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  • 1.
    Barker, Abigail
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Holm, Paul M.
    Peate, David W.
    Baker, Joel A.
    A 5 million year record of compositional variations in mantle sources to magmatism on Santiago, southern Cape Verde archipelago2010In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 160, no 1, p. 133-154Article in journal (Refereed)
    Abstract [en]

    High-precision Pb isotope data and Sr–Nd–Hf isotope data are presented together with major and trace element data for samples spanning the 4.6 Ma history of volcanism at Santiago, in the southern Cape Verde islands. Pb isotope data confirm the positive Δ8/4 signature of the southern islands indicating that the north–south compositional heterogeneity in the Cape Verde archipelago has persisted for at least 4.6 Ma. The Santiago volcanics show distinct compositional differences between the old, intermediate and young volcanics, and suggest greater involvement of an enriched mantle (EM1)-like source over time. Isotopic variations in the Santiago volcanics indicate convergence towards a homogeneous EM1-like end-member and distinct temporal variations in the FOZO-like end-member. Santiago and Santo Antão (a northern island, Holm et al. 2006), show a simultaneous decrease in 208Pb/204Pb of the high 206Pb/204Pb FOZO-like source with time. Such systematic archipelago-wide variations in the FOZO-like component suggest that this component is more likely to be present as a coherent package of recycled ocean crust rather than as multiple small heterogeneities dispersed in the upwelling mantle. The temporal variations in 208Pb/204Pb reflect minor lateral variations in Th/U of this recycled ocean crust package entering the melting zone beneath the islands. The location of the EM1-like component is more equivocal. A shallow lithospheric location is possible, but this would require a coincidence between spatial compositional variations in the lithosphere (EM1 is spatially restricted to the southern islands) and flow lines in the upwelling mantle revealed by seismic anisotropy. Therefore, we favour a deeper asthenospheric mantle source for the EM1-like source.

  • 2.
    Barker, Abigail
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Holm, Paul Martin
    Unniversity of Copenhagen.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    The role of eclogite in the mantle heterogeneity at Cape Verde2014In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 168, no 3, p. 1052-Article in journal (Refereed)
    Abstract [en]

    The Cape Verde hotspot, like many other Ocean Island Basalt provinces, demonstrates isotopic heterogeneity on a 100–200 km scale. The heterogeneity is represented by the appearance of an EM1-like component at several of the southern islands and with a HIMU-like component present throughout the archipelago. Where the EM1-like component is absent, a local DMM-like component replaces the EM1-like component. Various source lithologies, including peridotite, pyroxenite and eclogite have been suggested to contribute to generation of these heterogeneities; however, attempts to quantify such contributions have been limited. We apply the minor elements in olivine approach (Sobolev et al. in Nature 434:590–597, 2005; Science, doi:10.1126/science.1138113,2007), to determine and quantify the contributions of peridotite, pyroxenite and eclogite melts to the mantle heterogeneity observed at Cape Verde. Cores of olivine phenocrysts of the Cape Verde volcanics have low Mn/FeO and low Ni*FeO/MgO that deviate from the negative trend of the global array. The global array is defined by mixing between peridotite and pyroxenite, whereas the Cape Verde volcanics indicate contribution of an additional eclogite source. Eclogite melts escape reaction with peridotite either by efficient extraction in an area of poor mantle flow or by reaction of eclogite melts with peridotite, whereby an abundance of eclogite can seal off the melt from further reaction. Temporal trends of decreasing Mn/FeO indicate that the supply of eclogite melts is increasing. Modelling suggests the local DMM-like end-member is formed from a relatively peridotite-rich melt, while the EM1-like end-member has a closer affinity to a mixed peridotite–pyroxenite–eclogite melt. Notably the HIMU-like component ranges from pyroxenite–peridotite-rich melt to one with up to 77 % eclogite melt as a function of time, implying that sealing of melt pathways is becoming more effective.

  • 3.
    Barker, Abigail K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Ellam, R.M.
    Hansteen, T.H.
    Haris, C.
    Stillman, C.J.
    Andersson, A.
    Magmatic evolution of the Cadamosto Seamount, Cape Verde: Beyond the spatial extent of EM12012In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 163, no 6, p. 949-965Article in journal (Refereed)
    Abstract [en]

    The Cadamosto Seamount is an unusual volcanic centre from Cape Verde, characterised by dominantly evolved volcanics, in contrast to the typically mafic volcanic centres at Cape Verde that exhibit only minor volumes of evolved volcanics. The magmatic evolution of Cadamosto Seamount is investigated to quantify the role of magma-crust interaction and thus provide a perspective on evolved end-member volcanism of Cape Verde. The preservation of mantle source signatures by Nd-Pb isotopes despite extensive magmatic differentiation provides new insights into the spatial distribution of mantle heterogeneity in the Cape Verde archipelago. Magmatic differentiation from nephelinite to phonolite involves fractional crystallisation of clinopyroxene, titanite, apatite, biotite and feldspathoids, with extensive feldspathoid accumulation being recorded in some evolved samples. Clinopyroxene crystallisation pressures of 0.38-0.17 GPa for the nephelinites constrain this extensive fractional crystallisation to the oceanic lithosphere, where no crustal assimilants or rafts of subcontinental lithospheric mantle are available. In turn, magma-crust interaction has influenced the Sr, O and S isotopes of the groundmass and late crystallising feldspathoids, which formed at shallow crustal depths reflecting the availability of oceanic sediments and anhydrite precipitated in the ocean crust. The Nd-Pb isotopes have not been affected by these processes of magma-crust interaction and hence preserve the mantle source signature. The Cadamosto Seamount samples have high Pb-206/Pb-204 (> 19.5), high epsilon Nd (+6 to +7) and negative Delta 8/4Pb, showing affinity with the northern Cape Verde islands as opposed to the adjacent southern islands. Hence, the Cadamosto Seamount in the west is located spatially beyond the EM1-like component found further east. This heterogeneity is not encountered in the oceanic lithosphere beneath the Cadamosto Seamount despite greater extents of fractional crystallisation at oceanic lithospheric depths than the islands of Fogo and Santiago. Our data provide new evidence for the complex geometry of the chemically zoned Cape Verde mantle source.

