Chemical and isotopic changes induced by pyrometamorphism in metasedimentary xenoliths at Tongariro volcano, New Zealand

Pure, Leo R.; Charlier, B. L.; Wilson, C. J. N.; Gamble, J. A.; Vry, J. K.; Townsend, Dougal; Leonard, Graham S.

doi:10.1016/j.lithos.2021.106404

Cited by 5 publications

(23 citation statements)

References 67 publications

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“…To explain these outstanding issues, such as the differences in Pb isotopic ratios between the whole-rock and the melt phase (Figure 3.30), a second late-stage assimilant is also considered ). This assimilant likely represents a partial contribution from a Torlesselike metasedimentary xenolith, similar to that analysed (in post-assimilation form) by Pure et al (2021). While it would be thermodynamically difficult to melt such a lithology into a cooler, more silicic rhyolite melt, partial melting and assimilation of more fusible phases within these rocks, such as feldspar or biotite, may be possible.…”

Section: Assimilation Of a Metasedimentary-like Contaminantmentioning

confidence: 55%

“…While some Whakatāne 1 melt analyses lie on a 206 Pb/ 204 Pb-208 Pb/ 204 Pb mixing line between one such remnant metasedimentary xenolith and one of the modelled plutonic fragments (Brown et al 1998b;Pure et al 2021;Figure 3.30b), most record Pb isotopic compositions intermediate between the plutonic and Whakatāne 1 whole-rock compositions, and many of the other metasedimentary xenoliths, with seemingly similar trends (Pure et al 2021;Figure 3.30b). This indicates that some influence on the melt isotopic signatures by a metasedimentary lithology is plausible, even if the exact composition or amount of assimilation from such a contaminant cannot be exactly quantified from the data available.…”

Section: Assimilation Of a Metasedimentary-like Contaminantmentioning

confidence: 88%

“…As with the metasedimentary terrane greywackes and basaltic eruptives, these components vary widely in their isotopic signatures. 18.809-18.886 (Graham and Hackett 1987;Graham et al , 1990Sutton 1995;Cole et al 2001;Price et al 2005Price et al , 2010Price et al , 2012Waight et al 2017;Pure et al 2021;Figure 3.19). Plutonic fragments span the full range of compositions from gabbros to granites (e.g.…”

Section: Compositional End-members In the Tvzmentioning

confidence: 99%

“…McCormack et al 2009; shows that TVZ rhyolites can contain evidence for a mixture of all three metasediments in their petrogenesis, and xenoliths of both Torlesse and Waipapa have been co-erupted with the various TVZ magmas (e.g. Pure et al 2021). Even where one type of assimilant is assumed, it is known that the composition of each terrane is highly variable (e.g.…”

Section: Current Petrogenetic Models For Tvz Rhyolitesmentioning

confidence: 99%

“…for both the rhyolite and potential assimilants (Bowyer 2001;Price et al 2015;Rocco 2020;Pure et al 2021;Sas et al 2021) and modal mineralogies (Smith et al 2006) to investigate these processes using Whakatāne 1 as a case study. This magma was chosen because:…”

Section: Late-stage Contamination Of Young ōKataina Rhyolite Melts -A...mentioning

confidence: 99%

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Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

Elms¹

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This thesis investigates the magmatic processes that operated at Ōkataina volcanic centre prior to and during the rhyolitic events of its most recent eruption sequence, the Rotorua Subgroup (erupted since 25.4 ka), with a specific focus on timescales of human interest. Further context is derived with data from the 52.8 ka Rotoiti (caldera-forming) and Earthquake Flat eruptions, and selected Mangaone Subgroup events that occurred between the 52.8 and 25.4 ka. The regular occurrence of these events provides regular snapshots of the magmatic system over this time period. Whole-rock, glass, and mineral compositional data and timescales modelled from diffusion gradients are compared within geographical and physical volcanological contexts. These data provide a picture of the recent evolution of Ōkataina, shedding light on how quickly the volcano could awaken from its current dormancy to produce a new rhyolitic event, and what that event might be like. Geochemical data from Mangaone Subgroup eruptives show that the post-caldera magmatic system recovered over c. 27 kyr, with increasingly evolved and radiogenic compositions erupted during these events. The post-25.4 ka Rotorua Subgroup shows a more steady evolution, trending towards less radiogenic products towards the present day. Modern Ōkataina comprises three vent clusters, the intra-caldera Mt. Tarawera (formed by the 21.9 ka Ōkareka, 17.5 ka Rerewhakaaitu, 14 ka Waiohau and 1314 AD Kaharoa eruptive episodes) and Haroharo Massif (the 25.2 ka Te Rere, 9.4 ka Rotomā, 7.9 ka Mamaku and 5.5 ka Whakatāne), and the Ōkareka Embayment (the 25.2 ka Te Rere, 15.6 ka Rotorua) on the western edge of the caldera. Most eruptions were geochemically complex, with multiple magmas, some of which were repeated between eruptions. Variations in whole-rock and glass geochemistry are controlled by both the dominant mineral assemblage and external inputs, and relate to the geographical region and timing of when each magma erupted. Each vent region shows evidence for distinct features in its shallower magmatism (i.e. that producing the final-erupted magma compositions), super-imposed on temporal trends controlled by the deeper system. This deeper system beneath Haroharo and Tarawera appears to be more unitary or inter-connected. However, the Ōkareka Embayment is unique in that it appears to involve multiple magmatic systems. Back-scattered electron imaging of orthopyroxenes from the Rotorua, Waiohau and Whakatāne eruptives (and selected plagioclase from the Rotorua), coupled with major-element analyses of the orthopyroxenes, imply that open-system processes are common at Ōkataina, at least in the early stages of eruptible magma body assembly. These processes are reflected in diverse core compositions and complex zonation patterns, narrowing to more uniform rims that are in equilibrium with the compositions of the host melts. Not all cores are in equilibrium with the associated whole-rock compositions, but are in equilibrium with whole-rock compositions from other magmas erupted nearby, further demonstrating open-system crystal exchange and the repeated tapping of some magma sources from one event to another. Melt segregation and magma body assembly takes place over decades up to a century or two, with magma residence times on the order of centuries to millennia, or (if prematurely triggered) as short as months. Priming or triggering events such as heating by basaltic injection (common in the Ōkataina rhyolite eruptions) occur over decades prior to eruption. Quartz-hosted, sealed melt inclusions preserve volatile contents of c. 3-6 wt% H2O and c. 15-125 ppm CO2, with values tending to decrease in younger eruptions, although Waiohau samples have relatively low H2O, and the Rotorua samples have relatively low CO2. Overall, the Ōkataina eruptives have remarkably low CO2 contents compared with international datasets. There are weak correlations between H2O and CO2 contents coexisting in magmas within individual vent regions, but little system-wide coherence due to each region having differing trends (a step-wise drop at Tarawera versus a steady decrease in the young Haroharo eruptions). Scatter in data from sealed melt inclusions, and relatively lower H2O contents in open-ended inclusions (embayments) indicate pre-eruptive volatile losses, driven by crystallisation and/or open-system degassing. The H2O contents of the inner parts of embayments suggest an initial slow decompression at the start of the final magma ascent may also play a minor role. Magma ascent rates are low to moderate (0.1-4.4 m.s-1), with the Ōkareka Embayment eruptives having notably faster ascent rates than those from Tarawera or Haroharo. Both the sealed melt inclusion volatile contents and derived magma ascent rates are similar to those observed or inferred from other silicic eruptions worldwide and are notably comparable to those of super-eruptions, indicating that magma volume and overpressure do not influence ascent rate at eruption onset. Current geophysical observations suggest that a viable magma source currently exists under the southwestern end of Haroharo, and that basaltic diking activity is ongoing in the Ōkataina area. While basaltic eruptions can occur with little warning (e.g. Tarawera, 1886 CE), it is more likely that a future Ōkataina event will be prolonged and rhyolitic. The volcano can rejuvenate into an eruption-ready state within human lifetimes (i.e. decades), and final pre-eruptive warnings from geophysical monitoring could be as short as only a few hours. A new rhyolitic episode could have major impacts, lasting several years and involving both voluminous lavas and widespread fall deposition.

