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Laurent Godin - One of the best experts on this subject based on the ideXlab platform.
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Channel Flow ductile extrusion and exhumation in continental collision zones
Geological Society London Special Publications, 2006Co-Authors: M P Searle, Laurent GodinAbstract:This collection of 27 review and research papers provides an overview of the geodynamic concepts of Channel Flow and ductile extrusion in continental collision zones. The focal point for this volume is the proposal that the middle or lower crust acts as a ductile, partially molten Channel Flowing out from beneath areas of over-thickened crust, such as the Tibetan plateau, towards the topographic surface at plateau margins. This controversial proposal explains many features related to the geodynamic evolution of the plateau and, for example, extrusion and exhumation of the crystalline core of the Himalayan mountain chain to the south. In this volume thermal-mechanical models for Channel Flow, extrusion and exhumation are presented, and geological and geophysical evidence both for and against the applicability of such models to the Himalayan-Tibetan Plateau system, as well as older continental collision zones such as the Hellenides, the Appalachians and the Canadian Cordillera, are discussed.
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Channel Flow ductile extrusion and exhumation in continental collision zones an introduction
Geological Society London Special Publications, 2006Co-Authors: Laurent Godin, Djordje Grujic, M P SearleAbstract:The Channel Flow model aims to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya–Tibet system. Channel Flow describes a protracted Flow of a weak, viscous crustal layer between relatively rigid yet deformable bounding crustal slabs. Once a critical low viscosity is attained (due to partial melting), the weak layer Flows laterally due to a horizontal gradient in lithostatic pressure. In the Himalaya–Tibet system, this lithostatic pressure gradient is created by the high crustal thicknesses beneath the Tibetan Plateau and ‘normal’ crustal thickness in the foreland. Focused denudation can result in exhumation of the Channel material within a narrow, nearly symmetric zone. If Channel Flow is operating at the same time as focused denudation, this can result in extrusion of the mid-crust between an upper normal-sense boundary and a lower thrust-sense boundary. The bounding shear zones of the extruding Channel may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or thrust sense, depending on the relative velocity between the upper crust and the underlying extruding material. This introductory chapter addresses the historical, theoretical, geological and modelling aspects of Channel Flow, emphasizing its applicability to the Himalaya–Tibet orogen. Critical tests for Channel Flow in the Himalaya, and possible applications to other orogenic belts, are also presented. The hinterlands of collisional orogens are often characterized by highly strained, high-grade metamorphic rocks that commonly display features consistent with lateral crustal Flow and extrusion of material from mid-crustal depths towards the orogenic foreland. A recent model for lateral Flow of such weak mid-crustal layers has become widely known as the ‘Channel Flow’ model. The Channel Flow model has matured through efforts by several research groups and has also been applied to a variety of geodynamic settings. Thermal-mechanical modelling of collision zones, including the Himalayan–Tibetan system, has brought the concept of Channel Flow to the forefront of orogenic studies. Original contributors to the concept of Channel Flow initiated an important paradigm shift (Kuhn 1979), from geodynamic models of continental crust with finite rheological layering to the more encompassing Channel Flow model. This time-dependent midto lower crustal Flow process, which will be reviewed in this chapter, may progress into foreland fold-and-thrust tectonics in the upper crust, thereby providing a spatial and temporal link between the early development of a metamorphic core in the hinterland and the foreland fold-and-thrust belt at shallower structural levels. Outcomes and implications of such a viscous Flowing middle to lower crust include a dynamic coupling between mid-crustal and surface processes, and limitations to accurate retro-deformation of orogens (non-restorable orogens, e.g. Jamieson et al. 2006). This Special