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  • 1.
    Burchardt, Steffi
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Center for Natural Hazard and Disaster Science, Uppsala University, Uppsala, Sweden.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Palma, J. Octavio
    Y‐TEC–CONICET. Av. Del Petroleo s/n‐(Entre 129 y 143), Berisso (CP 1923), Buenos Aires, Argentina.
    Galland, Olivier
    Physics of Geological Processes, The NJORD Centre, University of Oslo.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Mair, Karen
    Physics of Geological Processes, The NJORD Centre, University of Oslo.
    Jerram, Dougal A.
    Dougal Earth Ltd. and CEED, University of Oslo.
    Hammer, Øyvind
    Natural History Museum, University of Oslo.
    Sun, Yang
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Progressive growth of the Cerro Bayo cryptodome, Chachahuén volcano, Argentina: implications for viscous magma emplacement2019Inngår i: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 124, s. 7934-7961, artikkel-id JGRB53599Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cryptodome and dome collapse is associated with volcanic hazards, such as, explosive eruptions, pyroclastic density currents, and volcanic edifice collapse. The study of the growth and evolution of volcanic domes provides vital information on the link between dome growth and the development of weakness zones that may cause collapse. The Cerro Bayo cryptodome is superbly exposed in the eroded Miocene Chachahuén volcano in the Neuquén basin, Argentina. Cerro Bayo is a >0.3 km3 trachyandesitic cryptodome that intruded within the uppermost kilometer of the Chachahuén volcano. Here we investigate the emplacement of the Cerro Bayo cryptodome using structural mapping, photogrammetry, 3D structural modelling and measurement of magma flow indicators, brittle deformation features and magnetic fabrics with anisotropy of magnetic susceptibility (AMS). Magma flow fabrics near the margin are concentric and indicate contact-parallel flow and internal inflation of the body. Magmatic and magnetic fabrics and fracture patterns in the interior of the cryptodome are more complex and outline several structural domains. These domains are separated by magmatic shear zones that accommodated intrusion growth. The shear zones locally overprint the earlier formed concentric fabric. The nature of the structural domains shows that emplacement of Cerro Bayo occurred in three stages that resemble the endogenous to exogenous growth of volcanic domes. The formation of magmatic shear zones during cryptodome formation may have a profound effect on cryptodome stability by creating weakness zones that increase the risk of collapse.

  • 2.
    Burchardt, Steffi
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Palma, J. Octavio
    Y-TEC – CONICET. Av. Del Petroleo s/n - (Entre 129 y 143), Berisso (CP 1923), Buenos Aires, Argentina .
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Galland, Olivier
    Physics of Geological Processes, The NJORD Centre, Department of Geosciences, University of Oslo, Box 1047, Blindern, 0316 Oslo, Norway.
    Almqvist, Bjarne S. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Mair, Karen
    Physics of Geological Processes, The NJORD Centre, Department of Geosciences, University of Oslo, Box 1047, Blindern, 0316 Oslo, Norway.
    Jerram, Dougal A.
    Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, Norway.
    Hammer, Øyvind
    Natural History Museum, University of Oslo, Box 1172, 0318 Oslo, Norway.
    Progressive growth of the Cerro Bayo cryptodome, Chachahuén volcano, Argentina – implications for viscous magma emplacementManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Cryptodome and dome collapse is associated with volcanic hazards, such as, explosive eruptions, pyroclastic flows, and volcanic edifice collapse. Study of the growth and evolution of volcanic domes provides vital information on the link between dome growth and the development of weakness zones that may cause collapse. The Cerro Bayo cryptodome is superbly exposed in the eroded Miocene Chachahuén volcano in the Neuquén basin, Argentina. Cerro Bayo is a >0.3 km3 trachyandesitic cryptodome that intruded within the uppermost kilometer of the Chachahuén volcano. Here we investigate the emplacement of the Cerro Bayo cryptodome using structural mapping, photogrammetry, 3D structural modelling and measurement of magma flow indicators, brittle deformation features and magnetic fabrics with anisotropy of magnetic susceptibility (AMS). Magma flow fabrics near the margin are concentric and indicate contact-parallel flow and internal inflation of the body. Magmatic and magnetic fabrics and fracture patters in the interior of the cryptodome are more complex and outline several structural domains. These domains are separated by magmatic shear zones that accommodated intrusion growth. The shear zones locally overprint the earlier formed concentric fabric. The nature of the structural domains shows that emplacement of Cerro Bayo occurred in three stages that resemble the endogenous to exogenous growth of volcanic domes. The formation of magmatic shear zones during cryptodome formation may have a profound effect on cryptodome stability by creating weakness zones that increase the risk of collapse.

  • 3.
    Geiger, Harri
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Deegan, Frances
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Stockholm Univ, Dept Geol Sci, Stockholm, Sweden.
    Troll, Valentin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Gudmundsson, Ólafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Tryggvason, Ari
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Krumbholz, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Harris, Chris
    Univ Cape Town, Dept Geol Sci, Rondebosch, South Africa.
    Magma plumbing for the 2014–2015 Holuhraun eruption, Iceland2016Inngår i: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 17, nr 8, s. 2953-2968Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The 2014–2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm butwas accompanied by caldera subsidence in the Barðarbunga central volcano 45 km to the southwest. Geophysicalmonitoring of the eruption identified a seismic swarm that migrated from Barðarbunga to theHoluhraun eruption site over the course of two weeks. In order to better understand this lateral connectionbetween Barðarbunga and Holuhraun, we present mineral textures and compositions, mineral-meltequilibriumcalculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraunsamples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from theBarðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system.Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption,wherein clinopyroxene and plagioclase crystallized at average depths of 17 km and 5 km,respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbingsystem facilitated magma mixing and assimilation of low-d18O Icelandic crust prior to eruption. In conjunctionwith the existing geophysical evidence for lateral migration, our results support a model of initial verticalmagma ascent within the Barðarbunga plumbing system followed by lateral transport of aggregatedmagma batches within the upper crust to the Holuhraun eruption site.

