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  • 1
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    Non-Volcanic Rifting of Continental Margins : A Comparison of Evidence from Land and Sea (2001)
    London : The Geological Society
    Details
    Description / Table of Contents: Non-volcanic continental margins may form up to 300f all present-day passive margins, and remnants of them are preserved in mountain belts. The papers in this volume demonstrate the benefits of integrating offshore and onshore studies, and illustrate the range of information obtained at different scales when comparing evidence from land and sea. Data sets collected across a range of spatial scales are evaluated: thin sections, cores, outcrops, seismic reflection profiles, and other geophysical data. The outcrop scale is crucial because it enables the spatial gulf to be bridged between DSDP and ODP cores and marine seismic data. There is also the problem that basins on land and beneath the sea inevitably have had different post-rift histories resulting in their contrasting present-day elevation. In mountain belts, portions of continental margins and oceanic crust are superbly exposed, but dismembered by subsequent compressional tectonics. Off present-day passive margins, extensional features have only been slightly deformed, if at all, by compressional movements, but are buried beneath significant thicknesses of post-rift sediments and so can only be sampled by ocean drilling at a small number of points. The first paper reviews the synergies that have occurred between investigations of the eastern North Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the Alps, and some later papers return to this theme. However, papers describing margins from other parts of the world show that it may be premature to use models based on the Atlantic and the Alps as the paradigm for all non-volcanic margins. The following 25 papers in the book are grouped under the following headings: (1) Margin overviews; (2) Exhumed crust and mantle; (3) Tectonics and stratigraphy; (4)Numerical models of extension and magmatism.
    Pages: Online-Ressource (585 Seiten)
    ISBN: 1862390916
    URL: http://sp.lyellcollection.org/content/187/1.toc
    Language: English
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    E-BOOK
  • 2
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    Lu–Hf geochronology of ultra-high-pressure eclogites from the Tromsø-Nappe, Scandinavian Caledonides: evidence for rapid subduction and exhumation (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Geochronology of ultra-high-pressure metamorphic rocks is able to constrain the timing and rates of subduction-zone processes. Lu–Hf garnet dating has the potential to yield information about the timing of the prograde evolution of subducting rocks under increasing pressure. In combination with other methods, it thus allows constraining the complete P–T–t path with high precision. Ultra-high-pressure eclogites from the Tromsø Nappe, the structurally highest tectonic unit of the Scandinavian Caledonides in northern Norway, were dated using Lu–Hf geochronology on garnet. A sample from Tromsdalstind yielded an age of 448.3 ± 3.6 Ma, interpreted as dating prograde garnet growth due to preserved zoning in the major-element and Lu contents of garnet grains. A sample from the diamond-bearing locality Tønsvika yielded an identical age of 449.4 ± 3.3 Ma. Garnet from this sample shows a weak zoning in Ca content and near-homogeneous Lu content. These ages are identical within error among each other and with published U–Pb ages of peak-eclogite-facies zircon and rutile/titanite from exhumation-related leucosome veins. Consequently, the entire subduction–exhumation cycle leading to the ultra-high-pressure eclogites lasted only very few millions of years during the Late Ordovician.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Agentúra na Podporu Výskumu a Vývoja (SK)
    Keywords: ddc:552.4 ; Lu–Hf geochronology ; UHP metamorphism ; Garnet ; Scandinavian Caledonides ; Tromsø Nappe
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
    Electronic Resource
    Electronic Resource
    Continental breakup by detachment faulting: field evidence and geochronological constraints (Tasna nappe, Switzerland) (1998)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 10 (1998), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Lower Tasna Detachment (LTD) is a low-angle fault contact between serpentinized peridotite below and continental basement above. It was formed during Jurassic to Early Cretaceous rifting of a Tethyan continental margin and later captured in a thrust nappe during Tertiary plate convergence. Foliated gabbro, gabbro mylonite, and granitoid mylonite occurring along the LTD record shearing under decreasing temperatures. U–Pb dating of zircon from the gabbro mylonite yielded a Permian age, interpreted as the age of gabbro intrusion, whereas the breakup of the passive margin occurred as late as Early Cretaceous. This suggests that the gabbro belongs to a prerift, lower to middle crustal intrusion ‘smeared out’ along the detachment by extensional faulting. The juxtaposition of mantle and upper crust along the Lower Tasna detachment may serve as a model for several seismic reflectors observed in distal passive continental margins (e.g. S reflector of the Galicia margin).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3121.1998.00187.x
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    Paper (German National Licenses)
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  • 4
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    Evolution of an Early Permian extensional detachment fault from synintrusive, mylonitic flow to brittle faulting (Grassi Detachment Fault, Orobic Anticline, southern Alps, Italy) (2008)
    In:  Geological Society Special Publication 298: 69-82.