Publication contains a selection of papers that were presented at the conference ‘Channel Flow, extrusion, and exhumation of lower to mid-crust in continental collision zones’ hosted by the Geological Society of London at Burlington House, in December 2004. Because most of the ongoing debate on crustal Flow focuses on the Cenozoic age Himalaya–Tibet collisional system, some of the key questions that are addressed in this volume include the following. . Does the model for Channel Flow in the Himalaya–Tibet system concur with all available geological and geochronological data? From: LAW, R. D., SEARLE, M. P. & GODIN, L. (eds) Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications, 268, 1–23. 0305-8719/06/$15.00 # The Geological Society of London 2006. . How do the pressure–temperature-time (P-T-t) data across the crystalline core of the Himalaya fit with the proposed Channel Flow? . Are the microstructural fabric data (pure shear and simple shear components) compatible with crustal extrusion (thickening or thinning of the slab)? . If the Channel Flow model is viable for the Himalaya–Tibet system, what may have initiated Channel Flow and ductile extrusion? . Why did the extrusion phase of the Himalayan metamorphic core apparently cease during the late Miocene–Pliocene? . Are some of the bounding faults of the potential Channel still active, or were they recently active? . Is the Himalayan Channel Flow model exportable to other mountain ranges? This introductory paper addresses the historical, theoretical, geological and modelling aspects of crustal Flow in the Himalaya–Tibet orogen. Critical tests for crustal Flow in the Himalaya, and possible applications to other orogenic belts, are presented and difficulties associated with applying these tests are discussed. Personal communication citations (pers. comm. 2004) identify comments expressed during the conference. The Himalaya–Tibetan plateau system The Himalaya–Tibet system initiated in Early Eocene times, following collision of the Indian and Eurasian plates (see Hodges (2000) and Yin & Harrison (2000) for reviews). The collision resulted in closure of the Tethyan Ocean, southward imbrication of the Indian crust, and northward continental subduction of Indian lower crust and mantle beneath Asia. The collision thickened the southern edge of the Asian crust to 70 km, and created the Tibetan Plateau, the largest uplifted part of the Earth’s surface with an average elevation of 5000 m (Fielding et al. 1994). The Himalayan orogen coincides with the 2500km-long topographic front at the southern limit of the Tibetan Plateau. It consists of five broadly parallel lithotectonic belts, separated by mostly north-dipping faults (Fig. 1). The Himalayan metamorphic core, termed the Greater Himalayan sequence (GHS), is bounded by two parallel and opposite-sense shear zones that were both broadly active during the Miocene (Hubbard & Harrison 1989; Searle & Rex 1989; Hodges et al. 1992, 1996). The Main Central thrust (MCT) zone marks the lower boundary of the GHS, juxtaposing the metamorphic core above the underlying Lesser Himalayan sequence. The South Tibetan detachment (STD) system defines the upper boundary roof fault of the GHS, marking the contact with the overlying unmetamorphosed Tethyan sedimentary sequence. The apparent coeval movement of the MCT and STD, combined with the presence of highly sheared rocks and high grade to migmatitic rocks within the GHS, has led many workers to view the GHS as a north-dipping, southward-extruding slab of mid-crustal material Flowing away from the thick southern edge of the Tibetan Plateau, towards the thinner foreland fold-thrust belt. Dynamics of Channel Flow The concepts of crustal extrusion and Channel Flow originated in the continental tectonics literature in the early 1990s. Unfortunately, these two processes are often referred to interchangeably without justification. One of the main points that emerged from the Burlington House conference was that a distinction between Channel Flow and crustal extrusion must be made. Parallel versus tapering bounding walls on Channel Flow and/or extrusion processes, and how these processes may replenish over time, are two resolvable parameters that are critical for distinguishing Channel Flow from extrusion. Brief definitions and overviews of the two processes are presented below. A more detailed overview of the mechanics of the related processes is provided by Grujic (2006).
M P Searle - One of the best experts on this subject based on the ideXlab platform.