  • 4.
    Latimer, Ben
    et al.
    1School of Biological, Earth and Environmental Sciences, University College Cork, Cork T23 N73K, Ireland.
    McCarthy, William
    2School of Earth & Environmental Sciences, University of St. Andrews, St. Andrews KY16 9TS, UK.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. 2School of Earth & Environmental Sciences, University of St. Andrews, St. Andrews KY16 9TS, UK.
    Reavy, John
    1School of Biological, Earth and Environmental Sciences, University College Cork, Cork T23 N73K, Ireland.
    Enclaves as mushy magma strain archives: New perspectives on composite magmatic fabrics in plutons2024Inngår i: Geosphere, E-ISSN 1553-040X, Vol. 20, nr 5, s. 1390-1410Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mineral fabrics within igneous intrusions can archive both tectonic and magmatic processes. However, whether magmatic state fabrics reflect primary magmatic processes or regional tectonic strain is often ambiguous. To investigate when fabrics are formed, one can compare the mineral fabrics to primary magmatic features, such as the interface between solidified magmas in mingling zones. The monzodioritic Fanad pluton shows a NNE-SSW–aligned petrofabric parallel to the strike of a nearby shear zone, with dioritic enclaves aligned parallel and oblique to this petrofabric. We therefore aimed to test if the enclaves’ internal fabrics are passive and align with enclave morphology or result from progressive overprint by regional tectonic strain. Crystallographic preferred orientation and anisotropy of magnetic susceptibility data from all enclaves and the host monzodiorite revealed a NNE-SSW petrofabric parallel to the regional tectonomagmatic fabric. However, anisotropy of anhysteretic remanent magnetization data within petrofabric-oblique enclaves revealed a primary fabric parallel to the enclave long axis. Therefore, we interpret enclave morphologies to reflect earlier magmatic state deformation, with fabrics being realigned to regional tectonic deformation. These two distinct petrofabrics were interpreted in the context of the magmatic processes and the evolving late Caledonian paleostress field, with earlier magma processes distinguished from subsequent tectonic overprinting occurring in the magmatic state. Our new data show that multiple fabrics are preserved within enclaves even though all fabric development occurred within a magmatic state. Our results also show that enclaves can effectively record successive strain events, providing new insight with which to decipher tectonomagmatic processes.

    Fulltekst (pdf)
    fulltext
  • 5.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Uppsala University.
    The dynamic emplacement of felsic magma in the upper crust2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Felsic magma intrudes earth’s upper crust through a variety of mechanisms. Magma intrusion growth and shape have mainly been explained in terms of host rock properties and intrusion depth, while considering the magma as an overpressurised fluid. However, volcanologists view a magma as a rheologically evolving fluid, which affects the magma flow in volcanic conduits. This thesis seeks to explore intrusion dynamics during magma emplacement by taking both the magma and the host rock into account. The first part of the thesis investigates the emplacement of the Sandfell laccolith/cryptodome, the Cerro Bayo cryptodome and the Mourne granite pluton. Both cryptodomes grew initially by inflation, which resulted in contact-parallel magma flow. Later during the emplacement, the rim of the intrusions viscously stalled as indicated by brecciation and fracturing in the intrusion rims, which then forced them to grow vertically. Our observations suggest that rheological changes in the magma during intrusion growth may control the shape of the cryptodomes/laccoliths. Previously proposed emplacement mechanisms of the Mourne Mountains granite pluton were tested by investigating host-rock deformation and the surrounding contact-metamorphic aureole. The aureole displays contact-metamorphic segregations that were later deformed by brecciation and shearing. The consistent regional fracture patterns in the pluton roof indicate that it was not widely domed, while the north-eastern wall of the pluton was deflected parallel to the strike of the contact. These observations suggest that multiple mechanisms emplaced the pluton, involving both floor subsidence and deflection of the roof and wall.

    The last part of the thesis studies the magma plumbing system to the Holuhraun 2014-15 eruption with mineral and whole-rock geochemistry and thermobarometry. The Holuhraun eruption was accompanied by subsidence in the Bárðarbunga caldera but occurred in the Askja volcanic system. Our results show that the Holuhraun eruption was fed from a vertically extensive magma plumbing system in the Bárðarbunga volcanic system.

    The works of this thesis highlight that felsic magma emplacement in the upper crust involves multiple and dynamic mechanisms that control the growth and shape of the intrusion and that the interplay between magma and host-rock properties needs to be considered.

    Fulltekst (pdf)
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    Download (jpg)
    presentationsbild
  • 6.
    Mattsson, Tobias
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. University of St. Andrews, UK; Uppsala University, Sweden.
    Benoît, Petri
    Almqvist, Bjarne
    McCarthy, William
    Burchardt, Steffi
    Palma, J. Octavio
    Hammer, Øyvind
    Galland, Olivier
    Decrypting magnetic fabrics (AMS, AARM, AIRM) through the analysis of mineral shape fabrics and distribution anisotropy2021Inngår i: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 126, nr 6, artikkel-id e2021JB021895Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X-ray micro-computed tomography to directly compare mineral shape-preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and > 50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: the magnetite and the amphibole shape fabrics and the magnetite spatial distribution. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P’ = 1.079). If shape fabrics and/or magnetite distribution are non-coaxial, the resulting AMS is weakly anisotropic (P’ = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first-order implications for the interpretation of petrofabrics using magnetic methods. 

  • 7.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Galland, Olivier
    The Njord Centre, University of Oslo.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Palma, J. Octavio
    Y-tec, Conicet.
    Magma Deformation During Laccolith Emplacement: Examples From Iceland And Argentina2018Inngår i: Geological Society of America Abstracts with Programs, 2018, Vol. 50, artikkel-id 18-11Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Felsic magma commonly pools within shallow mushroom-shaped magmatic intrusions, so-called laccoliths or cryptodomes, which can cause both explosive eruptions and collapse of the volcanic edifice. Deformation during laccolith emplacement is primarily considered to occur in the host rock. However, shallowly emplaced laccoliths show extensive internal, magmatic deformation. While deformation of magma in volcanic conduits is an important process for regulating eruptive behavior, the effects of magma deformation on intrusion emplacement remain largely unexplored. By combining field mapping, anisotropy of magnetic susceptibility and microstructural analysis, we studied the emplacement of two laccoliths emplaced within the upper kilometer of the crust in a single intrusive event. The rhyolitic Sandfell laccolith, Iceland, which intruded at a depth of 500 m and the dacitic Cerro Bayo laccolith, Argentina. The initial growth stage of the two laccoliths is characterized by contact parallel flow indicators that formed during inflation of the laccolith. The second growth stage encompass brecciation and fracturing in the rim of the intrusion. Fractures in the Sandfell laccolith occur in layers and individual fractures are parallel to strain-localization bands in coherent rhyolite. A dominantly oblate magmatic fabric in the fractured areas, S-C fabrics in flow bands and conjugate geometry of strain-localization bands and the fractures demonstrate that the magma was sheared and compacted by the continuous intrusion of magma into the bodies. This further implies that the rims of the magma bodies essentially solidified during the intrusive event. In the third stage of growth, the stalled rim of the laccolith is breached, which promotes vertical growth of the magma body facilitated by larger steeply-dipping faults and shear zones. Our observations indicate that syn-emplacement changes in magma rheology play a major role in the emplacement of viscous magma intrusions in the upper kilometer of the crust.

