| 1. |
- Whitley, Sean, et al.
(författare)
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Crustal CO2 contribution to subduction zone degassing recorded through calc-silicate xenoliths in arc lavas
- 2019
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Interaction between magma and crustal carbonate at active arc volcanoes has recently been proposed as a source of atmospheric CO2, in addition to CO2 released from the mantle and subducted oceanic crust. However, quantitative constraints on efficiency and timing of these processes are poorly established. Here, we present the first in situ carbon and oxygen isotope data of texturally distinct calcite in calc-silicate xenoliths from arc volcanics in a case study from Merapi volcano (Indonesia). Textures and C-O isotopic data provide unique evidence for decarbonation, magma-fluid interaction, and the generation of carbonate melts. We report extremely light delta C-13(PDB) values down to -29.3%o which are among the lowest reported in magmatic systems so far. Combined with the general paucity of relict calcite, these extremely low values demonstrate highly efficient remobilisation of crustal CO2 over geologically short timescales of thousands of years or less. This rapid release of large volumes of crustal CO2 may impact global carbon cycling.
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| 2. |
- Whitley, Sean, et al.
(författare)
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Magmatic and Metasomatic Effects of Magma-Carbonate Interaction Recorded in Calc-silicate Xenoliths from Merapi Volcano (Indonesia)
- 2020
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Ingår i: Journal of Petrology. - : OXFORD UNIV PRESS. - 0022-3530 .- 1460-2415. ; 61:4
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Tidskriftsartikel (refereegranskat)abstract
- Magma-carbonate interaction is an increasingly recognized process occurring at active volcanoes worldwide, with implications for the magmatic evolution of the host volcanic systems, their eruptive behaviour, volcanic CO2 budgets, and economic mineralization. Abundant calc-silicate skarn xenoliths are found at Merapi volcano, Indonesia. We identify two distinct xenolith types: magmatic skarn xenoliths, which contain evidence of formation within the magma; and exoskarn xenoliths, which more likely represent fragments of crystalline metamorphosed wall rocks. The magmatic skarn xenoliths comprise distinct compositional and mineralogical zones with abundant Ca-enriched glass (up to 10 wt % relative to lava groundmass), mineralogically dominated by clinopyroxene (En(15-43)Fs(14-36)Wo(41-51)) + plagioclase (An(37-100)) +/- magnetite in the outer zones towards the lava contact, and by wollastonite +/- clinopyroxene (En(17-38)Fs(8-34)Wo(49-59)) +/- plagioclase (An(46-100)) +/- garnet (Gr(s0-65)Adr(24-75)Sc(h0-76)) +/- quartz in the xenolith cores. These zones are controlled by Ca transfer from the limestone protolith to the magma and by the transfer of magma-derived elements in the opposite direction. In contrast, the exoskarn xenoliths are unzoned and essentially glassfree, representing equilibration at sub-solidus conditions. The major mineral assemblage in the exoskarn xenoliths is wollastonite + garnet (Grs(73-97)Adr(3-24)) + Ca-Al-rich clinopyroxene (CaTs0-38) + anorthite +/- quartz, with variable amounts of either quartz or melilite (Geh(42-91)) + spinel. Thermobarometric calculations, fluid-inclusion microthermometry and newly calibrated oxybarometry based on Fe-3+/Sigma Fe in clinopyroxene indicate magmatic skarn xenolith formation conditions of similar to 850 +/- 45 degrees C, < 100 MPa and at an oxygen fugacity between the NNO (nickel-nickel oxide) and HM (hematite-magnetite) buffer. The exoskarn xenoliths, in turn, formed at 510-910 degrees C under oxygen-fugacity conditions between NNO and air. These high oxygen fugacities are likely imposed by the large volumes of CO2 liberated from the carbonate. Halogen- and sulphur-rich mineral phases in the xenoliths testify to infiltration by a magmatic brine. In some xenoliths, this is associated with the precipitation of copper-bearing mineral phases by sulphur dissociation into sulphide and sulphate, indicating potential mineralization in the skarn system below Merapi. The compositions of many xenolith clinopyroxene and plagioclase crystals overlap with that of magmatic minerals, suggesting that the crystal cargo in Merapi magmas may contain a larger proportion of skarn-derived xenocrysts than previously recognized. Assessment of xenolith formation timescales demonstrates that magma-carbonate interaction and associated CO2 release could affect eruption intensity, as recently suggested for Merapi and similar carbonate-hosted volcanoes elsewhere.
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| 3. |
- Blythe, Lara S., 1984-
(författare)
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Understanding Crustal Volatiles : Provenance, Processes and Implications
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge of the provenance of crustal volatiles and the processes by which they are released is extremely important for the dynamics of magmatic systems. Presented here are the results of multiple investigations, which aim to understand magmatic volatile contamination from contrasting but complementary perspectives. The main methodologies used include He and C isotope values and CO2/3He ratios of volcanic gases and fluids; simulation of magma-carbonate interaction using high-pressure high-temperature experimental petrology; X-ray microtomography of vesiculated xenoliths and computer modeling. Findings show that the contribution from upper crustal volatiles can be substantial, and is dependant on the upper crustal lithology on which a volcano lies, as well as the composition of the magma supplied. Carbonate dissolution in particular is strongly controlled by the viscosity of the host magma. The details of the breakdown of vesiculated xenoliths is complex but has wide reaching implications, ranging from the dissemination of crustally derived materials through a magma body to highlighting that crustal volatiles are largely unaccounted for in both individual volcano and global volatile budgets. In synthesizing the conclusions from each of the individual perspectives presented, I propose the contribution of volatiles from crustal sources to play a significant role in many geological systems. This volatile component should be taken into consideration in future research efforts.
