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  • 1. Fomin, Ilya
    et al.
    Schiffer, Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Water, Hydrous Melting, and Teleseismic Signature of the Mantle Transition Zone2019Ingår i: Geosciences, ISSN 2076-3263, Vol. 9, nr 12, artikel-id 505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent geophysical and petrological observations indicate the presence of water and hydrous melts in and around the mantle transition zone (MTZ), for example, prominent low-velocity zones detected by seismological methods. Experimental data and computational predictions describe the influence of water on elastic properties of mantle minerals. Using thermodynamic relationships and published databases, we calculated seismic velocities and densities of mantle rocks in and around the MTZ in the presence of water for a plausible range of mantle potential temperatures. We then computed synthetic receiver functions to explore the influence of different water distribution patterns on the teleseismic signature. The results may improve our understanding and interpretation of seismic observations of the MTZ.

  • 2.
    Foulger, Gillian
    et al.
    Durham University.
    Doré, Anthony
    University of Utah.
    Emeleus, Henry
    Durham University.
    Franke, Dieter
    BGR.
    Geoffroy, Laurent
    Université de Bretagne Occidentale.
    Gernigon, Laurent
    NGU.
    Hey, Richard
    University of Hawaii.
    Holdsworth, Bob
    Durham University.
    Hole, Malcolm
    Aberdeen University.
    Höskuldsson, Ármann
    University of Iceland.
    Julian, Bruce
    Durham University.
    Petersen, Kenni
    Aarhus University.
    Schiffer, Christian
    Stephenson, Randell
    Aberdeen University.
    Stoker, Martyn
    University of Adelaide.
    The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge2019Ingår i: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 3.
    Gernigon, Laurent
    et al.
    Geological Survey of Norway (NGU), Trondheim, Norway.
    Franke, Dieter
    Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.
    Geoffroy, Laurent
    Institut Universitaire Européen de la Mer (IUEM), Plouzané, France.
    Schiffer, Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Dept. Earth Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK.
    Foulger, Gillian
    Dept. Earth Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK.
    Stoker, Martyn
    Australian School of Petroleum, University of Adelaide, Adelaide, SA 5005, Australia.
    Crustal fragmentation, magmatism, and the diachronous opening of the Norwegian-Greenland Sea2019Ingår i: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Norwegian-Greenland Sea (NGS) in the NE Atlantic comprises diverse tectonic regimes and structural features including sub-oceanic basins of different ages, microcontinents and conjugate volcanic passive margins, between the Greenland-Iceland-Faroe Ridge in the south and the Arctic Ocean in the north. We summarize the tectonic evolution of the area and highlight the complexity of the conjugate volcanic and rifted margins up to lithospheric rupture in the NGS. The highly magmatic breakup in the NGS was diachronous and initiated as isolated and segmented seafloor spreading centres. The early seafloor spreading system, initiating in the Early Eocene, gradually developed into atypical propagating systems with subsequent breakup(s) following a step-by-step thinning and rupture of the lithosphere. Newly-formed spreading axes propagated initially towards local Euler poles, died out, migrated or jumped laterally, changed their propagating orientation or eventually bifurcated. With the Palaeocene onset of volcanic rifting, breakup-related intrusions may have localized deformation and guided the final axis of breakup along distal regions already affected by pre-magmatic Late Cretaceous-Palaeocene and older extensional phases. The final line of lithospheric breakup may have been controlled by highly oblique extension, associated plate shearing and/or melt intrusions before and during Seaward Dipping Reflectors (SDRs) formation. The Inner SDRs and accompanying volcanics formed preferentially either on thick continental ribbons and/or moderately thinned continental crust. The segmented and diachronic evolution of the NGS spreading activity is also reflected by a time delay of 1–2 Myrs expected between the emplacement of the SDRs imaged at the Møre and Vøring margins. This complex evolution was followed by several prominent changes in spreading kinematics, the first occurring in the Middle Eocene at 47 Ma–magnetic chron C21r. Inheritance and magmatism likely influenced the complex rift reorganization resulting in the final dislocation of the Jan Mayen Microplate Complex from Greenland, in the Late Oligocene/Early Miocene.

