Ignimbrite flare-ups and their drivers: A New Zealand perspective

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© 2016 Elsevier B.V. Ignimbrite flare-ups are periods of intense silicic volcanism characterized by multiple caldera-forming eruptions that together evacuate 103 to 104 km3 of magma. Ignimbrite flare-ups of different ages and from different tectonic settings have been well documented; however, in the literature, the distinction between an ‘ignimbrite flare-up’ and a ‘magmatic flare-up’ is not always obvious. We argue that the distinction is an important one as magmatic flare-ups do not always necessitate an ignimbrite flare-up, and thus the drivers for both require more investigation. Here we focus our review on the North Island continental arc of New Zealand, which is rarely included in published comparative studies of arc magmatism. Yet, it is well known for its extraordinary production of high-silica rhyolite and intensity of caldera-forming eruptions relative to other active arc systems, and a highly resolved understanding of the subduction plate boundary characterized by a rapidly migrating arc. Much of the present-day geologic footprint of the active part of the arc, the Taupo Volcanic Zone (TVZ), was established in a remarkable ignimbrite flare-up event between ~ 350 and ~ 280 ka. During this time, eight ignimbrite-forming eruptions occurred, evacuating ~ 3000 km3 of magma, and formed calderas that pepper a 90 × 40 km area. We divide the flare-up into 3 pulses of caldera activity, and track the magmatic input from the build-up to the first pulse, through to the final caldera forming eruption of the last pulse. Based on a comparison between New Zealand and other documented examples worldwide, we propose three ignimbrite flare-up categories based on their longevity and intensity. Most ignimbrite flare-ups last 106 to 107 years (categories 2 and 1, respectively), erupt magma volumes exceeding 104 km3 and are interpreted to be driven from depth by high mantle flux (i.e. magmatic flare-ups). Here, we draw attention to a new, much shorter timescale flare-up (104 to 105 years; category 3) as exemplified by the ~ 350 to ~ 280 TVZ example. Using the erupted volumes for several documented flare-ups at the three category timescales, we calculate a mantle input based on published silicic intrusive:extrusive ratios and isotopically derived ratios for basaltic input. Our results show that category 3 ignimbrite flare-up eruption rates typically exceed 10 km3 kyr− 1, have multiple caldera-forming eruptions, and are defined by mantle input rates that can be sustained through the duration of the ignimbrite flare-up and are at least an order of magnitude above the longer timescale category 1 and 2 ignimbrite flare-ups. For the TVZ, such high ignimbrite productivity over just tens of thousands of years, is related to an efficient feedback loop between high mantle flux and accelerated rifting that together are responsible for a remarkably thin and extended continental crust. We argue, that despite its unique nature relative to other continental arcs, there may be important magmatic-tectonic feedbacks that can be gleaned from the highly resolved record of caldera and ignimbrite volcanism in the TVZ, and applied to studying short timescale ignimbrite flare-ups elsewhere.

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Earth-Science Reviews