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  • Articles  (97)
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  • 1
    Electronic Resource
    Electronic Resource
    Crustal thickening and ductile extension in the NE Greenland Caledonides: a metamorphic record from anatectic pelites (2000)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 18 (2000), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Caledonian orogenesis in NE Greenland resulted from the collision of Laurentia and Baltica during the Ordovician–Silurian. Anatectic pelites within the metasedimentary Smallefjord Sequence record a clockwise P–T  path, the result of early crustal thickening at c. 445–440 Ma and subsequent exhumation of the high-grade metamorphic core by a combination of ductile extension and tectonic denudation. The early prograde segment of the path followed a shallow, near-isothermal trajectory and attained a metamorphic peak of c. 9.0–10.0 kbar at 〉790 and 〈850 °C. Prograde metamorphism initiated anatexis of pelites in the kyanite stability field and continued with sillimanite stable. Inclusion trails in the garnet cores are textural remnants of early deformation, which occurred either before or during prograde metamorphism. The peak metamorphic conditions are anomalously high in the context of thermal models and P–T  paths for continental collision zones. The additional heat input required to promote migmatization may have been provided by advection as lower crustal high-pressure rocks and the uppermost mantle were uplifted following lithospheric thinning at an early stage in the orogeny. The prograde path was interrupted by the development of retrograde extensional shear fabrics defined by biotite+sillimanite and associated with garnet breakdown. Field observations indicate that ductile extension was accompanied by melt extraction, transport and emplacement of intracrustal granites dated at c. 430 Ma. Regional ductile extension and exhumation probably resulted from the development of gravitational instabilities within the overthickened crust during continental collision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1525-1314.2000.00282.x
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  • 2
    Electronic Resource
    Electronic Resource
    A Grenville Sm/Nd age for the Glenelg eclogite (1985)
    [s.l.] : Nature Publishing Group
    Nature 314 (1985), S. 754-754 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SANDERS et al.1 present data indicating that eclogites within the eastern Lewisian inlier at Glenelg equilibrated at 1,100 Myr BP at temperatures and pressures of -700 ?C and 〈 12 kbar. On the basis that the overlying Moine cover shcfws no sign of having exceeded conditions for the lower ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/314754a0
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  • 3
    Electronic Resource
    Electronic Resource
    U-Pb zircon geochronological evidence for Neoproterozoic events in the Glenfinnan Group (Moine Supergroup): the formation of the Ardgour granite gneiss, north-west Scotland (1997)
    Springer
    Contributions to mineralogy and petrology 128 (1997), S. 101-113 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma. Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050297
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  • 4
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    Progressive fold and fabric evolution associated with regional strain gradients: a case study from across a Scandian ductile thrust nappe, Scottish Caledonides (2010)
    In:  Geological Society Special Publication 335: 255-274.
    Details
    Publication Date: 2010-06-21
    Description: Fold and fabric patterns developed within a major Caledonian thrust nappe in NW Scotland reflect a progressive increase in regional D2 strain towards the basal ductile detachment. Within the upper greenschist to lower amphibolite facies thrust sheet, the main gently east-dipping foliations and SE-plunging transport-parallel lineations maintain a broadly similar orientation over c. 600 km2. Associated main phase, thrust-related folds (F2) are widely developed, and towards the base of the thrust sheet display progressive tightening and increasing curvilinearity of fold hinges ultimately resulting in sheath folds. Secondary folds (F3) are largely restricted to high-strain zones and are interpreted as flow perturbation folds formed during non-coaxial, top-to-the-NW ductile thrusting. These features are consistent with a structural model that incorporates plane strain pure-shear flattening with a superimposed and highly variable simple shear component focused into high-strain zones. The increase in strain over a distance of 30 km across strike is similar to the increasing deformation observed when structures are traced along strike to the north, and which are apparently related to proximity to basement-cover contacts. A U-Pb zircon age of 415{+/-}6 Ma obtained from a syn-D2 meta-granite confirms that regional deformation occurred during the Scandian phase of the Caledonian orogeny.
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  • 5
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    The Moine Supergroup of NW Scotland: insights into the analysis of polyorogenic supracrustal sequences (2010)
    In:  Geological Society Special Publication 335: 233-254.