  • 4.
    Barker, Abigail
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Univ Las Palmas, GEOVOL, La Palmas Gran Canaria 35017, Spain.
    Carracedo, Juan Carlos
    Univ Las Palmas, GEOVOL, La Palmas Gran Canaria 35017, Spain.
    Nicholls, Peter A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    The magma plumbing system for the 1971 Teneguía eruption on La Palma, Canary Islands2015In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 170, no 5-6, article id 54Article in journal (Refereed)
    Abstract [en]

    The 1971 Teneguía eruption is the most recent volcanic event of the Cumbre Vieja rift zone on La Palma. The eruption produced basanite lavas that host xenoliths, which we investigate to provide insight into the processes of differentiation, assimilation and magma storage beneath La Palma. We compare our results to the older volcanomagmatic systems of the island with the aim to reconstruct the temporal development of the magma plumbing system beneath La Palma.

    The 1971 lavas are clinopyroxene-olivine-phyric basanites that contain augite, sodic-augite and Aluminium augite. Kaersutite cumulate xenoliths host olivine, clinopyroxene including sodic-diopside, and calcic-amphibole, whereas an analysed leucogabbro xenolith hosts plagioclase, sodic-augite-diopside, calcic-amphibole and hauyne. Mineral and mineral-melt thermobarometry indicate that clinopyroxene and plagioclase in the 1971 Teneguía lavas crystallised at 20 to 45 km depth, coinciding with clinopyroxene and calcic-amphibole crystallisation in the kaersutite cumulate xenoliths at 25 to 45 km and clinopyroxene, calcic-amphibole and plagioclase crystallisation in the leucogabbro xenolith at 30 to 50 km.

    Combined mineral chemistry and thermobarometry suggest that the magmas had already crystallised, differentiated and formed multiple crystal populations in the oceanic lithospheric mantle. Notably, the magmas that supplied the 1949 and 1971 events appear to have crystallised deeper than the earlier Cumbre Vieja magmas, which suggests progressive underplating beneath the Cumbre Vieja rift zone. In addition, the lavas and xenoliths of the 1971 event crystallised at a common depth, indicating a reused plumbing system and progressive recycling of Ocean Island plutonic complexes during subsequent magmatic activity. 

  • 5.
    Barnes, Christopher J.
    et al.
    Polish Acad Sci, Inst Geol Sci, Krakow, Poland..
    Bukala, Michal
    Polish Acad Sci, Inst Geol Sci, Krakow, Poland..
    Callegari, Riccardo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Walczak, Katarzyna
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Kooijman, Ellen
    Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden..
    Kielman-Schmitt, Melanie
    Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Zircon and monazite reveal late Cambrian/early Ordovician partial melting of the Central Seve Nappe Complex, Scandinavian Caledonides2022In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 177, no 9, article id 92Article in journal (Refereed)
    Abstract [en]

    The Seve Nappe Complex (SNC) comprises continental rocks of Baltica that were subducted and exhumed during the Caledonian orogeny prior to collision with Laurentia. The tectonic history of the central SNC is investigated by applying in-situ zircon and monazite (Th-)U-Pb geochronology and trace element analysis to (ultra-)high pressure (UHP) paragneisses in the Avardo and Marsfjallet gneisses. Zircons in the Avardo Gneiss exposed at Sippmikk creek exhibit xenocrystic cores with metamorphic rims. Cores show typical igneous REE profiles and were affected by partial Pb-loss. The rims have flat HREE profiles and are interpreted to have crystallized at 482.5 +/- 3.7 Ma during biotite-dehydration melting and peritectic garnet growth. Monazites in the paragneiss are chemically homogeneous and record metamorphism at 420.6 +/- 2.0 Ma. In the Marsfjallet Gneiss exposed near Kittelfjall, monazites exhibit complex zoning with cores enveloped by mantles and rims. The cores are interpreted to have crystallized at 481.6 +/- 2.1 Ma, possibly during garnet resorption. The mantles and rims provide a dispersion of dates and are interpreted to have formed by melt-driven dissolution-reprecipitation of pre-existing monazites until 463.1 +/- 1.8 Ma. Depletion of Y, HREE, and U in the mantles and rims compared to the cores record peritectic garnet and zircon growth. Altogether, the Avardo and Marsfjallet gneisses show evidence of late Cambrian/early Ordovician partial melting (possibly in (U)HP conditions), Middle Ordovician (U)HP metamorphism, and late Silurian tectonism. These results indicate that the SNC underwent south-to-north oblique subduction in late Cambrian time, followed by progressive north-to-south exhumation to crustal levels prior to late Silurian continental collision.

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  • 6.
    Barnes, Christopher
    et al.
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
    Schneider, David
    Univ Ottawa, Dept Earth & Environm Sci, Ottawa, ON, Canada.
    Walczak, Katarzyna
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
    Bukala, Michal
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
    Kosminska, Karolina
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
    Tokarski, Tomasz
    AGH Univ Sci & Technol, Acad Ctr Mat & Nanotechnol, Krakow, Poland.
    Karlsson, Andreas
    Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden.
    High-spatial resolution dating of monazite and zircon revealsthe timing of subduction-exhumation of the Vaimok Lens in the Seve Nappe Complex (Scandinavian Caledonides)2019In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 174, no 1, article id 5Article in journal (Refereed)
    Abstract [en]

