John F. Dewey

John F. Dewey
University College Oxford, British Museum of Natural History, UC Davis, UT Austin · Earth Sciences

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250
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Publications

Publications (250)
Article
Searle (2022) argues, based on data from Scotland alone, that the deformation and metamorphism of the Scottish Highlands is continuously diachronous from the early Ordovician (Grampian) in the Dalradian of the Grampian Highlands to the mid-Silurian (Scandian) in the Moine of the Northwest Highlands. Necessarily, he disputes substantial offset along...
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We identify 14 mechanisms, marine and non-marine, one man made, that result and could result in the formation of boulder deposits after reviewing issues associated with clast shape, size and classification. Four of these mechanisms: storm deposits; waterspouts; cliff collapse; and catastrophic flooding below sea level, may produce deposits stretchi...
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The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to repre...
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Space probes in our solar system have examined all bodies larger than about 400 km in diameter and shown that Earth is the only silicate planet with extant plate tectonics sensu stricto. Venus and Earth are about the same size at 12 000 km diameter, and close in density at 5 200 and 5 500 kg.m-3 respectively. Venus and Mars are stagnant lid planets...
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Stephen Moorbath was an intellectual with eclectic interests across the sciences and humanities. In 1939, as a ten-year-old, he fled from Germany to England with his father. Stephen spent almost the whole of the rest of his life—from schoolboy to university professor—in Oxford, where he became one of the world's leading isotope geochemists. His aca...
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The McKenzie et al. (2019) model concerning the cause of the deep earthquakes in the Hindu Kush region in Asia greatly resembles the hidden subduction model proposed earlier. However, in the case of the Hindu Kush, the age of the disappearance of the Tethyan waters was early Jurassic and the sutures were overlain by early Cretaceous sedimentary cov...
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This second issue of the Canadian Journal of Earth Sciences special issue dedicated to Ali Mehmet Celâl Şengör for his outstanding contributions to plate tectonics and history of geology includes 11 research articles. These articles have diverse subject matters dealing with tectonic processes in California, Africa, Asia, Iceland, Europe, Canada, an...
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Celâl Şengör is one of the leading and most influential geologists of our time. He has made many significant contributions to the understanding of the evolution of our planet in many areas, including continental growth, Phanerozoic orogenic belts, continental rifts, transform faults, and mantle plumes.
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The Grampian Orogeny of western Ireland was formed during the mid‐Ordovician Grampian‐Taconic collision between a 5,600‐km system of oceanic arcs and the Laurentian margin. It is remarkable in that it preserves a complete sedimentary record of the arc‐continent collision process in the South Mayo Trough, which can be linked with deformation and met...
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The problem of the observed very rapid advection of heat into metamorphic thrust stacks is reviewed. Conductive models relying on the thermal relaxation of a thickened crust will not produce the observed Barrovian (medium temperature, medium pressure) assemblages within some short-lived orogens (e.g., western Ireland and Timor). Studies of the rate...
Article
I outline and discuss my career in the context of the history of structural geology and tectonics, the progressive developments that led to plate tectonics, the people who have encouraged and influenced me, the events that changed my life, my fifty six doctoral students who have taught me so much, and my principal interests in tectonics. I discuss,...
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In the first application of the developing plate tectonic theory to the pre-Pangaea world 50 years ago, attempting to explain the origin of the Paleozoic Appalachian–Caledonian orogen, J. Tuzo Wilson asked the question: ‘Did the Atlantic close and then reopen?’. This question formed the basis of the concept of the Wilson cycle: ocean basins opening...
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The origins of boulderite deposits are investigated with reference to the present-day foreshore of Annagh Head, NW Ireland, and the Lower Miocene Matheson Formation, New Zealand, to resolve disputes on their origin and to contrast and compare the deposits of tsunamis and storms. Field data indicate that the Matheson Formation, which contains boulde...
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In the first paragraph of his discussion of our paper, Burton sets up his definition of what he thinks should have been the structure and purpose of our paper, his opinion of what a review should be and then complains that we did not follow his definition. We reject his definition, having defined our purpose in the abstract of our review. We were i...