  • 8.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Syn-emplacement fracturing in the Sandfell laccolith, eastern Iceland2018Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Felsic magma commonly pools within mushroom-shaped magma chambers, so-called laccoliths or cryptodomes at shallow crustal levels, which can cause collapse of the volcanic edifice. While deformation of magma in volcanic conduits is an important process for regulating eruptive behaviour (Pistone et al., 2016), the bulk of the deformation associated with laccolith emplacement is considered to occur in the host-rock (Pollard & Johnson, 1973), and the effects of magma deformation on the intrusion emplacement is largely unexplored. Here we describe the deformation associated with the emplacement of the 0.5 km3 rhyolitic Sandfell laccolith in eastern Iceland, which formed in a single intrusive event. By combining field measurements, 3D modelling, anisotropy of magnetic susceptibility, and microstructural analysis, we quantify deformation that occurred in both the host-rock and the magma to investigate its effect on intrusion emplacement. Magmatic and magnetic fabric analyses reveal contact-parallel magma flow during the initial stages of intrusion emplacement. The magma flow fabric is overprinted by strain-localisation bands, which indicate that the magma subsequently became viscously stalled and was deformed by consecutively intruding magma. This change in magma rheology can be attributed to the interaction between the strain-localisation bands and the flow bands, which caused extensive fracture-rich layers in the magma and led to decompression degassing, crystallization, and rapid solidification of half of the magmatic body. Our observations indicate that syn-emplacement rheology change, and associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the emplacement of shallow viscous magma intrusions.

    References:

    Pistone, M., Cordonnier, B., Ulmer, P. & Caricchi, L. 2016: Rheological flow laws for multiphase magmas: An empirical approach. Journal of Volcanology and Geothermal Research 321, 158–170.

    Pollard, D.D. & Johnson, A.M. 1973: Mechanics of growth of some laccolithic intrusions in the Henry mountains, Utah, II: Bending and failure of overburden layers and sill formation. Tectonophysics 18, 311–354.

  • 9.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Uppsala centrum för hållbar utveckling, CSD Uppsala.
    Palma, J. Octavio
    Y-tec, Conicet.
    Galland, Olivier
    The Njord Centre, University of Oslo.
    Growth stages of cryptodomes: Examples from Iceland and Argentina2019Konferansepaper (Annet vitenskapelig)
  • 10.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Center for Natural Hazards and Disaster Science, Uppsala University, Uppsala, Sweden.
    Almqvist, Bjarne S. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Center for Natural Hazards and Disaster Science, Uppsala University, Uppsala, Sweden.
    Syn-Emplacement Fracturing in the Sandfell Laccolith, Eastern Iceland: Implications for Rhyolite Intrusion Growth and Volcanic Hazards2018Inngår i: Frontiers in Earth Science, E-ISSN 2296-6463, Vol. 6, artikkel-id 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Felsic magma commonly pools within shallow mushroom-shaped magmatic intrusions, so-called laccoliths or cryptodomes, which can cause both explosive eruptions and collapse of the volcanic edifice. Deformation during laccolith emplacement is primarily considered to occur in the host rock. However, shallowly emplaced laccoliths (cryptodomes) show extensive internal deformation. While deformation of magma in volcanic conduits is an important process for regulating eruptive behavior, the effects of magma deformation on intrusion emplacement remain largely unexplored. In this study, we investigate the emplacement of the 0.57 km3 rhyolitic Sandfell laccolith, Iceland, which formed at a depth of 500 m in a single intrusive event. By combining field measurements, 3D modeling, anisotropy of magnetic susceptibility (AMS), microstructural analysis, and FEM modeling we examine deformation in the magma to constrain its influence on intrusion emplacement. Concentric flow bands and S-C fabrics reveal contact-parallel magma flow during the initial stages of laccolith inflation. The magma flow fabric is overprinted by strain-localization bands (SLBs) and more than one third of the volume of the Sandfell laccolith displays concentric intensely fractured layers. A dominantly oblate magmatic fabric in the fractured areas and conjugate geometry of SLBs, and fractures in the fracture layers demonstrate that the magma was deformed by intrusive stresses. This implies that a large volume of magma became viscously stalled and was unable to flow during intrusion. Fine-grained groundmass and vesicle-poor rock adjacent to the fracture layers point to that the interaction between the SLBs and the flow bands at sub-solidus state caused the brittle-failure and triggered decompression degassing and crystallization, which led to rapid viscosity increase in the magma. The extent of syn-emplacement fracturing in the Sandfell laccolith further shows that strain-induced degassing limited the amount of eruptible magma by essentially solidifying the rim of the magma body. Our observations indicate that syn-emplacement changes in rheology, and the associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the emplacement of viscous magma intrusions in the upper kilometer of the crust.

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  • 11.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Mair, Karen
    Physics of Geological Processes, The NJORD Centre, Department of Geo-sciences, University of Oslo, Box 1047, Blindern, 0316 Oslo, Norway.
    Place, Joachim
    Formerly at the Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36, Uppsala, Sweden.
    Floor subsidence and roof and wall-rock deformation during the emplacement of the Mourne Mountains granite pluton; Insights from the regional fracture patternManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The Mourne Mountains magmatic centre in Northern Ireland consist of five successively emplaced granites and has traditionally been viewed as a type locality of a magma body emplaced by cauldron subsidence, primarily because the granites truncate the host-rock bedding. Cauldron subsidence makes space for magma through ring dyking and floor subsidence. However, the Mourne granites were more recently re-interpreted as laccoliths. Laccolith intrusions form by inflation and dome their hosts. Here we perform a detailed study of the deformation in the host rock to the Mourne granite pluton in order to test its emplacement mechanism. We use the regional fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-related deformation. In addition, we use virtual scan lines to investigate the fracture sets. The dip and azimuth of the regional fractures are very consistent on the roof of the intrusion and can be separated into four steeply-dipping sets dominantly striking SE, S, NE, and E, which rules out pluton-wide doming. In contrast, fracture orientations in the wall to the granites in the NE show contact-strike parallel shear. In several samples from the contact-metamorphic aureole, segregations are displaced by fractures and shear zones, and indicate that the initial granite intrusion did not cause significant deformation of the host, while later granite pulses deformed the aureole rocks. Based on the north-eastward inclined granite-granite contacts, sub-vertical joints in the granites inclined to the west, and the westward younging succession of the granites and the displaced metamorphic segregations, we propose that multiple mechanisms involving asymmetric ‘trap-door’ floor subsidence and deflection of the north-eastern wall of the intrusion parallel to a propagating ring-dyke accommodated the emplacement of the granites.