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Channel Flow ductile extrusion and exhumation in continental collision zones
Geological Society London Special Publications, 2006Co-Authors: M P Searle, Laurent GodinAbstract:This collection of 27 review and research papers provides an overview of the geodynamic concepts of Channel Flow and ductile extrusion in continental collision zones. The focal point for this volume is the proposal that the middle or lower crust acts as a ductile, partially molten Channel Flowing out from beneath areas of over-thickened crust, such as the Tibetan plateau, towards the topographic surface at plateau margins. This controversial proposal explains many features related to the geodynamic evolution of the plateau and, for example, extrusion and exhumation of the crystalline core of the Himalayan mountain chain to the south. In this volume thermal-mechanical models for Channel Flow, extrusion and exhumation are presented, and geological and geophysical evidence both for and against the applicability of such models to the Himalayan-Tibetan Plateau system, as well as older continental collision zones such as the Hellenides, the Appalachians and the Canadian Cordillera, are discussed.
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Channel Flow ductile extrusion and exhumation in continental collision zones an introduction
Geological Society London Special Publications, 2006Co-Authors: Laurent Godin, Djordje Grujic, M P SearleAbstract:The Channel Flow model aims to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya–Tibet system. Channel Flow describes a protracted Flow of a weak, viscous crustal layer between relatively rigid yet deformable bounding crustal slabs. Once a critical low viscosity is attained (due to partial melting), the weak layer Flows laterally due to a horizontal gradient in lithostatic pressure. In the Himalaya–Tibet system, this lithostatic pressure gradient is created by the high crustal thicknesses beneath the Tibetan Plateau and ‘normal’ crustal thickness in the foreland. Focused denudation can result in exhumation of the Channel material within a narrow, nearly symmetric zone. If Channel Flow is operating at the same time as focused denudation, this can result in extrusion of the mid-crust between an upper normal-sense boundary and a lower thrust-sense boundary. The bounding shear zones of the extruding Channel may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or thrust sense, depending on the relative velocity between the upper crust and the underlying extruding material. This introductory chapter addresses the historical, theoretical, geological and modelling aspects of Channel Flow, emphasizing its applicability to the Himalaya–Tibet orogen. Critical tests for Channel Flow in the Himalaya, and possible applications to other orogenic belts, are also presented. The hinterlands of collisional orogens are often characterized by highly strained, high-grade metamorphic rocks that commonly display features consistent with lateral crustal Flow and extrusion of material from mid-crustal depths towards the orogenic foreland. A recent model for lateral Flow of such weak mid-crustal layers has become widely known as the ‘Channel Flow’ model. The Channel Flow model has matured through efforts by several research groups and has also been applied to a variety of geodynamic settings. Thermal-mechanical modelling of collision zones, including the Himalayan–Tibetan system, has brought the concept of Channel Flow to the forefront of orogenic studies. Original contributors to the concept of Channel Flow initiated an important paradigm shift (Kuhn 1979), from geodynamic models of continental crust with finite rheological layering to the more encompassing Channel Flow model. This time-dependent midto lower crustal Flow process, which will be reviewed in this chapter, may progress into foreland fold-and-thrust tectonics in the upper crust, thereby providing a spatial and temporal link between the early development of a metamorphic core in the hinterland and the foreland fold-and-thrust belt at shallower structural levels. Outcomes and implications of such a viscous Flowing middle to lower crust include a dynamic coupling between mid-crustal and surface processes, and limitations to accurate retro-deformation of orogens (non-restorable orogens, e.g. Jamieson et al. 2006). This Special Publication contains a selection of papers that were presented at the conference ‘Channel Flow, extrusion, and exhumation of lower to mid-crust in continental collision zones’ hosted by the Geological Society of London at Burlington House, in December 2004. Because most of the ongoing debate on crustal Flow focuses on the Cenozoic age Himalaya–Tibet collisional system, some of the key questions that are addressed in this volume include the following. . Does the model for Channel Flow in the Himalaya–Tibet system concur with all available geological and geochronological data? From: LAW, R. D., SEARLE, M. P. & GODIN, L. (eds) Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications, 268, 1–23. 