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- Foulger, Gillian R., et al.
(author)
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The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge
- 2020
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In: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Research review (peer-reviewed)abstract
- The breakup of Laurasia to form the Northeast Atlantic Realm disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed that are underlain by magma-inflated, extended continental crust. North of the Greenland-Iceland-Faroe Ridge a new rift–the Aegir Ridge–propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge the proto-Reykjanes Ridge propagated north through the North Atlantic Craton along an axis displaced ~150 km to the west of the rift to the north. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed an ~300-km-wide transverse barrier. Thereafter, the ~150 × 300-km block of continental crust between the rift tips–the Iceland Microcontinent–extended in a distributed, unstable manner along multiple axes of extension. These axes repeatedly migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day in Iceland. It is the surface expression of underlying magma-assisted stretching of ductile continental crust that has flowed from the Iceland Microplate and flanking continental areas to form the lower crust of the Greenland-Iceland-Faroe Ridge. Icelandic-type crust which underlies the Greenland-Iceland-Faroe Ridge is thus not anomalously thick oceanic crust as is often assumed. Upper Icelandic-type crust comprises magma flows and dykes. Lower Icelandic-type crust comprises magma-inflated continental mid- and lower crust. Contemporary magma production in Iceland, equivalent to oceanic layers 2–3, corresponds to Icelandic-type upper crust plus intrusions in the lower crust, and has a total thickness of only 10–15 km. This is much less than the total maximum thickness of 42 km for Icelandic-type crust measured seismically in Iceland. The feasibility of the structure we propose is confirmed by numerical modeling that shows extension of the continental crust can continue for many tens of millions of years by lower-crustal ductile flow. A composition of Icelandic-type lower crust that is largely continental can account for multiple seismic observations along with gravity, bathymetric, topographic, petrological and geochemical data that are inconsistent with a gabbroic composition for Icelandic-type lower crust. It also offers a solution to difficulties in numerical models for melt-production by downward-revising the amount of melt needed. Unstable tectonics on the Greenland-Iceland-Faroe Ridge can account for long-term tectonic disequilibrium on the adjacent rifted margins, the southerly migrating rift propagators that build diachronous chevron ridges of thick crust about the Reykjanes Ridge, and the tectonic decoupling of the oceans to the north and south. A model of complex, discontinuous continental breakup influenced by crustal inhomogeneity that distributes continental material in growing oceans fits other regions including the Davis Strait, the South Atlantic and the West Indian Ocean.
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- Larsen, Eiliv, et al.
(author)
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A dated volcano-tectonic deformation event in Jan Mayen causing landlocking of Arctic charr
- 2021
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In: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 36:2, s. 180-190
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Journal article (peer-reviewed)abstract
- We provide the first documentation of tectonic deformation resulting from a volcanic eruption on the island of Jan Mayen. Vertical displacement of about 14 m southwest of the stratovolcano Beerenberg is associated with an eruption in ad 1732 on its southeastern flank. The age of the uplift event is bracketed by radiocarbon-dated driftwood buried by material deposited due to uplift, and by tephra from this eruption. Constraints, inferred from radiocarbon ages alone, allow for the possibility that uplift was completed prior to the ad 1732 eruption. However, the occurrence of tephra in the sediment column indicates that some displacement was ongoing during the eruption but ceased before the eruption terminated. We attribute the tectonic deformation to intrusion of shallow magma associated with the volcanic eruption. Our results complement previous studies of volcanic activity on Jan Mayan by providing precise age constraints for past volcanic activity. Also, it raises new hypotheses regarding the nature, timing and prevalence of precursor tectonic events to Jan Mayan eruptions. The uplift caused the complete isolation of a coastal lake by closing its outlet to the sea, thus landlocking the facultative migratory fish species Arctic charr (Salvelinus alpinus).
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| 4. |
- Larsen, Eiliv, et al.
(author)
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Volcanical and surficial process constraints on the formation of a lake basin in Jan Mayen, Norway
- 2022
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In: Quaternary Science Advances. - : Elsevier BV. - 2666-0334. ; 7
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Journal article (peer-reviewed)abstract
- The volcanic island of Jan Mayen, located in the Norwegian – Greenland Sea, has very few lake basins out of which only one, Lake Nordlaguna, holds a permanent lake throughout the year. The island is volcanic and has been glaciated, but the lake basin is not genetically typical for volcanic crater lakes or other common types of volcanic lakes. Nor is it typical for ice-scoured glacial lakes. Instead, the lake basin originated from a series of hydromagmatic and subglacial volcanic eruptions, which over time yielded an irregularly horseshoe-shaped chain of small mountains to form flanks of a bedrock basin. Potassium–Argon and Argon–Argon dates from these rock walls facing the lake yield ages ranging from about 564 to 21 ka. Subsequent glacier overriding only had a minor influence on the basin morphology, but contributed, as did other surface processes to its sediment infill. Following deglaciation, relative sea-level change led to the formation of a beach barrier that connects between the rock walls. Tectonic uplift recorded in sections and ground penetrating radar profiles around the lake perimeter and dated using radiocarbon and tephra geochemistry, is attributed to a historical eruption in 1732 CE that took place on the opposite side of the island, some 4–5 km away. The uplift blocked the last remaining passage between the basin and the ocean, leading to the present landlocked lacustrine environment.