  • 12.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Mair, Karen
    Physics of Geological Processes, The NJORD Center, Department of Geosciences, University of Oslo, Box 1047, Blindern, 0316 Oslo, Norway.
    Place, Joachim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Host-rock deformation during the emplacement of the Mourne Mountains granite pluton: Insights from the regional fracture pattern2020Inngår i: Geosphere, E-ISSN 1553-040X, Vol. 16, nr 1, s. 182-209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Mourne Mountains magmatic center in Northern Ireland consists offive successively intruded granites emplaced in the upper crust. The Mournegranite pluton has classically been viewed as a type locality of a magma bodyemplaced by cauldron subsidence. Cauldron subsidence makes space formagma through the emplacement of ring dikes and floor subsidence. However,the Mourne granites were more recently re-interpreted as laccoliths andbysmaliths. Laccolith intrusions form by inflation and dome their host rock.Here we perform a detailed study of the deformation in the host rock to theMourne granite pluton in order to test its emplacement mechanism. We use thehost-rock fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-relateddeformation. The dip and azimuth of the fractures are very consistent onthe roof of the intrusion and can be separated into four steeply inclined setsdominantly striking SE, S, NE, and E, which rules out pluton-wide doming. Incontrast, fracture orientations in the northeastern wall to the granites suggestshear parallel to the contact. Additionally, contact-metamorphic segregationsalong the northeastern contact are brecciated. Based on the host-rock fracturepattern, the contact aureole deformation, and the north-eastward–inclinedgranite-granite contacts, we propose that mechanisms involving either asymmetric“trap-door” floor subsidence or laccolith and bysmalith intrusion alongan inclined or curved floor accommodated the emplacement of the granitesand led to deflection of the northeastern wall of the intrusion.

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  • 13.
    Mattsson, Tobias
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    McCarthy, William
    Schmiedel, Tobias
    Transport of Magma in Granitic Mush Systems; an Example From the Götemar Pluton, Sweden2024Inngår i: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 25, nr 1, artikkel-id e2023GC011061Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Granitic magma bodies form in the ephemeral part of magma mush systems and are emplaced by a variety of mechanisms in different tectonic settings. This study investigates how granitic magma emplacement processes and tectonomagmatic interactions assert control over the architecture of mush state pluton-scale magma transport pathways. The 1.45 Ga shallow-crustal Gotemar pluton is a 4.5 km diameter circular pluton that consists of three granite units: a coarse-grained red granite, a medium-grained pale to red granite, and fine-grained pale microgranite sheets. We employed geological mapping supported by Anisotropy of Magnetic Susceptibility (AMS) to examine the magmatic and regional tectonic controls on late-stage magma transport in the Gotemar granitic magma mush system. Multiple parallel arcuate subhorizontal microgranite and medium-grained granite sheets (from 0.1 to 10s of meters thick) were mapped within the pluton. The arcuate sheets pinch out from the northern part of the pluton toward the SE inferring magma propagation direction. A dominant set of vertical granitic sheets within the granite body strikes NW-SE. The AMS fabrics are contact-parallel in the main medium-grained granite body and indicate inflation. Within the microgranite sheets, the AMS fabrics are parallel to the sheet strike and support a sheet propagation direction to the SE. The Gotemar pluton displays a clear link between arcuate (concentric) magma-transporting sheets and concentric strain-partitioning related to the intrusion of medium-grained granite magma. The vertical magma sheet orientations are consistent with an NE-SW extensional stress field that is associated with the extensional back-arc stress regime of the contemporary Hallandian Orogen. The eruptive products of volcanoes are thought to be stored in pockets of melt in crystal-dominated magmatic systems called crystal mushes prior to volcanic eruptions. An understanding of where magma is stored and how it is transported in mush systems is important in order to predict the eruptive behavior of the volcanic system. This contribution investigates the magma transport pathways in the Gotemar granite in Sweden and its relationship to local magmatic deformation and regional deformation related to the Hallandian mountain building event. We show that magma is transported in vertical sheets parallel to the front of the Hallandian Orogen and laterally in sub-horizontal arcuate sheets that reflect the circular shape of the granite pluton. Our study highlights the importance of understanding the shape and the formation of the magmatic granite body for deciphering the melt transport in the magma mush system under volcanoes. Subhorizontal magma transport in a granitic magma mush controlled by magma emplacement structuresVertical magma sheets in granitic magma mush controlled by the regional stress fieldMagma transported in concentric magma fingers in the circular Gotemar granite pluton

  • 14.
    Mattsson, Tobias
    et al.
    Department of Geological Sciences Stockholm University Stockholm Sweden;School of Earth and Environmental Sciences University of St. Andrews St. Andrews UK.
    McCarthy, William
    School of Earth and Environmental Sciences University of St. Andrews St. Andrews UK.
    Schmiedel, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Department of Geoscience & Engineering TU Delft Delft The Netherlands.
    Transport of Magma in Granitic Mush Systems; an Example From the Götemar Pluton, Sweden2024Inngår i: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 25, nr 1, artikkel-id e2023GC011061Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Granitic magma bodies form in the ephemeral part of magma mush systems and are emplaced by a variety of mechanisms in different tectonic settings. This study investigates how granitic magma emplacement processes and tectonomagmatic interactions assert control over the architecture of mush state pluton-scale magma transport pathways. The 1.45 Ga shallow-crustal Götemar pluton is a 4.5 km diameter circular pluton that consists of three granite units: a coarse-grained red granite, a medium-grained pale to red granite, and fine-grained pale microgranite sheets. We employed geological mapping supported by Anisotropy of Magnetic Susceptibility (AMS) to examine the magmatic and regional tectonic controls on late-stage magma transport in the Götemar granitic magma mush system. Multiple parallel arcuate subhorizontal microgranite and medium-grained granite sheets (from 0.1 to 10s of meters thick) were mapped within the pluton. The arcuate sheets pinch out from the northern part of the pluton toward the SE inferring magma propagation direction. A dominant set of vertical granitic sheets within the granite body strikes NW-SE. The AMS fabrics are contact-parallel in the main medium-grained granite body and indicate inflation. Within the microgranite sheets, the AMS fabrics are parallel to the sheet strike and support a sheet propagation direction to the SE. The Götemar pluton displays a clear link between arcuate (concentric) magma-transporting sheets and concentric strain-partitioning related to the intrusion of medium-grained granite magma. The vertical magma sheet orientations are consistent with an NE-SW extensional stress field that is associated with the extensional back-arc stress regime of the contemporary Hallandian Orogen.