    Details
    Publication Date: 2010-06-21
    Description: The Moine Supergroup of NW Scotland is a thick sequence of early Neoproterozoic sedimentary rocks, with minor igneous intrusions, that display evidence for multiple phases of regional deformation and metamorphism. The descriptions and interpretations of the Moine Schists' provided by the 1907 memoir (Peach et al. 1907) have been proved to be essentially correct and have laid the groundwork for a century of distinguished and influential research that has reached far beyond the confines of NW Scotland. The Survey workers recognized the sedimentary protoliths of these rocks, realized that they had been deposited unconformably on inliers of reworked basement gneisses that now occupy the cores of major folds, and understood the likely complexity of folding and the kinematic significance of mineral lineations. Further advances in understanding of the Moine rocks were mainly achieved through two techniques that were not available to the Survey workers of 100 years ago - geochronology and palaeomagnetism. Isotopic studies have confirmed the view of the Survey workers that the Moine rocks are of Precambrian age, and furthermore have demonstrated a complex, polyorogenic history.
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  • 6
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    Continental tectonics and mountain building. The legacy of Peach and Horne: an introduction (2010)
    In:  Geological Society Special Publication 335: 1-5.
    Details
    Publication Date: 2010-06-21
    Description: The world's mountain ranges are the clearest manifestations of long-term deformation of the continental crust. As such they have attracted geological investigations for centuries. Throughout this long history of research a few keynote publications stand out. One of the most important is the Geological Survey's 1907 memoir, The Geological Structure of the North-West Highlands of Scotland. The papers in this Special Publication celebrate the 100th anniversary of this remarkable book, placing the original findings in a present-day context by juxtaposing them against modern studies, not only from the NW Highlands, but also from elsewhere around the world. On first sight, the 1907 memoir by B. N. Peach and colleagues is simply a description of regional geology, albeit an exceptionally detailed one. However, the memoir outlines the Geological Survey's chief discoveries, and an abundance of minor ones, resulting from a decade of fieldwork in NW Scotland. At its height this activity occupied many of the most talented field geologists of Peach and Horne's generation and a significant number of the Scottish branch of the Survey. This team performed wondrous deeds, recognizing and interpreting many deformation structures on a variety of scales. The memoir describes these structures in a matter-of-fact manner, with occasional musings on their significance for broader tectonic processes. By focusing on the detail and establishing the supreme importance of getting the basic field relationships correct, the memoir's authors established the NW Highlands of Scotland as a prime location for training. Subsequent generations of geologists, from young students to...
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  • 7
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    Comparing Tibet-Himalayan and Caledonian crustal architecture, evolution and mountain building processes (2010)
    In:  Geological Society Special Publication 335: 207-232.
    Details
    Publication Date: 2010-06-21
    Description: The Himalaya-Tibet and Caledonide orogens are comparable in scale and are similar in various aspects. Regional suture zones are recognizable in both, although their identification is more problematic in the deeply eroded Caledonide orogen. Crustal-scale thrust belts, regional Barrovian metamorphism characterized by clockwise P-T paths, and migmatitic cores with crustally-derived leucogranite complexes are the dominant structural feature of both orogens. Both orogens also record calc-alkaline magmatism attributed to subduction activity prior to collision. Syn-orogenic extension accompanied crustal thickening in both orogens, however, the Caledonides also have a protracted record of late- to post-orogenic extension that is attributed to lithospheric delamination in combination with oblique plate divergence. The oblique nature of the Caledonian collision is also reflected in the development of regionally significant sinistral strike-slip faults and shear zones, whereas such structures are apparently not as significant within the Himalayan orogen. The major difference between the two orogens relates to their contrasting gross structure: the Caledonides has bivergent geometry with thrust belts developed in the pro- and retro-wedges, whereas the Himalaya has a thrust belt located only in the pro-wedge segment. These differing geometries are probably explicable with reference to pre-collision contrasts in rheology and/or inherited structures. As such, there is no reason to suggest that either example should be viewed as being a typical' product of collisional orogenesis - they likely represent end-members of a range of possible orogenic profiles.
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  • 8
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    Regional-scale lateral variation and linkage in ductile thrust architecture: the Oykel Transverse Zone, and mullions, in the Moine Nappe, NW Scotland (2010)
    In:  Geological Society Special Publication 335: 359-381.
