| 1. |
- Gardner, M., et al.
(author)
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Crustal differentiation processes at Krakatau volcano, Indonesia
- 2013
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In: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 54:1, s. 149-182
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Journal article (peer-reviewed)abstract
- Anak Krakatau is a basaltic andesite cone that has grown following the famous caldera-forming 1883 eruption of Krakatau. It breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week. We present new major and trace element data combined with whole-rock delta O-18, Sr and Nd isotope data for 1883, 1993 and 2002 Krakatau eruptive products and the surrounding crust. Bombs erupted from Anak Krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism, plastic deformation and partial melting. Contact-metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high-temperature metamorphism and incorporation at mid- to upper-crustal depth. Energy-constrained assimilation and fractional crystallization modelling of whole-rock data suggests that the Anak Krakatau magmas have a genetic relationship with the 1883 eruption products. The geochemical impact of crustal contaminants on whole-rock compositions is apparently small, and we conclude that low levels of assimilation of a quartzo-feldspathic sediment are recorded in Anak Krakatau magmas. Plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning, however, and are also isotopically variable with a total range in Sr-87/Sr-86 of 0 center dot 7043-0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry. This suggests that although shallow crustal assimilation appears to have had a limited effect on whole-rock chemistry, a complex late-stage differentiation history is recorded within the magma's cargo of crystals and xenoliths.
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| 2. |
- Meade, F. C., et al.
(author)
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Magma Ascent along a Major Terrane Boundary: Crustal Contamination and Magma Mixing at the Drumadoon Intrusive Complex, Isle of Arran, Scotland
- 2009
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In: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 50:12, s. 2345-2374
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Journal article (peer-reviewed)abstract
- The composite intrusions of Drumadoon and An Cumhann crop out on the SE coast of the Isle of Arran, Scotland and form part of the larger British and Irish Palaeogene Igneous Province, a subset of the North Atlantic Igneous Province. The intrusions (shallow-level dykes and sills) comprise a central quartz-feldspar-phyric rhyolite flanked by xenocryst-bearing basaltic andesite, with an intermediate zone of dark quartz-feldspar-phyric dacite. New geochemical data provide information on the evolution of the component magmas and their relationships with each other, as well as their interaction with the crust through which they travelled. During shallow-crustal emplacement, the end-member magmas mixed. Isotopic evidence shows that both magmas were contaminated by the crust prior to mixing; the basaltic andesite magma preserves some evidence of contamination within the lower crust, whereas the rhyolite mainly records upper-crustal contamination. The Highland Boundary Fault divides Arran into two distinct terranes, the Neoproterozoic to Early Palaeozoic Grampian Terrane to the north and the Palaeozoic Midland Valley Terrane to the south. The Drumadoon Complex lies within the Midland Valley Terrane but its isotopic signatures indicate almost exclusive involvement of Grampian Terrane crust. Therefore, although the magmas originated at depth on the northern side of the Highland Boundary Fault, they have crossed this boundary during their evolution, probably just prior to emplacement.
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| 3. |
- Barker, Abigail K., et al.
(author)
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Magmatic evolution of the Cadamosto Seamount, Cape Verde : Beyond the spatial extent of EM1
- 2012
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In: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 163:6, s. 949-965
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
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| 5. |
- Troll, Valentin R., et al.
(author)
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A large explosive silicic eruption in the British Palaeogene Igneous Province
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Journal article (peer-reviewed)abstract
- Large-volume pyroclastic eruptions are not known from the basalt-dominated British Palaeogene Igneous Province (BPIP), although silicic magmatism is documented from intra-caldera successions in central volcanoes and from small-volume ash-layers in the associated lava fields. Exceptions are the Sgùrr of Eigg (58.7 Ma) and Òigh-sgeir pitchstones in the Inner Hebrides (>30 km apart), which have been conjectured to represent remnants of a single large silicic event. Currently available major element data from these outcrops differ, however, creating a need to test if the two pitchstones are really related. We employ a systematic array of methods ranging from mineralogy to isotope geochemistry and find that samples from the two outcrops display identical mineral textures and compositions, major- and trace elements, and Sr-Nd-Pb-O isotope ratios, supporting that the two outcrops represent a single, formerly extensive, pyroclastic deposit. Available isotope constraints suggest a vent in the Hebridean Terrane and available radiometric ages point to Skye, ~40 km to the North. A reconstructed eruption volume of ≥5km3 DRE is derived, suggesting a VEI 5 event or larger. We therefore argue, contrary to long-held perception, that large-volume silicic volcanism and its associated climatic effects were likely integral to the BPIP during the opening of the North Atlantic.