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  • 15.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Stockholm University; University of St. Andrews.
    Petri, Benoit
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    McCarthy, William
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Palma, J. Octavio
    Hammer, Øyvind
    Galland, Olivier
    Decrypting Magnetic Fabrics (AMS, AARM, AIRM) Through the Analysis of Mineral Shape Fabrics and Distribution Anisotropy2021Inngår i: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 126, nr 6, artikkel-id e2021JB021895Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X-ray micro-computed tomography to directly compare mineral shape-preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and >50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: The magnetite and the amphibole shape fabrics and the magnetite distribution anisotropy. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P' = 1.079). If shape fabrics and/or magnetite distribution anisotropy are non-coaxial, the resulting AMS is weakly anisotropic (P' = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first-order implications for the interpretation of petrofabrics using magnetic methods.

    Fulltekst (pdf)
    fulltext
  • 16.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Yang, Sun
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Barker, Abigail K.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Disaster Science (CNDS), Uppsala University, Villavägen 16, 75236 Uppsala, Sweden.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Disaster Science (CNDS), Uppsala University, Villavägen 16, 75236 Uppsala, Sweden.
    Hammer, Øyvind
    Natural History Museum, University of Oslo, Box 1172, 0318 Oslo, Norway.
    Palma, J. Octavio
    Y-TEC – CONICET. Av. Del Petroleo s/n - (Entre 129 y 143), Berisso (CP 1923), Buenos Aires, Argentina.
    Galland, Olivier
    Physics of Geological Processes, The NJORD Centre, Department of Geosciences, University of Oslo, Box 1047, Blindern, 0316 Oslo, Norway.
    Jerram, Dougal A.
    Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, Norway.
    Ofierska, Weronika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Kuylenstierna, Elin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Quantifying the crystal cargo of the Cerro Bayo cryptodome, Argentina; A window into pre-emplacement magma processes and storage conditionsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Shallow plumbing systems with intermediate to evolved volcanic systems can show complex magma recycling and recharge systematics. Such evidence is often stored in the information looked within the crystal cargo found in shallow systems. The Cerro Bayo cryptodome provides a classic example of such processes and was emplaced in the upper kilometre of the Miocene, back-arc Chachahuén volcano. Cerro Bayo formed during an extensive dome-building (and collapse) stage of the Chachahuén volcano, and is composed of a porphyritic trachyandesite which contains numerous mafic enclaves. This contribution investigates the deeper magma plumbing system and magmatic processes preceding the emplacement of Cerro Bayo with petrography, mineral chemistry, crystal size distributions and thermobarometry. The main crystals found in Cerro Bayo are plagioclase and amphiboles, found as mixed phenocryst/antecryst and glomerocryts, constituting about 30 vol. % of the rock. Minor mineral phases include pyroxene, apatite and magnetite. Several crystal populations are identified within the Cerro Bayo, which indicate differences within the growth histories of the populations. Some plagioclase crystal display resorbed textures and show zones with sharp increases in An mol% (up to 25 %), indicative of recharge events with hot (more mafic) magma. Whereas other crystals record only small temperature shifts, likely induced by latent heat of crystallisation. Amphibole and clinopyroxene barometers yield average crystallisation pressure estimates that range from 740 to 1036 MPa, however, they overlap within error of the barometers, revealing a storage region prior to shallow emplacement at about 30 to 40 km depth in the lower crust. The voluminous crystal cargo, diverse zoning patterns, sieve-textured plagioclase and the abundant enclaves in Cerro Bayo suggest that the magma was derived from a crystal mush storage region that was mobilised and partly mixed by the recharge of mafic melt.

  • 17. Rhodes, E. L.
    et al.
    Barker, A. K.
    Burchardt, S.
    Hieronymus, C. F.
    Rousku, S. N.
    McGarvie, D. W.
    Mattsson, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. University of St Andrews, UK.
    Schmiedel, T.
    Ronchin, E.
    Witcher, T.
    Rapid Assembly and Eruption of a Shallow Silicic Magma Reservoir, Reyðarártindur Pluton, Southeast Iceland2021Inngår i: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 22, nr 11, artikkel-id e2021GC009999Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although it is widely accepted that shallow silicic magma reservoirs exist, and can feed eruptions, their dynamics and longevity are a topic of debate. Here, we use field mapping, geochemistry, 3D pluton reconstruction and a thermal model to investigate the assembly and eruptive history of the shallow Reyðarártindur Pluton, southeast Iceland. Primarily, the exposed pluton is constructed of a single rock unit, the Main Granite (69.9–77.7 wt.% SiO2). Two further units are locally exposed as enclaves at the base of the exposure, the Granite Enclaves (67.4–70.2 wt.% SiO2), and the Quartz Monzonite Enclaves (61.8–67.3 wt.% SiO2). Geochemically, the units are related and were likely derived from the same source reservoir. In 3D, the pluton has a shape characterized by flat roof segments that are vertically offset and a volume of >2.5 km3. The pluton roof is intruded by dikes from the pluton, and in two locations displays depressions associated with large dikes. Within these particular dikes the rock is partially to wholly tuffisitic, and rock compositions range from quartz monzonite to granite. We interpret these zones as eruption-feeding conduits from the pluton. A lack of cooling contacts throughout the pluton indicates rapid magma emplacement and a thermal model calculates the top 75 m would have rheologically locked up within 1,000 years. Hence, we argue that the Reyðarártindur Pluton was an ephemeral part of the wider plumbing system that feeds a volcano, and that timeframes from emplacement to eruption were rapid.

