Heterogeneity of volatile sources along the Halmahera arc, Indonesia

https://doi.org/10.1016/j.jvolgeores.2021.107342Get rights and content

Highlights

  • Arc-scale degassing budget of the Halmahera arc.

  • High fluid flux into the mantle wedge.

  • Sediment contribution into the magma source.

  • Increasing sediment contribution along the arc.

  • Evolution of magma genesis.

Abstract

The parallel Halmahera and Sangihe arcs in eastern Indonesia are sites of active arc-arc collision of considerable interest in developing understanding of the geodynamics and geochemistry of subduction zones. Owing to the comparative remoteness of the region, few ground-based studies of the volcanoes have been undertaken. Here, we report and integrate gas measurements and (isotope) geochemical analyses of lava samples for Dukono, Ibu, Gamkonora, Gamalama, and Makian volcanoes of the Halmahera arc. Summing gas fluxes for all five volcanoes indicates arc-scale emission budgets for H2O, CO2, SO2, H2S, and H2 of 96,300 ± 27,000, 2093 ± 450, 944 ± 400, 79 ± 20, and 15 ± 4 Mg/d, respectively. Dukono is the greatest source of SO2 and H2, while Ibu emits the most H2O and H2S. Both Gamalama and Ibu are significant CO2 sources. Dukono (farthest from the trench) releases the most CO2-poor gas. Geochemical and isotopic analyses of recent ejecta emphasize the role of high fluid fluxes in the mantle wedge, necessary for partial melting of depleted mantle. Pb, Nd, and Sr isotope ratios, combined with Ba/Nd, Zr/Nd, Ba/Th, and Zr/Nb ratios, provide evidence for compositional variability along the Halmahera arc, and indicate decreasing subducted sediment contribution from south (Makian, Gamalama) to north (Gamkonora, Ibu, Dukono). Additionally, fluids formed by dehydration of altered crust become prominent at the northern volcanoes. Isotopic and Ba/Nb ratios from the Neogene and Quaternary sources compared to the current magmas further emphasize the evolution of magma genesis since the Neogene.

Introduction

The Halmahera arc is situated in the northeastern part of Indonesia and extends in a roughly north-south direction between 3°N-1°S and 127°-128°E. It is the smallest of the four volcanic arcs that constitute the archipelago of Indonesia, with five active volcanoes, namely Dukono, Ibu, Gamkonora, Gamalama, and Makian (also known as Kie besi) from north to south (Fig. 1). Due to its comparative remoteness, difficulty of access and political, ethnic, and inter-faith unrest that persisted until the early 2000s (Goss, 2000; Bertrand, 2003), the Halmahera arc has been little studied, despite the fact that its volcanoes are among the most active in Indonesia. This situation is starting to be redressed with several recent studies highlighting the strong volcanic degassing source on Dukono (Carn et al., 2017; Bani et al., 2018), the fast-growing rate of Ibu lava dome since 1998 (Agustan et al., 2010; Saing et al., 2014), the magmatic signature of weak degassing at Gamkonora (Saing et al., 2020), and the interplay of hydrothermal, magmatic, and tectonic processes controlling recurrent eruptive activity of Gamalama volcano (Kunrat et al., 2020). Here, we report the first observations of gas compositions for Ibu volcano that, in combination with recently available data, enable an assessment of arc-scale gas emission budgets. We also highlight the compositional variability of magmas along the arc, based on analyses of recently erupted products.

Section snippets

Geodynamic setting and volcanic activity

The geodynamics of the Halmahera arc are intimately linked to the tectonic activity in the Molucca Sea, where the Sangihe forearc is overriding the Halmahera forearc (e.g., Hall and Wilson, 2000). The process constitutes a unique present-day example of an arc-to-arc collision arising from the double subduction of the Molucca Sea plate, which dips west beneath the Eurasian plate and east under the Philippine Sea plate (Fig. 1, Baker et al., 1994; Forde, 1997; Hall and Wilson, 2000; Zhang et al.,

Field measurements

SO2 flux measurements were made with passive ultraviolet spectrometers that scanned the plume from a fixed position and using the retrieval method of differential optical absorption spectroscopy (DOAS) (Fig. 2). Spectra were obtained with a variable step angle, depending on the plume size and the distance from the plume. The spectrometer used was an Ocean Optic USB2000+ with a spectral range of 290–440 nm and spectral resolution of 0.5 FWHM. The SO2 column amounts (ppm.m) were retrieved using

Arc degassing budget

Table 1 reports our SO2 flux estimates for Ibu volcano based on UV DOAS. Our new SO2 flux results for Ibu range between 50 and 140 Mg/d with a daily mean value of 105 Mg. This is an order of magnitude higher than the estimate reported by Saing et al. (2014) that corresponded to SO2 released by explosions only. Our new estimate integrates both passive and eruptive discharges, and as such may be considered more representative of Ibu's bulk plume flux of SO2 to the atmosphere.