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| 6. |
- Troll, Valentin R., et al.
(author)
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Petrogenesis of the Loch Bà ring-dyke and Centre 3 granites, Isle of Mull, Scotland
- 2021
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In: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 176:2
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Journal article (peer-reviewed)abstract
- The Loch Bà 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 Bà 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 Bà 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 Bà rhyolite (87Sr/86Sri = 0.716) imply a considerable contribution of local Moine-type metasedimentary crust (87Sr/86Sr = 0.717–0.736), whereas Loch Bà mafic inclusions (87Sr/86Sri = 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 (87Sr/86Sri = 0.709–0.716), are less intensely affected by crustal assimilation relative to the Loch Bá 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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| 7. |
- Wiesmaier, S., et al.
(author)
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Bimodality of lavas in the teide-pico viejo succession in tenerife-the role of crustal melting in the origin of recent phonolites
- 2012
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In: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 53:12, s. 2465-2495
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Journal article (peer-reviewed)abstract
- In Tenerife, lavas of the recent Teide-Pico Viejo central complex show a marked bimodality in composition from initially mafic lavas (200-30 ka) to highly differentiated phonolites (30-0 ka). After this abrupt change, the bimodality of the lavas continued to manifest itself between the now felsic Teide-Pico Viejo central complex and the adjacent, but exclusively mafic, rift zones. Whole-rock trace element fingerprinting distinguishes three compositional groups (mafic, transitional, felsic). Groundmass Sr-Nd-Pb-O and feldspar δ. 18O data demonstrate open-system behaviour for the petrogenesis of the Teide-Pico Viejo felsic lavas by high. 87Sr/. 86Sr ratios of up to 0·7049, uniform. 206Pb/. 204Pb (19·75-19·78), variable. 207Pb/. 204Pb (15·53-15·62) and heterogeneous δ. 18O values (5·43-6·80‰). However, ocean sediment contamination can be excluded because of the low. 206Pb/. 204Pb ratios of North Atlantic sediments. Isotope mixing hyperbolae reproduce the entire Teide-Pico Viejo succession and require an assimilant of predominantly felsic composition. Unsystematic and heterogeneous variation of δ. 18O in fresh and unaltered feldspars across the Teide-Pico Viejo succession indicates magmatic addition of diverse δ. 18O assimilants, altered near surface at high and low temperatures. The best fit for these requirements is provided by nepheline syenite that occurs as fresh or altered lithic blocks in voluminous pre-Teide ignimbrite deposits and is similarly heterogeneous in oxygen isotope composition. Nepheline syenite blocks are considered to represent deep remnants of associated earlier eruptions and were thus available for assimilation at depth. Rare earth element modelling indicates that nepheline syenite needs to be melted in bulk to form a suitable end-member composition. Using this assimilant, energy-constrained assimilation fractional crystallization (EC-AFC) modelling reproduces the bulk of the succession, which leads us to suggest that Teide-Pico Viejo petrogenesis is governed by assimilation and fractional crystallization. Both mixing hyperbolae and EC-AFC models indicate that assimilation is more pronounced for the more felsic lavas. The maximum assimilation is evident in the most strongly differentiated (and the most radiogenic in Sr) lava and computes to >97·8% of the assimilant. This most evolved eruption probably represents nepheline syenite bulk melts that formed spatially decoupled from juvenile material. This study therefore recognizes a wider variability of magmatic differentiation processes at Teide-Pico Viejo than previously thought.
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| 8. |
- Meade, F. C., et al.
(author)
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Bimodal magmatism produced by progressively inhibited crustal assimilation
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4199-
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Journal article (peer-reviewed)abstract
- The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.
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