Tephrostratigraphy in marine cores is an important tool for dating sedimentary sequences along the North Atlantic and in Western Europe. Most previously analyzed marine tephra were produced by Icelandic volcanoes, albeit rarely from the Krafla volcano, and require land-based records for validation. Two series of rhyolitic tephra emitted to the east of the Krafla volcano were recorded in the Eemian Rangá Formation in Northern Iceland, the two series being separated by the Grímsvötn 1 tephra known as “5e low bas IV” in marine core (∼127 ka). These rhyolitic deposits were seemingly ejected from the Hágangnahali paleocrater row (North of the Hágöng) and overlay the older Halarauður Ignimbrite. This rhyolitic activity persisted for ∼20 ka to the end of the Eemian last thermal optimum. probably initiated by deglaciation (MIS 6a/5e). It postdated the Halarauður ignimbrite. The ignimbrite and caldera formation were correlated with an ODP907 tephra, yielding a possible 207 ka age, but possibly older. These results constrain the main rhyolitic activity of Krafla to after the mid-Pleistocene transition, as observed for other “two-magma” volcanoes. Rhyolitic activity is non-systematically triggered by deglaciation, at least as analysed during the period 80–400 ka, but this genetic link is possibly valid for the late Pliocene of Iceland.

Widespread andesitic volcanism with several eruption centres occurred during the Middle Miocene in the Cserhat Hills, central-northern Hungary. In this time, an extensive dyke system developed in the area, where some dykes have exposed maximum length of 23 km, and maximum width of 25 m. This dyke system shows a change in its strike from E-W to NNW-SSE. Here we integrate new and previous field observations to derive structural maps and study dykes and fractures in the Cserhat Hills. K/Ar geochronology is used to understand the temporal evolution of regional fault patterns before, during and after the formation of the dykes and also to gain insights into the interaction between the dyke emplacement and the regional stress field. Fault-slip data were collected at 27 different sites along the dykes and were combined with reinterpreted datasets from 16 sites located at a distance from dykes. The field observations, integrated with the geochronological data sets suggests that dykes with different orientations were emplaced in two different eruptive cycles around 15.4 and 14.7 Ma. The deformation history of the Pannonian Basin involved a clockwise change in regional minimal stress axis, probably as a result of regional vertical-axis counter-clockwise block rotation. Our field observations suggest strike-slip stress regime may occur near propagating dyke tips, and the direction of minimal stress axis may have locally rotated counter-clockwise where dykes changed their strikes and emplaced along pre-existing fractures, mostly normal faults.

Les carrières souterraines d'Arras constituent un patrimoine naturel et historique remarquable : la craie coniacienne y a été exploitée depuis l’Antiquité en souterrain, puis après une période d’exploitation à ciel ouvert, à nouveau en souterrain au Moyen Âge. Un grand nombre de ces carrières ont été aménagées et reliées entre elles par un réseau de tunnels lors de la Grande Guerre, en vue de l'offensive d'avril 1917. Les coupes lithostratigraphiques réalisées dans les carrières d’Arras sont corrélables avec les coupes de référence du Boulonnais et du Kent. Les fractures sont extrêmement régulières et leur agencement se fait essentiellement suivant les directions N 105°-125° E (diaclases et quelques failles normales) et N 160°-180° E (décrochements senestres) ; elles ont largement guidé l'exploitation souterraine.

La prospection thématique menée à Arras (Pas-de-Calais), sur le site des carrières Wellington et Blenheim, a offert la possibilité d’observer l’exploitation souterraine de la craie de la fin du Moyen Âge et durant les Temps modernes. L’opération a mis au jour plusieurs fronts de taille et ateliers dont l’étude croisée des approches archéologique, géologique et historique a permis d’identifier la méthode d’extraction de la craie employée par les carriers et d’en comprendre les différentes étapes. En outre, les résultats obtenus sont encourageants et laissent entrevoir de nouvelles pistes de recherche que l’étude complète de la carrière Blenheim permettrait d’approfondir.