    Details
    Publication Date: 2010-06-21
    Description: Sharp lateral changes in structural geometry of ductile thrust stacks are not widely reported. A regional-scale lateral culmination wall forms the southern boundary of the Cassley Culmination in Moine rocks in the Caledonides of Sutherland, Northern Scotland. This culmination wall is part of the Oykel Transverse Zone (OTZ), a kilometre-scale shear zone characterized by constrictional finite strain fabrics aligned sub-parallel to the regional WNW-directed thrust transport direction. Main phase folds and fabrics in the transverse zone hanging wall are folded by main phase folds and fabrics in the footwall, thus recording foreland-propagating ductile deformation. South of the Cassley Culmination, shortening occurred uniformly, without development of discrete subsidiary thrusts; distributed deformation (fold development) alternated with localized thrusting within the culmination. The classic ESE-plunging mullions at Oykel Bridge are an integral part of the OTZ and were generated by constriction aligned sub-parallel to the transport direction. Constriction is attributed to differential, transtensional movement across the OTZ during culmination development. Subsequent formation of the underlying Assynt Culmination further accentuated upward-bulging of the Cassley Culmination, amplifying the lateral change across the transverse zone. The OTZ aligns with a pronounced gravity gradient on the south-western side of the Lairg gravity low. Interpretive modelling relates this gradient to a buried basement ramp that possibly controlled the location of the transverse zone.
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  • 9
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    Tectonic stratigraphy and structural continuity of the northernmost Moine Thrust Zone and Moine Nappe, Scottish Caledonides (2007)
    In:  Geological Society Special Publication 272: 121-142.
    Details
    Publication Date: 2007-10-08
    Description: The Moine Thrust Zone and overlying Moine Nappe represent classic ground in Scottish geology in which Neoproterozoic Moine metasedimentary rocks were translated towards the WNW over the Laurentian foreland comprising Lewisian basement gneisses and a Cambrian cover succession during Caledonian orogenesis at c. 430 Ma. Systematic mapping of both the Moine Nappe and underlying Moine Thrust Zone in the Loch Hope to Whiten Head region of Sutherland extends the tectonic stratigraphy developed in other parts of the thrust zone to the little-studied north coast section. An apparent continuum of deformation is recognized from the Moine Nappe down into the underlying thrust zone with a consistent gently ESE-dipping foliation associated with down-dip mineral and extension lineations. The polyphase fold history present within the Moine Nappe and the thrust zone results from progressive deformation during thrusting. Thrust-related fold axes and bedding-cleavage intersections are typically subparallel to the transport direction in high-strain zones, whereas gently north- or south-plunging attitudes are common in lower strain portions of the thrust zone. Thrusts are commonly deformed by folds developed within their footwalls, consistent with a foreland-propagating sequence of deformation. The newly defined Lochan Riabhach Thrust is interpreted as an out-of-sequence' structure that sliced at low angles across the thrust zone and toward the WNW after initial thrust stacking. Comparison with the downfaulted segment of the Moine Nappe and thrust zone exposed on the foreland at Faraid Head demonstrates cross-strike continuity of the thrust sheet template and structural history for at least 15 km to the NW.
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  • 10
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    Basement-influenced rifting and basin development: a reappraisal of post-Caledonian faulting patterns from the North Coast Transfer Zone, Scotland (2010)
    In:  Geological Society Special Publication 335: 795-826.
    Details
    Publication Date: 2010-06-21
    Description: The post-Caledonian development of the West Orkney Basin is regularly cited as a classic example of basement-influenced rifting. This paper presents the first detailed multidisciplinary analysis of the three-dimensional (3D) geometries and distribution of post-Caledonian faults in onshore northernmost Scotland, examining their relationships to basement fabrics and comparing them to rift-related structures developed offshore in the West Orkney Basin. Two phases of rift-related faulting are distinguished: 1) Devonian ENE-WSW extension localized in the east of the basin and related to regional sinistral transtension along the Great Glen Fault; and 2) Permo-Triassic NW-SE extension focused to the west of the basin and probably contemporaneous with movements along the Minch Fault. A complex North Coast Transfer Zone is developed along the northern Scottish coast linking Mesozoic rifts that reactivated Caledonian structures in the West Orkney Basin (Naver Thrust) to those bounding the North Minch Basin (Outer Hebrides Fault Zone). Polymodal faulting patterns are widespread in onshore exposures. Fault patterns vary due to changes in the obliquity between regional rifting vectors and variably orientated pre-existing structures in each basement terrane. The geometric complexity and spatial variations in fault patterns onshore can be correlated with changes in basement structures, despite limited direct reactivation of pre-existing fabrics.
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