Cover illustration Portion of one of the Geological Survey of Canada's finer resolution bedrock m... more Cover illustration Portion of one of the Geological Survey of Canada's finer resolution bedrock maps for southern Baffin Island (Nunavut, Canada). The map published at 1:100 000 scale documents the distribution of principal tectonostratigraphic units of the Lake Harbour Group: psammite and pelite (PLHp map unit) in yellow, marble (PLHc map unit) in blue, gabbro (PLHm map unit) in dark green, diorite (PLHd map unit) in pale green, peridotite (PLHu map unit) in purple, and leucogranite (PLHw map unit) in reddish brown. The stratigraphic basement (PRm map unit) to the Lake Harbour Group is shown in pink. Two generations of thrust faults (open and closed teeth on hanging wall of individual faults), post-thrusting folds (F 3 fold axes), and structural point data (strike and dip of planar fabric; trend and plunge of linear fabric) are also shown.
Leisure is an instrument used to facilitate the social integration of people with disabilities. H... more Leisure is an instrument used to facilitate the social integration of people with disabilities. However, it requires significant knowledge of the needs and expectations of this clientele, who often experience isolation, especially in rural areas. The general objective of this study was to attempt to identify and understand the realities experienced by the partners of the Quebec Association for Leisure for People with Disabilities, who offer various services and leisure activities to people with disabilities in rural Quebec. Through focus groups and semi-structured interviews with seventy local stakeholders, this study highlights the fact that the needs of organizations offering recreational activities to people with disabilities are increasingly urgent, especially in terms of finances, paratransit, accessibility, specialized human resources and consultation. This study also demonstrates that recreational activities are essential for the social and identity development of people with disabilities, but also for the development of more inclusive and connected rural communities.
Many concerns emerge related to the use of therapeutic recreation certification through the Natio... more Many concerns emerge related to the use of therapeutic recreation certification through the National Council for Therapeutic Recreation Certification (NCTRC) in Quebec (Canada). In addition to linguistic issues, Quebec stands out by the way it approaches certain social issues. As such, it is relevant to contribute to this special edition of the World Leisure Journal and explain the situation in Quebec. Indeed, the way the profession developed in Quebec is different, in some respects, from the model brought forward by the NCTRC's certification, especially for the components regarding the therapeutic use of leisure. A leisure-orientation model provided by a general recreation professional (recreologist or leisure technician) is a preferred model to help people with special needs in Quebec. The major strength of this model is certainly the fact that it mainly focuses on valuing the individual's potential and well-being rather than on reducing his or her incapacities. This paper gives a brief historical overview of the recreation profession in the field of health in Quebec and describes how it shapes the role of recreation practitioners. It then covers the strengths and weaknesses of the recreation and health model brought forward in Quebec. Finally, the development of an eventual adhesion to a national certification is explored.
It has long been recognized that there is a spatial association between large tracts of Precambri... more It has long been recognized that there is a spatial association between large tracts of Precambrian highgrade metamorphic rocks and the stable interiors of continents (e.g., Hoffman, 1988; Holmes, 1965). The implication of this association is that once formed, continental cores mostly behave as rigid plates (often termed cratons or shields), and relative motions are accommodated by strain along their margins. Analysis of the depth distribution of earthquakes, the thermal structure of the lithosphere, and exhumed mid/lower crustal rocks, indicates that the key ingredient for the strength of cratons is the presence of crust that is dominantly anhydrous (e.g., Jackson et al., 2008). Specifically, crust comprising a load-bearing network of nominally anhydrous minerals that have water contents of less than ∼ 100 ppm, and so obey "dry" flow-laws (e.g., Mackwell et al., 1998; Rybacki & Dresen, 2004), results in high strength, although minor volumes of
Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is nota... more Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is notably similar in scale, duration, and character (St-Onge et al. 2006). In THO, the tectonothermal evolution of the lower-plate involves (1) early thin-skinned thrusting and Barrovian metamorphism, (2) out-of-sequence thrusting and high-T metamorphism, and (3) fluid-localized re-equilibration, anatexis and leucogranite formation. The crustal evolution of the Indian lower-plate in HKTO involves (1) early subduction of continental crust to UHP (ultra-high pressure) eclogite depths, (2) regional Barrovian metamorphism, and (3) widespread high-T metamorphism, anatexis and leucogranite formation. The shallow depths of the high-T metamorphism in HKTO are consistent with early to mid-Miocene ductile flow of an Indian lower-plate mid-crustal channel, from beneath the southern Tibetan plateau to the Greater Himalaya. Melt weakening (Jamieson et al. 2004) of the lower-plate in THO is not observed at ...