    Details
    Publication Date: 2008-07-10
    Description: Lower Permian volcanic and sedimentary rocks of the Collio Formation in the Orobic Anticline do not rest with a depositional contact on the Variscan basement but are separated from it by the subhorizontal Grassi Detachment Fault, consisting of a cataclasite layer underlain by mylonite. Field relations indicate that both the cataclasite and the mylonite are Early Permian in age. The mylonite formed in a continuous process before, during, and after the intrusion of the Val Biandino Quartz Diorite in the footwall of the detachment fault. Microstructure and quartz texture of the mylonite indicate top-to-the-southeast displacement. Quartz textures of mylonite close to the intrusive bodies are characterized by c-axis single maxima near the Y-direction of the finite strain, indicating prism 〈a〉glide as the dominant gliding system and hence high temperatures (above c. 500 {degrees}C) during mylonitization. This is explained by heat advection through the rising quartz diorite melt. During detachment faulting, the footwall of the Grassi Detachment Fault was bowed up to form a metamorphic core complex. The Ponteranica Conglomerate was deposited as a proximal, syntectonic fan-delta on the southeast side of the metamorphic core complex late in its evolution. The unconformity of the Verrucano Lombardo over the Collio Formation and the basement results from erosion of the topography created by detachment faulting, core complex updoming, and block tilting. These results indicate dramatic SE-NW stretching (in present-day coordinates) of the South-Alpine crust during the Early Permian. The return from the thickened, orogenic crust at the end of the Hercynian orogeny to the normal crustal thickness (c. 30 km) of Late Permian and Early Triassic times was accommodated to a large extent by crustal extension, at least in this part of the southern Alps.
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  • 5
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    Introduction: analysing orogeny--the Alpine approach (2008)
    In:  Geological Society Special Publication 298: 1-4.
    Details
    Publication Date: 2008-07-10
    Description: The European Alps, the prototype collisional orogen and playground of geologists from all over the world, have been studied by generations of Earth scientists. The density of data is probably matched by no other mountain chain. Still, the Alpine chain is far from being over-studied, since many fundamental questions have not yet found a satisfactory and generally accepted answer, e.g. the formation of the Western Alpine arc. In recent years however, tectonic research on the Alpine mountain chains has made dramatic progress due to new findings (e.g. coesite), new methods (e.g. GPS), and new—or newly considered—concepts (e.g. subduction roll-back). Our picture of the Alpine orogeny has changed completely. Extremely important for Alpine research, the opening of borders between western and eastern parts of Europe has opened new perspectives: seen from the east, the Alps are the result of the junction of the Dinarides and the Carpathians. Parts of the Alpine evolution, e.g. Jurassic tectonics in the Northern Calcareous Alps, can only be understood in the context of processes in the Internal Dinarides and Internal Carpathians. The exchange of information and ideas between Alpine, Carpathian, Pannonian and Dinaride Earth scientists—in which Stefan Schmid played and still plays a most important role—has been fruitful for all sides. The present volume on the Alps, Carpathians and Dinarides (Fig. 1) includes articles that are related to key aspects of the tectonic evolution of these mountain chains. These articles are examples of the Alpine approach to orogeny, which combines careful fieldwork with a broad variety of laboratory methods, and integrates this into the extensive and detailed knowledge base that has been accumulated over a long history of geological research...
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  • 6
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    The role of detachment faulting in the formation of an ocean-continent transition: insights from the Iberia Abyssal Plain (2001)
    In:  Geological Society Special Publication 187: 405-428.
    Details
    Publication Date: 2001-01-01
    Description: The Iberia Abyssal Plain segment of the West Iberia margin was drilled during Ocean Drilling Program Legs 149 and 173 and has been extensively studied geophysically. We present new microstructural investigations and new age data. These, together with observed distribution of upper- and lower-crustal and mantle rocks along the ocean-continent transition suggest the existence of three detachment faults, one of which was previously unrecognized. This information, together with a simple kinematic inversion of the reinterpreted seismic section Lusigal 12, allows discussion of the kinematic evolution of detachment faulting in terms of the temporal sequence of faulting, offset along individual faults, and thinning of the crust during faulting. Our study shows that the detachment structures recognized in the seismic profile became active only during a final stage of rifting when the crust was already considerably thinned to c. 12 km. The total amount of extension accommodated by the detachment faults is of the order of 32.6 km corresponding to a {beta} factor of about two. During rifting, the mode of deformation changed oceanwards. Initial listric faulting led to asymmetric basins, accommodating low amounts of extension, and was followed by a situation in which the footwall was pulled out from underneath a relatively stable hanging wall accommodating high amounts of extension. Deformation along the latter faults resulted in a conveyor-belt type sediment accumulation in which the exhumed footwall rocks were exposed, eroded and redeposited along the same active fault system.
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  • 7
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    Introduction: the land and sea approach (2001)
    In:  Geological Society Special Publication 187: 1-8.