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Archean cratons have map patterns and rock associations that are diagnostic of the Wilson Cycle. The North China Craton (NCC) consists of several distinctly different tectonic units, but the delineation and understanding of the significance of individual sutures and the rocks between them has been controversial. We present an actualistic tectonic d...
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The current view regarding the timing of regionally developed penetrative tectonic fabrics in sedimentary rocks is that their development postdates lithification of those rocks. In this case, fabric development is achieved by a number of deformation mechanisms, including grain rigid body rotation, crystal-plastic deformation, and pressure solution....
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In the Irish and British Caledonides, the early Ordovician Grampian Orogeny was the result of collision between the Laurentian rifted margin and an oceanic island arc. The Connemara terrain in western Ireland differs in position and character from all other parts of the exposed Dalradian rocks of the Grampian Orogen in lying south of the collided a...
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Zagorevski & van Staal (2014) question our model (Dewey & Casey 2013) in which we invoked forearc suprasubduction zone (SSZ) spreading to form the Bay of Islands Ophiolite Complex (BOIC) as part of the Notre Dame arc of the Appalachian–Caledonian Orogen. We interpret the formation of the BOIC to have occurred by spreading proximal to a ridge–trench...
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The purpose of this review paper is to identify and outline some critical questions about the geology and tectonic evolution of the Scottish Caledonides in their wider Caledonian/Appalachian context. We outline what we think we know and what we perceive to be some important problems from about 1.0 Ga (Grenville Orogeny) to the Middle Devonian (Acad...
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In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few...
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Coesite-bearing eclogites in several deep crustal metamorphic assemblages now exposed in extensionally-collapsed orogens indicate the tectonic denudation of more than 90 km of crustal rocks and pre-collapsed crustal thicknesses of at least 120 km. For mountain ranges and orogenic plateaux up to 5 km in elevation and average crustal densities of abo...
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The early Ordovician (c. 485 Ma) Bay of Islands Ophiolite Complex was obducted onto the Laurentian rifted margin as the fore-arc of an oceanic arc that collided with the margin during the mid-Ordovician (c. 470 Ma). The subduction zone was nucleated on an oceanic transform-fracture zone, part of whose remnants occur as the polyphase-deformed and in...
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The principal enigma of large obducted ophiolite slabs is that they clearly must have been generated by some form of organized sea-floor spreading/plate-accretion, such as may be envisioned for the oceanic ridges, yet the volcanics commonly have arc affinity (Miyashiro) with boninites (high-temperature/low-pressure, high Mg and Si andesites), which...
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Ordovician strata of the South Mayo Trough in western Ireland contain clastic deposits that represent materials eroded from a large and diverse continental area over a time scale that spans much of the Earth's history. Therefore, it is a useful region to use detrital zircons to construct a continental crustal growth model. Here, we report integrate...
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Synopsis Three main stages are recognized in the evolution of the Scottish Caledonian orogen. Firstly, the development of the depositional framework from late Pre-Cambrian to early Ordovician times is outlined, The thick Moine and Dalradian sediments, accumulating on a continental rise, are shown to be equivalent to the shelf sequence of the forela...
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We offer a kinematic solution to the “ophiolite enigma, paradox or conundrum”, which is that obducted large-slab full-sequence ophiolite complexes must have originated by organized sea-floor spreading (e.g. sheeted dyke complexes), which indicates an origin at oceanic ridges, yet have geochemical affinities that link them to arcs, especially fore-a...
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The geology of western Ireland preserves a record of the collision of the Lough Nafooey arc with the Laurentian margin which caused the mid-Ordovician Grampian Orogeny. Remarkably, a basin, the South Mayo Trough, accumulated some 9km of sedimentary and volcanic rocks before, during and after this event. Thrusting, believed to be during the post-Gra...
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There is no one model, no paradigm, that uniquely defines arc–continent collision. Natural examples and modelling of arc–continent collision show that there is a large degree of, and variation in, complexity that depend on a number of key first-order parameters and the nature of the main players; the continental margin and the arc–trench complex (t...
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The Ordovician strata of the South Mayo Trough in western Ireland were deposited as a conformable sequence, first in the forearc of a north-facing oceanic arc, then in a synorogenic basin above the arc-continent collisional Grampian orogen, then in an extensional hanging-wall basin above the exhuming Dalradian metamorphic complex and, finally, in a...
