| 1. |
- Schiffer, Christian, et al.
(författare)
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High Arctic geopotential stress field and implications for geodynamic evolution
- 2018
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Ingår i: Geological Society Special Publication. - 0305-8719 .- 2041-4927. ; 460:1
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Tidskriftsartikel (refereegranskat)abstract
- We use new models of crustal structure and the depth of the lithosphere–asthenosphere boundary to calculate the geopotential energy and its corresponding geopotential stress field for the High Arctic. Palaeostress indicators such as dykes and rifts of known age are used to compare the present day and palaeostress fields. When both stress fields coincide, a minimum age for the configuration of the lithospheric stress field may be defined. We identify three regions in which this is observed. In north Greenland and the eastern Amerasia Basin, the stress field is probably the same as that present during the Late Cretaceous. In western Siberia, the stress field is similar to that in the Triassic. The stress directions on the eastern Russian Arctic Shelf and the Amerasia Basin are similar to that in the Cretaceous. The persistent misfit of the present stress field and Early Cretaceous dyke swarms associated with the High Arctic Large Igneous Province indicates a short-lived transient change in the stress field at the time of dyke emplacement. Most Early Cretaceous rifts in the Amerasia Basin coincide with the stress field, suggesting that dyking and rifting were unrelated. We present new evidence for dykes and a graben structure of Early Cretaceous age on Bennett Island.
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| 2. |
- Eken, Tuna, et al.
(författare)
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New insights into crustal properties of Anatolia and its surroundings inferred from P‐coda autocorrelation inversions
- 2021
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Ingår i: Journal of Geophysical Research - Solid Earth. - : American Geophysical Union (AGU). - 2169-9313 .- 2169-9356. ; 126:12
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Tidskriftsartikel (refereegranskat)abstract
- Constraints on crustal and uppermost mantle structure provide key information for understanding the geodynamic processes that have shaped the geological expressions and are currently causing deformation in Anatolia. We apply a novel method of Bayesian inversion of autocorrelated teleseismic P-wave coda data to retrieve the crustal and uppermost mantle structures beneath Anatolia and southeast Europe. Our inversion provides estimates of Moho depth variations and crustal velocity structure (e.g., Vp, Vs, and Vp/Vs ratio). The Moho architecture in the study area can be summarized by i) an overall west-to-east increase in the Moho depth from Greece to eastern Anatolia, ii) a homogeneously thin crustal structure beneath Greece, iii) complex, small-scale crustal features and variations in western and central Anatolia, and iv) relatively long-wavelength variations, but overall thick crust in eastern Anatolia. The apparent relation between the Moho depth variations and suture/fault zones implies a dominant control of structural inheritance on the past deformation in Anatolia. The overall Moho architecture appears to correlate well with the topography in Anatolia, although with some exceptions, in particular at smaller wavelength. These local inconsistencies in the topography-Moho depth relation suggest a more complex, wavelength-dependent isostatic state compared to what is expected from simple Airy isostasy. The observed deviations may originate from elastic effects, lithospheric density changes, or sub-lithospheric dynamic effects. Obvious large lateral variations in Vp, Vs and Vp/Vs ratio estimates in our model can relate to such density variations within the crust especially between tectonic domains.
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| 3. |
- Fomin, Ilya, et al.
(författare)
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Water, Hydrous Melting, and Teleseismic Signature of the Mantle Transition Zone
- 2019
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Foulger, Gillian R., et al.
(författare)
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A new paradigm for the North Atlantic Realm
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Foulger, Gillian R., et al.
(författare)
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The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Forskningsöversikt (refereegranskat)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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| 6. |
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| 7. |
- Gernigon, Laurent, et al.
(författare)
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Crustal fragmentation, magmatism, and the diachronous opening of the Norwegian-Greenland Sea
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 8. |
- Jess, Scott, et al.