0305-8719/06/$15.00 # The Geological Society of London 2006. . How do the pressure–temperature-time (P-T-t) data across the crystalline core of the Himalaya fit with the proposed Channel Flow? . Are the microstructural fabric data (pure shear and simple shear components) compatible with crustal extrusion (thickening or thinning of the slab)? . If the Channel Flow model is viable for the Himalaya–Tibet system, what may have initiated Channel Flow and ductile extrusion? . Why did the extrusion phase of the Himalayan metamorphic core apparently cease during the late Miocene–Pliocene? . Are some of the bounding faults of the potential Channel still active, or were they recently active? . Is the Himalayan Channel Flow model exportable to other mountain ranges? This introductory paper addresses the historical, theoretical, geological and modelling aspects of crustal Flow in the Himalaya–Tibet orogen. Critical tests for crustal Flow in the Himalaya, and possible applications to other orogenic belts, are presented and difficulties associated with applying these tests are discussed. Personal communication citations (pers. comm. 2004) identify comments expressed during the conference. The Himalaya–Tibetan plateau system The Himalaya–Tibet system initiated in Early Eocene times, following collision of the Indian and Eurasian plates (see Hodges (2000) and Yin & Harrison (2000) for reviews). The collision resulted in closure of the Tethyan Ocean, southward imbrication of the Indian crust, and northward continental subduction of Indian lower crust and mantle beneath Asia. The collision thickened the southern edge of the Asian crust to 70 km, and created the Tibetan Plateau, the largest uplifted part of the Earth’s surface with an average elevation of 5000 m (Fielding et al. 1994). The Himalayan orogen coincides with the 2500km-long topographic front at the southern limit of the Tibetan Plateau. It consists of five broadly parallel lithotectonic belts, separated by mostly north-dipping faults (Fig. 1). The Himalayan metamorphic core, termed the Greater Himalayan sequence (GHS), is bounded by two parallel and opposite-sense shear zones that were both broadly active during the Miocene (Hubbard & Harrison 1989; Searle & Rex 1989; Hodges et al. 1992, 1996). The Main Central thrust (MCT) zone marks the lower boundary of the GHS, juxtaposing the metamorphic core above the underlying Lesser Himalayan sequence. The South Tibetan detachment (STD) system defines the upper boundary roof fault of the GHS, marking the contact with the overlying unmetamorphosed Tethyan sedimentary sequence. The apparent coeval movement of the MCT and STD, combined with the presence of highly sheared rocks and high grade to migmatitic rocks within the GHS, has led many workers to view the GHS as a north-dipping, southward-extruding slab of mid-crustal material Flowing away from the thick southern edge of the Tibetan Plateau, towards the thinner foreland fold-thrust belt. Dynamics of Channel Flow The concepts of crustal extrusion and Channel Flow originated in the continental tectonics literature in the early 1990s. Unfortunately, these two processes are often referred to interchangeably without justification. One of the main points that emerged from the Burlington House conference was that a distinction between Channel Flow and crustal extrusion must be made. Parallel versus tapering bounding walls on Channel Flow and/or extrusion processes, and how these processes may replenish over time, are two resolvable parameters that are critical for distinguishing Channel Flow from extrusion. Brief definitions and overviews of the two processes are presented below. A more detailed overview of the mechanics of the related processes is provided by Grujic (2006).
G Q Chen - One of the best experts on this subject based on the ideXlab platform.
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analytical solution for scalar transport in open Channel Flow slow decaying transient effect
Journal of Hydrology, 2014Co-Authors: G Q ChenAbstract:Summary It is well known that the extensively applied Taylor dispersion model only predicts the longitudinally distributed mean concentration. While at the same time, applications as the risk assessment for toxic pollutant transport in environmental fluid Flows require detailed information on the cross-sectional concentration distribution. As shown by some recent progress (Wu, Z., Chen, G.Q., 2014, J. Fluid Mech., 740, 196–213.), the deviation of transverse concentration from the mean can be remarkable for a very long time, which is termed as the slow-decaying transient effect. Thus it is important to examine the process of concentration evolution for scalar transport in laminar open Channel Flow. In this paper, the idealized case of a uniform and instantaneous scalar release across the Channel is analytically explored by a two-scale perturbation analysis. The validity of the Taylor dispersion model for the mean concentration is discussed by the obtained analytical solution. For the first time, the two-dimensional concentration distribution for the open Channel Flow is explored analytically. Corresponding time scales for the concentration evolution are determined, indicating that the process for the vertical concentration difference to diminish will be much slower than that for the mean concentration to become Gaussian. Dominated by the so-called slow-decaying transient effect, the uniform vertical distribution needs to be modified to predict the vertical concentration distribution correctly.
