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. 2017 Jan 25:7:40624.
doi: 10.1038/srep40624.

Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz

David A Budd  1 , Valentin R Troll  1   2 , Frances M Deegan  1   3 , Ester M Jolis  1 , Victoria C Smith  4 , Martin J Whitehouse  3 , Chris Harris  5 , Carmela Freda  2 , David R Hilton  6 , Sæmundur A Halldórsson  6   7 , Ilya N Bindeman  8
Affiliations

Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz

David A Budd et al. Sci Rep. .

Abstract

Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ18O values. Overall, Toba quartz crystals exhibit comparatively high δ18O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ18O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum ∆core-rim = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ18O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ18O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.

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Figures

Figure 1
Figure 1. Location of study area.
Map of northern Sumatra (adapted from GeoMapApp; www.geomapapp.org). The red ellipse designates the crustal swell of the Batak Tumor, upon which the Toba caldera sits (in blue). The topographic swell is believed to result from upward pressure from the buoyant Toba magma system. Yellow stars indicate sampling sites. Inset: Map of western Indonesia, with Toba volcano marked as white star (modified after ref. 62).
Figure 2
Figure 2. Textural and oxygen isotopic zoning in YTT zircon.
Cathodoluminescence (CL) images of YTT zircons are shown with associated Secondary Ionisation Mass Spectrometry (SIMS) δ18O analysis spots. The data reveal a complex system with variable δ18O inputs. Notably, analyses are limited to two to three SIMS spots per crystal due to the relatively small crystal size of zircon. Error bars = 1σ and white scale bars = 50 μm. Data from ref. .
Figure 3
Figure 3. δ18O magma values for Toba.
The δ18O quartz data are converted to equilibrium magma values assuming Δ18Oquartz-rhyolite = 0.5‰ at a temperature interval of 750–780 °C (ref. 31). SIMS zircon data are converted to magma values using the fractionation factor of ref. and are then compared with LF crystal data (this study), conventional fluorination crystal data (CF; ref. 32), and available zircon SIMS data from ref. . The grey bar marks the δ18O value of a typical Sunda arc mantle-type basalt composition (MORB or I-MORB), and the blue bar denotes the highest δ18O values that can be obtained by closed-system crystal fractionation from a Sunda arc basaltic parent magma. The orange bars denote the δ18O values of the crustal materials in the region. Our new quartz data overlap with the published zircon and quartz data from the YTT, but additionally document isotopic excursions towards both higher and lower δ18O values than previously reported. Abbreviations in figure: CF, Conventional Fluorination; LF, Laser Fluorination; MORB, Mid-Ocean Ridge Basalt; SIMS, Secondary Ionisation Mass Spectrometry.
Figure 4
Figure 4. CL images and measured SIMS δ18O traverses across selected quartz crystals from the YTT.
Grey shading on the Cathodoluminescence (CL) images defines distinct textural and compositional domains. Numbered red squares on the CL images correspond to analysis spots on the inset δ18O plots. Insets: Grey shading on graphs indicates textural domains and horizontal red bars indicate individual δ18O zone averages. Orange bars indicate high- and low-δ18Oquartz from basement granitoids of the Toba region. Error bars = 1σ. Crystals (a–f) (part 1) display an overall core to rim decrease in δ18O values, while crystals (g–o) (part 2) show no significant core to rim variation in δ18O value. Individual analysis points that deviate from the crystal average in (g–o) are considered outliers, and are potentially due to small inclusions of foreign material in the analysis.
Figure 5
Figure 5. Magma diversification at Toba.
(a) Summary figure of whole rock and mineral δ18O values. MORB value is given as 5.7 ± 0.2‰ (ref. 64) and the sedimentary range is from 9 to 28.5‰ (refs 36, 65). Assimilation of crustal material (S-type granites, paragneisses or sediments) will increase δ18O values, whilst assimilation of high-temperature altered material will lower δ18O values. The Toba data are overall strongly displaced towards high-δ18O crustal values. (b) Binary mixing relationship between average YTT quartz core δ18Omagma (SIMS) value (n = 78) and a high silica hydrothermally-altered contaminant with δ18O = 0‰ (assumed value as a result of high-temperature alteration, cf. refs , and 31). Approximately 25% mixing and assimilation with a low-δ18O component is required to bring the average core δ18O values (representing the ambient magma) to the lowest measured quartz rim value, reflecting a mixture of ambient magma and low-δ18O material for those portions of the YTT system that crystallised the low δ18O quartz rims. Binary mixing calculation of ambient YTT rhyolite with a basalt replenishment is provided in Supplementary Figure 1.
Figure 6
Figure 6. Conceptual sketch of quartz isotope stratigraphy and magma reservoir dynamics.
(a) The variations recorded in quartz crystal chemistry demonstrate the utility of crystal oxygen isotope stratigraphy to fingerprint silicic magma evolution at high spatial resolution. (b) The results of this study are interpreted to reflect uptake of a high δ18O component from the crust before quartz saturation and consequent crystallisation (Stage 1), and subsequent assimilation of low-δ18O roof materials by the YTT magma (Stage 2) during the final period of caldera unrest prior to the cataclysmic YTT eruption. This stage may have lasted several hundred years. Note that the timing of Stage 1 is less certain, and if the highest δ18O quartz cores represent xenocrystals derived from the crust then the high δ18O component could have been introduced tens of thousands of years before the YTT eruption (see text for details).
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References

    1. Davidson J. P., Hora J. M., Garrison J. M. & Dungan M. A. Crustal forensics in arc magmas. J. Volcanol. Geotherm. Res. 140, 157–170 (2005).
    1. Valley J. W. & Kita N. T. In situ oxygen isotope geochemistry by ion microprobe. Mineral. Assoc. Canada Short Course 19–63 (2009).
    1. Valley J. W. et al.. Nano- and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. Am. Mineral. 100 (2015).
    1. Valley J. W. Oxygen Isotopes in Zircon. Rev. Mineral. Geochemistry 53, 343–385 (2003).
    1. Ferry J. M., Kitajima K., Strickland A. & Valley J. W. Ion microprobe survey of the grain-scale oxygen isotope geochemistry of minerals in metamorphic rocks. Geochim. Cosmochim. Acta 144, 403–433 (2014).

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