DOI: 10.1016/j.epsl.2020.116243
论文题名: Using thermo-mechanical models of subduction to constrain effective mantle viscosity
作者: Garel F. ; Thoraval C. ; Tommasi A. ; Demouchy S. ; Davies D.R.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 539 语种: 英语
中文关键词: dislocation creep
; mantle viscosity
; olivine
; rheology parameterization
; subduction dynamics
; thermo-mechanical numerical modeling
英文关键词: Algebra
; Creep
; Crystals
; Dynamics
; Elasticity
; Fits and tolerances
; Mechanisms
; Silicate minerals
; Strain rate
; Structural geology
; Viscosity
; Dislocation dynamics models
; Geophysical observations
; Glacial Isostatic Adjustments
; Slab sinking velocities
; Strain rate dependence
; Thermomechanical model
; Upper mantle viscosity
; Viscoplastic deformation
; Parameterization
; deformation mechanism
; dislocation
; mantle convection
; model
; olivine
; parameterization
; strain rate
; stress
; subduction
; temperature
; thermomechanics
; upper mantle
; viscosity
英文摘要: Mantle convection and plate dynamics transfer and deform solid material on scales of hundreds to thousands of km. However, viscoplastic deformation of rocks arises from motions of defects at sub-crystal scale, such as vacancies or dislocations. In this study, results from numerical experiments of dislocation dynamics in olivine for temperatures and stresses relevant for both lithospheric and asthenospheric mantle (800–1700 K and 50–500 MPa; Gouriet et al., 2019) are used to derive three sigmoid parameterizations (erf, tanh, algebraic), which express stress evolution as a function of temperature and strain rate. The three parameterizations fit well the results of dislocation dynamics models and may be easily incorporated into geodynamical models. Here, they are used in an upper mantle thermo-mechanical model of subduction, in association with diffusion creep and pseudo-brittle flow laws. Simulations using different dislocation creep parameterizations exhibit distinct dynamics, from unrealistically fast-sinking slabs in the erf case to very slowly-sinking slabs in the algebraic case. These differences could not have been predicted a priori from comparison with experimentally determined mechanical data, since they principally arise from feedbacks between slab sinking velocity, temperature, drag, and buoyancy, which are controlled by the strain rate dependence of the effective asthenosphere viscosity. Comparison of model predictions to geophysical observations and to upper-mantle viscosity inferred from glacial isostatic adjustment shows that the tanh parameterization best fits both crystal-scale and Earth-scale constraints. However, the parameterization of diffusion creep is also important for subduction bulk dynamics since it sets the viscosity of slowly deforming domains in the convecting mantle. Within the range of uncertainties of experimental data and, most importantly, of the actual rheological parameters prevailing in the upper mantle (e.g. grain size, chemistry), viscosity enabling realistic mantle properties and plate dynamics may be reproduced by several combinations of parameterizations for different deformation mechanisms. Deriving mantle rheology cannot therefore rely solely on the extrapolation of semi-empirical flow laws. The present study shows that thermo-mechanical models of plate and mantle dynamics can be used to constrain the effective rheology of Earth's mantle in the presence of multiple deformation mechanisms. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/164977
Appears in Collections: 气候变化与战略
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作者单位: Géosciences Montpellier, Univ. Montpellier, CNRS, Montpellier, France; Research School of Earth Sciences, The Australian National University, Canberra, Australia
Recommended Citation:
Garel F.,Thoraval C.,Tommasi A.,et al. Using thermo-mechanical models of subduction to constrain effective mantle viscosity[J]. Earth and Planetary Science Letters,2020-01-01,539