Table 2 presents the

Arc-scale degassing budget

The volcanic emission budget from the Indonesia arcs has so far been estimated based on inferences and extrapolations (Andres and Kasgnoc, 1998; Halmer et al., 2002; Aiuppa et al., 2019; Fischer et al., 2019; Bani et al., 2020), because direct measurements are available for only a few volcanoes. The most extensive volcanic degassing inventory for the archipelago is that of Carn et al. (2017), which is based on satellite observations. However, it represents only 20 out of 78 volcanoes in

Conclusions

We have reported the first arc-scale gas emission budget for the Halmahera arc, indicating daily fluxes of the order of 96,300 Mg/d of H2O, 2093 Mg/d CO2, 944 Mg/d SO2, 79 Mg/d of H2S, and 15 Mg/d of H2. The main source of SO2 and H2 from the arc is Dukono, whereas Ibu releases the greatest quantities of H2O and H2S. Gamalama and Ibu are the main sources of CO2. Dukono, situated about 80 km from the trench, is a CO2-poor gas source compared with the other volcanoes, although hydrothermal

Credit authorship contribution statement

P. Bani: Conceptualization, Methodology, Investigation, Formal analysis, Writing original draft, Writting reviews & editing. F. Nauret: Conceptualization, Methodology, Formal analysis, Writting original draft. C. Oppenheimer: Methodology, Resources, Writting review & editing. A. Aiuppa: Methodology, Resources, Writting review & editing. B.U. Saing: Investigation. N. Haerani: Investigation. H. Alfianti: Investigation. M. Marlia: Investigation. V. Tsanev: Methology, Resources, Software.

Declaration of Competing Interest

None.

Acknowledgments

This research was supported by IRD under the JEAI-COMMISSION program in collaboration with CVGHM. It has also benefited from the “Science & Impact” program from the French Embassy in Indonesia. A.A. acknowledges funding from the DECADE Initiative of the Deep Carbon Observatory and from the MIUR (under grant PRIN2017-2017LMNLAW). We thank M. Benbakkar, C. Fonquernie, C. Boseg, D. Auclair, M. Gannoun, K. Suchorski and C. Liorzou for the lab. Support and rock analyses in the Laboratoire Magmas et

References (65)

  • A.W. Hofmann

    Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust

    Earth Planet. Sci. Lett.

    (1988)
  • S. Kunrat et al.

    First gas and thermal measurements at the frequently erupting Gamalama volcano (Indonesia) reveal a hydrothermally dominated magmatic system

    J. Volcanol. Geotherm. Res.

    (2020)
  • C. Oppenheimer et al.

    Pulsatory magma supply to a phonolite lava lake

    Earth Planet. Sci. Lett.

    (2009)
  • U.B. Saing et al.

    Ibu volcano, a center of spectacular dacite dome growth and long-term continuous eruptive discharges

    J. Volcanol. Geotherm. Res.

    (2014)
  • H. Shinohara

    A new technique to estimate volcanic gas composition: plume measurements with a portable multi-sensor system

    J. Volcanol. Geotherm. Res.

    (2005)
  • R.B. Symonds et al.

    Magmatic gas scrubbing: implications for volcano monitoring

    J. Volcanol. Geotherm. Res.

    (2001)
  • S. Turner et al.

    238U/230Th disequilibria, magma petrogenesis, and flux rates beneath the depleted Tonga-Kermadec island arc

    Geochim. Cosmochim. Acta

    (1997)
  • S. Voigt et al.

    The temperature dependence (203–293 K) of the absorption cross sections of O3 in the 230–850 nm region measured by Fourier-transform spectroscopy

    J. Photochem. Photobiol. A Chem.

    (2001)
  • W.M. White et al.

    High-precision analysis of Pb isotope ratios by multi-collector ICP-MS

    Chem. Geol.

    (2000)
  • C.-F. You et al.

    Trace element behavior in hydrothermal experiments: implications for fluid processes at shallow depths in subduction zones

    Earth Planet. Sci. Lett.

    (1996)
  • Kimata F. Agustan et al.

    Measuring ground deformation of the tropical volcano, Ibu, using ALOS-PALSAR data

    Rem. Sens. Lett.

    (2010)
  • A. Aiuppa et al.

    Chemical mapping of a fumarolic field: La Fossa Crater, Vulcano Island (Aeolian Islands, Italy)

    Geophys. Res. Lett.

    (2005)
  • A. Aiuppa et al.

    CO2 flux emissions from the Earth’s most actively degassing volcanoes, 2005–2015

    Sci. Rep.

    (2019)
  • R.J. Andres et al.

    A time-averaged inventory of subaerial volcanic sulfur emissions

    J. Geophys. Res.-Atmos.

    (1998)
  • Badan-Geologi

    Data Dasar Gunung Api, Wilaya Timur

  • S. Baker et al.

    Geology and jungle fieldwork in eastern Indonesia

    Geol. Today

    (1994)
  • P. Bani et al.

    Dukono, the predominant source of volcanic degassing in Indonesia, sustained by a depleted Indian-MORB

    Bull. Volcanol.

    (2018)
  • P. Bani et al.

    Elevated CO2 Emissions during Magmatic-Hydrothermal Degassing at Awu Volcano, Sangihe Arc, Indonesia

    Geosciences

    (2020)
  • J.A. Barrat et al.

    Determination of rare earth elements in sixteen silicate reference samples by icp-ms after tm addition and ion exchange separation

    Geostand. Newslett.

    (1996)
  • Conflict in Maluku

  • A. Buck

    New equations for computing vapor pressure and enhancement factor

    J. Appl. Meteorol. (1962–1982)

    (1981)
  • M. Burton et al.

    Magmatic gas composition reveals the source depth of slug-driven strombolian explosive activity

    Science

    (2007)
  • Cited by (4)

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