(författare)
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Compilation of Apatite Fission-Track Data from the Northeast Atlantic Realm: A Jigsaw Puzzle with Missing Pieces
- 2024
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Ingår i: Lithosphere. - 1941-8264 .- 1947-4253. ; 2024:Special 14
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Tidskriftsartikel (refereegranskat)abstract
- The northeast (NE) Atlantic is one of the best-studied geological regions in the world, incorporating a wide array of geological phenomena including extensional tectonism, passive margin development, orogenesis, and breakup-related volcanism. Apatite fission-track (AFT) thermochronology has been an important tool in studying the onshore evolution of the NE Atlantic for several decades. Unfortunately, large regional-scale studies are rare, making it difficult to study geological processes across the whole region. In this work, a compilation of published AFT data is presented from across Fennoscandia, the British Isles, East Greenland, and Svalbard, with the goal of providing an accessible overview of the data and how this vast body of work has improved our understanding of the region’s evolution. Alongside a review of previous literature, interpolated maps of fission track age and mean track length (MTL) highlight regional trends in the data that may result from major first-order processes and areas of low sample density that should be targeted for future study. Additionally, in the absence of metadata required for thermal history modeling, apparent exhumation rate estimates are calculated from available elevation profiles and the timing of major exhumation events inferred from “boomerang plots” of fission track ages against MTL values. Across Fennoscandia, data suggests that the opening of the NE Atlantic and exhumation of the margin have clearly played a major role in the thermal history of the upper crust. The remaining areas of Britain, Ireland, East Greenland, and Svalbard all present more complex trends consistent with a combination of the NE Atlantic’s opening and the interplay between specific bedrock geology of sampling sites and localized geological processes. Areas of low sample density include southern Britain, NE Britain, southeast Greenland, southern Svalbard, and Eastern Fennoscandia, each of which provides the natural laboratory required to answer many unresolved questions.
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| 9. |
- Jess, Scott, et al.
(författare)
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Sediment supply on the West Greenland passive margin : redirection of a large pre-glacial drainage system
- 2020
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 177:6, s. 1149-1160
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Tidskriftsartikel (refereegranskat)abstract
- The Mesozoic–Cenozoic separation of Greenland and North America produced the small oceanic basins of theLabrador Sea and Baffin Bay, connected via a complex transform system through the Davis Strait. During rifting and partialbreakup sedimentary basins formed that record the changing regional sediment supply. The onshore and offshore stratigraphyof Central West Greenland outlines the presence of a major fluvial system that existed during the Cretaceous and was laterredirected in the Early Cenozoic by the formation of the West Greenland Igneous Province. Hydrological analysis ofGreenland’s isostatically balanced basement topography outlines two major drainage systems that likely flowed acrossGreenland prior to the onset of glaciation and emptied into the Sisimiut Basin within the Davis Strait, offshoreWest Greenland.The course of the northern drainage system suggests that it initially flowed NW into the Cretaceous/Palaeocene NuussuaqBasin, before being redirected SW around the West Greenland Igneous Province in the Mid-Palaeocene. Moreover,characteristics of these two drainage systems suggest they acted as a single larger fluvial system, prior to the onset of glaciation,that was likely the primary source of sediment across CentralWest Greenland throughout the Cretaceous and Palaeogene. Thisscenario provides a greater understanding of theWest Greenland margin’s late Cenozoic evolution, which differs from previousinterpretations that hypothesize a period of considerable post-rift tectonism and uplift. This work highlights the importance oflarge pre-glacial drainage systems across North Atlantic passive margins and their relevance when studying post-riftstratigraphy in rifted margin settings.
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| 10. |
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| 11. |
- Kind, Rainer, et al.
(författare)
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Sp converted waves reveal the structure of the lithosphere below the Alps and their northern foreland
- 2023
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Ingår i: Geophysical Journal International. - : Oxford University Press. - 0956-540X .- 1365-246X. ; 235:2, s. 1832-1848
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the lithosphere is reflecting its evolution. The Moho of the European lithosphere has already been studied intensively. This is, however, not yet the case for the lower boundary of the lithosphere, i.e., the lithosphere-asthenosphere boundary (LAB). We are using S-to-P converted seismic waves to study the structures of the Moho and the LAB beneath Europe including the greater Alpine Area with data from the AlpArray project and the European networks of permanent seismic stations. We use plain waveform stacking of converted waves without deconvolution and compare the results with stacking of deconvolved traces. We also compare Moho depths determinations using S-to-P converted waves with those obtained by other seismic methods. We present more detailed information about negative velocity gradients (NVG) below the Moho. Its lower bound may be interpreted as representing the LAB. We found that the thickness of the European mantle lithosphere is increasing from about 50°N towards the Alps along the entire east-west extension of the Alps. The NVG has also an east dipping component towards the Pannonian Basin and the Bohemian Massif. The Alps and their northern foreland north of about 50°N are surrounded in the east, west and north by a north dipping mantle lithosphere. Along 50°N, where the NVG is reversing its dip direction towards the north, is also the area along which the volcanoes of the European Cenozoic Rift System are located. Our results possibly indicate that the Alpine collision has deformed the entire lithosphere of the Alpine foreland as far north as about 50°N.
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| 12. |
- Longley, Luke, et al.
