Stratigraphy, paleomagnetism, geochronology and structure of silicic volcanic rocks, Waiotapu/Paeroa range area, New Zealand

Grindley, G. W.; Mumme, T. C.; Kohn, B. P.

doi:10.1016/0375-6505(94)90014-0

Cited by 27 publications

(23 citation statements)

References 24 publications

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“…Although several age determinations have been achieved on the Paeroa Subgroup ignimbrites (Keall, 1988;Grindley et al, 1994;Houghton et al, 1995; this study), there is overlap in their associated analytical uncertainties. These ignimbrites, where exposed along the Paeroa fault scarp, show evidence for intermittent emplacement in the form of local deposition of co-ignimbrite ash, and some vitrophyric contacts that imply partial cooling of previously erupted units.…”

Section: Paeroa Subgroup Ignimbritesmentioning

confidence: 92%

Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand

Downs

Wilson

Cole

et al. 2014

Geological Society of America Bulletin

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We here explore the temporal and spatial relationships between the contrasting sources for two eruptive episodes that collectively represent the Whakamaru Group, the largest ignimbrite-forming sequence in the ~2 m.y. history of the Taupo Volcanic Zone in New Zealand. At 349 ± 4 ka (weighted mean at 2σ), the >1500 km 3 widespread Whakamaru Group ignimbrites and ~700 km 3 Rangitawa Tephra fallout were erupted in association with collapse of the 40 km long by 25 km wide rectilinear Whakamaru caldera. New 40 Ar/ 39 Ar age data presented here show that the co-magmatic >110 km 3 Paeroa Subgroup ignimbrites, previously included as part of the Whakamaru Group, are slightly younger and were erupted at 339 ± 5 ka (weighted mean at 2σ). New fi eld evidence also presented here demonstrates that the Paeroa Subgroup ignimbrites came from a source geographically separated from vents for the widespread Whakamaru Group ignimbrites. The presence of co-ignimbrite lag breccias, sizes of vent-derived lithic clasts, thicknesses of exposed and subsurface deposits, and morphologies of deposits imply that eruptions of the Paeroa Subgroup occurred from a linear source (the Paeroa linear vent zone), coinciding with the present-day northeast-striking Paeroa fault, and outside (northeast) of the earlier Whakamaru caldera collapse area. No separate caldera has been recognized, although three nearby areas may have undergone eruption-related subsidence. Residual magma from the Whakamaru or adjacent Kapenga caldera areas may have migrated toward the Paeroa linear vent zone during eruptive episodes, resulting in subsidence in either, or both, of these areas. Shallow plutons are also inferred to lie beneath near source fault blocks (Paeroa and Te Weta) on each side of the fault, and eruption-related subsidence may have been expressed as movement across the Paeroa fault and localized subsidence in the southern Paeroa fault block. Subsequent secular, rift-related displacement along the Paeroa fault has obscured the Paeroa linear vent zone.

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Section: Paeroa Subgroup Ignimbritesmentioning

confidence: 92%

Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand

Downs

Wilson

Cole

et al. 2014

Geological Society of America Bulletin

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“…Second, 40 Ar/ 39 Ar age dating of the Ohakuri and Mamaku deposits yields a best age estimate of 240 ± 10 ka (all errors are 1 SD) for their paired eruptions (Leonard 2003;Gravley et al 2006). Published fission-track ages on the Ohakuri Formation in Grindley et al (1994) of 250 ± 30 and 300 ± 30 ka (with a standard weighted mean age of 280 ± 30 ka) conflict with a 275 ± 10 ka 40Ar/39Ar age determination from the underlying Pokai ignimbrite (Leonard 2003) that is separated from the Mamaku/Ohakuri eruption products by a well-developed paleosol.…”