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| 4. |
- Jeffery, Adam J., et al.
(författare)
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The pre-eruptive magma plumbing system of the 2007–2008 dome-forming eruption of Kelut volcano, East Java, Indonesia
- 2013
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 166:1, s. 275-308
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Tidskriftsartikel (refereegranskat)abstract
- Kelut volcano, East Java, is an active volcanic complex hosting a summit crater lake that has been the source of some of Indonesia’s most destructive lahars. In November 2007, an effusive eruption lasting approximately 7 months led to the formation of a 260-m-high and 400-m-wide lava dome that displaced most of the crater lake. The 2007–2008 Kelut dome comprises crystal-rich basaltic andesite with a texturally complex crystal cargo of strongly zoned and in part resorbed plagioclase (An47–94), orthopyroxene (En64–72, Fs24–32, Wo2–4), clinopyroxene (En40–48, Fs14–19, Wo34–46), Ti-magnetite (Usp16–34) and trace amounts of apatite, as well as ubiquitous glomerocrysts of varying magmatic mineral assemblages. In addition, the notable occurrence of magmatic and crustal xenoliths (meta-basalts, amphibole-bearing cumulates, and skarn-type calc-silicates and meta-volcaniclastic rocks) is a distinct feature of the dome. New petrographical, whole rock major and trace element data, mineral chemistry as well as oxygen isotope data for both whole rocks and minerals indicate a complex regime of magma-mixing, decompression-driven resorption, degassing and crystallisation and crustal assimilation within the Kelut plumbing system prior to extrusion of the dome. Detailed investigation of plagioclase textures alongside crystal size distribution analyses provide evidence for magma mixing as a major pre-eruptive process that blends multiple crystal cargoes together. Distinct magma storage zones are postulated, with a deeper zone at lower crustal levels or near the crust-mantle boundary (>15 km depth), a second zone at mid-crustal levels (~10 km depth) and several magma storage zones distributed throughout the uppermost crust (<10 km depth). Plagioclase-melt and amphibole hygrometry indicate magmatic H2O contents ranging from ~8.1 to 8.6 wt.% in the lower crustal system to ~1.5 to 3.3 wt.% in the mid to upper crust. Pyroxene and plagioclase δ18O values range from 5.4 to 6.7 ‰, and 6.5 to 7.6 ‰, respectively. A single whole rock analysis of the 2007–2008 dome lava gave a δ18O value of 7.6 ‰, whereas meta-basaltic and calc-silicate xenoliths are characterised by δ18O values of 6.2 and 10.3 ‰, respectively. Magmatic δ18O values calculated from individual pyroxene and plagioclase analyses range from 5.7 to 7.0 ‰, and 6.2 to 7.4 ‰, respectively. This range in O-isotopic compositions is explained by crystallisation of pyroxenes in the lower to mid-crust, where crustal contamination is either absent or masked by assimilation of material having similar δ18O values to the ascending melts. This population is mixed with isotopically distinct plagioclase and pyroxenes that crystallised from a more contaminated magma in the upper crustal system. Binary bulk mixing models suggest that shallow-level, recycled volcaniclastic sedimentary rocks together with calc-silicates and/or limestones are the most likely contaminants of the 2007–2008 Kelut magma, with the volcaniclastic sediments being dominant.
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| 5. |
- Satow, Chris, et al.
(författare)
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Eruptive activity of the Santorini Volcano controlled by sea-level rise and fall
- 2021
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 14:8, s. 586-592
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Tidskriftsartikel (refereegranskat)abstract
- Sea-level change is thought to influence the frequencies of volcanic eruptions on glacial to interglacial timescales. However, the underlying physical processes and their importance relative to other influences (for example, magma recharge rates) remain poorly understood. Here we compare an approximately 360-kyr-long record of effusive and explosive eruptions from the flooded caldera volcano at Santorini (Greece) with a high-resolution sea-level record spanning the last four glacial-interglacial cycles. Numerical modelling shows that when the sea level falls by 40 m below the present-day level, the induced tensile stresses in the roof of the magma chamber of Santorini trigger dyke injections. As the sea level continues to fall to -70 or -80 m, the induced tensile stress spreads throughout the roof so that some dykes reach the surface to feed eruptions. Similarly, the volcanic activity gradually disappears after the sea level rises above -40 m. Synchronizing Santorini's stratigraphy with the sea-level record using tephra layers in marine sediment cores shows that 208 out of 211 eruptions (both effusive and explosive) occurred during periods constrained by sea-level falls (below -40 m) and subsequent rises, suggesting a strong absolute sea-level control on the timing of eruptions on Santorini-a result that probably applies to many other volcanic islands around the world. Sea-level lowstands over the last 360,000 years strongly controlled the timing of eruptions of the Santorini Volcano, according to an analysis of tephras and sea-level records, as well as numerical modelling of the underlying magma chamber.
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