<p>Texturally complex monazite grains within two granulite-facies pelitic migmatite... more <p>Texturally complex monazite grains within two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry to quantitatively determine the spatial variation in trace element chemistry with a 4-5 μm resolution (with up to 1883 analyses per grain). The maps demarcate growth zones, some of which were cryptic with conventional imaging, highlighting the 3-D complexity of monazite grains that have experienced multiple episodes of growth and resorption during high-grade metamorphism. Associated monazite trace element systematics are highly variable, both within domains interpreted to have grown in a single event, and between samples that experienced similar metamorphic conditions and mineral assemblages. This result cautions against generalised petrological interpretations being made about monazite trace element signatures as it suggests sample-specific controls. Nevertheless, by quantifying monazite textures, a related U-Pb dataset is re-interpreted, allowing ages to be extracted from a continuum of concordant data. The results reveal a ~45 Myr interval between prograde metamorphism and retrograde melt crystallisation in the study region, emphasising the long-lived nature of heat flow in high-grade metamorphic terranes. Careful characterisation of monazite grains suggests that continuum-style U-Pb datasets can be decoded to provide insights into the rates of metamorphic processes.</p>
Crustal shortening and thickening to ~70-85 km in the Tibetan Plateau occurred both before and ma... more Crustal shortening and thickening to ~70-85 km in the Tibetan Plateau occurred both before and mainly after the ~50 Ma India-Asia collision. Potassic-ultrapotassic shoshonitic and adakitic lavas erupted across the Qiangtang (~50-29 Ma) and Lhasa blocks (~30-10 Ma) indicate a hot mantle, thick crust and eclogitic root during that period. The progressive northward underthrusting of cold, Indian mantle lithosphere since collision shut off the source in the Lhasa block at ~10 Ma. Late Miocene-Pleistocene shoshonitic volcanics in North Tibet require hot mantle. We review the major tectonic processes proposed for Tibet including ‗rigid-block‘, continuum and crustal flow as well as the geological history of the major strikeslip faults. We examine controversies concerning the cumulative geological offsets and the discrepancies between geological, Quaternary and geodetic slip rates. Low present-day slip rates measured from GPS and InSAR along the Karakoram and Altyn Tagh faults in addition t...
Recent Circum-Arctic digital compilations of magnetic, gravity and bathymetry data have been anal... more Recent Circum-Arctic digital compilations of magnetic, gravity and bathymetry data have been analyzed in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. The new grids have been mathematically filtered in order to assist in the regional characterization of magnetic and gravity domains and boundaries. In particular, we have analyzed the frequency content, amplitudes, and patterns of regional magnetic anomalies in areas with disputed crustal structure and tectonic evolution (like Alpha-Mendeleev Ridge). The interpretation of potential field and its derivatives has been compared with recently released map of Arctic geology. CIRCUM-ARCTIC MAPPING PROJECT: NEW MAGNETIC AND ANOMALY MAP OF THE ARCTIC An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC and Norway-NGU) since 2005...