    In-situ monazite Th-U-total Pb dating and zircon LA-ICP-MS depth-profiling was applied to metasedimentary rocks from the Vaimok Lens in the Seve Nappe Complex (SNC), Scandinavian Caledonides. Results of monazite Th-U-total Pb dating, coupled with major and trace element mapping of monazite, revealed 603 +/- 16 Ma Neoproterozoic cores surrounded by rims that formed at 498 +/- 10 Ma. Monazite rim formation was facilitated via dissolution-reprecipitation of Neoproterozoic monazite. The monazite rims record garnet growth as they are depleted in Y2O3 with respect to the Neoproterozoic cores. Rims are also characterized by relatively high SrO with respect to the cores. Results of the zircon depth-profiling revealed igneous zircon cores with crystallization ages typical for SNC metasediments. Multiple zircon grains also exhibit rims formed by dissolution-reprecipitation that are defined by enrichment of light rare earth elements, U, Th, P, +/- Y, and +/- Sr. Rims also have subdued Eu anomalies ( Eu/Eu* approximate to 0.6-1.2) with respect to the cores. The age of zircon rim formation was calculated from three metasedimentary rocks: 480 +/- 22 Ma; 475 +/- 26 Ma; and 479 +/- 38 Ma. These results show that both monazite and zircon experienced dissolution-reprecipitation under high-pressure conditions. Caledonian monazite formed coeval with garnet growth during subduction of the Vaimok Lens, whereas zircon rim formation coincided with monazite breakdown to apatite, allanite and clinozoisite during initial exhumation.

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  • 7.
    Blythe, Lara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology. School of Physical and Geographical Science, Keele University, Keele, UK.
    Deegan, Frances
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Freda, C
    Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy.
    Jolis, Ester Muños
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Masotta, M
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Misiti, V.
    Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy.
    Taddeucci, J.
    Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy.
    CO2 bubble generation and migration during magma–carbonate interaction2015In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 169, no 4, article id 42Article in journal (Refereed)
    Abstract [en]

    We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to be liberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions.

  • 8.
    Blythe, Lara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Deegan, Frances
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Freda, C.
    Jolis, Ester Muños
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Masotta, M.
    Misiti, V.
    Taddeucci, J.
    Troll, V.R.
    Time-monitored vesiculation processes in magma-carbonate interaction experiments2014In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967Article in journal (Other academic)
  • 9.
    Callegaro, S.
    et al.
    Univ Oslo, Ctr Earth Evolut & Dynam, Oslo, Norway..
    Svensen, H. H.
    Univ Oslo, Ctr Earth Evolut & Dynam, Oslo, Norway..
    Neumann, E. R.
    Univ Oslo, Ctr Earth Evolut & Dynam, Oslo, Norway..
    Polozov, A. G.
    Russian Acad, Inst Geol Ore Deposits Petrog Mineral & Geochem, Moscow, Russia..
    Jerram, D. A.
    Univ Oslo, Ctr Earth Evolut & Dynam, Oslo, Norway.;DougalEARTH Ltd, Solihull, W Midlands, England..
    Deegan, Frances
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Planke, S.
    Univ Oslo, Ctr Earth Evolut & Dynam, Oslo, Norway.;Volcan Basin Petr Res VBPR, Oslo, Norway..
    Shiganova, O. , V
    Ivanova, N. A.
    Siberian Sci Res Inst Geol, Geophys & Mineral Resources, Novosibirsk, Russia..
    Melnikov, N. , V
    Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis2021In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 176, no 7, article id 49Article in journal (Refereed)
    Abstract [en]

    A vast portion of the plumbing system of the Siberian Traps Large Igneous Province (STLIP) is emplaced in the Tunguska Basin, where borehole data reveal ubiquitous and abundant sills with great lateral extension. These intrusions intersect Cambrian-Ordovician evaporite, carbonate and siliciclastic series, and locally coal-bearing Permian host rocks, with a high potential for thermogenic gas generation. Here we present new geochemical data from 71 magmatic and 4 sedimentary rock samples from the Tunguska Basin center and periphery, recovered from 15 deep sills intercepted by boreholes. The studied samples are all low-Ti basalt and basaltic andesites, confirming absence of high-Ti and alkaline STLIP magmatism in the Tunguska Basin. The sills derive from picritic parental melts produced by extensive melting of a mantle source with recycled crustal components below a thinned lithosphere (50-60 km), within the spinel stability field. The mantle source was dominantly peridotitic, with enriched pyroxenitic domains formed by recycled lower crust, in agreement with previous models for the main tholeiitic STLIP phase. Limited amounts (up to 5%) of highly radiogenic granitoids or moderately radiogenic metapelites were assimilated in upper crustal magma reservoirs. After emplacement, sills intruded in Cambrian evaporites assimilated marlstones and interacted with the evaporitic host rocks, probably via fluids and brines. This is the first time that such process is described in subvolcanic rocks from all across the volcanic basin. The sills are correlated geochemically with the established chemostratigraphy for the on-craton STLIP lava piles and intrusions (Norilsk region). Sills correlated with the Morongovsky-Mokulaevsky Fm. and the Norilsk-type intrusions are the most voluminous, present all across the central Tunguska Basin, and bear the strongest evidence of interaction with evaporites. Massive discharge of thermogenic volatiles is suggested by explosive pipes and hydrothermal vent structures throughout the Tunguska Basin. We propose that this voluminous pulse of magmatism is a good candidate for the hitherto unidentified early intrusive phase of the STLIP, and may link the deep Tunguska basin sills to the end-Permian environmental crisis.

