@article{ZieglerRajabiHeidbachetal.2016, author = {Ziegler, Moritz O. and Rajabi, Mojtaba and Heidbach, Oliver and Hersir, Gylfi Pall and Agustsson, Kristjan and Arnadottir, Sigurveig and Zang, Arno}, title = {The stress pattern of Iceland}, series = {Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth}, volume = {674}, journal = {Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-1951}, doi = {10.1016/j.tecto.2016.02.008}, pages = {101 -- 113}, year = {2016}, abstract = {Iceland is located on the Mid-Atlantic Ridge which is the plate boundary between the Eurasian and the North American plates. It is one of the few places on earth where an active spreading centre is located onshore but the stress pattern has not been extensively investigated so far. In this paper we present a comprehensive compilation of the orientation of maximum horizontal stress (S-Hmax). In particular we interpret borehole breakouts and drilling induced fractures from borehole image logs in 57 geothermal wells onshore Iceland. The borehole results are combined with other stress indicators including earthquake focal mechanism solutions, geological information and overcoring measurements resulting in a dataset with 495 data records for the S-Hmax orientation. The reliability of each indicator is assessed according to the quality criteria of the World Stress Map project The majority of S-Hmax orientation data records in Iceland is derived from earthquake focal mechanism solutions (35\%) and geological fault slip inversions (26\%). 20\% of the data are borehole related stress indicators. In addition minor shares of S-Hmax orientations are compiled, amongst others, from focal mechanism inversions and the alignment of fissure eruptions. The results show that the S-Hmax orientations derived from different depths and stress indicators are consistent with each other. The resulting pattern of the present-day stress in Iceland has four distinct subsets of S-Hmax orientations. The S-Hmax orientation is parallel to the rift axes in the vicinity of the active spreading regions. It changes from NE-SW in the South to approximately N-S in central Iceland and NNW-SSE in the North. In the Westfjords which is located far away from the ridge the regional S-Hmax rotates and is parallel to the plate motion. (C) 2016 Elsevier B.V. All rights reserved.}, language = {en} } @article{GreenfieldWinderRawlinsonetal.2022, author = {Greenfield, Tim and Winder, Tom and Rawlinson, Nicholas and Maclennan, John and White, Robert S. and {\´A}g{\´u}stsd{\´o}ttir, Thorbj{\"o}rg and Bacon, Conor Andrew and Brandsd{\´o}ttir, Bryndis and Eibl, Eva P. S. and Glastonbury-Southern, Esme and Gudnason, Egill {\´A}rni and Hersir, Gylfi P{\´a}ll and Hor{\´a}lek, Josef}, title = {Deep long period seismicity preceding and during the 2021 Fagradalsfjall eruption, Iceland}, series = {Bulletin of volcanology : official journal of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)}, volume = {84}, journal = {Bulletin of volcanology : official journal of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)}, number = {12}, publisher = {Springer}, address = {Berlin ; Heidelberg ; New York}, issn = {0258-8900}, doi = {10.1007/s00445-022-01603-2}, pages = {20}, year = {2022}, abstract = {We use a dense seismic network on the Reykjanes Peninsula, Iceland, to image a group of earthquakes at 10-12 km depth, 2 km north-east of 2021 Fagradalsfjall eruption site. These deep earthquakes have a lower frequency content compared to earthquakes located in the upper, brittle crust and are similar to deep long period (DLP) seismicity observed at other volcanoes in Iceland and around the world. We observed several swarms of DLP earthquakes between the start of the study period (June 2020) and the initiation of the 3-week-long dyke intrusion that preceded the eruption in March 2021. During the eruption, DLP earthquake swarms returned 1 km SW of their original location during periods when the discharge rate or fountaining style of the eruption changed. The DLP seismicity is therefore likely to be linked to the magma plumbing system beneath Fagradalsfjall. However, the DLP seismicity occurred similar to 5 km shallower than where petrological modelling places the near-Moho magma storage region in which the Fagradalsfjall lava was stored. We suggest that the DLP seismicity was triggered by the exsolution of CO2-rich fluids or the movement of magma at a barrier to the transport of melt in the lower crust. Increased flux through the magma plumbing system during the eruption likely adds to the complexity of the melt migration process, thus causing further DLP seismicity, despite a contemporaneous magma channel to the surface.