BUILD-UP TO AN IGNIMBRITE FLARE-UP: GEOLOGIC EVIDENCE FOR MAGMATIC-TECTONIC-VOLCANIC INTERPLAY IN THE CENTRAL TAUPO VOLCANIC ZONE, NEW ZEALAND

The central Taupo Volcanic Zone (TVZ) in New Zealand is notable for its high frequency of caldera-forming eruptions and voluminous ignimbrite output (greater than 6,000 cubic kilometers of magma equivalent over its 2 million year history), i.e. an ignimbrite flare-up. The central TVZ can be subdivided into episodes of escalated volcanism followed by periods of relative quiescence. One such episode lasted 100 thousand years (from approximately 340 to 240 ka) and erupted more than 3,000 cubic kilometers of magma (half of the total central TVZ output) from 7 caldera sources that, together, encompass most of the central TVZ.

Recent geologic investigations (field investigations and an Ar-Ar program) have revealed a series of events (volcanic and tectonic) that may represent the build-up to the 340 to 240 ka “flare-up” of ignimbrite volcanism. On the Bay of Plenty coast at the northern end of the TVZ a series of debris flows, triggered by a weather bomb rainfall event in 2005, scoured the inner walls of several stream valleys and exposed a new stratigraphic sequence more than 200 metres thick and covering an age range from 700 to 320 ka. Of particular importance is the evidence in the stratigraphic sequence for a major shift in the TVZ volcano-tectonic regime at ca. 370 ka just prior to the 340 to 240 ka episode. With respect to ignimbrite flare-ups worldwide, this kind of resolution of the potential interplay between tectonic and magmatic-volcanic processes is not as obvious. The young TVZ could help answer some of the questions posed at other large silicic systems with respect to what controls episodic magmatism and volcanism associated with ignimbrite flare-ups. In addition, in the TVZ, we can assess the controls on flare-ups at different timescales, i.e. the million year vs. the hundred thousand year scale.