Rainer Friedrich - One of the best experts on this subject based on the ideXlab platform.
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dns of passive scalar transport in turbulent supersonic Channel Flow
2005Co-Authors: Holger Foysi, Rainer FriedrichAbstract:Direct numerical simulations (DNS) of compressible supersonic Channel Flow of air at Reynolds numbers ranging from Re τ = 180 to Re τ = 560 and Mach numbers ranging from M = 0.3 to M = 3.0 have been performed. A Navier-Stokes solver of high order accuracy has been vectorized and parallelized to run efficiently on the Hitachi SR8000-F1. Budgets of the Reynolds stresses and the passive scalar fluxes are presented, as well as explanations concerning the reduction of the pressure-correlation terms, using a Green's function approach.
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compressibility effects and turbulence scalings in supersonic Channel Flow
Journal of Fluid Mechanics, 2004Co-Authors: Holger Foysi, Sutanu Sarkar, Rainer FriedrichAbstract:Turbulence in supersonic Channel Flow is studied using direct numerical simulation. The ability of outer and inner scalings to collapse profiles of turbulent stresses onto their incompressible counterparts is investigated. Such collapse is adequate with outer scaling when sufficiently far from the wall, but not with inner scaling. Compressibility effects on the turbulent stresses, their anisotropy, and their balance equations are identified. A reduction in the near-wall pressure-strain, found responsible for the changed Reynolds-stress profiles, is explained using a Green's-function-based analysis of the pressure field
I Vallet - One of the best experts on this subject based on the ideXlab platform.
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pressure density temperature and entropy fluctuations in compressible turbulent plane Channel Flow
Journal of Fluid Mechanics, 2014Co-Authors: G A Gerolymos, I ValletAbstract:We investigate the fluctuations of thermodynamic state variables in compressible aerodynamic wall turbulence, using results of direct numerical simulation (DNS) of compressible turbulent plane Channel Flow. The basic transport equations governing the behaviour of thermodynamic variables (density, pressure, temperature and entropy) are reviewed and used to derive the exact transport equations for the variances and fluxes (transport by the fluctuating velocity field) of the thermodynamic fluctuations. The scaling with Reynolds and Mach number of compressible turbulent plane Channel Flow is discussed. Statistics and correlation coefficients of the thermodynamic fluctuations are examined. Finally, detailed budgets of the transport equations for the variances and fluxes of the thermodynamic variables are analysed. The implications of these results, leading both to the understanding of the thermodynamic interactions in compressible wall turbulence and to possible improvements in statistical modelling, are assessed. Finally, the required extension of existing DNS data to fully characterise this canonical Flow is discussed.
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pressure density temperature and entropy fluctuations in compressible turbulent plane Channel Flow
arXiv: Fluid Dynamics, 2013Co-Authors: G A Gerolymos, I ValletAbstract:We investigate the fluctuations of thermodynamic state-variables in compressible aerodynamic wall-turbulence, using results of direct numerical simulation (DNS) of compressible turbulent plane Channel Flow. The basic transport equations governing the behaviour of thermodynamic variables (density, pressure, temperature and entropy) are reviewed and used to derive the exact transport equations for the variances and fluxes (transport by the fluctuating velocity field) of the thermodynamic fluctuations. The scaling with Reynolds and Mach number of compressible turbulent plane Channel Flow is discussed. Correlation coefficients and higher-order statistics of the thermodynamic fluctuations are examined. Finally, detailed budgets of the transport equations for the variances and fluxes of the thermodynamic variables from a well-resolved DNS are analysed. Implications of these results both to the understanding of the thermodynamic interactions in compressible wall-turbulence and to possible improvements in statistical modelling are assessed. Finally, the required extension of existing DNS data to fully characterise this canonical Flow is discussed.