From north to south, the Tibetan plateau is composed of the Kun Lun, Qiangtang and Lhasa terranes... more From north to south, the Tibetan plateau is composed of the Kun Lun, Qiangtang and Lhasa terranes. Traditionally, it was suggested that these terranes were progressively accreted onto the southern margin of the stable North Asian craton since the early Mesozoic [1]. However, the recent discovery of a late Permian eclogite belt, known as the Sumdo eclogites, in the middle of the Lhasa terrane has complicated this model [2]. Coupled with the subsequent identification of Permian islandarc volcanics, dismembered ophiolite units and several late Triassic to early Jurassic amphibolitefacies metamorphic belts associated with coeval magmatism to the north of Sumdo, the eclogites have been interpreted to mark the location of a previously unrecognised suture zone within the Lhasa terrane [3,4]. While links have been drawn between all of these localities, no study has worked systematically across the suture zone, so that tectonostratigraphic assemblages, structural elements and the thermal evo...
The Cenozoic Himalaya-Tibet orogen is generally regarded as the archetypal continental collision ... more The Cenozoic Himalaya-Tibet orogen is generally regarded as the archetypal continental collision zone and is often used as an analogue for interpreting ancient orogenic events. However, given the wide diversity observed in present-day collisional mountain belts, the extent to which such inferences can be made remains debated. In this Review, we compare the metamorphic and magmatic record of the Himalaya-Tibet orogen to four ancient orogens — the Palaeozoic Caledonian orogen, the Meso-Neoproterozoic Grenville and Sveconorwegian orogens, and the Palaeoproterozoic Trans-Hudson orogen — to establish the controls on the underlying dynamics and the nature of the resulting rock record. The similarities in rock records, and, thus, thermal conditions, are interpreted to result from comparable foreland strengths, resulting in similar maximum crustal thicknesses. Apparent differences in the records are mainly attributed to variation in exposed structural level rather than fundamentally different tectonic processes. We, therefore, suggest that foreland rheology is a critical factor in determining the effectiveness of orogen comparisons. Future research is required to investigate the causes and consequences of lateral variability in mountain belts, in particular, focussing on the record of orogens smaller than those considered here, and to understand if and why mountain building processes have varied through Earth history. The links between modern collisional mountain belts and those preserved in the geological record are debated. This Review compares the Himalayan-Tibetan orogen with four ancient mountain belts and uses their similarities and differences to investigate the factors that control mountain building. The metamorphic and magmatic rock record of five major orogens — Himalaya-Tibet, Caledonian, Grenville, Sveconorwegian and Trans-Hudson — are compared. Commonalities include pre-collisional accretionary tectonics and magmatism, and post-collisional continental underthrusting, crustal thickening and associated metamorphism. The post-collisional commonalities are likely to be due to similarities in the strengths of the plates bounding the mountain belts supporting similar crustal thicknesses. Differences include the dominant metamorphic grade exposed at the present erosion surface and the preservation of high-pressure and low-temperature rocks. The causes of these differences are mainly attributed to contrasts in exposed structural level, rather than differences in the underlying tectonic processes. The metamorphic and magmatic rock record of five major orogens — Himalaya-Tibet, Caledonian, Grenville, Sveconorwegian and Trans-Hudson — are compared. Commonalities include pre-collisional accretionary tectonics and magmatism, and post-collisional continental underthrusting, crustal thickening and associated metamorphism. The post-collisional commonalities are likely to be due to similarities in the strengths of the plates bounding the mountain belts supporting similar crustal thicknesses. Differences include the dominant metamorphic grade exposed at the present erosion surface and the preservation of high-pressure and low-temperature rocks. The causes of these differences are mainly attributed to contrasts in exposed structural level, rather than differences in the underlying tectonic processes.
The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style meta... more The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the struc...
Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary ... more Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary rocks of the Greater Himalayan Series (GHS) in Nepal documents a single, long-lived passive-margin succession that was deposited along the northern margin of the Indian Craton. In the Langtang area, Paleoproterozoic gneisses are unconformably overlain by a succession of upper Neoproterozoic–Ordovician fluvio-deltaic quartzite, basinal pelite and psammitic beds that grade upsection into micaceous semipelite and pelite. U–Pb zircon geochronology yields maximum depositional ages between c. 815 and 460 Ma for the GHS in Langtang. Regional variations in the composition and thickness of the GHS along the length of the Himalaya are attributed to siliciclastic depocentres centred on Zanskar in northern India, Langtang and Everest in central to western Nepal, which contrast with coeval marine carbonate shelf deposition in the Annapurna region. The protolith lithostratigraphy documented for Langtang provides a coherent framework for interpreting subsequent Cenozoic Himalayan deformation, specifically the homogeneously distributed layer-normal shortening (i.e. flattening) and layer-parallel stretching (i.e. transport-parallel stretching) that characterizes the GHS. Within the context of a single protracted northern Indian marginal sedimentary succession, the distinction between the Lesser, Greater and Tethyan Himalaya is structural rather than lithostratigraphic in origin.