  • 4.
    Peace, Alexander
    et al.
    McMaster University.
    Phethean, Jordan
    University of Derby.
    Franke, Dieter
    BGR.
    Foulger, Gillian
    Durham University.
    Schiffer, Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Welford, Kim
    Memorial University.
    McHone, Greg
    Rocchi, Sergio
    Universita di Pisa.
    Schnabel, Michael
    BGR.
    Doré, Anthony
    University of Utah.
    A review of Pangaea dispersal and Large Igneous Provinces – In search of a causative mechanism2019Ingår i: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, artikel-id 102902Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The breakup of Pangaea was accompanied by extensive, episodic, magmatic activity. Several Large Igneous Provinces (LIPs) formed, such as the Central Atlantic Magmatic Province (CAMP) and the North Atlantic Igneous Province (NAIP). Here, we review the chronology of Pangaea breakup and related large-scale magmatism. We review the Triassic formation of the Central Atlantic Ocean, the breakup between East and West Gondwana in the Middle Jurassic, the Early Cretaceous opening of the South Atlantic, the Cretaceous separation of India from Antarctica, and finally the formation of the North Atlantic in the Mesozoic-Cenozoic. We demonstrate that throughout the dispersal of Pangaea, major volcanism typically occurs distal from the locus of rift initiation and initial oceanic crust accretion. There is no location where extension propagates away from a newly formed LIP. Instead, LIPs are coincident with major lithosphere-scale shear movements, aborted rifts and splinters of continental crust rifted far out into the oceanic domain. These observations suggest that a fundamental reappraisal of the causes and consequences of breakup-related LIPs is in order.

  • 5.
    Schiffer, Christian
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Doré, Anthony
    University of Utah.
    Foulger, Gillian
    Durham University.
    Franke, Dieter
    BGR.
    Geoffroy, Laurent
    Université de Bretagne Occidentale.
    Gernigon, Laurent
    NGU.
    Holdsworth, Bob
    Durham University.
    Kusznir, Nick
    University of Liverpool.
    Lundin, Erik
    Equinor.
    McCaffrey, Ken
    Durham University.
    Peace, Alexander
    McMaster University.
    Petersen, Kenni
    Aarhus University.
    Phillips, Thomas
    Durham University.
    Stephenson, Randell
    Aberdeen University.
    Stoker, Martyn
    University of Adelaide.
    Welford, Kim
    Memorial University.
    Structural inheritance in the North Atlantic2019Ingår i: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The North Atlantic, extending from the Charlie Gibbs Fracture Zone to the north Norway-Greenland-Svalbard margins, is regarded as both a classic case of structural inheritance and an exemplar for the Wilson-cycle concept. This paper examines different aspects of structural inheritance in the Circum-North Atlantic region: 1) as a function of rejuvenation from lithospheric to crustal scales, and 2) in terms of sequential rifting and opening of the ocean and its margins, including a series of failed rift systems. We summarise and evaluate the role of fundamental lithospheric structures such as mantle fabric and composition, lower crustal inhomogeneities, orogenic belts, and major strike-slip faults during breakup. We relate these to the development and shaping of the NE Atlantic rifted margins, localisation of magmatism, and microcontinent release. We show that, although inheritance is common on multiple scales, the Wilson Cycle is at best an imperfect model for the Circum-North Atlantic region. Observations from the NE Atlantic suggest depth dependency in inheritance (surface, crust, mantle) with selective rejuvenation depending on time-scales, stress field orientations and thermal regime. Specifically, post-Caledonian reactivation to form the North Atlantic rift systems essentially followed pre-existing orogenic crustal structures, while eventual breakup reflected a change in stress field and exploitation of a deeper-seated, lithospheric-scale shear fabrics. We infer that, although collapse of an orogenic belt and eventual transition to a new ocean does occur, it is by no means inevitable.

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