Le rift islandais actuel est constitué de trois branches, chacune incluant plusieurs systèmes volcano-tectoniques disposés en échelon. Il a été précédé de rifts plus anciens, dits « paléo-rifts », et est décalé vers l’est par rapport à l’axe de la dorsale médio-atlantique. Il est relié à celle-ci par deux zones transformantes qui sont le siège d’une microséismicité permanente et de séismes majeurs. Histoire, géométrie et mécanismes de ces différentes structures tectoniques sont présentés dans cette étude.

L’Islande est une école de géologie à ciel ouvert. Cette île volcanique jeune et isolée au milieu de l’Atlantique, découverte récemment, est couverte de manière récurrente par les glaciers. C’est de plus un enregistreur de la circulation thermohaline et du climat régional. La superposition d’un point chaud et de la ride médio-atlantique contrôle depuis le Néogène son fonctionnement, entre éruptions, séismes, crues et géothermie.

Chapter 1 Iceland, in the Lineage of Two Oceans Brigitte Van Vliet-Lanoë, Brigitte Van Vliet-LanoëSearch for more papers by this authorFrançoise Bergerat, Françoise BergeratSearch for more papers by this authorRené Maury, René MaurySearch for more papers by this authorHervé Guillou, Hervé GuillouSearch for more papers by this authorLaurent Geoffroy, Laurent GeoffroySearch for more papers by this author Brigitte Van Vliet-Lanoë, Brigitte Van Vliet-LanoëSearch for more papers by this authorFrançoise Bergerat, Françoise BergeratSearch for more papers by this authorRené Maury, René MaurySearch for more papers by this authorHervé Guillou, Hervé GuillouSearch for more papers by this authorLaurent Geoffroy, Laurent GeoffroySearch for more papers by this author Book Author(s): First published: 30 July 2021 https://doi.org/10.1002/9781119850922.ch1 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onEmailFacebookTwitterLinkedInRedditWechat Summary Situated in the Northeast Atlantic, Iceland is located within a particularly complex geodynamic evolutionary domain, illustrating the problems inherent to the break-up of continents in the plate tectonic model, especially the recycling of ancient structures such as the suture of the Iapetus Ocean and its paleoslab active during the Silurian. Iceland is generally presented as arising from the interaction between a thermal anomaly in the upper mantle, interpreted as a hot spot at the top of a plume, and a major axis of oceanic expansion, the Mid-Atlantic Ridge (MAR ). The major components of the North Atlantic domain are the MAR, the North Atlantic Igneous Province, the Icelandic hot spot and the Greenland–Iceland–Faroe Ridge. One of the characteristics of Iceland is its sustained volcanic activity, accompanied by hydrothermal activity and almost permanent seismicity, although most of the time it is of low intensity and localized. 1.4. References Allen, R.M., Nolet, G., Morgan, W.J., Vogfjörd, K., Bergsson, B.H., Erlendsson, P., Foulger, G.R., Jakobsdóttir, S.S., Julian, B.R., Pritchard, M., Ragnarsson, S., Stefánsson, R. (2002). Imaging the mantle beneath Iceland using integrated seismological techniques. J. Geophys. Res. Atmos ., 107(12) [Online]. Available at: http://doi.org/10.1029/2001 JB000595. Anderson, D.L. (2001). 