Journal ArticleDOI
Interaction of metamorphism, deformation and exhumation in large convergent orogens
TLDR
In this paper, coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles.Abstract:
Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr−1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m−3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m−3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen.read more
Citations
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Journal ArticleDOI
Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation
TL;DR: C coupled thermal–mechanical numerical models are used to show that these two processes—channel flow and ductile extrusion—may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low-viscosity material.
Journal ArticleDOI
Crustal channel flows: 1. Numerical models with applications to the tectonics of the Himalayan‐Tibetan orogen
TL;DR: In this article, a thermal-mechanical numerical model was used to examine the development of mid-crustal channel flows in large hot orogens, where radioactive self-heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large-scale horizontal flow.
Journal ArticleDOI
Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction
TL;DR: The channel flow model has been used to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya-Tibet system as mentioned in this paper.
Journal ArticleDOI
Crustal channel flows: 2. Numerical models with implications for metamorphism in the Himalayan-Tibetan orogen
TL;DR: In this article, a thermal-mechanical model (HT1) that includes midcrustal channel flow is compatible with many features of the Himalayan-Tibetan system.
Journal ArticleDOI
The role of viscous heating in Barrovian metamorphism of collisional orogens: thermomechanical models and application to the Lepontine Dome in the Central Alps
TL;DR: In this paper, the results of 2D numerical modeling of continental collision involving subduction of the lithospheric mantle demonstrate that geologically plausible stresses and strain rates may result in orogen-scale viscous heat production of 0.1 to > 1 muW m(-3), which is comparable to or even exceeds bulk radiogenic heat production within the crust.
References
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Journal ArticleDOI
Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation
TL;DR: C coupled thermal–mechanical numerical models are used to show that these two processes—channel flow and ductile extrusion—may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low-viscosity material.
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