| 1. |
- Rhodes, Emma, 1990-, et al.
(author)
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Insights into the magmatic processes of a shallow, silicic storage zone: Reyðarártindur Pluton, Iceland
- 2019
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Conference paper (other academic/artistic)abstract
- 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].
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| 2. |
- Rhodes, Emma, 1990-, et al.
(author)
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Rapid Assembly and Eruption of a Shallow Silicic Magma Reservoir, Reyðarártindur Pluton, Southeast Iceland
- 2021
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In: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 22:11
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Journal article (peer-reviewed)abstract
- 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 Reyoarartindur 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 km(3). 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 Reyoarartindur Pluton was an ephemeral part of the wider plumbing system that feeds a volcano, and that timeframes from emplacement to eruption were rapid.
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| 3. |
- Rhodes, Emma, 1990-, et al.
(author)
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Rapid formation and eruption of a silicic magma chamber
- 2022
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Conference paper (other academic/artistic)abstract
- 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
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| 6. |
- Burchardt, Steffi, 1982-, et al.
(author)
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Progressive growth of the Cerro Bayo cryptodome, Chachahuén volcano, Argentina : implications for viscous magma emplacement
- 2019
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In: Journal of Geophysical Research - Solid Earth. - 2169-9313 .- 2169-9356. ; 124, s. 7934-7961
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Burchardt, Steffi, et al.
(author)
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Progressive growth of the Cerro Bayo cryptodome, Chachahuén volcano, Argentina – implications for viscous magma emplacement
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Other publication (other academic/artistic)abstract
- 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.
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| 8. |
- Geiger, Harri, et al.
(author)
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Magma plumbing for the 2014-2015 Holuhraun eruption, Iceland
- 2016
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In: Geochemistry Geophysics Geosystems. - 1525-2027. ; 17:8, s. 2953-2968
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Journal article (peer-reviewed)abstract
- The 2014-2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Baroarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Baroarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Baroarbunga and Holuhraun, we present mineral textures and compositions, mineral-melt-equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Baroarbunga 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 approximate to 17 km and approximate to 5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated magma mixing and assimilation of low-O-18 Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical magma ascent within the Baroarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.
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| 9. |
- Mattsson, Tobias, 1990-, et al.
(author)
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Floor subsidence and roof and wall-rock deformation during the emplacement of the Mourne Mountains granite pluton; Insights from the regional fracture pattern
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Other publication (other academic/artistic)abstract
- 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.
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| 11. |
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| 14. |
- Mattsson, Tobias, 1990-, et al.
(author)
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Quantifying the crystal cargo of the Cerro Bayo cryptodome, Argentina; A window into pre-emplacement magma processes and storage conditions
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Other publication (other academic/artistic)abstract
- 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.
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| 15. |
- Mattsson, Tobias, 1990-, et al.
(author)
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The sub-volcanic structure of the Alnö carbonatite complex, Sweden
- 2014
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In: Geophysical Research Abstracts.
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Conference paper (other academic/artistic)abstract
- The Alnö ring complex is one of the best known carbonatite complexes in the world, with ca. 100 scientific articles published since 1895. The Alnö complex hosts a suite of alkaline silicate and carbonatite rocks and is the type-location for the occurrence of magmatic carbonatites (Stutzer 1907). Many questions are left to be answered, however, in particular the detailed sub-surface structure of the complex is not well constrained. Two general models exist based on a two-dimensional downdip projection of magmatic sheets in relationship to a fixed point at the surface (von Eckermann, 1948; Kresten, 1980). Von Eckermann’s model identifies several foci of magmatic sheets between depths of 1 km to 8km, whilst Kresten’s model indicates that most magmatic sheets originated from a single evolving magma chamber at a depth of 1 km. To test these models we employed the Move® software package and produced a 3D model from the available data of sheet intrusions (see Burchardt et al. 2013 for the method). The model provides insights into the magma plumbing system and displays a highly complex sub-volcanic structure with several shallow magma chambers at depths of ca. 1 km below the surface. In addition, our model shows that a southward vergence of many magmatic sheets indicates that the source of these intrusion moved southward during the active phase at Alnö, consistent with Kresten’s evolving main magma body. A single large magma chamber was recently suggested on the basis of seismic profiles (Andersson et al. 2013) and was pinpointed at 3 km below the surface. Our models indicate that this larger magma chamber probably represents the final stage of magmatic activity of Alnö, while Alnö’s initial magma plumbing system was most likely a multi-pocket system with several storage levels, thus explaining the high abundance of magmatic sheets of divergent orientation and lithology.