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  • 10.
    Chadwick, J.P.
    et al.
    Department of Petrology, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Waight, T.E.
    Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark.
    van der Zwan, F.M.
    Department of Petrology, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.
    Schwarzkopf, L.M.
    GeoDocCon, Unterpferdt 8, 95176 Konradsreuth, Germany.
    Petrology and geochemistry of igneous inclusions in recent Merapi deposits: a window into the sub-volcanic plumbing system2013In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 165, no 2, p. 259-282Article in journal (Refereed)
    Abstract [en]

    Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, geochemistry and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co-magmatic enclaves typically display liquid–liquid relationships with their host rocks, indicating mixing and mingling of distinct magmas. Co-magmatic enclaves are basaltic in composition and occasionally display chilled margins, whereas highly crystalline basaltic-andesite inclusions usually lack chilling. Plutonic inclusions have variable grain sizes and occasionally possess crystal layering with a spectrum of compositions spanning from gabbro to diorite. Plagioclase, pyroxene and amphibole are the dominant phases present in both the inclusions and the host lavas. Mineral compositions of the inclusions largely overlap with compositions of minerals in recent and historic basaltic-andesites and the enclaves they contain, indicating a cognate or ‘antelithic’ nature for most of the plutonic inclusions. Many of the plutonic inclusions plot together with the host basaltic-andesites along fractional crystallisation trends from parental basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi magmas that spans the full depth of the crust, indicating a multi-chamber magma system with high amounts of semi-molten crystalline mush. There, crystallisation, crystal accumulation, magma mixing and mafic recharge take place. Comparison of the barometric results with whole rock Sr, Nd, and Pb isotope data for the inclusions suggests input of crustal material as magma ascends from depth, with a significant late addition of sedimentary material from the uppermost crust. The type of multi-chamber plumbing system envisaged contains large portions of crystal mush and provides ample opportunity to recycle the magmatic crystalline roots as well as interact with the surrounding host lithologies.

  • 11.
    Dahrén, Börje
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Andersson, Ulf B.
    Chadwick, Jane P.
    Gardner, Mairi F.
    Jaxybulatov, Kairly
    Koulakov, Ivan
    Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions2012In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 163, no 4, p. 631-651Article in journal (Refereed)
    Abstract [en]

    Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km, while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.

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  • 12.
    Day, James M. D.
    et al.
    Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA 92093 USA..
    Pearson, D. Graham
    Univ Alberta, Dept Earth & Atmospher Sci, Edmonton, AB T6G 2E3, Canada..
    Kjarsgaard, Bruce A.
    Geol Survey Canada, 601 Booth St, Ottawa, ON K1A 0E8, Canada..
    Barker, Abigail
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Nowell, Geoff M.
    Univ Durham, Dept Earth Sci, Durham DH1 3LE, England..
    Joyce, Nancy
    Geol Survey Canada, 601 Booth St, Ottawa, ON K1A 0E8, Canada..
    Lowry, David
    Royal Holloway Univ London, Dept Earth Sci, Egham TW20 0EX, England..
    Sarkar, Chiranjeeb
    Univ Alberta, Dept Earth & Atmospher Sci, Edmonton, AB T6G 2E3, Canada..
    Harrison, Christopher
    Geol Survey Canada, 3303-33 St NW, Calgary, AB T2L 2A7, Canada..
    Early Eocene Arctic volcanism from carbonate-metasomatized mantle2023In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 178, no 12, article id 91Article in journal (Refereed)
    Abstract [en]

    Melilitite, nephelinite, basanite, and alkali basalt, along with phonolite differentiates, form the Freemans Cove Complex (FCC) in the south-eastern extremity of Bathurst Island (Nunavut, Canada). New Ar-40/Ar-39 chronology indicates their emplacement between similar to 56 and similar to 54 million years ago within a localized extensional structure. Melilitites and nephelinites, along with phonolite differentiates, likely relate to the beginning and end phases of extension, whereas alkali basalts were emplaced during a main extensional episode at similar to 55 Ma. The melilitites, nephelinites, and alkali basalts show no strong evidence for significant assimilation of crust, in contrast to some phonolites. Partial melting occurred within both the garnet- and spinel-facies mantle and sampled sources with He, O, Nd, Hf, and Os isotope characteristics indicative of peridotite with two distinct components. The first, expressed in higher degree partial melts, represents a relatively depleted component ("A"; He-3/He-4 similar to 8 R-A, epsilon(i)(Nd) similar to + 3 epsilon(Hf)i similar to + 7, gamma(Os)i similar to 0). The second was an enriched component ("B" He-3/He-4 < 3 R-A, epsilon(Nd)i < - 1 epsilon(Hf)i < + 3, gamma(Os)i > + 70) sampled by the lowest degree partial melts and represents carbonate-metasomatized peridotite. Magmatism in the FCC shows that rifting extended from the Labrador Sea to Bathurst Island and reached a zenith at similar to 55 Ma, during the Eurekan orogeny. The incompatible trace-element abundances and isotopic signatures of FCC rocks indicate melt generation occurred at the base of relatively thin lithosphere at the margin of a thick craton, with no mantle plume influence. FCC melt compositions are distinct from other continental rift magmatic provinces worldwide, and their metasomatized mantle source was plausibly formed synchronously with emplacement of Cretaceous kimberlites. The FCC illustrates that the range of isotopic compositions preserved in continental rift magmas are likely to be dominated by temporal changes in the extent of partial melting, as well as by the timing and degree of metasomatism recorded in the underlying continental lithosphere.

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  • 13. Fassmer, Kathrin
    et al.
    Klonowska, Iwona
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Walczak, Katarzyna
    Andersson, Barbro
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Froitzheim, Nikolaus
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Fonseca, Raul
    Munker, Carsten
    Janák, Marian
    Slovak Academy of Sciences.
    Whitehouse, Martin
    Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken, Seve Nappe Complex, Sweden2017In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 172, no 11-12, article id 103Article in journal (Refereed)
    Abstract [en]

    The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430-400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high-and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between similar to 505 and similar to 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jamtland). New age determinations were performed on eclogite and garnet-phengite gneiss at Tjeliken in northern Jamtland. Thermodynamic modelling yielded peak metamorphic conditions of 25-27 kbar/680-760 degrees C for the garnet-phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25-26 kbar/650-700 degrees C). Metamorphic rims of zircons from the garnet-phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 +/- 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458 +/- 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm-Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jamtland during the Middle Ordovician in a fast subduction-exhumation cycle.

