The role of viscous heating in Barrovian metamorphism of collisional orogens: thermomechanical models and application to the Lepontine Dome in the Central Alps

Abstract

Thermal models for Barrovian metamorphism driven by doubling the thickness of the radiogenic crust typically meet difficulty in accounting for the observed peak metamorphic temperature conditions. This difficulty suggests that there is an additional component in the thermal budget of many collisional orogens. Theoretical and geological considerations suggest that viscous heating is a cumulative process that may explain the heat deficit in collision orogens. The results of 2D numerical modelling 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 lW m )3 , which is comparable to or even exceeds bulk radiogenic heat production within the crust. Thermally induced buoyancy is responsible for crustal upwelling in large domes with metamorphic temperatures up to 200°C higher than regional background temperatures. Heat is mostly generated within the uppermost mantle, because of large stresses in the highly viscous rocks deforming there. This thermal energy may be transferred to the overlying crust either in the form of enhanced heat flow, or through magmatism that brings heat into the crust advectively. The amplitude of orogenic heating varies with time, with both the amplitude and time-span depending strongly on the coupling between heat production, viscosity and collision strain rate. It is argued that geologically relevant figures are applicable to metamorphic domes such as the Lepontine Dome in the Central Alps. We conclude that deformation-generated viscous dissipation is an important heat source during collisional orogeny and that high metamorphic temperatures as in Barrovian type metamorphism are inherent to deforming crustal regions.

Polyphase formation and exhumation of high‐ to ultrahigh‐pressure rocks in continental subduction zone: Numerical modeling and application to the Sulu ultrahigh‐pressure terrane in eastern China

“…The initial temperature gradient in the asthenospheric mantle is 0.5°C km À1 . For the lower boundary an infinity-like thermal condition is imposed [Burg and Gerya, 2005;Gerya et al, 2008]. In the orogenic area of the model the lithospheric temperature profile is gradually bent downward along the shape of the subducting slab (Figure 2b).…”

“…This type of boundary condition is applied widely in the numerical models of subduction and collision [e.g., Toussaint et al, 2004a;Burg and Gerya, 2005;Yamato et al, 2007;Warren et al, 2008b;Currie et al, 2007], assuming that in the globally confined threedimensional system of plates, local ''external forcing'' imposed on a 2-D section of a plate and representing tectonic forces coming either from different slabs or from different sections of the same laterally nonuniform slab can be significant. Although slab pull is considered the most significant global 3-D driving force in subduction and it may be questioned why lateral plate push is a starting boundary condition in the models, removing this kind of lateral push from the 2-D model is not necessarily the most realistic option since in this case the plate will be driven only by the local negative buoyancy generated in exactly the same 2-D section.…”

“…As a first approximation, volumetric melt fraction M is assumed to increase linearly with temperature accordingly to the following relations [Burg and Gerya, 2005]:…”

“…[3] Besides the systematic geological/petrological studies of the UHP terranes, analog [e.g., Chemenda et al, 1995Chemenda et al, , 1996Chemenda et al, , 2000Boutelier et al, 2004] and numerical modeling [e.g., Beaumont et al, 2001;Burov et al, 2001;Toussaint et al, 2004a;Burg and Gerya, 2005;Gerya et al, 2008;Yamato et al, 2007Yamato et al, , 2008Warren et al, 2008aWarren et al, , 2008bCurrie et al, 2007] become more and more important for investigating the continental subduction processes associated with burial and exhumation of crustal rocks. Two contrasting tectonic styles of continental subduction are predicted on the basis of numerical experiments: one-sided subduction (overriding plate does not subduct) and two-sided subduction (both plates subduct together) [Tao and O'Connell, 1992;Pope and Willett, 1998;Faccenda et al, 2008;Warren et al, 2008a], also with some other intermediate possibilities; while only the one-sided subduction can produce significant syntectonic UHP rocks exhumation [Warren et al, 2008a].…”

Uplifts formation features in continental collision structures (evolution modeling)

“…Beaumont et al, 2001;Burg and Gerya, 2005;Burov et al, 2001;England, Thompson, 1984;Willett et al, 1993] and significant progress has been achieved in understanding of orogenic processes. The numerical studies of collision are based on models with different aspects and details of collisional orogens, which also includes constraints from the thermal structure observed in mountain chains by thermobarometric studies [e.g.…”