ABSTRACT An integrated field, petrological and geochronological study of the Basong Tso region of... more ABSTRACT An integrated field, petrological and geochronological study of the Basong Tso region of south-eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high-grade metamorphic belts are recognised in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25 ◦C at c. 204–201 Ma, whereas the Zhala complex experienced peak metamorphic conditions of 5.0 ± 1.0 kbar and 740 ± 40 ◦C at c. 198–192 Ma. Microstructural analysis suggests that the two belts share a common early prograde history, after which the Basong Tso complex attained peak conditions following rapid burial, and the Zhala complex approached peak conditions along an isobaric path. Overall it is inferred that the Basong Tso and Zhala complexes represent the lower and upper structural levels of an evolving orogen that underwent Barrovian-type metamorphism following collision (M1), followed by Buchan-style overprinting at higher structural levels due to heat advection by syn-tectonic granites (M2). Mylonitisation (sensu lato) of the Basong Tso complex and juxtaposition of the two units occurred after attainment of peak conditions. The dominance of Mesozoic regional metamorphism across most of the Tibetan plateau indicates that Cenozoic crustal thickening processes, where present, are only manifest at depth.This article is protected by copyright. All rights reserved.
Hall Peninsula, on SE Baffin Island, Canada, exposes a lithologically diverse mid-crustal section... more Hall Peninsula, on SE Baffin Island, Canada, exposes a lithologically diverse mid-crustal section of the Paleoproterozoic Trans-Hudson Orogen, which features Paleoproterozoic supracrustal strata overlying Archean crystalline basement. Recent mapping, combined with petrological studies and U-Pb monazite dating, provides new insights into the tectonothermal history of the internal zone of the orogen, as well as mid-crustal orogenic processes in general. Peak metamorphic grade is constrained to progressively increase westward from mid-amphibolite-to granulite-facies conditions and three regional deformation events are recognized: east-directed thinskinned crustal shortening (D 1); east-vergent, thickskinned thrusting and folding (D 2); late-orogenic, north-south-directed, thickskinned folding (D 3). Equilibrium phase diagram modeling constrained by garnet compositional transects in pelite indicates peak mid-amphibolite-facies conditions on the eastern peninsula of $720-740 C and 6Á25-7Á25 kbar, followed by cooling and late muscovite growth. In accordance with field evidence for extensive biotite dehydration melting, peak metamorphic conditions of granulitefacies pelite on the western peninsula are estimated at $810-890 C and $6Á1-7Á35 kbar. In situ U-Pb monazite geochronology (laser ablation inductively coupled plasma mass spectrometry) constrains the timing of peak metamorphism and concurrent D 1 deformation throughout the peninsula to between c. 1850 and 1825 Ma, coincident with the accretion of crustal blocks and arc terranes during the amalgamation of the orogenic upper plate. A younger population of c. 1800 Ma monazite implies fluid-assisted dissolution-reprecipitation of older monazite, possibly related to the terminal collision of the amalgamated upper plate Churchill domain with the lower plate Superior craton. Combined with published observations, the integrated geochronological and petrological data suggest that the crustal section exposed on Hall Peninsula remained at elevated temperatures (>550 C) for $100 Myr after the thermal peak. Despite significant crustal thickening and sustained high temperatures, which are comparable with those of large, hot orogens, the crustal section records no evidence of midcrustal ductile (channel) flow or rapid exhumation during orogenic collapse.