  • 14.
    Högdahl, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Sjöström, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Persson Nilsson, Katarina
    Geol Survey Sweden, S-75328 Uppsala, Sweden.
    Claesson, Stefan
    Swedish Museum Nat Hist, Lab Isotope Geol, S-10405 Stockholm, Sweden.
    Konecny, Patrik
    Geol Survey Slovak Republ, Bratislava 81704, Slovakia.
    Reactive monazite and robust zircon growth in diatexitesand leucogranites from a hot, slowly cooled orogen: implicationsfor the Palaeoproterozoic tectonic evolution of the central Fennoscandian Shield, Sweden2012In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 163, no 1, p. 167-188Article in journal (Refereed)
    Abstract [en]

    Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens, small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites and leucogranites from two Svecofennian domains yields older, coeval and younger U–Pb SIMS and EMP ages than zircon from the same rock. As zircon precipitated during the melt-bearing stage, its U–Pb ages reflect the timing of peak metamorphism, which is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87–1.86 and 1.82–1.80 Ga. The younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred at 1.83–1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening accommodated by major thrusting.

  • 15.
    Jaranowski, Maciej
    et al.
    Polish Acad Sci, Inst Geol Sci, Res Ctr Krakow, Senacka 1, PL-31002 Krakow, Poland..
    Budzyn, Bartosz
    Polish Acad Sci, Inst Geol Sci, Res Ctr Krakow, Senacka 1, PL-31002 Krakow, Poland..
    Barnes, Christopher J. J.
    Polish Acad Sci, Inst Geol Sci, Res Ctr Krakow, Senacka 1, PL-31002 Krakow, Poland..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Al Mickiewicza 30, PL-30059 Krakow, Poland..
    Slama, Jiri
    Czech Acad Sci, Inst Geol, Rozvojova 269, Prague 6, Czech Republic..
    Kozub-Budzyn, Gabriela A. A.
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Al Mickiewicza 30, PL-30059 Krakow, Poland..
    Kosminska, Karolina
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Al Mickiewicza 30, PL-30059 Krakow, Poland..
    U-Pb and trace element zircon and apatite petrochronology of eclogites from the Scandinavian Caledonides2023In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 178, article id 47Article in journal (Refereed)
    Abstract [en]

    The petrochronological records of eclogites in the Scandinavian Caledonides are investigated using EPMA and LA-ICPMS of zircon and apatite for U-Pb geochronology, combined with major and trace element characteristics. Metamorphic zircon from two eclogites from the Lofoten-Vesteralen Complex (Lofoten Archipelago region) collectively yielded a Concordia age 427.8 & PLUSMN; 5.7 Ma and an upper intercept U-Pb age 425 & PLUSMN; 30 Ma. Apatites from the same eclogites provided U-Pb lower intercepts at 322 & PLUSMN; 28 Ma and 354 & PLUSMN; 33 Ma, with the latter also yielding a younger age of 227 & PLUSMN; 24 Ma. Two eclogites from the Lower Seve Nappe (Northern Jamtland) demonstrate different zircon and apatite age records. Metamorphic zircon provided Concordia ages of 467.2 & PLUSMN; 5.9 Ma and 444.5 & PLUSMN; 5.5 Ma, which resolve the age of prograde metamorphism and zircon growth during retrogression, respectively. The lower intercept U-Pb ages of apatites from the same eclogites are 436 & PLUSMN; 18 and 415 & PLUSMN; 25 Ma, respectively. In combination with their geochemical characteristics, they suggest two separate stages of exhumation of eclogite bodies in the Lower Seve Nappe. Zircons from an eclogite from the Blaho Nappe (Nordoyane Archipelago) yielded a continuum of concordant U-Pb dates from ca. 435 to 395 Ma, which suggests several cycles of HT metamorphism within short intervals. Distinctive trace element characteristics of apatites from the Blaho Nappe eclogite suggest formation coeval with zircon and garnet during HT metamorphism, but Pb diffusion behaved as an open system until cooling during exhumation of the nappe at 390 & PLUSMN; 12 Ma (lower intercept U-Pb age of apatite). To summarize, this study presents the high potential of coupled zircon and apatite petrochronology of eclogites in resolving their metamorphic evolution, particularly with respect to using trace element characteristics of apatites to constrain the records of their growth, alterations and the meaning of their U-Pb age record.

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  • 16.
    Jeffery, Adam J.
    et al.
    School of Physical and Geographical Sciences, Keele University, UK.
    Gertisser, Ralf
    School of Physical and Geographical Sciences, Keele University, UK.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Jolis, Ester M.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Dahrén, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Harris, Chris
    University of Cape Town, South Africa.
    Tindle, Andrew G.
    CEPSAR (Centre for Earth, Planetary, Space and Astronomy Research), The Open University, UK.
    Preece, Katie
    University of East Anglia.
    O'Driscoll, Brain
    Humaida, Hanik
    Balai Penyelidikan dan Pengembangan Teknologi, Indonesia.
    Chadwick, Jane P.
    Science Gallery, Trinity College Dublin, Dublin.
    The pre-eruptive magma plumbing system of the 2007–2008 dome-forming eruption of Kelut volcano, East Java, Indonesia2013In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 166, no 1, p. 275-308Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Jolis, Ester Muñoz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Freda, C.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Deegan, Frances M.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Blythe, Lara S.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    McLeod, C. L.
    Davidson, J. P.
    Experimental simulation of magma-carbonate interaction beneath Mt. Vesuvius, Italy2013In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 166, no 5, p. 1335-1353Article in journal (Refereed)
    Abstract [en]

    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 A degrees 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 and Sr-87/Sr-86, coupled with intense CO2 vesiculation at the melt-carbonate interface. Binary mixing between carbonate 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.

