The basement morphology under Tongariro National Park, southern Taupo Volcanic Zone

Robertson, E. I.; Davey, F. J.

doi:10.1080/00288306.2018.1518247

Cited by 7 publications

(20 citation statements)

References 10 publications

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“…The low resistivity layer is interpreted by Ingham et al (2009) as alteration caused by the outflow of acidic hydrothermal fluids, while the surface resistive layer is interpreted as dry volcanic ash and lava. Gravity and magnetic studies of the Tongariro Volcanic Center (Miller & Williams-Jones, 2016;Robertson & Davey, 2018) place the nonmagnetic greywacke basement at an elevation of 0 to 500 m below sea level, although this is poorly constrained under Mt. Ruapehu.…”

Section: Geologic Background and Previous Geophysical Studiesmentioning

confidence: 99%

Three‐Dimensional Mapping of Mt. Ruapehu Volcano, New Zealand, From Aeromagnetic Data Inversion and Hyperspectral Imaging

et al. 2020

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Combining 3‐D inversion of high‐resolution aeromagnetic data with airborne hyperspectral imaging creates a new method to map buried structure and hydrothermal alteration, applied to Mt. Ruapehu volcano, New Zealand. Hyperspectral imaging is sensitive to surface mineralogy including alteration minerals, while magnetic vector inversion reveals the volumetric distribution of magnetic susceptibility from which we interpret buried geology. Probability assessment from multiple model regularizations provides an important model uncertainty estimate. At Ruapehu, hyperspectral imaging highlights two main regions of surface alteration: the Pinnacle Ridge and the southeast flanks. The magnetic model of Pinnacle Ridge shows that alteration seen at surface continues to depth, but strongly magnetic, unaltered dikes form the core of the ridge. On the southeast flanks, the magnetic model also shows alteration imaged on the surface continues to depth; however, a previously unknown, magnetized sill intrudes part of the flank. Several smaller demagnetized regions are modeled, unlike at neighboring Mt. Tongariro where the hydrothermal system created a large demagnetized core. We propose that these differences relate to spatially focused (Ruapehu) vs distributed (Tongariro) eruption vents, the degree of faulting of the edifice and its glaciation history. Lava‐ice interaction produces fine‐grained lavas with measured magnetic susceptibilities similar to some moderately altered lavas, illustrating that care must be taken in the interpretation of magnetic data in the absence of geological information. The combination of hyperspectral imaging and aeromagnetic data inversion distinguishes shallow surface weathering from deeper‐seated hydrothermally altered rock masses, with implications for the magnitude and probability of collapse events.

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Section: Geologic Background and Previous Geophysical Studiesmentioning

confidence: 99%

Three‐Dimensional Mapping of Mt. Ruapehu Volcano, New Zealand, From Aeromagnetic Data Inversion and Hyperspectral Imaging

et al. 2020

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“…Subsequent studies focussed on a range of topics, including the margins and basement of the TVZ (e.g. Modriniak and Studt 1959;Stern 1979Stern , 1985Stagpoole 1994;Villamor et al 2017;Robertson and Davey 2018), calderas (e.g. Rogan 1982;Hunt 1992;Wilson et al 1995;Davy and Caldwell 1998;Stratford and Stern 2008;Seebeck et al 2010;Soengkono 2011Soengkono , 2012, geothermal fields (e.g.…”

Section: Introductionmentioning

confidence: 99%

A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand

Stagpoole

Miller

Tontini

et al. 2020

New Zealand Journal of Geology and Geophysics

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The Taupō Volcanic Zone (TVZ) is characterised by a negative residual gravity anomaly that correlates with a zone of normal faulting, subsidence and voluminous silicic volcanism from c. 2 Ma. A steep gravity gradient is associated with downfaulting of the Mesozoic metasedimentary basement at its eastern and western margins, and all known calderas are associated with prominent local gravity lows. New Bouguer and residual gravity anomaly maps are presented that show improved detail over previous maps. The western margin of the TVZ shows as a series of parallel northeast-trending boundaries and northwest-trending step-over zones. The new map also reveals the complex boundaries of the Okataina caldera, and greater detail north of Taupō where gravity lows at Reporoa and Mihi form part of a larger and more extensive, elliptical low-gravity feature, suggesting that they may be separate collapse areas within a larger caldera complex. Around the margins of the TVZ, the Hauraki graben/rift and sedimentary basins at Hamilton, Waimiha, Galatea and Waiohau are also characterised by low residual gravity.

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“…is supported by gravity survey data that shows the volcanic base boundary at 750-850 m a.s.l. under Ngauruhoe (Robertson and Davey, 2018). This value is in general agreement with other geophysical studies.…”

Section: Total Edifice Volume Of Tongarirosupporting

confidence: 92%

“…that separates Tertiary (probably Miocene) sediments and overlying mixed volcanic deposits, in the saddle between Tongariro and Ruapehu. Other gravity survey data presented by Miller and Williams-Jones (2016) show an average density of 2300 kg/m 3 , which corresponds to Miocene sediments (Robertson and Davey, 2018), occurs at ~750 m a.s.l. If alternative datum elevations are used for computing the total edifice volume, the results are 101 km 3 (for 700 m a.s.l.)…”

Section: Total Edifice Volume Of Tongariromentioning

confidence: 81%

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The volcanic and magmatic evolution of Tongariro volcano, New Zealand