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| 16. |
- Mezheyeuski, Artur, et al.
(author)
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An immune score reflecting pro- and anti-tumoural balance of tumour microenvironment has major prognostic impact and predicts immunotherapy response in solid cancers
- 2023
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In: EBioMedicine. - : Elsevier. - 2352-3964. ; 88
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Journal article (peer-reviewed)abstract
- Background: Cancer immunity is based on the interaction of a multitude of cells in the spatial context of the tumour tissue. Clinically relevant immune signatures are therefore anticipated to fundamentally improve the accuracy in predicting disease progression.Methods: Through a multiplex in situ analysis we evaluated 15 immune cell classes in 1481 tumour samples. Single-cell and bulk RNAseq data sets were used for functional analysis and validation of prognostic and predictive associations.Findings: By combining the prognostic information of anti-tumoural CD8+ lymphocytes and tumour supportive CD68+CD163+ macrophages in colorectal cancer we generated a signature of immune activation (SIA). The prognostic impact of SIA was independent of conventional parameters and comparable with the state-of-art immune score. The SIA was also associated with patient survival in oesophageal adenocarcinoma, bladder cancer, lung adenocarcinoma and melanoma, but not in endometrial, ovarian and squamous cell lung carcinoma. We identified CD68+CD163+ macrophages as the major producers of complement C1q, which could serve as a surrogate marker of this macrophage subset. Consequently, the RNA-based version of SIA (ratio of CD8A to C1QA) was predictive for survival in independent RNAseq data sets from these six cancer types. Finally, the CD8A/C1QA mRNA ratio was also predictive for the response to checkpoint inhibitor therapy.Interpretation: Our findings extend current concepts to procure prognostic information from the tumour immune microenvironment and provide an immune activation signature with high clinical potential in common human cancer types.
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| 17. |
- Rhodes, Emma, 1990-, et al.
(author)
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The plutonic-volcanic connection – Preliminary results from Reyðarártindur pluton, Iceland
- 2019
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In: Subvolcanic Processes.
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Conference paper (other academic/artistic)abstract
- Reyðarártindur is a granophyre pluton exposed in East Iceland, which prior to this field season had not been mapped in detail. Dated at 7.30 ± 0.06 Ma, the ~ 15 km2 pluton was emplaced into the flat-lying basaltic lava flows of the Neogene rift zone and felsic volcanic deposits of the Lon Central Volcano (Padilla, 2015). The intrusion is the oldest of the South-East Iceland Intrusive Suite, and these plutons are interpreted to be the shallow plumbing systems of late Tertiary volcanic centres (Cargill et al., 1928; Furman et al., 1992; Padilla, 2015).Glacial erosion has carved a valley through the centre of Reyðarártindur, exposing cross sections of the roof, the pluton interior and overlying volcanic rocks likely associated to Reyðarártindur. These features make it an ideal study area of pluton-volcano connection. We have conducted field mapping, sampling and photogrammetry with the aim to investigate plutonic-volcanic-tectonic processes.The pluton is NNW-SSE trending, which is in contrast to the NE-SW regional dyke trend. While the pluton walls are steeply-dipping, the pluton roof is mostly flat but offset up to 100m by steep dip-slip faults. Many of these faults are intruded by felsic dykes, in some cases connecting the pluton to overlying volcanic rocks. Using photogrammetry, we have mapped the shallowly dipping basaltic host rock, the faults and dykes in the pluton roof. We will present first results on the shape of the magma body and the pluton roof structure. We will then discuss the implications of the roof structures and the pluton shape for the plutonic-volcanic connection and the evolution of the Reyðarártindur intrusion. ReferencesCargill, H., Hawkes, L., and Ledeboen, J. (1928). The major intrustions of South-Eastern Iceland. Q. J. Geol. Soc. 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. Bull. Volcanol. 55, 45–62. doi:10.1007/BF00301119.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].
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