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Abstract

The spatial and temporal distributions of volcaniclastic deposits in arc-related basins refl ect a complex interplay between tectonic, volcanic, and magmatic processes that is typically diffi cult to unravel. We take advantage of comprehensive geothermal drill hole stratigraphic records within the Taupo-Reporoa Basin (TRB), and integrate them with new 40 Ar/ 39 Ar age determinations, existing age data, and new mapping to develop a four-dimensional model of basin evolution in the central Taupo Volcanic Zone (TVZ), New Zealand. Here, exceptional rhyolitic productivity and high rates of extensional tectonism have resulted in the formation of at least eight calderas and two subparallel, northeast-trending rift basins, each of which is currently subsiding at 3 to 4 mm/yr: the Taupo fault belt (TFB) to the northwest and the TRB to the southeast (the main subject of this paper). The basins are separated in the northeast by a high-standing, fault-controlled range termed the Paeroa block, which is the focus of mapping for this study, and in the southwest by an along strike alignment of smaller scale faults and an associated region of lower relief. Stratigraphic age constraints within the Paeroa block indicate that a single basin (~120 km long by 60 km wide) existed within the central TVZ until 339 ± 5 ka (Paeroa Subgroup eruption age), and it is inferred to have drained to the west through a narrow and deep constriction, the presentday Ongaroto Gorge. Stratigraphic evidence and fi eld relationships imply that development of the Paeroa block occurred within 58 ± 26 k.y. of Paeroa Subgroup emplacement, but in two stages. The northern Paeroa block underwent uplift and associated tilting fi rst, followed by the southern Paeroa block. Elevations (>500 m above sea level) of lacustrine sediments within the southern Paeroa block are consistent with elevations of rhyolite lavas in the Ongaroto Gorge, the outlet to the paleolake in which these sediments were deposited, and indicate that the Paeroa block has remained relatively stable since development. East of the Paeroa block, stratigraphic relationships show that movement along the Kaingaroa Fault zone, the eastern boundary of the central TVZ, is associated with volcano-tectonic events. Stratigraphic and age data are consistent with rapid formation of the paired TRB and TFB at 339 ± 5 ka, and indicate that gradual, secular rifting is punctuated by volcano-tectonic episodes from time to time. Both processes infl uence basin evolution.

A review of the Rotokawa Geothermal Field, New Zealand

“…The structure of the Rotokawa Geothermal Field is documented in a number of publications (Anderson, 2011;Bannister et al, 2008;Bowyer and Holt, 2010;Collar and Browne, 1985;Davidson et al, 2012;Downs et al, 2014;Grindley, 1961;Grindley et al, 1985;Krupp and Seward, 1987;Massiot et al, 2012Massiot et al, , 2015McNamara et al, 2014;Rae, 2007;Wallis et al, 2013). The surface geology at Rotokawa contains ample evidence of an active structural environment.…”

“…In the north of the field, surface geology is dominated by the Oruahineawe and Kaimanawa rhyolite domes and surrounding pumice breccias (Anderson, 2011;Downs et al, 2014). In the east, it is dominated by the 0.71 Ma andesites of Rolles Peak (Wilson et al, 1995), and in the west by rhyolite lavas exposed at the Aratiatia Dam and Rapids (Rae, 2007).…”

“…The initial andesitic volcanism would have involved magmas migrating through faults and fractures to the surface >∼1.9 Ma, constructing a large volcano under Rotokawa, potentially centred along the western border of the Rotokawa Geothermal Field based on lateral variation in thickness of the andesite (Anderson, 2011;Browne et al, 1992;Chambefort et al, 2014). A thick andesite unit overlying greywacke basement in the Ngatamariki Geothermal Field is likely to be part of the Rotokawa andesite complex (Chambefort et al, 2014;Downs et al, 2014), but petrographical and geochemical comparison of these two units indicates possible separate eruptive centres, with basaltic andesite present at Rotokawa, and more dacite/andesite composition volcanism at Ngatamariki (Anderson, 2011;Browne et al, 1992). The classification of the samples used to define the dacitic composition in these studies as andesites is refuted however by Chambefort et al (2014) who reclassify them as younger reworked breccias or conglomerates.…”

“…Regional geological modelling of the Taupo-Reporoa Basin suggests that the Rotokawa Andesite complex is centred on the Rotokawa Geothermal Field, with limited lateral extent to both the north and south (Downs et al, 2014;Eastwood et al, 2013). The initial andesitic volcanism would have involved magmas migrating through faults and fractures to the surface >∼1.9 Ma, constructing a large volcano under Rotokawa, potentially centred along the western border of the Rotokawa Geothermal Field based on lateral variation in thickness of the andesite (Anderson, 2011;Browne et al, 1992;Chambefort et al, 2014).…”

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

“…Spera 1988b;Busby 2004Busby , 2012. Modern examples include the Cascades, where the volcanoes sit in a half graben (Williams and McBirney 1979;Mooney and Weaver 1989), the lowstanding Alaskan Peninsula (Burk 1965;Fliedner and Klemperer 2000) where volcanoes such as Augustine are partially submerged in Cook Inlet (Power et al 2010), the Kamchatka Peninsula of easternmost Russia where towering stratovolcanoes sit in huge faultbounded troughs (Erlich 1968(Erlich , 1979Levin et al 2002a, b), to New Zealand where the Taupo zone sector of the arc is actively extending as calderas and stratocones erupt within it (Houghton et al 1991;Harrison and White 2006;Downs et al 2014), and the Central American arc where volcanoes are aligned in a long linear depression (Williams et al 1964;Williams and McBirney 1969;Burkhart and Self 1985;MacKenzie et al 2008).…”