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The Moine Thrust zone ofNWScotland marks the Caledonian orogenic front and in the Assynt region consists of several west-vergent major thrust sheets (Moine, Ben More, Glencoul and Sole Thrust sheets) that place allochthonous rocks onto the Lewisian basement and Torridon Group cover in the west. Here we present two new balanced and restored sections...
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Obliquity of the strain velocity field to the deformation zone boundary requires strain to be triaxial. At the plate boundary scale, fault geometries predicted by transtensional theory better explain observed fault patterns in the northern Eastern California shear zone–Walker Lane area than do 2D plane strain predictions. Structural provinces in th...
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Ophiolites and ophiolite complexes have been recognized as having an oceanic affinity or origin since the classic work of Ian Gass in the 1950's on the Troodos Complex. A problem has been that the term ophiolite has included a very diverse range of meanings from obscure slivers of mafic and ultramafic rocks of doubtful origin in orogenic belts to l...
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Transtension in the upper crustal brittle field, at the lithospheric scale, involves some difficult kinematic problems that result from the non-coaxial component of bulk strain, which generates rotation about vertical axes and the internal deformation of rotating blocks. Plate boundary zone deformation in the non-plane-strain brittle field cannot i...
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The focus of this work is the description of non-plane strain brittle deformation through field observations and theoretical applications. The seismically and volcanically active Coso—China Lake region in the transtensional Eastern California shear zone is an exemplary location for field observation of brittle structure. The region deforms in a con...
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Strain distribution in crustal-scale transtensional zones with non-parallel Zone boundaries is heterogeneous., with higher strain gradients in the narrower parts of the zone. Kinematic modeling of such zones Shows that, for a constant displacement vector and finite displacement of he zone boundary, the finite strain achieved at a point is dependent...
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DEWEY, J.F. & ROSENBAUM, M.S. (2008). Future avenues of research in the Welsh Borderland, with particular reference to terrane tectonics. Proceedings of the Shropshire Geological Society, 13, 104-113. What happens at plate boundaries where tectonic plates diverge, converge and slide past each other is considered in relation to the deep geology of t...
Chapter
High-resolution heavy mineral data from the Ordovician of the South Mayo Trough, western Ireland is subject to a detailed statistical analysis. The aim of this study is to develop new techniques for treating such data thereby providing an independent and objective way to help elucidate the stratigraphy and tectonic history of the region. A new meth...
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Although the deformation of foliated rocks by kink and glide mechanisms has been studied in detail in recent years, fundamental differences of opinion have emerged, particularly as a result of experimental work. Most theories concerning the relationship of kink-bands to stress-fields are empirically based. Evidence on whether kink-bands are the res...
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Some deep crustal features underlying the Campos basin are best recognized in a few reflection seismic sections that have been reprocessed recently to 10 s two-way traveltime. A prominent climbing-to-the-basin reflector is interpreted as the Moho, and a relatively steep fracture zone is, probably, the first example so far of an extensional fault cr...
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A composite tectonic profile, from Clew Bay to central Murrisk is constructed and the sequence of structural events from the Upper Cambrian to post-Wenlock—pre-Viséan (C2 S2) times is outlined. Four main structural episodes affected the Dalradian rocks in pre-Arenig times. ‘Taconic’ thrusting and concentric folding were important, and finally a com...
Chapter
The main conclusion of this paper is that some form of plate tectonics started at ca. 3.0 Ga or possibly as early as 3.1 Ga., and that, since then, plate tectonics has steadily become dominant over plumes as a mechanism of heat loss. Modern plate tectonics started at ca. 0.6 Ga. The volume history of the continental crust is one of fast Early Arche...
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Transtension is oblique divergence between bounding plates or blocks, and combines a coaxial orthogonal extension with a deformation zone boundary parallel noncoaxial component to generate bulk non-plane (triaxial) constrictional strain. The instantaneous stretching direction bisects the acute angle between the direction of divergence (transport di...