Cover illustration Portion of one of the Geological Survey of Canada's finer resolution bedrock m... more Cover illustration Portion of one of the Geological Survey of Canada's finer resolution bedrock maps for southern Baffin Island (Nunavut, Canada). The map published at 1:100 000 scale documents the distribution of principal tectonostratigraphic units of the Lake Harbour Group: psammite and pelite (PLHp map unit) in yellow, marble (PLHc map unit) in blue, gabbro (PLHm map unit) in dark green, diorite (PLHd map unit) in pale green, peridotite (PLHu map unit) in purple, and leucogranite (PLHw map unit) in reddish brown. The stratigraphic basement (PRm map unit) to the Lake Harbour Group is shown in pink. Two generations of thrust faults (open and closed teeth on hanging wall of individual faults), post-thrusting folds (F 3 fold axes), and structural point data (strike and dip of planar fabric; trend and plunge of linear fabric) are also shown.
Leisure is an instrument used to facilitate the social integration of people with disabilities. H... more Leisure is an instrument used to facilitate the social integration of people with disabilities. However, it requires significant knowledge of the needs and expectations of this clientele, who often experience isolation, especially in rural areas. The general objective of this study was to attempt to identify and understand the realities experienced by the partners of the Quebec Association for Leisure for People with Disabilities, who offer various services and leisure activities to people with disabilities in rural Quebec. Through focus groups and semi-structured interviews with seventy local stakeholders, this study highlights the fact that the needs of organizations offering recreational activities to people with disabilities are increasingly urgent, especially in terms of finances, paratransit, accessibility, specialized human resources and consultation. This study also demonstrates that recreational activities are essential for the social and identity development of people with disabilities, but also for the development of more inclusive and connected rural communities.
Many concerns emerge related to the use of therapeutic recreation certification through the Natio... more Many concerns emerge related to the use of therapeutic recreation certification through the National Council for Therapeutic Recreation Certification (NCTRC) in Quebec (Canada). In addition to linguistic issues, Quebec stands out by the way it approaches certain social issues. As such, it is relevant to contribute to this special edition of the World Leisure Journal and explain the situation in Quebec. Indeed, the way the profession developed in Quebec is different, in some respects, from the model brought forward by the NCTRC's certification, especially for the components regarding the therapeutic use of leisure. A leisure-orientation model provided by a general recreation professional (recreologist or leisure technician) is a preferred model to help people with special needs in Quebec. The major strength of this model is certainly the fact that it mainly focuses on valuing the individual's potential and well-being rather than on reducing his or her incapacities. This paper gives a brief historical overview of the recreation profession in the field of health in Quebec and describes how it shapes the role of recreation practitioners. It then covers the strengths and weaknesses of the recreation and health model brought forward in Quebec. Finally, the development of an eventual adhesion to a national certification is explored.
It has long been recognized that there is a spatial association between large tracts of Precambri... more It has long been recognized that there is a spatial association between large tracts of Precambrian highgrade metamorphic rocks and the stable interiors of continents (e.g., Hoffman, 1988; Holmes, 1965). The implication of this association is that once formed, continental cores mostly behave as rigid plates (often termed cratons or shields), and relative motions are accommodated by strain along their margins. Analysis of the depth distribution of earthquakes, the thermal structure of the lithosphere, and exhumed mid/lower crustal rocks, indicates that the key ingredient for the strength of cratons is the presence of crust that is dominantly anhydrous (e.g., Jackson et al., 2008). Specifically, crust comprising a load-bearing network of nominally anhydrous minerals that have water contents of less than ∼ 100 ppm, and so obey "dry" flow-laws (e.g., Mackwell et al., 1998; Rybacki & Dresen, 2004), results in high strength, although minor volumes of
Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is nota... more Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is notably similar in scale, duration, and character (St-Onge et al. 2006). In THO, the tectonothermal evolution of the lower-plate involves (1) early thin-skinned thrusting and Barrovian metamorphism, (2) out-of-sequence thrusting and high-T metamorphism, and (3) fluid-localized re-equilibration, anatexis and leucogranite formation. The crustal evolution of the Indian lower-plate in HKTO involves (1) early subduction of continental crust to UHP (ultra-high pressure) eclogite depths, (2) regional Barrovian metamorphism, and (3) widespread high-T metamorphism, anatexis and leucogranite formation. The shallow depths of the high-T metamorphism in HKTO are consistent with early to mid-Miocene ductile flow of an Indian lower-plate mid-crustal channel, from beneath the southern Tibetan plateau to the Greater Himalaya. Melt weakening (Jamieson et al. 2004) of the lower-plate in THO is not observed at ...
