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The Iceland Microcontinent and a Continental Greenland-Iceland-Faroe Ridge

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The Iceland Microcontinent and a Continental Greenland-Iceland-Faroe Ridge EARTH-102926; No of Pages 35 Earth-Science Reviews xxx (xxxx) xxx Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev 1Q3 The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge Q52Q4 Gillian R. Foulger a,⁎,TonyDoréb, C. Henry Emeleus a,1, Dieter Franke c, Laurent Geoffroy d, Laurent Gernigon e, 3 Richard Hey f, Robert E. Holdsworth a, Malcolm Hole g, Ármann Höskuldsson h,BruceJuliana,NickKuszniri, 4 Fernando Martinez j, Ken J.W. McCaffrey a, James H. Natland k,AlexPeacel,2, Kenni Petersen m, 5 Christian Schiffer a, Randell Stephenson n, Martyn Stoker o 6 a Department of Earth Sciences, Durham University, Science Laboratories, South Rd. DH1 3LE, UK 7 b Statoil UK Ltd., Statoil House, 11a Regent Street, London SW1Y 4ST, UK 8 c Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute for Geosciences and Natural Resources), Germany 9 d Université de Bretagne Occidentale, Brest, 29238 Brest, CNRS, UMR 6538, Laboratoire Domaines Océaniques, 29280 Plouzané, France 10 e Norges Geologiske Undersøkelse (NGU), Geological Survey of Norway, Leiv Erikssons vei 39, N-7491 Trondheim, Norway 11 f Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA 12 g Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB243UE, UK 13 h Háskóli Íslands (University of Iceland), Sturlugötu 7, 101 Reykjavík, Iceland 14 i School of Environmental Sciences, University of Liverpool, Jane Herdman Building, Liverpool L69 3GP, UK 15 j Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA 16 k Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA 17 l Department of Earth Sciences, Memorial University of Newfoundland, St. Johns, Newfoundland A1B 3X5, Canada 18 m Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark 19 n School of Geosciences, Geology and Petroleum Geology, Meston Building, King's College, University of Aberdeen, Aberdeen AB24 3UE, UK 20 o Australian School of Petroleum, University of Adelaide, Adelaide, South Australia 5005, Australia 21 22 article info abstract 23 Article history: The breakup of Laurasia to form the Northeast Atlantic Realm disintegrated an inhomogeneous collage of cratons 33 24 Received 26 September 2018 sutured by cross-cutting orogens. Volcanic rifted margins formed that are underlain by magma-inflated, ex- 34 25 Received in revised form 8 August 2019 tended continental crust. North of the Greenland-Iceland-Faroe Ridge a new rift–the Aegir Ridge–propagated 35 26 Accepted 8 August 2019 36 27 south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge the proto-Reykjanes Ridge prop- Available online xxxx 37 2829303132 agated north through the North Atlantic Craton along an axis displaced ~150 km to the west of the rift to the fl 38 62 Keywords: north. Both propagators stalled where the con uence of the Nagssugtoqidian and Caledonian orogens formed 39 63 Atlantic an ~300-km-wide transverse barrier. Thereafter, the ~150 × 300-km block of continental crust between the rift 64 Iceland tips–the Iceland Microcontinent–extended in a distributed, unstable manner along multiple axes of extension. 40 65 Continental breakup These axes repeatedly migrated or jumped laterally with shearing occurring between them in diffuse transfer 41 66 Tectonics zones. This style of deformation continues to the present day in Iceland. It is the surface expression of underlying 42 67 Icelandic-type crust magma-assisted stretching of ductile continental crust that has flowed from the Iceland Microplate and flanking 43 68 SDRs continental areas to form the lower crust of the Greenland-Iceland-Faroe Ridge. Icelandic-type crust which un- 44 69 Geochemistry derlies the Greenland-Iceland-Faroe Ridge is thus not anomalously thick oceanic crust as is often assumed. 45 70 Geophysics Upper Icelandic-type crust comprises magma flows and dykes. Lower Icelandic-type crust comprises magma- 46 inflated continental mid- and lower crust. Contemporary magma production in Iceland, equivalent to oceanic 47 layers 2–3, corresponds to Icelandic-type upper crust plus intrusions in the lower crust, and has a total thickness 48 of only 10–15 km. This is much less than the total maximum thickness of 42 km for Icelandic-type crust measured 49 seismically in Iceland. The feasibility of the structure we propose is confirmed by numerical modeling that shows 50 extension of the continental crust can continue for many tens of millions of years by lower-crustal ductile flow. A 51 composition of Icelandic-type lower crust that is largely continental can account for multiple seismic observa- 52 tions along with gravity, bathymetric, topographic, petrological and geochemical data that are inconsistent 53 UNCORRECTEDwith a gabbroic composition for Icelandic-type lowerPROOF crust. It also offers a solution to difficulties in numerical 54 models for melt-production by downward-revising the amount of melt needed. Unstable tectonics on the 55 Greenland-Iceland-Faroe Ridge can account for long-term tectonic disequilibrium on the adjacent rifted margins, 56 the southerly migrating rift propagators that build diachronous chevron ridges of thick crust about the Reykjanes 57 ⁎ Corresponding author. Q6 E-mail address: [email protected] (G.R. Foulger). 