Pure¹

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<p>Detailed mapping studies of Quaternary stratovolcanoes provide critical frameworks for examining the long-term evolution of magmatic systems and volcanic behaviour. For stratovolcanoes that have experienced glaciation, edifice-forming products also act as climate-proxies from which ice thicknesses can be inferred at specific points in time. One such volcano is Tongariro, which is located in the southern Taupō Volcanic Zone of New Zealand’s North Island. This study presents the results of new detailed mapping, geochronological and geochemical investigations on edifice-forming materials to reconstruct Tongariro’s volcanic and magmatic history which address the following questions: (1) Does ice coverage on stratovolcanoes influence eruptive rates and behaviour (or record completeness)? (2) What is the relationship between magmatism, its expression (i.e. volcanism) and external but related processes such as tectonics? (3) How are intermediate-composition magmas assembled and what controls their diversity? (4) What are the relative proportions of mantle-derived and crust-derived materials in intermediate composition arc magmas? (5) Do genetic relationships exist between andesite and rhyolite magmas in arc settings? Samples from 250 new field localities in under-examined areas of Tongariro were analysed for major oxide, trace element and Sr-Nd-Pb isotope compositions. Analyses were performed on whole-rock, groundmass and xenolith samples. The stratigraphic framework for these geochemical data was established from field observations and 29 new 40Ar/39Ar age determinations, which were synthesised with volume estimates and petrographic observations for all Tongariro map units. Mapping results divide Tongariro into 36 distinct map units (at their greatest level of subdivision) which were organised into formations and constituent members. New 40Ar/39Ar age determinations reveal continuous eruptive activity at Tongariro from at least 230 ka to present, including during glacial periods. This adds to the discovery of an inlier of old basaltic-andesite (512 ± 59 ka) on Tongariro’s NW sector that has an unclear source vent. Hornblende-phyric andesite boulders, mapped into the Tupuna Formation (new), yield the oldest 40Ar/39Ar age determination (304 ± 11 ka) for materials confidently attributed to Tongariro. Tupuna Formation andesites are correlated with Turakina Formation debris flows that were deposited between 349 to 309 ka in the Wanganui Basin, ~100 km south of Tongariro, which indicates that Ruapehu did not exist at this time, at least not in its current form. Tongariro has a total edifice volume of ~90 km3, 19 km3 of which is represented by exposed mapped units. The total ringplain volume immediately adjacent to Tongariro contains ~60 km3 of material. The volume of exposed glacial deposits are no more than 1 km3. During periods of major ice coverage, edifice-building rates on Tongariro were only 17-21 % of edifice-building rates during warmer climatic periods. Because shifts in edifice-building rates do not coincide with changes in erupted compositions, differences in edifice-building rates reflect a preservation bias. Materials erupted during glacial periods were emplaced onto ice masses and conveyed to the ringplain as debris, which explains reduced preservation rates at these times. MgO concentrations in Tongariro stratigraphic units with ages between 230 and 0 ka display successive and irregular cyclicity that occurs over ~10-70 kyr intervals, which reflect episodes of enhanced mafic magma replenishment. During these cycles, more rapid (≤10 kyr) increases in MgO concentrations to ≥5-9 wt% are followed by gradual declines to ~2-5 wt%, with maxima at ~230, ~160, ~117, ~88, ~56, ~35, ~17.5 ka and during the Holocene. Contemporaneous variations in Tongariro and Ruapehu magma compositions (e.g. MgO, Rb/Sr, Sr-Nd-Pb isotope ratios) for the 200-0 ka period coincide with reported zircon growth model-ages in Taupō magmas. This contemporaneity reflects regional tectonic processes that have externally regulated and synchronised the timings of elevated mafic replenishment episodes versus periods of prolonged crustal residence at each of these volcanoes. Isotopic Sr-Nd-Pb data from metasedimentary xenoliths, groundmass separates and whole-rock samples indicate that two or three separate metasedimentary terranes (in the upper 15 km of the crust) were assimilated into Tongariro magmas. These are the Kaweka terrane and the Waipapa or Pahau terranes (or both). Subhorizontal juxtapositioning of these terranes is indicated by the coexistence of multiple terranes in the same eruptive units. Paired whole-rock and groundmass (interstitial melt) samples have effectively equal Sr-Nd-Pb isotope ratios for the complete range of Tongariro compositions. Despite intra-crystal isotopic heterogeneities that are likely widespread, the new data show that crystal fractionation and assimilation occur in approximately equal balance for essentially all Tongariro eruptives. Assimilated country rock accounts for 22-31 wt% of the average Tongariro magma. Initial evolution from a Kakuki basalt-type to a Tongariro Te Rongo Member basaltic-andesite reflects the addition of 17 % assimilated metasedimentary basement with a mass assimilation rate/mass crystal fractionation rate ratio—a.k.a. ‘r value’ of 1.8-3.5. Subsequent evolution from a Te Rongo Member basaltic-andesite to other Tongariro eruptive compositions represents 5-14 % more assimilated crust (r values of ~0.1-1.0). Magma evolution from high (>1) to lower (0.1-1.0) r values can explain the dearth of andesitic melt inclusions in (bulk) andesite magmas observed globally. High relative assimilation rates characterise rapid evolution from basalt to basaltic-andesite bulk compositions which contain andesitic interstitial melts. Thus, andesitic melt inclusions have a reduced chance of being preserved in crystals which can explain their low representation in global datasets.</p>

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The basement morphology under Tongariro National Park, southern Taupo Volcanic Zone

Cited by 7 publications

References 10 publications

Three‐Dimensional Mapping of Mt. Ruapehu Volcano, New Zealand, From Aeromagnetic Data Inversion and Hyperspectral Imaging

Three‐Dimensional Mapping of Mt. Ruapehu Volcano, New Zealand, From Aeromagnetic Data Inversion and Hyperspectral Imaging

A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand

The volcanic and magmatic evolution of Tongariro volcano, New Zealand

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