<p>Texturally complex monazite grains within two granulite-facies pelitic migmatite... more <p>Texturally complex monazite grains within two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry to quantitatively determine the spatial variation in trace element chemistry with a 4-5 μm resolution (with up to 1883 analyses per grain). The maps demarcate growth zones, some of which were cryptic with conventional imaging, highlighting the 3-D complexity of monazite grains that have experienced multiple episodes of growth and resorption during high-grade metamorphism. Associated monazite trace element systematics are highly variable, both within domains interpreted to have grown in a single event, and between samples that experienced similar metamorphic conditions and mineral assemblages. This result cautions against generalised petrological interpretations being made about monazite trace element signatures as it suggests sample-specific controls. Nevertheless, by quantifying monazite textures, a related U-Pb dataset is re-interpreted, allowing ages to be extracted from a continuum of concordant data. The results reveal a ~45 Myr interval between prograde metamorphism and retrograde melt crystallisation in the study region, emphasising the long-lived nature of heat flow in high-grade metamorphic terranes. Careful characterisation of monazite grains suggests that continuum-style U-Pb datasets can be decoded to provide insights into the rates of metamorphic processes.</p>
Crustal shortening and thickening to ~70-85 km in the Tibetan Plateau occurred both before and ma... more Crustal shortening and thickening to ~70-85 km in the Tibetan Plateau occurred both before and mainly after the ~50 Ma India-Asia collision. Potassic-ultrapotassic shoshonitic and adakitic lavas erupted across the Qiangtang (~50-29 Ma) and Lhasa blocks (~30-10 Ma) indicate a hot mantle, thick crust and eclogitic root during that period. The progressive northward underthrusting of cold, Indian mantle lithosphere since collision shut off the source in the Lhasa block at ~10 Ma. Late Miocene-Pleistocene shoshonitic volcanics in North Tibet require hot mantle. We review the major tectonic processes proposed for Tibet including ‗rigid-block‘, continuum and crustal flow as well as the geological history of the major strikeslip faults. We examine controversies concerning the cumulative geological offsets and the discrepancies between geological, Quaternary and geodetic slip rates. Low present-day slip rates measured from GPS and InSAR along the Karakoram and Altyn Tagh faults in addition t...
Recent Circum-Arctic digital compilations of magnetic, gravity and bathymetry data have been anal... more Recent Circum-Arctic digital compilations of magnetic, gravity and bathymetry data have been analyzed in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. The new grids have been mathematically filtered in order to assist in the regional characterization of magnetic and gravity domains and boundaries. In particular, we have analyzed the frequency content, amplitudes, and patterns of regional magnetic anomalies in areas with disputed crustal structure and tectonic evolution (like Alpha-Mendeleev Ridge). The interpretation of potential field and its derivatives has been compared with recently released map of Arctic geology. CIRCUM-ARCTIC MAPPING PROJECT: NEW MAGNETIC AND ANOMALY MAP OF THE ARCTIC An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC and Norway-NGU) since 2005...