}, language = {en} } @phdthesis{Bredow2017, author = {Bredow, Eva}, title = {Geodynamic models of plume-ridge interaction}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411732}, school = {Universit{\"a}t Potsdam}, pages = {104}, year = {2017}, abstract = {According to the classical plume hypothesis, mantle plumes are localized upwellings of hot, buoyant material in the Earth's mantle. They have a typical mushroom shape, consisting of a large plume head, which is associated with the formation of voluminous flood basalts (a Large Igneous Province) and a narrow plume tail, which generates a linear, age-progressive chain of volcanic edifices (a hotspot track) as the tectonic plate migrates over the relatively stationary plume. Both plume heads and tails reshape large areas of the Earth's surface over many tens of millions of years. However, not every plume has left an exemplary record that supports the classical hypothesis. The main objective of this thesis is therefore to study how specific hotspots have created the crustal thickness pattern attributed to their volcanic activities. Using regional geodynamic models, the main chapters of this thesis address the challenge of deciphering the three individual (and increasingly complex) Réunion, Iceland, and Kerguelen hotspot histories, especially focussing on the interactions between the respective plume and nearby spreading ridges. For this purpose, the mantle convection code ASPECT is used to set up three-dimensional numerical models, which consider the specific local surroundings of each plume by prescribing time-dependent boundary conditions for temperature and mantle flow. Combining reconstructed plate boundaries and plate motions, large-scale global flow velocities and an inhomogeneous lithosphere thickness distribution together with a dehydration rheology represents a novel setup for regional convection models. The model results show the crustal thickness pattern produced by the plume, which is compared to present-day topographic structures, crustal thickness estimates and age determinations of volcanic provinces associated with hotspot activity. Altogether, the model results agree well with surface observations. Moreover, the dynamic development of the plumes in the models provide explanations for the generation of smaller, yet characteristic volcanic features that were previously unexplained. Considering the present-day state of a model as a prediction for the current temperature distribution in the mantle, it cannot only be compared to observations on the surface, but also to structures in the Earth's interior as imaged by seismic tomography. More precisely, in the case of the Réunion hotspot, the model demonstrates how the distinctive gap between the Maldives and Chagos is generated due to the combination of the ridge geometry and plume-ridge interaction. Further, the Rodrigues Ridge is formed as the surface expression of a long-distance sublithospheric flow channel between the upwelling plume and the closest ridge segment, confirming the long-standing hypothesis of Morgan (1978) for the first time in a dynamic context. The Réunion plume has been studied in connection with the seismological RHUM-RUM project, which has recently provided new seismic tomography images that yield an excellent match with the geodynamic model. Regarding the Iceland plume, the numerical model shows how plume material may have accumulated in an east-west trending corridor of thin lithosphere across Greenland and resulted in simultaneous melt generation west and east of Greenland. This provides an explanation for the extremely widespread volcanic material attributed to magma production of the Iceland hotspot and demonstrates that the model setup is also able to explain more complicated hotspot histories. The Iceland model results also agree well with newly derived seismic tomographic images. The Kerguelen hotspot has an extremely complex history and previous studies concluded that the plume might be dismembered or influenced by solitary waves in its conduit to produce the reconstructed variable melt production rate. The geodynamic model, however, shows that a constant plume influx can result in a variable magma production rate if the plume interacts with nearby mid-ocean ridges. Moreover, the Ninetyeast Ridge in the model is created by on-ridge activities, while the Kerguelen plume was located beneath the Australian plate. This is also a contrast to earlier studies, which described the Ninetyeast Ridge as the result of the Indian plate passing over the plume. Furthermore, the Amsterdam-Saint Paul Plateau in the model is the result of plume material flowing from the upwelling toward the Southeast Indian Ridge, whereas previous geochemical studies attributed that volcanic province to a separate deep plume. In summary, the three case studies presented in this thesis consistently highlight the importance of plume-ridge interaction in order to reconstruct the overall volcanic hotspot record as well as specific smaller features attributed to a certain hotspot. They also demonstrate that it is not necessary to attribute highly complicated properties to a specific plume in order to account for complex observations. Thus, this thesis contributes to the general understanding of plume dynamics and extends the very specific knowledge about the Réunion, Iceland, and Kerguelen mantle plumes.}, language = {en} }