(författare)
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The Davis Strait proto-microcontinent : The role of plate tectonic reorganization in continental cleaving
- 2024
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Ingår i: Gondwana Research. - : Elsevier. - 1342-937X .- 1878-0571. ; 133, s. 14-29
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Tidskriftsartikel (refereegranskat)abstract
- A prolonged period of rifting and seafloor spreading between Greenland and North America formed the Labrador Sea and Baffin Bay oceanic basins, connected by the Davis Strait. However, disagreement exists regarding the exact plate motions between Greenland and Canada, as well as the tectonic evolution of the Davis Strait, with previous models unable to explain the origin of anomalously thick continental crust within the seaway. Here, we present a new plate tectonic reconstruction of Greenland’s separation from Canada, constrained by a new comprehensive set of mid-ocean ridge (MOR) and transform fault lineaments identified using free-air, vertical gradient, and filtered directional gradient maps from the Sandwell and Smith gravity data. Furthermore, the reinterpretation of seismic reflection data offshore West Greenland, along with a newly compiled crustal thickness model, identifies an isolated terrane of relatively thick (19–24 km) continental crust that was separated from Greenland during a newly recognised phase of E-W extension along West Greenland’s margin. We interpret this continental block as an incompletely rifted microcontinent, which we term the Davis Strait proto-microcontinent. Our reconstruction suggests release of the proto-microcontinent coincided with a change in the spreading orientation from ∼ 58 to 49 Myr during the alignment of Canada and Greenland's rifted margins, indicating a fundamental control of lithospheric structure on plate motions. Proto-microcontinent separation was induced by transpression along a newly recognised NE-SW trending transform margin that joined the Labrador Sea and Baffin Bay, prior to development of the Ungava Fracture Zone (UFZ). The location of this transform margin is constrained using our crustal thickness model, which demonstrates a sharp NE-SW trending continent-ocean transition across the northern Saglek basin. We term this newly identified first-order tectonic feature the Pre-Ungava Transform Margin (Pre-UTM), which accommodated early NE-SW motion between Greenland and Canada. Our identified mechanism of microcontinent formation may be widely applicable to other microcontinents around the globe, and further study is merited to understand the role of plate motion changes and transpression in microcontinent calving.
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| 13. |
- Peace, Alexander L., et al.
(författare)
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A review of Pangaea dispersal and Large Igneous Provinces : In search of a causative mechanism
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 14. |
- Peace, Alexander L., et al.
(författare)
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Evidence for Basement Reactivation during the Opening of the Labrador Sea from the Makkovik Province, Labrador, Canada : Insights from Field Data and Numerical Models
- 2018
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Ingår i: Geosciences. - : MDPI. - 2076-3263. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- The onshore exposures adjacent to modern, offshore passive continental margins may preserve evidence of deformation from the pre-, syn-, and post-rift phases of continental breakup that allow us to investigate the processes associated with and controlling rifting and breakup. Here, we characterize onshore brittle deformation and pre-rift basement metamorphic mineral fabric from onshore Labrador in Eastern Canada in the Palaeoproterozoic Aillik Domain of the Makkovik Province. Stress inversion (1) was applied to these data and then compared to (2) numerical models of hybrid slip and dilation tendency, (3) independent calculations of the regional geopotential stress field, and (4) analyses of palaeo-stress in proximal regions from previous work. The stress inversion shows well-constrained extensional deformation perpendicular to the passive margin, likely related to pre-breakup rifting in the proto-Labrador Sea. Hybrid slip and dilatation analysis indicates that inherited basement structures were likely oriented in a favorable orientation to be reactivated during rifting. Reconstructed geopotential stresses illuminate changes of the ambient stress field over time and confirm the present paleo-stress estimates. The new results and numerical models provide a consistent picture of the late Mesozoic-Cenozoic lithospheric stress field evolution in the Labrador Sea region. The proto-Labrador Sea region was characterized by a persistent E-W (coast-perpendicular) extensional stress regime, which we interpret as the pre-breakup continental rifting that finally led to continental breakup. Later, the ridge push of the Labrador Sea spreading ridge maintained this general direction of extension. We see indications for anti-clockwise rotation of the direction of extension along some of the passive margins. However, extreme persistent N-S-oriented extension as indicated by studies further north in West Greenland cannot be confirmed.
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| 15. |
- Peace, Alexander L., et al.
(författare)
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Halokinetically Overprinted Tectonic Inversion of the Penobscot 3D Volume Offshore Nova Scotia, Canada
- 2024
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Ingår i: Pure and Applied Geophysics. - 0033-4553 .- 1420-9136.