From north to south, the Tibetan plateau is composed of the Kun Lun, Qiangtang and Lhasa terranes... more From north to south, the Tibetan plateau is composed of the Kun Lun, Qiangtang and Lhasa terranes. Traditionally, it was suggested that these terranes were progressively accreted onto the southern margin of the stable North Asian craton since the early Mesozoic [1]. However, the recent discovery of a late Permian eclogite belt, known as the Sumdo eclogites, in the middle of the Lhasa terrane has complicated this model [2]. Coupled with the subsequent identification of Permian islandarc volcanics, dismembered ophiolite units and several late Triassic to early Jurassic amphibolitefacies metamorphic belts associated with coeval magmatism to the north of Sumdo, the eclogites have been interpreted to mark the location of a previously unrecognised suture zone within the Lhasa terrane [3,4]. While links have been drawn between all of these localities, no study has worked systematically across the suture zone, so that tectonostratigraphic assemblages, structural elements and the thermal evo...
The Cenozoic Himalaya-Tibet orogen is generally regarded as the archetypal continental collision ... more The Cenozoic Himalaya-Tibet orogen is generally regarded as the archetypal continental collision zone and is often used as an analogue for interpreting ancient orogenic events. However, given the wide diversity observed in present-day collisional mountain belts, the extent to which such inferences can be made remains debated. In this Review, we compare the metamorphic and magmatic record of the Himalaya-Tibet orogen to four ancient orogens — the Palaeozoic Caledonian orogen, the Meso-Neoproterozoic Grenville and Sveconorwegian orogens, and the Palaeoproterozoic Trans-Hudson orogen — to establish the controls on the underlying dynamics and the nature of the resulting rock record. The similarities in rock records, and, thus, thermal conditions, are interpreted to result from comparable foreland strengths, resulting in similar maximum crustal thicknesses. Apparent differences in the records are mainly attributed to variation in exposed structural level rather than fundamentally different tectonic processes. We, therefore, suggest that foreland rheology is a critical factor in determining the effectiveness of orogen comparisons. Future research is required to investigate the causes and consequences of lateral variability in mountain belts, in particular, focussing on the record of orogens smaller than those considered here, and to understand if and why mountain building processes have varied through Earth history. The links between modern collisional mountain belts and those preserved in the geological record are debated. This Review compares the Himalayan-Tibetan orogen with four ancient mountain belts and uses their similarities and differences to investigate the factors that control mountain building. The metamorphic and magmatic rock record of five major orogens — Himalaya-Tibet, Caledonian, Grenville, Sveconorwegian and Trans-Hudson — are compared. Commonalities include pre-collisional accretionary tectonics and magmatism, and post-collisional continental underthrusting, crustal thickening and associated metamorphism. The post-collisional commonalities are likely to be due to similarities in the strengths of the plates bounding the mountain belts supporting similar crustal thicknesses. Differences include the dominant metamorphic grade exposed at the present erosion surface and the preservation of high-pressure and low-temperature rocks. The causes of these differences are mainly attributed to contrasts in exposed structural level, rather than differences in the underlying tectonic processes. The metamorphic and magmatic rock record of five major orogens — Himalaya-Tibet, Caledonian, Grenville, Sveconorwegian and Trans-Hudson — are compared. Commonalities include pre-collisional accretionary tectonics and magmatism, and post-collisional continental underthrusting, crustal thickening and associated metamorphism. The post-collisional commonalities are likely to be due to similarities in the strengths of the plates bounding the mountain belts supporting similar crustal thicknesses. Differences include the dominant metamorphic grade exposed at the present erosion surface and the preservation of high-pressure and low-temperature rocks. The causes of these differences are mainly attributed to contrasts in exposed structural level, rather than differences in the underlying tectonic processes.
The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style meta... more The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the struc...
Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary ... more Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary rocks of the Greater Himalayan Series (GHS) in Nepal documents a single, long-lived passive-margin succession that was deposited along the northern margin of the Indian Craton. In the Langtang area, Paleoproterozoic gneisses are unconformably overlain by a succession of upper Neoproterozoic–Ordovician fluvio-deltaic quartzite, basinal pelite and psammitic beds that grade upsection into micaceous semipelite and pelite. U–Pb zircon geochronology yields maximum depositional ages between c. 815 and 460 Ma for the GHS in Langtang. Regional variations in the composition and thickness of the GHS along the length of the Himalaya are attributed to siliciclastic depocentres centred on Zanskar in northern India, Langtang and Everest in central to western Nepal, which contrast with coeval marine carbonate shelf deposition in the Annapurna region. The protolith lithostratigraphy documented for Langtang provides a coherent framework for interpreting subsequent Cenozoic Himalayan deformation, specifically the homogeneously distributed layer-normal shortening (i.e. flattening) and layer-parallel stretching (i.e. transport-parallel stretching) that characterizes the GHS. Within the context of a single protracted northern Indian marginal sedimentary succession, the distinction between the Lesser, Greater and Tethyan Himalaya is structural rather than lithostratigraphic in origin.