1 Deceased. 2 Currently at School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. https://doi.org/10.1016/j.earscirev.2019.102926 0012-8252/© 2019 Published by Elsevier B.V. Please cite this article as: G.R. Foulger, T. Doré, C.H. Emeleus, et al., The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge, Earth-Sci. Rev., https://doi.org/10.1016/j.earscirev.2019.102926 2 G.R. Foulger et al. / Earth-Science Reviews xxx (xxxx) xxx Ridge, and the tectonic decoupling of the oceans to the north and south. A model of complex, discontinuous con- 58 tinental breakup influenced by crustal inhomogeneity that distributes continental material in growing oceans fits 59 other regions including the Davis Strait, the South Atlantic and the West Indian Ocean. 60 © 2019 Published by Elsevier B.V. 61 71 7273 7475 Contents 76 Listofacronyms.SeealsoTable2........................................................ 0 77 1. Introduction............................................................... 0 78 2. ContinentalbreakupformingtheNortheastAtlanticRealm.......................................... 0 79 2.1. High-velocitylowercrust...................................................... 0 80 2.2. SeafloorspreadingnorthandsouthoftheGreenland-Iceland-FaroeRidge................................ 0 81 2.2.1. NorthoftheGreenland-Iceland-FaroeRidge......................................... 0 82 2.2.2. SouthoftheGreenland-Iceland-FaroeRidge......................................... 0 83 3. TheGreenland-Iceland-FaroeRidge..................................................... 0 84 3.1. Crustalstructure.......................................................... 0 85 3.2. The Faroe-Shetland basin – abellwetherofGIFRtectonicinstability................................... 0 86 4. AnewmodelfortheGreenland-Iceland-FaroeRidge............................................. 0 87 4.1. Massbalance............................................................ 0 88 4.2. Problemsandparadoxessolved................................................... 0 89 5. Thermo-mechanicalmodeling....................................................... 0 90 6. Geochemistry............................................................... 0 91 6.1. Compositionofthemeltsource................................................... 0 92 6.2. Temperatureofthemeltsource................................................... 0 93 6.3. 3He/4He.............................................................. 0 94 7. Discussion................................................................ 0 95 7.1. TheGreenland-Iceland-FaroeRidge.................................................. 0 96 7.2. Crustal flow............................................................ 0 97 7.3. Magmatism............................................................ 0 98 7.3.1. TheconceptoftheNorthAtlanticIgneousProvince...................................... 0 99 7.3.2. Magmavolume...................................................... 0 100 7.3.3. Thechevronridges..................................................... 0 101 7.3.4. TheNorthAtlanticgeoidhigh................................................ 0 102 7.3.5. RegionsanalogoustotheGIFR................................................ 0 103 7.3.6. RegionsanalogoustotheNEAtlanticRealm.......................................... 0 104 8. Conclusions................................................................ 0 105 Uncitedreferences............................................................... 0 106 Acknowledgments............................................................... 0 107 References................................................................... 0 108 109Q7 List of acronyms. See also Table 2 in the development of the spectacularly successful continental drift 128 and plate tectonic theories, e.g., with the discovery of symmetrical mag- 129 110 netic anomalies across the Reykjanes Ridge, it has also defied predic- 130 tions made by this theory that are
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