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Tidskriftsartikel (refereegranskat)abstract
- Polyphase fault evolution through reactivation is a globally observed phenomenon on passive margins. These structures play a crucial role in petroleum systems, offer vital constraints on rift and passive margin kinematics, and, in certain instances, serve as global markers for far-field stresses. Despite the significance of reactivated faults, understanding their kinematic evolution, existence, extent, and interactions within fault populations is often limited. This underscores the need for comprehensive investigations, including considerations of halokinesis in this process. This study presents a structural interpretation of a relay ramp identified in the Penobscot 3D seismic reflection survey offshore Nova Scotia, Canada. The ramp is characterized by two major SSE-dipping faults accompanied by smaller antithetic and synthetic normal faults with a general ENE-WSW strike. The two major faults exhibit evidence of reverse deformation in their lower sections, transitioning to normal offsets in their upper portions. Smaller faults predominantly affect younger strata without evidence of reactivation. Fault throw analysis indicates coupled movement on the main faults during both reverse and normal deformation intervals. Structural analysis suggests that these structures initially formed as reverse faults due to halokinesis and were subsequently reactivated during oceanward salt migration. The timing of Atlantic margin halokinesis aligns broadly with previously documented large-scale kinematic reorganization periods, suggesting similar kinematic events triggered salt movements in the Penobscot area. The observed kinematic dichotomy at depth is crucial, highlighting the potential oversight of polyphase deformation in areas where seismic data only captures near-surface structures. Recognising salt's role in kinematic reactivation is vital, explaining inversion phenomena and generating economically important trapping structures globally. This study implies that reactivation of structures in passive margins may be more widespread than previously acknowledged, particularly if seismic data only captures upper portions of structures.
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| 16. |
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| 17. |
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| 18. |
- Schiffer, Christian, et al.
(författare)
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Localized crustal deformation along the central North Anatolian Fault Zone revealed by joint inversion of P-receiver functions and P-wave polarizations
- 2019
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Ingår i: Geophysical Journal International. - : OXFORD UNIV PRESS. - 0956-540X .- 1365-246X. ; 217:1, s. 682-702
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Tidskriftsartikel (refereegranskat)abstract
- The North Anatolian Fault Zone (NAFZ) is a major plate boundary that separates the Eurasian Plate to the north from the Anatolian Plate to the south and is associated with powerful damaging earthquakes. Despite numerous studies of the crust and upper mantle across the NAFZ, our understanding of the exact mechanisms and distribution of deformation with depth is still limited. Accurate models of the crustal velocity structure are key to assess seismic hazard associated with strike-slip deformation. Here, we address this need by employing a novel method that jointly inverts receiver function waveforms and P-wave polarizations to recover S-wave velocity structure from the surface to the upper mantle. The method is applied to a dense teleseismic data set collected across a segment of the central NAFZ in Turkey. The results provide important new constraints on the sedimentary thickness, depth to basement and Moho discontinuity beneath the region. Our estimates of uppermost sedimentary thickness range from 0 km in some areas (e.g. in the Central Pontides) to 6 km in the Cankiri Basin. Smaller basins are scattered along the NAFZ. A similar pattern is observed for the basement depth, with values exceeding 10 km beneath the Cankiri Basin, where the Moho is shallowest with a depth of similar to 32 km. The Moho reaches a maximum depth of similar to 42 km beneath the Central Pontides. Most other areas have an average Moho depth of 35-38 km. The results reveal clear structural-tectonic relationships in the crust: areas of fundamentally different sedimentary and crustal architecture are bounded by faults and suture zones. The NAFZ appears to accommodate small-scale basin and basement-highs, and acts as a thick-skinned (i.e. full crustal-scale) boundary between laterally displaced crustal blocks to the north and south. Seismicity clusters are centred on areas of low Vp/Vs ratios that may be representative of weak zones.
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| 19. |
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| 20. |
- Schiffer, Christian, et al.
(författare)
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Seismic probing of buried ancient terrane boundaries - insight into Fennoscandia’s Palaeoproterozoic continental formation
- 2024
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Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 405, s. 107376-107376
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Tidskriftsartikel (refereegranskat)abstract
- Terrane boundaries are usually mapped from structures, lithologies and ages of the bedrock geology. Geophysical studies occasionally used to image terrane boundaries at depth typically yield localised information. In this contribution we demonstrate that it is possible to map Palaeoproterozoic terrane boundaries over large areas in northwest Fennoscandia through modelling of the crustal structure using receiver function inversion. Our new model suggests the existence of three “arms” of thick crust interpreted as deep expressions of Palaeoproterozoic terrane boundaries. We also observe previously unknown high velocity lower crust that we relate to Palaeoproterozoic rifting. The deep structural information shows that crustal structures can be preserved over billions of years and yields a three-dimensional crustal terrane model. This model improves our understanding of Palaeoproterozoic tectonics and continent formation processes.
