Permian andesitic volcanism was present, although localised. A modern analogue for the setting of the Emmaville Volcanics is the Quaternary Taupo Volcanic Zone (New Zealand).
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