  • 18.
    Kosminska, Karolina
    et al.
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Fassmer, Kathrin
    Univ Innsbruck, Inst Geol, Innsbruck, Austria..
    McClelland, William C.
    Univ Iowa, Dept Earth & Environm Sci, Iowa City, IA USA..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Coble, Matthew
    GNS Sci, Surface Geosci Dept, Lower Hutt, New Zealand..
    Thomas, Jay
    Syracuse Univ, Dept Earth & Environm Sci, Syracuse, NY USA..
    Manecki, Maciej
    AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland..
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bazarnik, Jakub
    Polish Geol Inst, Natl Res Inst, Carpathian Branch, Krakow, Poland..
    Münker, Carsten
    Univ Cologne, Inst Geol & Mineral, Cologne, Germany..
    Monazite in the eclogite and blueschist of the Svalbard Caledonides: its origin and forming-reactions2023In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 178, article id 61Article in journal (Refereed)
    Abstract [en]

    High-pressure low-temperature rocks from Svalbard are an excellent target for studying metamorphic reactions in Phanerozoic subduction zones. This study reveals the presence of monazite in an eclogite and a blueschist from the Vestgotabreen Complex, southwestern Svalbard. In order to investigate the monazite-forming reaction, we obtained pressure-temperature estimates coupled with U-Pb and Lu-Hf dating. Combined geothermobarometry allows to constrain three evolutionary stages of garnet growth in the eclogite: nucleation (1.6 & PLUSMN; 0.3 GPa at 460 & PLUSMN; 60 & DEG;C), peak-pressure (2.3 & PLUSMN; 0.3 GPa at 507 & PLUSMN; 60 & DEG;C), and peak-temperature (2.1 & PLUSMN; 0.3 GPa at 553 & PLUSMN; 60 & DEG;C). A zircon age of 482 & PLUSMN; 10 Ma is interpreted to belong to the prograde part of the pressure-temperature path. Monazite forms inclusions within garnet rims, or it is surrounded by allanite and apatite, altogether forming pseudomorphs of a tabular shape in the matrix. Textures, geothermobarometry and geochronology support the conclusion the monazite formed under high-pressure conditions at 471 & PLUSMN; 6 Ma. We propose that the monazite crystallization in the eclogite happened due to a decomposition of accessory phases during the decompression after peak-pressure of the metamorphic cycle. Monazite in the blueschist occurs as inclusions in garnet cores and gives an indicative age of 486 & PLUSMN; 6 Ma, which is interpreted to reflect the prograde growth of the garnet. Lu-Hf garnet dating resolves an age of peak-pressure metamorphism in the blueschist at 471.1 & PLUSMN; 4 Ma under conditions of 2.0 & PLUSMN; 0.03 GPa and 500 & PLUSMN; 30 & DEG;C. The Vestgotabreen Complex provides evidence for an early Ordovician modern-style subduction system in the proximity of the Baltica margin. Hence, this study also supports the tectonic models that favour a mixed Baltican and Laurentian provenance of south-western Svalbard.

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  • 19.
    Muir, Duncan D.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Blundy, Jon D.
    Hutchinson, Michael C.
    Rust, Alison C.
    Petrological imaging of an active pluton beneath Cerro Uturuncu, Bolivia2014In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 167, no 3, p. 980-Article in journal (Refereed)
    Abstract [en]

    Uturuncu is a dormant volcano in the Altiplano of SW Bolivia. A present day similar to 70 km diameter interferometric synthetic aperture radar (InSAR) anomaly roughly centred on Uturuncu's edifice is believed to be a result of magma intrusion into an active crustal pluton. Past activity at the volcano, spanning 0.89 to 0.27 Ma, is exclusively effusive and almost all lavas and domes are dacitic with phenocrysts of plagioclase, orthopyroxene, biotite, ilmenite and Ti-magnetite plus or minus quartz, and microlites of plagioclase and orthopyroxene set in rhyolitic groundmass glass. Plagioclasehosted melt inclusions (MI) are rhyolitic with major element compositions that are similar to groundmass glasses. H2O concentrations plotted versus incompatible elements for individual samples describe a trend typical of near-isobaric, volatile-saturated crystallisation. At 870 degrees C, the average magma temperature calculated from Fe-Ti oxides, the average H2O of 3.2 +/- 0.7 wt% and CO2 typically <160 ppm equate to MI trapping pressures of 50-120 MPa, approximately 2-4.5 km below surface. Such shallow storage precludes the role of dacite magma emplacement into preeruptive storage regions as being the cause of the observed InSAR anomaly. Storage pressures, whole-rock (WR) chemistry and phase assemblage are remarkably consistent across the eruptive history of the volcano, although magmatic temperatures calculated from Fe-Ti oxide geothermometry, zircon saturation thermometry using MI and orthopyroxenemelt thermometry range from 760 to 925 degrees C at NNO +/- 1 log. This large temperature range is similar to that of saturation temperatures of observed phases in experimental data on Uturuncu dacites. The variation in calculated temperatures is attributed to piecemeal construction of the active pluton by successive inputs of new magma into a growing volume of plutonic mush. Fluctuating temperatures within the mush can account for sieve-textured cores and complex zoning in plagioclase phenocrysts, resorption of quartz and biotite phenocrysts and apatite microlites. That Fe-Ti oxide temperatures vary by similar to 50-100 degrees C in a single thin section indicates that magmas were not homogenised effectively prior to eruption. Phenocryst contents do not correlate with calculated magmatic temperatures, consistent with crystal entrainment from the mush during magma ascent and eruption. Microlites grew during ascent from the magma storage region. Variability in the proportion of microlites is attributed to differing ascent and effusion rates with faster rates in general for lavas >0.5 Ma compared to those <0.5 Ma. High microlite contents of domes indicate that effusion rates were probably slowest in dome-forming eruptions. Linear trends in WR major and trace element chemistries, highly variable, bimodal mineral compositions, and the presence of mafic enclaves in lavas demonstrate that intrusion of more mafic magmas into the evolving, shallow plutonic mush also occurred further amplifying local temperature fluctuations. Crystallisation and resorption of accessory phases, particularly ilmenite and apatite, can be detected in MI and groundmass glass trace element covariation trends, which are oblique to WRs. Marked variability of Ba, Sr and La in MI can be attributed to temperature-controlled, localised crystallisation of plagioclase, orthopyroxene and biotite within the evolving mush.