ABSTRACT An integrated field, petrological and geochronological study of the Basong Tso region of... more ABSTRACT An integrated field, petrological and geochronological study of the Basong Tso region of south-eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high-grade metamorphic belts are recognised in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25 ◦C at c. 204–201 Ma, whereas the Zhala complex experienced peak metamorphic conditions of 5.0 ± 1.0 kbar and 740 ± 40 ◦C at c. 198–192 Ma. Microstructural analysis suggests that the two belts share a common early prograde history, after which the Basong Tso complex attained peak conditions following rapid burial, and the Zhala complex approached peak conditions along an isobaric path. Overall it is inferred that the Basong Tso and Zhala complexes represent the lower and upper structural levels of an evolving orogen that underwent Barrovian-type metamorphism following collision (M1), followed by Buchan-style overprinting at higher structural levels due to heat advection by syn-tectonic granites (M2). Mylonitisation (sensu lato) of the Basong Tso complex and juxtaposition of the two units occurred after attainment of peak conditions. The dominance of Mesozoic regional metamorphism across most of the Tibetan plateau indicates that Cenozoic crustal thickening processes, where present, are only manifest at depth.This article is protected by copyright. All rights reserved.
Hall Peninsula, on SE Baffin Island, Canada, exposes a lithologically diverse mid-crustal section... more Hall Peninsula, on SE Baffin Island, Canada, exposes a lithologically diverse mid-crustal section of the Paleoproterozoic Trans-Hudson Orogen, which features Paleoproterozoic supracrustal strata overlying Archean crystalline basement. Recent mapping, combined with petrological studies and U-Pb monazite dating, provides new insights into the tectonothermal history of the internal zone of the orogen, as well as mid-crustal orogenic processes in general. Peak metamorphic grade is constrained to progressively increase westward from mid-amphibolite-to granulite-facies conditions and three regional deformation events are recognized: east-directed thinskinned crustal shortening (D 1); east-vergent, thickskinned thrusting and folding (D 2); late-orogenic, north-south-directed, thickskinned folding (D 3). Equilibrium phase diagram modeling constrained by garnet compositional transects in pelite indicates peak mid-amphibolite-facies conditions on the eastern peninsula of $720-740 C and 6Á25-7Á25 kbar, followed by cooling and late muscovite growth. In accordance with field evidence for extensive biotite dehydration melting, peak metamorphic conditions of granulitefacies pelite on the western peninsula are estimated at $810-890 C and $6Á1-7Á35 kbar. In situ U-Pb monazite geochronology (laser ablation inductively coupled plasma mass spectrometry) constrains the timing of peak metamorphism and concurrent D 1 deformation throughout the peninsula to between c. 1850 and 1825 Ma, coincident with the accretion of crustal blocks and arc terranes during the amalgamation of the orogenic upper plate. A younger population of c. 1800 Ma monazite implies fluid-assisted dissolution-reprecipitation of older monazite, possibly related to the terminal collision of the amalgamated upper plate Churchill domain with the lower plate Superior craton. Combined with published observations, the integrated geochronological and petrological data suggest that the crustal section exposed on Hall Peninsula remained at elevated temperatures (>550 C) for $100 Myr after the thermal peak. Despite significant crustal thickening and sustained high temperatures, which are comparable with those of large, hot orogens, the crustal section records no evidence of midcrustal ductile (channel) flow or rapid exhumation during orogenic collapse.
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