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Abstract
AbstractCrustal-scale channel flow numerical models support recent interpretations of Himalayan—Tibetan tectonics proposing that gravitationally driven channel flows of low-viscosity, melt-weakened, middle crust can explain both outward growth of the Tibetan Plateau and ductile extrusion of the Greater Himalayan Sequence. We broaden the numerical model investigation to explore three flow modes: homogeneous channel flow (involving laterally homogeneous crust); heterogeneous channel flow (involving laterally heterogeneous lower crust that is expelled and incorporated into the mid-crustal channel flow); and the hot fold nappes style of flow (in which mid-/lower crust is forcibly expelled outward over a lower crustal indentor to create fold nappes that are inserted into the mid-crust). The three flow modes are members of a continuum in which the homogeneous mode is driven by gravitational forces but requires very weak channel material. The hot fold nappe mode is driven tectonically by, for example, collision with a strong crustal indentor and can occur in crust that is subcritical for homogeneous flows. The heterogeneous mode combines tectonic and gravitationally driven flows. Preliminary results also demonstrate the existence and behaviour of mid-crustal channels during advancing and retreating dynamical mantle lithosphere subduction. An orogen temperature—magnitude (T-M) diagram is proposed and the positions of orogens in T-M space that may exhibit the flow modes are described, together with the characteristic positions of a range of other orogen types.
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Affiliation(s)
- C. Beaumont
- Oceanography Department, Dalhousie University
Halifax, Nova Scotia, Canada B3H 4J1
| | - M. H. Nguyen
- Oceanography Department, Dalhousie University
Halifax, Nova Scotia, Canada B3H 4J1
- Department of Earth Sciences, Dalhousie University
Halifax, Nova Scotia, Canada B3H 3J5
| | - R. A. Jamieson
- Department of Earth Sciences, Dalhousie University
Halifax, Nova Scotia, Canada B3H 3J5
| | - S. Ellis
- Institute for Geological and Nuclear Sciences
Lower Hutt, New Zealand
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Godin L, Grujic D, Law RD, Searle MP. Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction. ACTA ACUST UNITED AC 2006. [DOI: 10.1144/gsl.sp.2006.268.01.01] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractThe 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.
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Affiliation(s)
- L. Godin
- Department of Geological Sciences & Geological Engineering, Queen’s University
Kingston, Ontario, K7L 3N6, Canada
| | - D. Grujic
- Department of Earth Sciences, Dalhousie University
Halifax, Nova Scotia, B3H 4J1, Canada
| | - R. D. Law
- Department of Geological Sciences, Virginia Tech.
Blacksburg, VA 24061, USA
| | - M. P. Searle
- Department of Earth Sciences, Oxford University
Oxford, OX1 3PR, UK
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