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Chauvet, F., Geoffroy, L., Guillou, H., Maury, R.C., Le Gall, B., Agranier, A., Aviana, A. (2019). Eocene continental breakup in Baffin Bay. Tectonophysics, 757, 170–186. Courtillot, V., Richards, M., Duncan, R. (1989). Flood basalts and hotspot tracks: Plume heads and tails. Science, 246(4926), 103–107. Courtillot, V., Davaille, A., Besse, J., Stock, J. (2003). Three distinct types of hotspots in the Earth's mantle. Earth Planet Sci. Lett., 205, 295–308. Cramer, B.S., Toggweiler, J.R., Wright, J.D., Katz, M.E., Miller, K.G. (2009). Ocean overturning since the late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation. Paleoceanography, 24(14) [Online]. Available at: http://doi.org/10.1029/2008PA001683. Einarsson, P. and Sæmundsson, K. (1987). Earthquake epicenters 1982–1985 and volcanic systems in Iceland. In Í hlutarins eðli. Festschrift for Þorbjörn Sigurgeirsson, Sigfússon, Þ.I. (ed.). Menningarsjóður, Reykjavík. Foulger, G.R. (2012). Are "hot spots" hot spots? J. Geodin., 58, 1–28. Foulger, G.R. and Anderson, D.L. (2005). A cool model for the Iceland hotspot. J. Volcan. Geotherm. Res., 141, 1–22. Foulger, G.R., Pritchard, M.J., Julian, B.R., Evans, J.R., Allen, R.M., Nolet, G., Morgan, W.J., Bergsson, B.H., Erlendsson, P., Jakobsdóttir, S., Ragnarsson, S., Stefánsson, R., Vogfjörð, K.S. (2001). Seismic tomography shows that upwelling beneath Iceland is confined to the upper mantle . Geophys. J. Inter., 146, 504–530. Foulger, G.R., Natland, J.H., Anderson, D.L. (2005). A source for Icelandic magmas in remelted Iapetus crust. J. Volcan. Geotherm. Res., 141, 23–44. Hjartarson, Á., Erlendsson, Ö., Blischke, A. (2017). The Greenland–Iceland–Faroe Ridge complex. In The NE Atlantic Region: A Reappraisal of Crustal Structure, Tectonostratigraphy and Magmatic Evolution, G. Péron-Pinvidic, J.R. Hopper, M. Stoker, C. Gaina, T. Funck, U.E. Árting, J.C. Doornenbal (eds). Geological Society of London, London. Jakobsdóttir, S.S. (2008). Seismicity in Iceland: 1994–2007. Jökull, 58, 75–100. Jokat, W., Ritzmann, O., Schmidt-Aursch, M.C., Drashev, G.S., Snow, J.E. (2003). Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge. Nature, 423(6943), 962–965. Lisiecki, L.E. and Raymo, M.E. (2005). A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography, 20 [Online]. Available at: http://doi.org/10.1029/2004PA001071. Kominz, M.A., Browning, J.V., Miller, K.G., Sugarman, P.J., Mizintseva, S., Scotese, C.R. (2008). Late Cretaceous to Miocene sea-level estimates from the New Jersey and Delaware coastal plain coreholes: An error analysis. Basin Res., 20(2), 211–226. Martos, Y.M., Catalan, M., Jordan, T.A., Golynsky, A., Golynsky, D., Eagles, G., Vaughan, D.G. (2017). Heat flux distribution of Antarctica unveiled. Geophys. Res. Lett., 44, 11417–11426. Meyer, R., Van Wijk, J., Gernigon, L. (2007). The North Atlantic Igneous Province: A review of models for its formation. Geol. Soc. Amer., 430, 525–552. Miller, K.G., Kominz, M.A., Browning, J.V., Wright, J.D., Mountain, G.S., Katz, M.E., Sugarman, P.J., Cramer, B.S., Christie-Blick, N., Pekar, S.F. (2005). The Phanerozoic record of global sea-level change. Science, 310, 1293–1296. Miller, K.G., Mountain, G.S., Wright, J.D., Browning, J.V. (2011). A 180-million-year record of sea level and ice volume variations from continental margin and deep-sea isotopic records. Oceanography, 24(2), 40–53. Montagner, J.P. (2010). Panaches chauds : mythe ou réalité ? Pour la science : la terre à cœur ouvert, 67, 46–54. Morgan, W.J. (1971). Convective plumes in the lower mantle. Nature, 230, 42–43. Nunns, A.G., Talwani, M., Lorentzen, G.R., Vogt, P.R., Sigurgeirsson, T., Kristjánsson, L., Larsen, H.C., Vopel, D. (1983). Magnetic anomalies over Iceland and surrounding seas. In Structure and Development of the Greenland–Scotland Ridge, M.H.P. Bott, S. Saxov, M. Talwani, J. Thiede (eds). Plenum, New York. Rehnström, E.F. (2010). Prolonged Paleozoic magmatism in the East Greenland Caledonides: Some constraints from U-Pb ages and Hf isotopes. Journal of Geology, 118, 447–465. Rowley, D.B. (2013). Sea level: Earth's dominant elevation. Implications for duration and magnitudes of sea level variations. J. Geol., 21(5), 445–454. Saunders, A.D., Fitton, J.G., Kerr, A.C., Norry, M.J., Kent, R.W. (1997). The North Atlantic Igneous Province. In Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism, J.J. Mahoney and M.F. Coffin (eds). American Geophysical Union, Washington. Tarduno, J. (2010). La mobilité des points chauds. Pour la science : la terre à cœur ouvert, 67, 56–61. Van Vliet-Lanoë, B., Vandenberghe, N., Laignel, B., Laurent, M., Lauriat-Rage, A., Louwye, S., Mansy, J.L., Meilliez, F., Mercier, D., Hallegouët, B., Laquement, F., Michel, Y., Moguedet, G. (2002). 