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Section: Assimilation Of a Metasedimentary-like Contaminantmentioning

confidence: 55%

Section: Assimilation Of a Metasedimentary-like Contaminantmentioning

confidence: 88%

Section: Compositional End-members In the Tvzmentioning

confidence: 99%

Section: Current Petrogenetic Models For Tvz Rhyolitesmentioning

confidence: 99%

Section: Late-stage Contamination Of Young ōKataina Rhyolite Melts -A...mentioning

confidence: 99%

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Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

Elms¹

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The compositional diversity and temporal evolution of an active andesitic arc stratovolcano: Tongariro, Taupō Volcanic Zone, New Zealand

Pure

Wilson

Charlier

et al. 2023

Contrib Mineral Petrol

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New geochemical data, including Sr–Nd–Pb isotopes for whole-rock and groundmass samples, are reported for edifice-forming eruptives at Tongariro volcano, New Zealand, which span its ~ 350 ka to late Holocene history. Tongariro eruptives are medium-K basaltic-andesites to dacites (53.0–66.2 wt% SiO2) that evolved via assimilation-fractional crystallisation (AFC) processes partly or mostly in the uppermost 15 km of the crust. When ordered chronologically using a high-resolution 40Ar/39Ar-dated eruptive stratigraphy, the compositional data show systematic 10–130 kyr cycles. Mafic replenishment events inferred from MgO values occurred at ~ 230, ~ 151, ~ 88 and ~ 56 ka and in the late Holocene, with high-MgO flank vents erupting at ~ 160, ~ 117, ~ 35 and ~ 17.5 ka. Cycles in Sm/Nd, 87Sr/86Sr, 143Nd/144Nd and Pb isotopic ratios, which are decoupled from MgO, K2O and Rb/Sr cycles, indicate periods of prolonged crustal residence of magmas from ~ 230 to ~ 100 ka and ~ 95 to ~ 30 ka. AFC modelling shows that intermediate and silicic melt compositions, with r-values between 0.1 and 1, are needed to reproduce Tongariro compositional arrays. AFC models also indicate that ~ 20% of the average Tongariro magma comprises assimilated (meta)sedimentary basement material. Locally, Tongariro and adjacent Ruapehu volcanoes attain their most crust-like 87Sr/86Sr and 143Nd/144Nd compositions at ~ 100 and ~ 30 ka, paralleling with zircon model-age crystallisation modes at the rhyolitic Taupō volcano ~ 50 km to the NNE. These coincidences suggest that the timing and tempo of magma assembly processes at all three volcanoes were contemporaneous and may have been tectonically influenced since at least 200 ka.

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Crustal basement terranes under the Taupō Volcanic Zone, New Zealand: Context for hydrothermal and magmatic processes

Mortimer

Charlier

Rooyakkers

et al. 2023

Journal of Volcanology and Geothermal Research

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Chemical and isotopic changes induced by pyrometamorphism in metasedimentary xenoliths at Tongariro volcano, New Zealand

Cited by 5 publications

References 67 publications

Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

The compositional diversity and temporal evolution of an active andesitic arc stratovolcano: Tongariro, Taupō Volcanic Zone, New Zealand

Crustal basement terranes under the Taupō Volcanic Zone, New Zealand: Context for hydrothermal and magmatic processes

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