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| 21. |
- Schiffer, Christian, et al.
(författare)
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Structural inheritance in the North Atlantic
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 206
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Forskningsöversikt (refereegranskat)abstract
- 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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| 22. |
- Schiffer, Christian, et al.
(författare)
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The crustal structure in the Northwest Atlantic region from receiver function inversion – Implications for basin dynamics and magmatism
- 2022
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 825
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Tidskriftsartikel (refereegranskat)abstract
- The Labrador Sea and Baffin Bay form an extinct Palaeogene oceanic spreading system, divided by a major continental transform, the Davis Strait, with the whole region defined as the Northwest Atlantic. The Davis Strait hosts the Ungava Fault Zone and is the central structural element of the Davis Strait Large Igneous Province (DSIP) that formed broadly coeval with continental breakup to its north and south. While constraints on the crustal structure in this region primarily exist in the offshore, crustal models are limited onshore, which makes an interpretation of regional structures as well as the extent, and therefore origin of the DSIP extremely difficult to ascertain. Here, we have collected all available teleseismic data from the Northwest Atlantic margins and applied a receiver function inversion to retrieve station-wise velocity models of the crust and uppermost mantle. We integrate the outcomes with published controlled-source seismic data and regional crustal models to make inferences about the crustal structure and evolution of the Northwest Atlantic. In particular, we focused on constraining the spatial extent and origin of high velocity lower crust (HVLC), and determining whether it is generically related to the Davis Strait Igneous Province, syn-rift exhumed and serpentinised mantle, or pre-existing lower crustal bodies such as metamorphosed lower crust or older serpentinised mantle rocks. The new results allow us to better spatially constrain the DSIP and show the possible spatial extent of igneous-type HVLC across Southwest Greenland, Northwest Greenland and Southeast Baffin Bay. Similarly, we are able to relate some HVLC bodies to possible fossil collision/subduction zones/terrane boundaries, and in some instances to exhumed and serpentinised mantle.
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| 23. |
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| 24. |
- Schiffer, Christian, et al.
(författare)
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The Moho Architecture and Its Role for Isostasy : Insights From the Lofoten‐Vesterålen Rifted Margin, Norway
- 2023
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Ingår i: Journal of Geophysical Research - Solid Earth. - : American Geophysical Union (AGU). - 2169-9313 .- 2169-9356. ; 128:5
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Tidskriftsartikel (refereegranskat)abstract
- The crustal structure of the Nordland and Troms region, Norway, has received growing scientific attention because (a) the region is one of the most seismically active areas of mainland Norway, and (b) there are differing interpretations of the crustal structure but none of the proposed models simultaneously satisfy gravity, topography and crustal isostasy. At the core of the puzzle is the Lofoten-Vesterålen archipelago, which exhibits considerable variations in crustal thickness, seemingly inconsistent with the topographic expression along this geomorphic structure. The prevalent view has been that the crust beneath the southern Lofoten is extremely thin (∼20 km). This has recently been disputed. Here, we address this debate by producing new lithospheric models in the region from joint inversion of receiver functions and P-wave polarizations at 62 seismic stations. Our results are consistent with the regional trends from other models, including a shallow Moho in the southern Lofoten. Moreover, our results detect a low-velocity layer in the uppermost mantle, which appears to be highly relevant to isostasy in the region. We conclude that the crustal structure in the region may not be as controversial as the recent debate suggested. What appears more urgent to understand is how the concept of isostasy is defined, and how it relates to the layered structure of the lithosphere. In particular, our findings emphasize the importance of conceptualizing the Moho as a transition zone with considerable thickness and internal structural variations, rather than a simple velocity discontinuity.Plain Language SummaryThe Nordland and Troms region, Norway, is one of the most seismically active areas of mainland Norway. To understand the occurrence of earthquakes, we need to understand the forces acting on and in the tectonic plate, the lithosphere, which consists of the crust and the underlying lithospheric mantle. One set of forces are caused by the distribution of masses and thereby variations of potential energy within the lithosphere. However, in the study area the structure of the lithosphere and the internal mass distribution is debated. So far, none of the proposed models can satisfactorily explain the geological observations. In particular the crust and topography seem to have a paradoxical relation. To gather more information, we develop another complementary model of the lithospheric structure based on a seismological method not yet applied in the area to this extent. Our new seismological study roughly confirms previous models of the crust. However, the model includes a hitherto unseen structure beneath the crust that may be key to understanding the relationship between topography and crust. This may have general and global implications for lithospheric structure.
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