The Miocene Waipiata Volcanic Field, New Zealand, is an eroded phreatomagmatic intracontinental
volcanic field formed during a period of weak lithospheric extension. The field includes
remnants of at least 55 volcanoes in an area of similar to 5000 km(2). Vent-filling
deposits comprising predominantly lava (e.g. plugs, necks, lava flows, or dykes),
often associated with thin basal phreatomagmatic pyroclastic deposits, were classified
as type I vents and are inferred to be the remnants of scoria cones. Vents represented
by predominantly pyroclastic infill are classified as type 2 vents and are inferred
to have been the substructures of phreatomagmatic tuff ring and/or maar volcanoes.
Type 3 vent complexes are groups of closely spaced or overlapping vents, with voluminous
preserved lava flows; they are inferred to be the remnants of volcanoes comprising
adjoining to coalescing maars and tuff rings with magmatic explosive and effusive
products. Pyroclastic rocks of most of the Waipiata vents record initial phreatomagmatic
explosive activity fuelled by groundwater, followed by strombolian-style eruptions.
Aligned and clustered vents are accommodated to structural features of the regional
basement rock (Otago Schist). (C) 2003 Elsevier Science B.V. All rights reserved.