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The Namaqua-Natal Orogen evolved between about 2000 and 1000Ma as part of an orogenic system that assembled the Rodinian supercontinent, and “wraps” the Archaean Kaapvaal Craton to the south and west. The Orogen includes the western ultra-high-temperature sapphirine/hercynite-granulite-facies Namaqualand Terrane, structurally overlain, to the north...
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The heavy mineral components of Ordovician greywacke turbidites of the Southern Uplands (subduction-accretion prism) Terrane were studied using high-resolution heavy mineral analysis. Diagnostic heavy minerals and the discovery of hitherto unreported species provide a new insight into the interplay of sediment fluxes, tectonic controls and provenan...
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In contrast to continent/continent collision, arc-continent collision generates very short-lived orogeny because the buoyancy-driven impedance of the subduction of continental lithosphere, accompanied by arc/suprasubduction-zone ophiolite obduction, is relieved by subduction polarity reversal (flip). This tectonic principle is illustrated by the ea...
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In contrast to continent/continent collision, arc-continent collision generates very short-lived orogeny because the buoyancy-driven impedance of the subduction of continental lithosphere, accompanied by arc/suprasubduction-zone ophiolite obduction, is relieved by subduction polarity reversal (flip). This tectonic principle is illustrated by the ea...
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A detailed field and microstructural investigation of mineral fabrics in the late-Caledonian Galway Granite Batholith ([similar]400 Ma) provides insights into the relationship between emplacement-related deformation and crystallization state. These relationships are used to infer the regional instantaneous strain pattern at the time of intrusion. A...
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Robert Millner Shackleton, who died peacefully in his sleep on 3 May 2001, was born on 30 December 1909 in Purley, Surrey, the son of John Millner Shackleton (an electrical engineer of Irish derivation who, at one time, worked for the Post Office telephones) and Agnes Mitford Shackleton (née Abraham). He was distantly related to the Antarctic explo...
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The Caledonian geology of western Ireland records the collision of two arc complexes with the Laurentian Margin during the closure of the Iapetus Ocean. An earlier complex collided with this hitherto passive margin in the mid-Ordovician during the Grampian Orogeny. Subsequently, arc magmatism developed along the Laurentian margin and continued unti...
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Collision of the oceanic Lough Nafooey Island Arc with the passive margin of Laurentia after 480 Ma in western Ireland resulted in the deformation, magmatism and metamorphism of the Grampian Orogeny, analogous to the modern Taiwan and Miocene New Guinea Orogens. After ∼470 Ma, the metamorphosed Laurentian margin sediments (Dalradian Supergroup) now...
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The late Silurian to mid- or late Devonian interval in the Caledonides was a period dominated, sequentially, by sinistral transpression, strike-slip and transtension during the development of mainly non-marine `red-bed' basins following the Ludlow-Pridoli transition from marine to terrestrial sedimentation. The tectonic event that led to and genera...
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Heavy minerals in Ordovician successions in western Ireland record, in the Upper Arenig Sheeffry Formation, the erosion of an ophiolite/island arc complex. The appearance of staurolite and garnet at a basin-wide horizon in the Lower Llanvirn Upper Derrylea Formation signals the unroofing of the Dalradian metamorphic complex. Parts of the Ordovician...
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Ophiolites sensu lato originate in a variety of ways in several tectonic environments. None represents obducted sheets from the oceanic crust and mantle of large oceans; subduction destroys the oceanic lithosphere very effectively. The Jurassic Balkan and Greek ophiolites were obducted from the floors of young, very narrow oceans, and the Alpinotyp...
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Transtension is the oblique divergence between bounding plates or blocks that combines a coaxial orthogonal extension with a deformation zone boundary-parallel, noncoaxial, component, which generates a bulk constrictional strain. The coaxial component determines the rate and amount of crustal/lithospheric thinning and part of the horizontal extensi...
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The Cenozoic tectonic history of Ireland is advancing into a new phase of data and understanding, built upon the work of eminent Irish geologists, such as Frank Mitchell and Gordon Herries-Davies. From topographic and fluvial studies, it is now clear that the Irish landscape is young and dynamic, certainly post-Mesozoic and that it was developed pr...