    Details
    Publication Date: 2001-01-01
    Description: The idea for a special publication on non-volcanic margins arose during Ocean Drilling Program (ODP) Leg 173 off West Iberia, prompted by ODP's decision to cease publishing the scientific results volumes as hard copy. The Shipboard Scientific Party favoured an open scientific meeting and associated publication. But they did not want to produce a book that was a scientific results volume by another name, but rather contribute to a publication that had a much broader scope than just reporting results obtained off West Iberia. These thoughts, and many scientific discussions during the Leg, were influenced by the presence on board of scientists who also work on Alpine geology: hence the evidence from land and sea' approach that underlies the content of this publication. However, when planning the meeting, we were very conscious of the fact that the West Iberia and Alpine examples might not be typical of other non-volcanic margins. We were keen, therefore, to ensure that margins in other parts of the world were discussed, including a margin that is active today, and that was visited by the JOIDES Resolution not long after Leg 173 took place (Leg 180: Woodlark Basin). We caution, therefore, that it may be premature to use models based on the Iberia and Tethyan margins as the paradigm for all non-volcanic margins. The first paper in this book, by Boillot & Froitzheim, reviews the synergies that have occurred between investigations of the eastern Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the ... This 250-word extract was created in the absence of an abstract.
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  • 8
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    Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions (2001)
    In:  Geological Society Special Publication 187: 9-30.
    Details
    Publication Date: 2001-01-01
    Description: During the last 20 years, regional studies on the West Iberia margin and on the former margins of the Tethys have considerably advanced the understanding of processes related to continental break-up and the onset of sea-floor spreading. However, some questions remain outstanding. To tentatively answer these, a coherent interpretation of available data is proposed, based on the detachment fault concept applied to the continental as well as the oceanic lithosphere, and on the hypothesis of a multi-staged rifting process. The interpretation addresses the nature of the lower crust beneath non-volcanic passive margins, the origin of ophicalcites, the probable time gap between syn- or post-rift crystallization of gabbros and extrusion of basalts on the sea floor, and the significance of dipping reflectors within oceanic lithosphere adjacent to non-volcanic passive margins. The interpretation also considers the symmetry v. asymmetry of continental rifting and break-up, the location of the ocean-continent boundary, and the possible association of magnetic quiet zones with ultramafic sea floor (serpentinized peridotite) bordering non-volcanic passive margins.
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  • 9
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    Ultrahigh-pressure metamorphism and exhumation of garnet peridotite in Pohorje, Eastern Alps (2006)
    In:  Journal of Metamorphic Geology, pp. 19-31, vol. 24, no. 1
    Details
    Publication Date: 2006
    Keywords: TF IV ; Task Force IV ; Ultra-Deep Continental Crust Subduction (UDCCS)
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    BIBLIOGRAPHY ILP
  • 10
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    Triassic to Early Jurassic (c. 200 Ma) UHP metamorphism in the Central Rhodopes: evidence from U-Pb-Th dating of monazite in diamond-bearing gneiss from Chepelare (Bulgaria) (2016)
    Wiley
    Details
    Publication Date: 2016-01-12
    Description: Evidence for ultrahigh-pressure metamorphism (UHPM) in the Rhodope Metamorphic Complex comes from occurrence of diamond in pelitic gneisses, variably overprinted by granulite facies metamorphism, known from several areas of the Rhodopes. However, tectonic setting and timing of UHPM are not interpreted unanimously. Linking age to metamorphic stage is a prerequisite for reconstruction of these processes. Here we use monazite in diamond-bearing gneiss from Chepelare (Bulgaria) to date the diamond-forming UHPM event in the Central Rhodopes. The diamond-bearing gneiss comes from a strongly deformed, lithologically heterogeneous zone (Chepelare Mélange) sandwiched between two migmatized orthogneiss units, known as Arda-I and Arda-II. Diamond, identified by Raman micro-spectroscopy, shows the characteristic band mostly centred between 1332 and 1330 cm −1 . The microdiamond occurs as single grains or polyphase diamond + carbonate inclusions, rarely with CO 2 . Thermodynamic modelling shows that garnet was stable at UHP conditions of 3.5-4.6 GPa and 700-800 °C, in the stability field of diamond, and was re-equilibrated at granulite facies/partial melting conditions of 0.8-1.2 GPa and 750-800 °C. The texture of monazite shows older central parts and extensive younger domains which formed due to metasomatic replacement in solid residue and/or overgrowth in melt domains. The monazite core compositions, with distinctly lower Y, Th and U contents, suggest its formation in equilibrium with garnet. The U–Th–Pb dating of monazite using electron microprobe analysis yielded a c . 200 Ma age for the older cores with low Th, Y, U and high La/Nd ratio, and a c . 160 Ma age for the dominant younger monazite enriched in Th, Y, U and HREE. The older age of around 200 Ma is interpreted as the timing of UHPM whereas the younger age of around 160 Ma as granulite facies/partial melting overprint. Our results suggest that UHPM occurred in Late Triassic to Early Jurassic time, in the framework of collision and subduction of continental crust after the closure of Palaeotethys. This article is protected by copyright. All rights reserved.
    Print ISSN: 0263-4929
    Electronic ISSN: 1525-1314
    Topics: Geosciences
    Published by Wiley
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