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Chapter 2 Iceland, an Emerging Ocean Rift Françoise Bergerat, Françoise BergeratSearch for more papers by this authorBrigitte Van Vliet-Lanoë, Brigitte Van Vliet-LanoëSearch for more papers by this author Françoise Bergerat, Françoise BergeratSearch for more papers by this authorBrigitte Van Vliet-Lanoë, Brigitte Van Vliet-LanoëSearch for more papers by this author Book Author(s): First published: 30 July 2021 https://doi.org/10.1002/9781119850922.ch2 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onEmailFacebookTwitterLinkedInRedditWechat Summary Regardless of the nature and origin of hot spots and whether they are fixed or mobile, the fact remains that there is a major thermal anomaly under Iceland, commonly referred to as the "Icelandic hot spot". The Mid-Atlantic Ridge migrated westward relative to the Icelandic hotspot, but after a few million years, the westward-trailing part of the rift gradually became inactive, and a new rift was the apex of the mantle plume. The Icelandic rift is located more than 100 km away from the accretion axis of the oceanic ridge. Present-day deformations in Iceland are well documented by data acquired through the networks established and developed since the late 1980s. The Icelandic rift presents notable structural differences compared to the submerged parts of the ridge. The main feature of fracturing in the Icelandic rift is the deformation partitioning between normal faults, open fractures and fractures injected by volcanic material. 2.5. References Acocella, V., Guðmundsson, Á., Funiciello, R. (2000). Interaction and linkage of extension fractures and normal faults: Examples from the rift zone of Iceland. J. Struct. Geol., 22, 1233–1246. Acocella, V., Korme, T., Salvini, F. (2003). 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Southern Iceland is one of the main outlets of the Icelandic ice sheet and is subject to seismicity of both tectonic and volcanic origins along the South Iceland Seismic Zone (SISZ). A sedimentary complex spanning Marine Isotopic Stage 6 (MIS 6) to the present includes evidence of both activities. It includes a continuous sedimentary record since the Eemian interglacial period, controlled by a rapid deglaciation, followed by two marine glacioisostasy-forced transgressions, separated by a regression phase connected to an intra-MIS 5e glacial advance. This record has been constrained by tephrostratigraphy and dating. Analysis of this record has provided better insights into the interconnectedness of hydrology and volcanic and tectonic activity during deglaciations and glaciations. Low-intensity earthquakes recurrently affected the water-laid sedimentation during the early stages of unloading, accompanying rifting events, dyke injection, and fault reactivations. During full interglacial periods, earthquakes were significantly less frequent but of higher magnitude along the SISZ, due to stress accumulation, favored by low groundwater levels and more limited magma production. Occurrence of volcanism and seismicity in Iceland is commonly related to rifting events. Subglacial volcanic events seem moreover to have been related to stress unlocking related to limited or full unloading/deglaciation events. Major eruptions were mostly located at the melting margin of the ice sheet.