Modeling of craton stability using a viscoelastic rheology

Beuchert, Marcus; Podladchikov, Y. Y.; Simon, Nina; Rüpke, Lars

doi:10.1029/2009jb006482

Cited by 14 publications

(13 citation statements)

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“…The implied high relative strength of the lithosphere is generally consistent with previous investigations that use present-day thermal structure and emphasize the role of dehydration in promoting longevity of cratonic mantle lithosphere. Geodynamic studies 14,15 , however, indicate that long-term preservation of cratonic keels requires a minimum ratio of 1,000:1 between viscosities of the lithosphere and asthenosphere. Consequently, the temporal evolution of viscosity in our model favours a cold initial state.…”

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confidence: 96%

“…studies have investigated the impact of crustal heat production on one-dimensional mantle thermal evolution and isostasy 12,13 , and/or constraints on viscosity and buoyancy on the basis of two-dimensional geodynamic simulations 14,15 , the effects of secular variations, endmember initial conditions and the consequences for isopycnicity have not been considered. Here, we consider spatiotemporal evolution of these characteristics over a time span of up to 3.0 Gyr following keel formation.…”

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confidence: 99%

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Ephemeral isopycnicity of cratonic mantle keels

Eaton

Perry

2013

Nature Geosci

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Cratons, the ancient nuclei of continents that have been stable for billions of years, are underlain by keels of lithosphere with strongly melt-depleted compositions 1,2 . These cratonic keels may have formed either from partial melting in a mantleplume environment 3,4 , or alternatively by melting at shallow depths in a subduction zone, during the successive accretion of slabs of oceanic lithosphere 5 . The stability of cratonic keels has been attributed to a pervasive state of near-neutral buoyancy-isopycnicity-created by offsetting thermal and compositional effects on density 6 . However, it is unclear how an isopycnic state can be sustained over geological time 2 . Here we simulate the evolution of a simplified southern African cratonic keel, initiated in either a hot-plume or a cold-slab environment, over 3 billion years, using a numerical model that incorporates secular cooling of the mantle, coupled with gradual loss of radiogenic heating in the lithosphere. We find that the simulation that starts from a cold-slab environment best explains the subsidence history of the southern African craton 7 . However, irrespective of how the cratonic keel formed, we find that the isopycnic state is inherently ephemeral: a cratonic keel that is approximately isopycnic under present conditions was more, or less, buoyant in the geologic past.The lithosphere, Earth's relatively rigid outer shell, moves coherently with plate motions above the underlying, more easily deformed asthenosphere. The lithosphere-asthenosphere boundary (LAB) thus forms a mechanical detachment that accommodates relative motion between the plate and underlying mantle; as such, it represents the most extensive plate boundary on Earth 1 . Yet, owing to the scarcity of representative geological samples 8 , even fundamental physical parameters remain uncertain, particularly beneath Archaean cratons 9 . The mantle underlying these regions may be compositionally stratified 10 , and possesses a distinctive, dehydrated and strongly melt-depleted composition that differs fundamentally from modern analogues 3 . This mantle region, sometimes denoted as tectosphere 6 , is stabilized against convection under present mantle conditions owing to its intrinsic buoyancy and relatively high viscosity 2 . The buoyancy and rheology of cratons under thermal conditions in the geologic past are unknown, however, particularly during the early stages of lithospheric evolution.The formation of cratonic lithospheric mantle (CLM) is contentious and various models have been proposed, of which two may be considered as thermal endmembers. One model invokes formation of CLM within a hot Archaean plume environment, where CLM peridotites represent residues and/or cumulates from high-degree partial melting at significant depth 3,4 . A second model postulates formation of CLM by melting at shallower depths, associated with underthrusting and imbrication of subducted oceanic lithosphere 5 . Both of these models attribute longevity of CLM to intrinsic buoyancy arising from a strongly melt...