Section: Ohakuri Formation Summarised and Redefinedmentioning

confidence: 93%

“…The group includes tuffs, welded ignimbrites, dacite/andesite lavas, and some greywacke pebble conglomerate units that are elsewhere separately named Waikora Formation. However, revisions to the stratigraphy and subsequent age dating (Grindley et al 1994;Houghton et al 1995;Leonard 2003;Gravley 2004;Gravley et al 2006) of surface rocks correlated with the Ohakuri type locality has shown that it is wholly younger than the Whakamaru group ignimbrites. There is thus a dichotomy in use of the term Ohakuri: the type locality and its mapped surface deposits represent a wholly different suite of deposits from those labelled as Ohakuri Group in records from geothermal drillholes.…”

Section: Thlamentioning

confidence: 99%

“…Other rocks inferred to be >340 k.y. old are either given informal names where they consist of thick pyroclastic units (e.g., at Waiotapu; Grindley et al 1994), or at Wairakei, Ohaaki, Rotokawa, and Kawerau geothermal fields referred to as Waikora Formation. However, the term Waikora Formation as originally defined was restricted to pre-Whakamaru sedimentary units that were rich in rounded greywacke clasts (Grindley & Browne 1968; P. R. L. Browne pers.…”

Section: Alternative Names For Ohakuri Group Rocks In Geothermal Drilmentioning

confidence: 99%

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The nature and age of Ohakuri Formation and Ohakuri Group rocks in surface exposures and geothermal drillhole sequences in the central Taupo Volcanic Zone, New Zealand

Gravley¹,

Wilson

Rosenberg

et al. 2006

New Zealand Journal of Geology and Geophysics

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“…(1) Steepness of fault dips (Grindley 1959(Grindley , 1965Grindley et al 1994). (2) En echelon geometry of fault traces (Cochrane & Tianfeng 1983;Cole 1990), dikes, and fissures (Nairn & Cole 1981;Nairn 1981).…”

Section: Extension In the Taupo Volcanic Zonementioning

confidence: 99%

Extensional fault kinematics within the Taupo Volcanic Zone, New Zealand: Soft‐linked segmentation of a continental rift system

Rowland

Sibson

2001

New Zealand Journal of Geology and Geophysics

150

130

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The Taupo Volcanic Zone (TVZ) is a young (<2 Ma) arc-backarc system in continental crust at the southern end of the Havre Trough characterised by intense volcanism and geothermal activity. An extensional fault belt (known locally as the Taupo Fault Belt) can be traced semicontinuously within the TVZ from Ruapehu in the southwest to the Bay of Plenty coast in the northeast. Contained within the belt are numerous active volcanic centres (andesitic, basaltic, rhyolitic) and geothermal systems. Kinematic studies demonstrate that normal faulting predominates within the fault belt, which we interpret as a distributed rift system (here termed the Ruaumoko Rift System), within which rift axes are locally defined by crudely symmetric dispositions of northwest-and southeast-dipping faults. The entire fault belt is partitioned along-strike into offset rift segments defined by association with discrete rift axes. Fault dips, where measurable, are generally steep (8 > 60°). Systematic fracture sets occur in all rock types in the TVZ and generally show a strong northeast-southwest trend, indicating a component of extensional strain distributed throughout the rock mass. Extension is predominantly orthogonal to the rift axes except in "accommodation zones" where interaction between offset rifting segments perturbs the stress field, locally enhancing permeability. The varying trends of extensional structures lie perpendicular to least principal stress trajectories in a locally heterogeneous stress field with normal dip-slip as the predominant fault mechanism.

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Stratigraphy, paleomagnetism, geochronology and structure of silicic volcanic rocks, Waiotapu/Paeroa range area, New Zealand

Cited by 27 publications

References 24 publications

Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand

Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand

The nature and age of Ohakuri Formation and Ohakuri Group rocks in surface exposures and geothermal drillhole sequences in the central Taupo Volcanic Zone, New Zealand

Extensional fault kinematics within the Taupo Volcanic Zone, New Zealand: Soft‐linked segmentation of a continental rift system

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