  • 18.
    Rhodes, Emma
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Barker, Abigail
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Hieronymus, Christoph F.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Rousku, Sabine
    McGarvie, Dave
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Schmiedel, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Witcher, Taylor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Rapid formation and eruption of a silicic magma chamber2022Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Shallow magmatic reservoirs have been identified at many volcanoes worldwide. However, questions still remain regarding their size, dynamics and longevity. The Reyðarártindur Pluton exposed in Southeast Iceland provides a superb example to investigate the above questions. Here, we use field mapping, sampling, geochemistry, 3D pluton shape modelling and a numerical thermal model to reconstruct the assembly and eruptive history of the shallow magma body.

    In 3D, the c. 2.5 km3 pluton has a castle-like shape characterised by flat roof segments that are vertically offset along steep faults. The exposed pluton is constructed largely of a single rock unit, the Main Granite (69.9 to 77.6 wt.% SiO2). Two additional units occur only as enclaves: the Granite Enclaves (67.4 to 70.2 wt.% SiO2), and the Quartz Monzonite Enclaves (61.8 to 67.3 wt.% SiO2). However, geochemistry clearly indicates that the units are related and hence were likely derived from the same source reservoir. 

    In two locations, the pluton roof displays depressions associated with large dykes. Within these two dykes the rock is partially to wholly tuffisitic, and geochemical compositions range from quartz monzonite to granite. We interpret these dykes as eruption-feeding conduits from the pluton. Additionally, we speculate that the mingling of magmatic units with compositional ranges from quartz monzonite to granite within the conduits indicates that injection of new magma into the reservoir triggered eruption. 

    Rapid pluton construction is indicated by ductile contacts between units in the pluton and a thermal model calculates the top 75 m would have rheologically locked up within 1000 years. Hence, we argue that the pluton was a short-lived part of the wider magmatic system that fed the associated volcano, and that timeframes from emplacement to eruption were limited to 1000 years.

    Rhodes, E. Barker, A. K. Burchardt, S. et al. (2021). Rapid assembly and eruption of a shallow silicic magma reservoir, Reyðarártindur Pluton, Southeast Iceland. G-Cubed. DOI: 10.1029/2021GC009999

  • 19.
    Rhodes, Emma
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Barker, Abigail
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Schmiedel, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Witcher, Taylor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Insights into the magmatic processes of a shallow, silicic storage zone: Reyðarártindur Pluton, Iceland2019Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Reyðarártindur is one of several felsic plutons exposed in Southeast Iceland, interpreted to be the shallow plumbing systems of late Neogene volcanic centres (Cargill et al., 1928; Furman et al., 1992; Padilla, 2015). These plutons are considered to preserve analogous plumbing systems to the central volcanoes active in Iceland today (Furman et al., 1992). Reyðarártindur is the oldest pluton in Southeast Iceland at 7.30 ± 0.06 Ma (Padilla, 2015), and has been conveniently incised by the Reyðará River, making it ideal for an in-depth study of the external and internal geometry of a shallow rift-zone magma plumbing system.

    In order to analyse mechanisms of magma emplacement, we have conducted detailed structural mapping of the pluton and its basaltic host rock using drone-based photogrammetry. To complement this, we have also extensively sampled and analysed the geochemistry and petrology of the pluton interior. An outline of the pluton is shown in Figure 1, highlighting that the pluton is NNW-SSE trending, which is in contrast to the NE-SW regional dyke trend. A total thickness of 500 m and a calculated volume of 1.5 km3 is exposed. While the pluton walls are steeply-dipping, the pluton roof is mostly flat. Deviations from the flat roof occur in the form of areas that are cut by steep dip-slip faults with displacements of up to 100 m. Roof faulting creates both structural highs (horsts) and lows (grabens, as well as a monoclinal structure) in the roof. Many of the faults are intruded by felsic dykes, some of them seem to have been the feeders of surface eruptions.

    An estimated 95% of the pluton volume is rhyolitic in composition, with 73-76 wt.% SiO2. Geochemically, the magma in the majority of the pluton is similar, but hand samples and thin sections show a large variety of textures. In the lower part of the exposure there is a zone of mingling and mixing between a matrix magma and several different types of silicic enclaves (Figure 1). The matrix magma is more mafic with an SiO2 content of 68-73 wt.% and the enclaves vary in nature with no systematic shape, size or aspect ratio. There are at least two types of enclaves, and the predominant type is a coarse grained trachydacite with 64-69 wt.% SiO2. These less evolved compositions are limited to a 1 km stretch of the riverbed in the centre of the pluton. Closer to the wall contacts (i.e. to the north and south of the mingling zone), the composition of the magma returns to that of the main magma body, as observed at higher elevations.

    Our poster aims to summarise our results and present interpretations of the magmatic processes preserved in the Reyðarártindur pluton. Our preliminary results indicate that the pluton was emplaced by a combination of floor subsidence and roof doming, and that the pluton structure was modified during further magma intrusion into, and eruption from, the pluton.

     Fig. 1 – Map of the Reyðarártindur Pluton, South-East Iceland.

     

    References

     

    Cargill, H., Hawkes, L., and Ledeboen, J. (1928). The major intrustions of South-Eastern Iceland. Quarterly Journal of the Geological Society of London 84, 505–539.

    Furman, T., Meyer, P. S., and Frey, F. (1992). Evolution of Icelandic central volcanoes: evidence from the Austurhorn intrusion, southeastern Iceland. Bulletin of Volcanology. 55, 45–62.

    Padilla, A. (2015). Elemental and isotopic geochemistry of crystal-melt systems: Elucidating the construction and evolution of silicic magmas in the shallow crust, using examples from southeast Iceland and southwest USA [PhD Dissertation: Vanderbilt University].