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Recent advances in our understanding of Palaeozoic tectonics, and in the precise dating of tectonic events require exact definitions of terminology. The Caledonian Orogeny is here redefined to include all the Cambrian, Ordovician, Silurian and Devonian tectonic events associated with the development and closure of those parts of the Iapetus Ocean,...
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The previous conflict between stratigraphical and geochronological evidence for the age of the Grampian orogeny in Scotland and Ireland has now been largely resolved. Dalradian deposition continued on the Laurentian margin through late Proterozoic into Ordovician time. The Grampian orogeny was a brief, arc-accretion event that took place around the...
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Ordovician orogeny affected the Laurentian margin of the Appalachian-Caledonian Belt from the Southern Appalachians to the British Isles and is dated, stratigraphically, as post-uppermost Lower Cambrian and pre-upper Llandovery. Geochronological data favour a short Grampian orogeny from c. 470 to 460 Ma during the late Arenig-mid-Llanvirn, which is...
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FULL PDF AVAILABLE ON REQUEST FROM ROGER HIGGS. The tectonic evolution of the Cenozoic mountain ranges fault systems and basins that comprise the roughly east-west Caribbean/South America plate boundary zone from Colombia to Trinidad was controlled principally by highly oblique dextral convergence between the Caribbean and South American Plates. Th...
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This paper is part of the special publication Continental transpressional and transtensional tectonics (eds R.E. Holdsworth, R.A. Strachan and J.F. Dewey). Transpression and transtension are strike-slip deformations that deviate from simple shear because of a component of, respectively, shortening or extension orthogonal to the deformation zone. Th...
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This paper is part of the special publication Continental transpressional and transtensional tectonics (eds R.E. Holdsworth, R.A. Strachan and J.F. Dewey). In the Western Gneiss Region (WGR) in the Scandinavian Caledonides, Scandian eclogites (P = 16 to >28 kbar) occur in a large area of reworked Proterozoic gneisses, structurally below a series of...
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Many present-day and ancient continental deformation systems appear to have formed due to significantly oblique relative plate motions. Transpression and transtension zones are formed where the oblique motions involve components of compression and extension, respectively. This book (special publication No. 135) covers the recent advances in our und...
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Sequence stratigraphy of third-order cycles is not determined by global eustasy but by local and regional tectonics interplaying with long-wavelength sea-level change. We can discern no mechanism that can cause the necessary short-wavelength, large-amplitude sea-level changes implicit in globally synchronous eustatic third-order cycles. Some mechan...
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The Wilson Cycle, the repeated opening and closing of oceans, commonly along roughly the same lines, is here attributed to the presence of eclogite-facies roots of partially collapsed orogens. We present a finite-element thermal model that suggests that such roots will weaken the orogenic lithosphere relative to that of the adjacent foreland for hu...
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The Central Andes in Bolivia and northern Chile form part of a wide and obliquely convergent plate-boundary zone where the oceanic Nazca plate is being subducted beneath the continental South American plate. In the latest Cretaceous and Palaeocene, this part of the Central Andes formed a volcanic arc along what is today the forearc region of northe...
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Gravity anomaly and topography data are used to define the effective elastic thickness of the lithosphere, Te, in the bend region of the Central Andes. Values of Te increase from nearly zero, north and south of the bend, to values greater than 50 km at the bend in Bolivia. There is a close correlation between Te and the style and magnitude of the s...
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Palaeomagnetic and structural studies of the Dalsfjord Nappe, western Norway, show that the basal low-angle detachment (Dalsfjord Fault) is a long-lived fault zone, and that the most important phase of faulting was of Devonian extension, probably nucleated on an earlier Silurian (Scandian) thrust. Fault rocks produced during subsequent movements in...
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Nearly 90 mm a−1 of relative plate convergence is absorbed in the Andean plate-boundary zone. The pattern of active tectonics shows remarkable variations in the way in which the plate slip vector is partitioned into displacement and strain and the ways in which compatibility between different segments is solved. Along any traverse across the plate-...
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During continental collision in the middle Silurian, the thickness of the lithosphere under the Caledonides of S. Norway was doubled by subduction of the western margin of Baltica, including the Western Gneiss Region, under Laurentia. Crustal rocks of the Baltic plate reached sub-Moho depths of near 100 km or more as inferred from the presence of c...