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- Mattsson, Hannes B., 1975-
(author)
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Volcanism at the tip of a propagating rift : the Heimaey volcanic centre, south Iceland
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Primary magmas are generated by 4-6% partial melting near the garnet-spinel stability fields beneath Heimaey (i.e. 80-65 km depth). The magmas fractionate 31% olivine and clinopyroxene en-route to ponding at the base of the crust (and forming a parental Vestmannaeyjar magma). Abundant normally zoned phenocrysts of olivine and plagioclase, in combination with curvilinear trends in major element variation diagrams and heterogeneous isotope ratios (similar to MORB) suggests that the rock suite evolved by fractional crystallization and that crustal contamination and/or magma-mixing was insignificant. Although Heimaey rocks are devoid of clinopyroxene as a phenocryst phase, decreasing ratios of CaO/Al2O3 and Sc/Y with increasing degree of fractionation suggest that clinopyroxene was present as a fractionating phase. The most evolved lava on Heimaey (Eldfell) can be successfully related to the most primitive (Stórhöfði) through 73% fractional crystallization of an olivine + clinopyroxene + plagioclase + titanomagnetite assemblage. Individual magma batches were emplaced into different levels of the crust where they evolved separately from each other prior to eruption. The lack of equilibrium phenocryst assemblages in the Heimaey rocks suggests that the residence times in crustal magma chambers were short. Upon eruption, the pathways used by the rising magma are probably zones of weaknesses associated with extensional stress exerted by the propagating Eastern Volcanic Zone (as indicated by the preferentially aligned eruptive fissures). When magmas erupt in a shallow marine environment, tuff-cones are formed as a result of explosive interactions between magma and water/sediment mixtures. Tuffs comprise about 65% of total erupted volume on Heimaey. The tuff cones deposits consists of normally graded planar air-fall deposits and undulating cross-bedded base-surge deposits, with an increase in frequency of base-surge deposits closer to the vent regions. The distribution of crustal xenoliths in the Sæfell tuff-cone suggests that there is a downward migration of explosion foci in tuff cone forming eruptions, and that a diatreme (at least 820 meters deep) formed during the eruption. This is also supported by the steep dip (35-45°) measured for ring-fractures at the crater-rim of the tuff cone, which creates sharp unconformities between early and late stage tuff-deposits. A zone of graded tuff-breccias (5-20 m thick) marks the transition from phreatomagmatic to subaerial activity. The subaerial stage is characterized by effusive lava emplacement and the formation of scoria cones and lava ponds inside the tuff-cones. The most common type of lava flows found on Heimaey are inflated pahoehoe (e.g. the Helgafell lava field). Based on measurements of lava inflation features (i.e. the thickness of the upper-vesicular crust of flow-lobes) in the Helgafell lava field an eruption duration was estimated for that eruption (11-12 months). This estimate seems reasonable as it yields an averaged volumetric effusion rate of 0.05-0.06 km3/month, which is similar to the 1963-1967 Surtsey eruption (0.02 km3/month) and the 1973 Eldfell eruption (0.04 km3/month) considering that the estimate does not account for early spatter-fed flows. The oldest units on Heimaey (i.e. the six units comprising the Norðurklettar formation) formed over a short time span following the deglaciation of southern Iceland 10-9.3 ka ago. The Stórhöfði eruption occurred sometime between 9-6 ka, Sæfell and Helgafell to approximately 6 ka, and finally the Eldfell eruption, which occurred in 1973. Heimaey is believed to represent the early stage of forming a central volcano in the Vestmannaeyjar system, mainly because (1) the average erupted volumes for a single eruption are twice (0.33 km3 DRE) that previously reported as an average for Vestmannaeyjar, (2) there have been close to 1 eruption/km2 on Heimaey, compared to 0.1 eruption/km2 as average for the Vestmannaeyjar system, and (3) the occurrence of more evolved lavas, such as the hawaiites of Dalfjallshryggur and Eldfell, suggesting that a crustal magma chamber is developing under the island.
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