     

  • 20. Rhodes, Emma
    et al.
    Burchardt, Steffi
    Greiner, Sonja H. M.
    Mattsson, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. University of St Andrews, Scotland.
    Sigmundsson, Freysteinn
    Schmiedel, Tobias
    Barker, Abigail K.
    Witcher, Taylor
    Volcanic unrest as seen from the magmatic source: Reyðarártindur pluton, Iceland2024Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 14, artikkel-id 962Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    How the Earth’s crust accommodates magma emplacement influences the signals that can be detected by monitoring volcano seismicity and surface deformation, which are routinely used to forecast volcanic eruptions. However, we lack direct observational links between deformation caused by magma emplacement and monitoring signals. Here we use field mapping and photogrammetry to quantify deformation caused by the emplacement of at least 2.5 km3 of silicic magma in the Reyðarártindur pluton, Southeast Iceland. Our results show that magma emplacement triggered minor and local roof uplift, and that magma reservoir growth was largely aseismic by piecemeal floor subsidence. The occurrence and arrangement of fractures and faults in the reservoir roof can be explained by magmatic overpressure, suggesting that magma influx was not fully accommodated by floor subsidence. The tensile and shear fracturing would have caused detectable seismicity. Overpressure eventually culminated in eruption, as evidenced by exposed conduits that are associated with pronounced local subsidence of the roof rocks, corresponding to the formation of an asymmetric graben at the volcano surface. Hence, the field observations highlight processes that may take place within silicic volcanoes, not accounted for in widely used models to interpret volcanic unrest.

  • 21.
    Rhodes, Emma
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Greiner, Sonja H. M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Sigmundsson, Freysteinn
    University of Iceland.
    Schmiedel, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. TU Delft.
    Barker, Abigail
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Disaster Science (CNDS), Uppsala University, Villavägen 16, 75236 Uppsala, Sweden.
    Witcher, Taylor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Volcanic unrest as seen from the magmatic source: Reyðarártindur pluton, Iceland2024Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 14, artikkel-id 962Artikkel i tidsskrift (Fagfellevurdert)
  • 22.
    Samrock, Lisa K.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Jensen, Max J.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Troll, Valentin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Geiger, Harri
    3D modelling of the Tejeda Caldera cone-sheet swarm, Gran Canaria, Canary Islands, Spain2015Inngår i: Geophysical Research Abstracts, 2015, Vol. 17, artikkel-id EGU2015-958Konferansepaper (Annet vitenskapelig)
  • 23.
    Schmiedel, Tobias
    et al.
    Uppsala Universitet, Sweden.
    Burchardt, Steffi
    Uppsala Universitet, Sweden.
    Mattsson, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. University of St. Andrews, UK.
    Guldstrand, Frank
    Oslo Universitet, Norway.
    Galland, Olivier
    Oslo Universitet, Norway.
    Palma, Joaquín Octavio
    Subsecretariat of Mining of the Province of Buenos Aires, Argentina; National University of La Plata, Argentina.
    Skogby, Henrik
    Swedish Museum of Natural History, Sweden.
    Emplacement and Segment Geometry of Large, High-Viscosity Magmatic Sheets2021Inngår i: Minerals, E-ISSN 2075-163X, Vol. 11, nr 10, artikkel-id 1113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding magma transport in sheet intrusions is crucial to interpreting volcanic unrest. Studies of dyke emplacement and geometry focus predominantly on low-viscosity, mafic dykes. Here, we present an in-depth study of two high-viscosity dykes (106 Pa·s) in the Chachahuén volcano, Argentina, the Great Dyke and the Sosa Dyke. To quantify dyke geometries, magma flow indicators, and magma viscosity, we combine photogrammetry, microstructural analysis, igneous petrology, Fourier-Transform-Infrared-Spectroscopy, and Anisotropy of Magnetic Susceptibility (AMS). Our results show that the dykes consist of 3 to 8 mappable segments up to 2 km long. Segments often end in a bifurcation, and segment tips are predominantly oval, but elliptical tips occur in the outermost segments of the Great Dyke. Furthermore, variations in host rocks have no observable impact on dyke geometry. AMS fabrics and other flow indicators in the Sosa Dyke show lateral magma flow in contrast to the vertical flow suggested by the segment geometries. A comparison with segment geometries of low-viscosity dykes shows that our high-viscosity dykes follow the same geometrical trend. In fact, the data compilation supports that dyke segment and tip geometries reflect different stages in dyke emplacement, questioning the current usage for final sheet geometries as proxies for emplacement mechanism.

  • 24. Schmiedel, Tobias
    et al.
    Burchardt, Steffi
    Mattsson, Tobias
    Guldstrand, Frank
    Galland, Olivier
    Palma, Joaquín
    Skogby, Henrik
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Emplacement and Segment Geometry of Large, High-Viscosity Magmatic Sheets2021Inngår i: Minerals, E-ISSN 2075-163X, Vol. 11, nr 10, s. 1-34, artikkel-id 1113Artikkel i tidsskrift (Fagfellevurdert)
  • 25. Troll, V. R.
    et al.
    Mattsson, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Uppsala University, Sweden .
    Upton, B. G. J.
    Emeleus, C. H.
    Donaldson, C. H.
    Meyer, R.
    Weis, F.
    Dahrén, B.
    Heimdal, T. H.
    Fault-Controlled Magma Ascent Recorded in the Central Series of the Rum Layered Intrusion, NW Scotland2020Inngår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 61, nr 10, artikkel-id egaa093Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Palaeogene layered ultrabasic intrusion of the Isle of Rum forms the hearth of the Rum Igneous Centre in NW-Scotland. The regional Long Loch Fault, which is widely held to represent the feeder system to the layered magma reservoir, dissects the intrusion and is marked by extensive ultrabasic breccias of various types. Here we explore the connection between the layered ultrabasic cumulate rocks and breccias of central Rum that characterize the fault zone (the ‘Central Series’) and evaluate their relationship with the Long Loch Fault system. We show that fault splays in the Central Series define a transtensional graben above the Long Loch Fault into which portions of the layered units subsided and collapsed to form the extensive breccias of central Rum. The destabilization of the cumulate pile was aided by intrusion of Ca-rich ultrabasic magmas along the faults, fractures and existing bedding planes, creating a widespread network of veins and dykelets that provided a further means of disintegration and block detachment. Enrichment in LREE and compositional zoning in intra cumulate interstices suggest that the collapsed cumulates were infiltrated by relatively evolved plagioclase-rich melt, which led to extensive re-crystallization of interstices. Clinopyroxene compositions in Ca-rich gabbro and feldspathic peridotite veins suggest that the intruding magma was also relatively water-rich, and that pyroxene crystallized dominantly below the current level of exposure. We propose that the Long Loch Fault opened and closed repeatedly to furnish the Rum volcano with a pulsing magma conduit. When the conduit was shut, pressure built up in the underlying plumbing system, but was released during renewed fault movements to permit dense and often crystal-rich ultrabasic magmas to ascend rapidly from depth. These spread laterally on arrival in the shallow Rum magma reservoir, supplying repetitive recharges of crystal-rich magma to assemble the rhythmic layering of the Rum layered intrusion.

