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| 2. |
- Goluchowska, Karolina, et al.
(författare)
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The role of crustal contamination in magma evolution of Neoproterozoic metaigneous rocks from Southwest Svalbard
- 2022
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 370
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Tidskriftsartikel (refereegranskat)abstract
- Late Neoproterozoic metavolcanic rocks occur along the Southwest coast of Svalbard. The protoliths of the metavolcanic rocks from Wedel Jarlsberg Land and Nordenskiold Land are mainly diabase, basalt and felsic tuff of tholeiitic affinity associated with continental magmatism. We investigate the magma evolution of the meta-volcanic rocks paying particular attention to processes of magma-crust interaction and assess potential sources of crustal contamination. These goals are achieved by employing trace element geochemistry, as well as Sr and Nd isotope geochemistry. Metavolcanic rocks from the South (Orvindalen and Werenskioldbreen) have higher LREE, LILE and Th compared to rocks from the North (Nordenskiold Land), which are relatively enriched in Sr. Incompatible element ratios like Th/La, Th/Nb, La/Nb, Th/Yb and Nb/Yb also decrease from South to North. The Nd-143/Nd-144(635 Ma) ranges from 0.511396 to 0.512356 and increases from South to North. For Sr isotopes, the metavolcanic rocks show a wide range, however in the South we observe Sr-87/Sr-86(635 Ma) of 0.70407-0.73043 and in the North Sr-87/Sr-86(635 Ma) of 0.70410-0.71028. Energy Constrained - Assimilation and Fractional Crystallization (EC-AFC) modelling indicates that the extent of magma contamination is highest in the South. Additionally the modelling suggests fractional crystallization and assimilation of granulite or amphibolite followed by shale for the metavolcanic rocks in the South and for the North mixtures of carbonate and shale contributed. This geographical pattern of assimilation reflects the upper crustal metasedimentary sequences, where phyllites are common in the South (Orvindalen and Werenskioldbreen) and carbonates are more common in the North (Nordenskiold Land). Density contrasts and impermeable layers within the continental crust would likely have acted as barriers to ascending magma, forcing it to stall and providing opportunities for magma-crust interaction.
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| 3. |
- Troll, Valentin R., et al.
(författare)
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A large explosive silicic eruption in the British Palaeogene Igneous Province
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Troll, Valentin R., et al.
(författare)
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Petrogenesis of the Loch Bà ring-dyke and Centre 3 granites, Isle of Mull, Scotland
- 2021
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 176:2
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Wiesmaier, Sebastian, et al.
(författare)
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Magmatic Differentiation in the Teide–Pico Viejo Succession : Isotope Analysis as a Key to Deciphering the Origin of Phonolite Magma
- 2013
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Ingår i: Teide Volcano. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642258923 - 9783642258930 ; , s. 173-190
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Bokkapitel (refereegranskat)abstract
- In Tenerife, lavas of the recent Teide–Pico Viejo central complex show a marked bimodality in composition from initially mafic lava (200–30 ka) to highly differentiated phonolite (30–0 ka). Groundmass Sr–Nd–Pb–O and feldspar 18O data demonstrate open system behaviour for the petrogenesis of Teide–Pico Viejo felsic lavas, but contamination by ocean sediment can be excluded due to the low 206Pb/204Pb ratios of North Atlantic sediment. Isotope mixing hyperbolae require an assimilant of predominantly felsic composition for the Teide–Pico Viejo succession. Unsystematic and heterogeneous variation of 18O in fresh and unaltered feldspars across the Teide–Pico Viejo succession indicates magmatic addition of diverse 18O assimilants, best matched by nepheline syenites that occur as fresh and altered lithic blocks in voluminous pre-Teide ignimbrite deposits. Rare earth element modelling indicates that nepheline syenite needs to be melted in bulk to form a suitable end-member composition. Energy-Constrained Assimilation Fractional Crystallisation (EC-AFC) modelling reproduces the bulk of the succession, which implies that the petrogenesis of Teide–Pico Viejo lavas is governed by the coupled assimilation of nepheline syenite during fractional crystallisation. The most differentiated (and most radiogenic) lava computes to >97.8 % assimilant, likely represented by a nepheline syenite bulk melt that formed by underplating with juvenile mafic material. These recent research developments therefore recognise a wider variability of magmatic differentiation processes at Teide–Pico Viejo than previously considered.
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