  • 20.
    Peters, Stefan T. M.
    et al.
    Geowissenschaftliches Zentrum Georg August Univ t, Abt Isotopengeol, Goldschmidtstr 1, D-37077 Gottingen, Germany.;Vrije Univ Amsterdam, Fac Aard Levenswetenschappen, Boelelaan 1085, NL-1081 HV Amsterdam, Netherlands..
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Weis, Franz A.
    Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden..
    Dallai, Luigi
    CNR, Ist Geosci & Georisorse, Via Moruzzi 1, I-56124 Pisa, Italy..
    Chadwick, Jane P.
    Vrije Univ Amsterdam, Fac Aard Levenswetenschappen, Boelelaan 1085, NL-1081 HV Amsterdam, Netherlands.;Trin Coll Dublin, Sci Gallery, Pearse St, Dublin, Ireland..
    Schulz, Bernhard
    TU Bergakademie Freiberg, Inst Mineral, Brennhausgasse 14, D-09599 Freiberg, Saxony, Germany..
    Amphibole megacrysts as a probe into the deep plumbing system of Merapi volcano, Central Java, Indonesia2017In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 172, no 4, article id 16Article in journal (Refereed)
    Abstract [en]

    Amphibole has been discussed to potentially represent an important phase during early chemical evolution of arc magmas, but is not commonly observed in eruptive arc rocks. Here, we present an in-depth study of metastable calcic amphibole megacrysts in basaltic andesites of Merapi volcano, Indonesia. Radiogenic Sr and Nd isotope compositions of the amphibole megacrysts overlap with the host rock range, indicating that they represent antecrysts to the host magmas rather than xenocrysts. Amphibolebased barometry suggests that the megacrysts crystallised at pressures of >500 MPa, i.e., in the mid-to lower crust beneath Merapi. Rare-earth element concentrations, in turn, require the absence of magmatic garnet in the Merapi feeding system and, therefore, place an uppermost limit for the pressure of amphibole crystallisation at ca. 800 MPa. The host magmas of the megacrysts seem to have fractionated significant amounts of amphibole and/or clinopyroxene, because of their low Dy/Yb ratios relative to the estimated compositions of the parent magmas to the megacrysts. The megacrysts' parent magmas at depth may thus have evolved by amphibole fractionation, in line with apparently coupled variations of trace element ratios in the megacrysts, such as e.g., decreasing Zr/Hf with Dy/Yb. Moreover, the Th/U ratios of the amphibole megacrysts decrease with increasing Dy/Yb and are lower than Th/U ratios in the basaltic andesite host rocks. Uranium in the megacrysts' parent magmas, therefore, may have occurred predominantly in the tetravalent state, suggesting that magmatic fO(2) in the Merapi plumbing system increased from below the FMQ buffer in the mid-to-lower crust to 0.6-2.2 log units above it in the near surface environment. In addition, some of the amphibole megacrysts experienced dehydrogenation (H-2 loss) and/or dehydration (H2O loss), as recorded by their variable H2O contents and D/H and Fe3+/Fe2+ ratios, and the release of these volatile species into the shallow plumbing system may facilitate Merapi's often erratic eruptive behaviour.

  • 21.
    Troll, Valentin R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Nicoll, Graeme R.
    Neftex, 97 Jubilee Ave,Milton Pk, Abingdon OX14 4RW, Oxon, England..
    Ellam, Robert M.
    Scottish Univ Environm Res Ctr SUERC, Rankine Ave, East Kilbride G75 0QF, Scotland..
    Emeleus, C. Henry
    Univ Durham, Dept Earth Sci, South Rd, Durham DH1 3LE, England..
    Mattsson, Tobias
    Univ Stockholm, Dept Geol Sci, Svante Arrheniusvag 8C, Stockholm, Sweden..
    Petrogenesis of the Loch Bà ring-dyke and Centre 3 granites, Isle of Mull, Scotland2021In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 176, no 2, article id 16Article in journal (Refereed)
    Abstract [en]

    The Loch Ba ring-dyke and the associated Centre 3 granites represent the main events of the final phase of activity at the Palaeogene Mull igneous complex. The Loch Ba ring-dyke is one of the best exposed ring-intrusions in the world and records intense interaction between rhyolitic and basaltic magma. To reconstruct the evolutionary history of the Centre 3 magmas, we present new major- and trace-element, and new Sr isotope data as well as the first Nd and Pb isotope data for the felsic and mafic components of the Loch Ba intrusion and associated Centre 3 granites. We also report new Sr, Nd and Pb isotope data for the various crustal compositions from the region, including Moine and Dalradian metasedimentary rocks, Lewisian gneiss, and Iona Group metasediments. Isotope data for the Loch Ba rhyolite (Sr-87/Sr-86(i) = 0.716) imply a considerable contribution of local Moine-type metasedimentary crust (Sr-87/Sr-86 = 0.717-0.736), whereas Loch Ba mafic inclusions (Sr-87/Sr-86(i) = 0.704-0.707) are closer to established mantle values, implying that felsic melts of dominantly crustal origin mixed with newly arriving basalt. The Centre 3 microgranites (Sr-87/Sr-86(i) = 0.709-0.716), are less intensely affected by crustal assimilation relative to the Loch Ba rhyolite. Pb-isotope data confirm incorporation of Moine metasediments within the Centre 3 granites. Remarkably, the combined Sr-Nd-Pb data indicate that Centre 3 magmas record no detectable interaction with underlying deep Lewisian gneiss basement, in contrast to Centre 1 and 2 lithologies. This implies that Centre 3 magmas ascended through previously depleted or insulated feeding channels into upper-crustal reservoirs where they resided within and interacted with fertile Moine-type upper crust prior to eruption or final emplacement.