  • 26.
    Troll, Valentin R.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Emeleus, C. Henry
    Dept. of Earth Sciences, Durham University, South Road, Durham, DH1 3LE, UK.
    Nicoll, Graeme R.
    Neftex Insights, Halliburton, 97 Jubilee Avenue, Milton Park, Abingdon, Oxfordshire, OX14 4RW, UK.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Ellam, Robert M.
    Scottish Universities Environmental Research Centre (SUERC), Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, G75 0QF, UK.
    Donaldson, Colin H.
    Dept. of Geography and Geosciences, University of St Andrews, North Street, St Andrews, KY16 9AL, UK.
    Harris, Chris
    Dept. of Geological Sciences, University of Cape Town, Rondebosch, 7701 South Africa.
    A large explosive silicic eruption in the British Palaeogene Igneous Province2019Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 9, artikkel-id 494Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 27.
    Troll, Valentin R.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Naturresurser och hållbar utveckling.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Stockholm Univ, Dept Geol Sci, Svante Arrhenius Vag 8, S-11418 Stockholm, Sweden..
    Upton, B. G. J.
    Univ Edinburgh, Sch Geosci, West Mains Rd, Edinburgh EH9 3JW, Midlothian, Scotland..
    Emeleus, C. H.
    Univ Durham, Dept Earth Sci, South Rd, Durham DH1 3LE, England..
    Donaldson, C. H.
    Univ Durham, Dept Earth Sci, South Rd, Durham DH1 3LE, England.;Univ St Andrews, Sch Earth & Environmet Sci, St Andrews KY16 9AL, Fife, Scotland..
    Meyer, R.
    Minist Mobilite & Travaux Publ, Serv Geol Luxembourg, 23 Rue Chemin Fer, L-8057 Bertrange, Luxembourg..
    Weis, Franz
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Dahrén, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Heimdal, T. H.
    Univ Oslo, ZEB Bygget, CEED, Saelands Vei 2A, N-0371 Oslo, Norway..
    Fault-Controlled Magma Ascent Recorded in the Central Series of the Rum Layered Intrusion, NW Scotland2020Inngår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 61, nr 10, artikkel-id egaa093Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Palaeogene layered ultrabasic intrusion of the Isle of Rum forms the hearth of the Rum Igneous Centre in NW-Scotland. The regional Long Loch Fault, which is widely held to represent the feeder system to the layered magma reservoir, dissects the intrusion and is marked by extensive ultrabasic breccias of various types. Here we explore the connection between the layered ultrabasic cumulate rocks and breccias of central Rum that characterize the fault zone (the 'Central Series') and evaluate their relationship with the Long Loch Fault system. We show that fault splays in the Central Series define a transtensional graben above the Long Loch Fault into which portions of the layered units subsided and collapsed to form the extensive breccias of central Rum. The destabilization of the cumulate pile was aided by intrusion of Ca-rich ultrabasic magmas along the faults, fractures and existing bedding planes, creating a widespread network of veins and dykelets that provided a further means of disintegration and block detachment. Enrichment in LREE and compositional zoning in intra cumulate interstices suggest that the collapsed cumulates were infiltrated by relatively evolved plagioclase-rich melt, which led to extensive re-crystallization of interstices. Clinopyroxene compositions in Ca-rich gabbro and feldspathic peridotite veins suggest that the intruding magma was also relatively water-rich, and that pyroxene crystallized dominantly below the current level of exposure. We propose that the Long Loch Fault opened and closed repeatedly to furnish the Rum volcano with a pulsing magma conduit. When the conduit was shut, pressure built up in the underlying plumbing system, but was released during renewed fault movements to permit dense and often crystal-rich ultrabasic magmas to ascend rapidly from depth. These spread laterally on arrival in the shallow Rum magma reservoir, supplying repetitive recharges of crystal-rich magma to assemble the rhythmic layering of the Rum layered intrusion.

    Fulltekst (pdf)
    fulltext
  • 28. Troll, Valentin R.
    et al.
    Nicoll, Graeme R.
    Ellam, Robert M.
    Emeleus, C. Henry
    Mattsson, Tobias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Petrogenesis of the Loch Bà ring-dyke and Centre 3 granites, Isle of Mull, Scotland2021Inngår i: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 176, nr 2, artikkel-id 16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 29.
    Witcher, Taylor
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Hazards and Disaster Science, Sweden.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Hazards and Disaster Science, Sweden.
    Mattsson, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Centre for Natural Hazards and Disaster Science, Sweden;School of Earth and Environmental Sciences, University of St. Andrews, Bute Building, Queen's Terrace, KY16 9TS St Andrews, UK.
    Heap, Michael J.
    McCarthy, William
    Development of permeable networks by viscous-brittle deformation in a shallow rhyolite intrusion. Part 1: Field evidence2024Inngår i: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 454, artikkel-id 108166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Efficient outgassing of shallow magma bodies reduces the risk of explosive eruption. Silica-rich magmas are too viscous for exsolved gas bubbles to escape the system through buoyant forces alone, and so volatile overpressure is often released through deformation-related processes. Here we present a case study on magma-emplacement-related deformation in a shallow (500 m depth) rhyolite intrusion (the Sandfell laccolith, Eastern Iceland) to investigate the establishment and evolution of degassing and outgassing networks in silicic sub-volcanic intrusions. We observe viscous and brittle deformation features: from vesiculated flow bands that organized into 'pore channels' in the ductile regime, to uniform bands of tensile fractures (‘fracture bands’) that grade into breccia and gouge in the brittle regime. Through field mapping, structural analysis, and anisotropy of magnetic susceptibility (AMS), we show that the deformation spectrum, observed all over the laccolith, represents stages of degassing (viscous processes) and outgassing (brittle processes) that resulted in the formation of interconnected permeable networks through the growth and linkage of fracture bands. Areas with concentrations of higher degrees of brittle deformation are proximal to abruptly changing AMS fabrics and point to laccolith-scale strain partitioning in the magma linked to different stages of laccolith growth. The establishment of intrusion-scale permeable networks through the cumulation of discrete magma fractures would have profoundly assisted the outgassing of the entire laccolith. Therefore, fracture banding captures viscous and brittle processes working in tandem as an efficient outgassing mechanism, and should be considered in sub-volcanic intrusions elsewhere.

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