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Department of Earth Sciences, Durham University,
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- PublicationOpen AccessStrontium isotope systematics of experimentally produced melts: understanding magma-carbonate interaction at Merapi volcano, Indonesia(2009-06-21)
; ; ; ; ; ; ; ;DEEGAN, F.M.; Uppsala University, Uppsala, Sweden ;TROLL, V.R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;FREDA, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;MCLEOD, C.; Durham University, Durham, United Kingdom ;MALARKEY, J.; Durham University, Durham, United Kingdom ;DAVIDSON, J.P.; Durham University, Durham, United Kingdom ;CHADWICK, J.P.; Vrije Universiteit, Amsterdam, Netherlands; ; ; ; ; ; There is considerable evidence for ongoing, late-stage interaction between the magmatic system at Merapi volcano, Indonesia, and local crustal carbonate. In order to resolve the interaction processes in detail, we have performed a series of time-variable carbonate dissolution experiments in silicate melt using Merapi basaltic-andesite and local limestone as starting materials, at magmatic pressure and temperature. Major element profiling of the experimental products has identified strongly contrasting compositional domains of glass: a Ca-enriched zone containing up to 36 wt% CaO, and an unaffected, Ca-normal zone containing 8 to 10 wt% CaO. To investigate the systematics of strontium isotopes and trace elements (TE) during carbonate assimilation, we have used micro-sampling and high-precision analytical techniques to measure 87Sr/86Sr ratios and TE concentrations over the magma-carbonate and intra-melt interfaces in two of our experimental products. The isotope variation between the different glass compositions is distinct, with 87Sr/86Sr ranging from 0.705641 in the Ca-normal glass to 0.706532 in the Ca-enriched glass. The upper end of this range is considerably more radiogenic than the range reported for Merapi whole rock volcanic products (0.70501 to 0.70583, Gertisser & Keller, 2003 J Pet, 44, 457-489). Our data hence support a model of assimilation of crustal carbonate with highly radiogenic 87Sr/86Sr (0.708799) at Merapi volcano. Given that the starting materials used in the experiments have markedly distinct 87Sr/86Sr values we here present new and detailed insights about the behaviour of Sr isotopes during carbonate assimilation, with a focus on the processes that operate across the carbonate-melt interface and the intra-melt transitions. Strontium is a reliable tracer of magma-crust interaction and so we anticipate that our results will significantly help to quantify our comprehension of magma-carbonate interaction processes occurring at Merapi volcano.142 87 - PublicationRestrictedExperimental simulation of magma–carbonate interaction beneath Mt. Vesuvius, Italy(2013)
; ; ; ; ; ; ; ;Jolis, E. M.; Department of Earth Sciences, CEMPEG, Uppsala University ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Troll, V. R.; Department of Earth Sciences, CEMPEG, Uppsala University ;Deegan, F. M.; Department of Geosciences, Swedish Museum of Natural History ;Blythe, L. S.; Department of Earth Sciences, CEMPEG, Uppsala University, ;McLeod, C. L.; Department of Earth Sciences, Durham University, ;Davidson, J. P.; Department of Earth Sciences, Durham University,; ; ; ; ; ; We simulated the process of magma–carbonate interaction beneath Mt. Vesuvius in short duration piston-cylinder experiments under controlled magmatic conditions (from 0 to 300 s at 0.5 GPa and 1,200 C), using a Vesuvius shoshonite composition and upper crustal limestone and dolostone as starting materials. Backscattered electron images and chemical analysis (major and trace elements and Sr isotopes) of sequential experimental products allow us to identify the textural and chemical evolution of carbonated products during the assimilation process. We demonstrate that melt–carbonate interaction can be extremely fast (minutes), and results in dynamic contamination of the host melt with respect to Ca, Mg and87Sr/86Sr, coupled with intense CO2 vesiculation at the melt–carbonate interface. Binary mixing between carbon- ate and uncontaminated melt cannot explain the geochemical variations of the experimental charges in full and convection and diffusion likely also operated in the charges. Physical mixing and mingling driven by exsolving volatiles seems to be a key process to promote melt homogenisation. Our results reinforce hypotheses that magma–carbonate interaction is a relevant and ongoing process at Mt. Vesuvius and one that may operate not only on a geological, but on a human timescale.228 31 - PublicationOpen AccessMagma-Carbonate Interaction Processes and Associated CO2 Release at MerapiVolcano, Indonesia: Insights from Experimental Petrology(2010-02-25)
; ; ; ; ; ; ; ;Deegan, F. M.; DEPARTMENT OF EARTH SCIENCES, UPPSALA UNIVERSITY, VILLAVAGEN 16, 75236 UPPSALA, SWEDEN ;Troll, V. R.; DEPARTMENT OF EARTH SCIENCES, UPPSALA UNIVERSITY, VILLAVAGEN 16, 75236 UPPSALA, SWEDEN ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Misiti, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Chadwick, J. P.; DEPARTMENT OF PETROLOGY (FALW), VRIJE UNIVERSITEIT, 1081 HV AMSTERDAM, THE NETHERLANDS ;McLeod, C. L.; DEPARTMENT OF EARTH SCIENCES, THE UNIVERSITY OF DURHAM, DURHAM DH1 3LE, UK ;Davidson, J. P.; DEPARTMENT OF EARTH SCIENCES, THE UNIVERSITY OF DURHAM, DURHAM DH1 3LE, UK; ; ; ; ; ; There is considerable evidence for continuing, late-stage interaction between the magmatic system at Merapi volcano, Indonesia, and local crustal carbonate (limestone). Calc-silicate xenoliths within Merapi basaltic-andesite eruptive rocks display textures indicative of intense interaction between magma and crustal carbonate, and Merapi feldspar phenocrysts frequently contain crustally contaminated cores and zones. To resolve the interaction processes between magma and limestone in detail we have performed a series of time-variable decarbonation experiments in silicate melt, at magmatic pressure and temperature, using a Merapi basaltic-andesite and local Javanese limestone as starting materials.We have used in situ analytical methods to determine the elemental and strontium isotope composition of the experimental products and to trace the textural, chemical, and isotopic evolution of carbonate assimilation. The major processes of magma^carbonate interaction identified are: (1) rapid decomposition and degassing of carbonate; (2) generation of a Ca-enriched, highly radiogenic strontium contaminant melt, distinct from the starting material composition; (3) intense CO2 vesiculation, particularly within the contaminated zones; (4) physical mingling between the contaminated and unaffected melt domains; (5) chemical mixing between melts. The experiments reproduce many of the features of magma^carbonate interaction observed in the natural Merapi xenoliths and feldspar phenocrysts. The Ca-rich, high 87Sr/86Sr contaminant melt produced in the experiments is considered as a precursor to the Ca-rich (often ‘hyper-calcic’) phases found in the xenoliths and the contaminated zones inMerapi feldspars.The xenoliths also exhibit micro-vesicular textures that can be linked to the CO2 liberation process seen in the experiments.This study, therefore, provides well-constrained petrological insights into the problem of crustal interaction at Merapi and points toward the substantial impact of such interaction on the volatile budget of the volcano.265 630