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  • 22. van der Zwan, Froukje M.
    et al.
    Chadwick, Jane P.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Textural history of recent basaltic-andesites and plutonic inclusions from Merapi volcano2013In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 166, no 1, p. 43-63Article in journal (Refereed)
    Abstract [en]

    Mt. Merapi in Central Java is one of the most active stratovolcanoes on Earth and is underlain by a multistage plumbing system. Crystal size distribution analyses (CSD) were carried out on recent Merapi basaltic-andesites and co-eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales. The basaltic-andesites exhibit log-linear, kinked-upwards CSD curves for plagioclase and clinopyroxene that can be separated into two main textural populations. Large plagioclase phenocrysts (a parts per thousand yen1.6 mm) make up one population, but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid-crustal levels. This population was subsequently influenced by crystal accumulation and the onset of crustal assimilation, including the incorporation of high-Ca skarn-derived xenocrysts. Textural re-equilibration is required for these crystals to form a single population in CSD. A second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals < 1.6 mm in size. Crustal assimilation is indicated by, for example, oxygen isotopes and based on the CSD data, crystallisation combined with contamination is likely semi-continuous in these upper crustal storage chambers. The CSD data observed in the basaltic-andesite samples are remarkably consistent and require a large-volume steady state magmatic system beneath Merapi in which late textural equilibration plays a significant role. Plagioclase CSDs of co-eruptive magmatic and plutonic inclusions may contain a third crystal population (< 1 mm) not found in the lavas. This third population has probably formed from enhanced degassing of portions of basaltic-andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic-andesite mush inclusions. A suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep Merapi plumbing system, as deduced from CSD patterns and mineral assemblages.

  • 23. Weidendorfer, Daniel
    et al.
    Schmidt, Max W.
    Mattsson, Hannes B.
    Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites2016In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 171, no 5Article in journal (Refereed)
    Abstract [en]

    The carbonatites of Brava Island, Cape Verde hot spot, allow to investigate whether they represent small mantle melt fractions or form through extreme fractionation and/or liquid immiscibility from CO2-bearing silicate magmas. The intrusive carbonatites on Brava Island are part of a strongly silica-undersaturated pyroxenite, ijolite, nephelinite, nepheline syenite, combeite foiditite, carbonatite series. The major and trace element composition of this suite is reproduced by a model fractionating olivine, clinopyroxene, perovskite, biotite, apatite, titanite, sodalite and FeTi oxides, all present as phenocrysts in the rocks corresponding to their fractionation interval. Fractionation of 90 wt% crystals reproduces the observed geochemical trend from the least evolved ultramafic dikes (bulk X-Mg = 0.64) to syenitic compositions. The modelled fractional crystallization leads to alkali enrichment, driving the melt into the carbonatite silicate miscibility gap. An initial CO2 content of 4000 ppm is sufficient to saturate in CO2 at the point where the rock record suggests continuing unmixing carbonatites from nephelinites to nepheline syenites after 61 wt% fractionation. Such immiscibility is also manifested in carbonatite and silicate domains on a hand specimen scale. Furthermore, almost identical primary clinopyroxene, biotite and carbonate compositions from carbonatites and nephelinites to nepheline syenites substantiate their conjugate character and our unmixing model. The modelled carbonatite compositions correspond to the natural ones except for their much higher alkali contents. The alkali-poor character of the carbonatites on Brava and elsewhere is likely a consequence of the release of alkali rich CO2 + H2O fluids during final crystallization, which cause fenitization in adjacent rocks. We propose a general model for carbonatite generation during alkaline magmatism, where the fractionation of heavily Si-undersaturated, alkaline parent melts results in alkali and CO2 enrichment in the evolving melt, ultimately leading to immiscibility between carbonatites and evolved Si-undersaturated alkaline melts. Early saturation in feldspathoids or feldspars would limit alkali enrichment preventing the formation of carbonatites. The complete and continuous fractionation line from almost primitive melts to syenitic compositions on Brava underlines the possibly important role of intrusives for hot spot volcanism.

  • 24.
    Wiesmaier, Sebastian
    et al.
    Department of Geology, Trinity College Dublin, 2 College Green, Dublin 2, Ireland.
    Deegan, Frances M
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Troll, Valentin R
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Carracedo, Juan Carlos
    Estación Volcanológica de Canarias, IPNA-CSIC, Av. Astrofísica Francisco Sanchez 3, 38206 La Laguna, Tenerife, Spain.
    Chadwick, Jane P
    Department of Petrology (FALW), Vrjie Universiteit, 1081 HV Amsterdam, The Netherlands.
    Chew, David M
    Department of Geology, Trinity College Dublin, 2 College Green, Dublin 2, Ireland.
    Magma mixing in the 1100 AD Montaña Reventada composite lava flow, Tenerife, Canary Islands: Interaction between rift zone and central volcano plumbing systems2011In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 162, no 3, p. 651-669Article in journal (Refereed)
    Abstract [en]

    Zoned eruption deposits commonly show a lower felsic and an upper mafic member, thought to reflect eruption from large, stratified magma chambers. In contrast, the Montaña Reventada composite flow (Tenerife) consists of a lower basanite and a much thicker upper phonolite. A sharp interface separates basanite and phonolite, and chilled margins at this contact indicate the basanite was still hot upon emplacement of the phonolite, i.e. the two magmas erupted in quick succession. Four types of mafic to intermediate inclusions are found in the phonolite. Inclusion textures comprise foamy quenched ones, others with chilled margins and yet others that are physically mingled, reflecting progressive mixing with a decreasing temperature contrast between the end-members. Analysis of basanite, phonolite and inclusions for majors, traces and Sr, Nd and Pb isotopes show the inclusions to be derived from binary mixing of basanite and phonolite end-members in ratios of 2:1 to 4:1. Although, basanite and phonolite magmas were in direct contact, contrasting 206Pb/204Pb ratios show that they are genetically distinct (19.7193(21)–19.7418(31) vs. 19.7671(18)–19.7807(23), respectively). We argue that the Montaña Reventada basanite and phonolite first met just prior to eruption and had limited interaction time only. Montaña Reventada erupted from the transition zone between two plumbing systems, the phonolitic Teide-Pico Viejo complex and the basanitic Northwest rift zone. A rift zone basanite dyke most likely intersected the previously emplaced phonolite magma chamber. This led to eruption of geochemically and texturally unaffected basanite, with the inclusion-rich phonolite subsequently following into the established conduit.

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