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Ephemeral isopycnicity of cratonic mantle keels

Eaton

Perry

2013

Nature Geosci

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“…The role played by composition-dependent rheology has been previously questioned by Beuchert et al (2010), with the argument that published numerical models have insufficient temperature dependent viscosity contrast, which could drives an artificial requirement for composition dependent rheology. Our research confirms that the viscosity contrast of 10 5 , normally used in many geodynamic modelling, is not suitable for modelling long term craton stability ( Figure 5B).…”

Section: Comparison With Previous Workmentioning

confidence: 99%

“…Long term craton stability may not only be affected by the strength of the cratonic root itself, but also by the viscous properties of the surrounding mantle and lithosphere Beuchert et al, 2010). In this section, models are designed to investigate the effects of pressure-dependent viscosity and the maximum lithospheric viscosity cut-off.…”

Section: Mantle Viscositymentioning

confidence: 99%

“…Based on a scaling research, Sleep (2003) indicates that a viscosity factor of 20 with weakly temperature dependent viscosity is needed for survival of cratonic lithosphere. Furthermore, Beuchert et al (2010) argued that thermal craton stability in stagnant lid approach for billions years could be provided by sufficiently high temperature-dependent viscosity contrast (10 7 to 10 10 ) even without invoking any compositional difference. While it is well known from petrological studies that the cratonic lithosphere is compositionally distinct from oceanic lithospheric mantle and even post-Archean continental lithospheric mantle (Boyd, 1989;Pearson and Wittig, 2008), the conflicting modelling results show that it remains far from clear to what extent composition-dependent rheology is required.…”

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Craton stability and longevity: The roles of composition-dependent rheology and buoyancy

Wang

Hunen

Pearson

et al. 2014

Earth and Planetary Science Letters

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. (2014) 'Craton stability and longevity : the roles of composition-dependent rheology and buoyancy.', Earth and planetary science letters., 391 . pp. 224-233.Further information on publisher's website:http://dx.doi.org/10. 1016/j.epsl.2014.01.038 Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Earth and Planetary Science Letters, 391, 2014Letters, 391, , 10.1016Letters, 391, /j.epsl.2014 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract:Survival of thick cratonic roots in a vigorously convecting mantle system for billions of years has long been studied by the geodynamical community. High strength of the cratonic root is generally considered to be the most important factor, but the role of lithospheric mantle depletion and dehydration in this strengthening is still debated. Geodynamical models often argue for a significant strength or buoyancy contrast between cratonic and non-cratonic mantle lithosphere, induced by mantle depletion and dehydration. But recent laboratory experiments argue for only a modest effect of dehydration strengthening. Can we reconcile laboratory experiments and geodynamical models?We perform and discuss new numerical models to investigate craton stability and longevity with different composition-dependent rheology and buoyancy. Our results show that highly viscous and possibly buoyant cratonic root is essential to stabilise a geometry in which thick cratonic lithosphere and thinner non-cratonic lithosphere coexist for billions of years. Using nonNewtonian rheology, a modest strengthening factor of Δη=3 can protect compositionally buoyant cratonic roots from erosion by mantle convection for over billions of years. A larger strengthening factor (Δη=10) can maintain long term craton stability even with little or no intrinsic buoyancy. Such composition-dependent rheology is comparable to the laboratory experiments. This implies that a strict isopycnic state of cratonic lithosphere may not be necessary for the preservation of a cratonic root, provided a sufficient level of compositional strengthening is present.

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The role of viscoelasticity in subducting plates

Farrington

Moresi

Capitanio

2014

Geochem Geophys Geosyst

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Subduction of tectonic plates into Earth's mantle occurs when one plate bends beneath another at convergent plate boundaries. The characteristic time of deformation at these convergent boundaries approximates the Maxwell relaxation time for olivine at lithospheric temperatures and pressures, it is therefore by definition a viscoelastic process. While this is widely acknowledged, the large-scale features of subduction can, and have been, successfully reproduced assuming the plate deforms by a viscous mechanism alone. However, the energy rates and stress profile within convergent margins are influenced by viscoelastic deformation. In this study, viscoelastic stresses have been systematically introduced into numerical models of free subduction, using both the viscosity and shear modulus to control the Maxwell relaxation time. The introduction of an elastic deformation mechanism into subduction models produces deviations in both the stress profile and energy rates within the subduction hinge when compared to viscous only models. These variations result in an apparent viscosity that is variable throughout the length of the plate, decreasing upon approach and increasing upon leaving the hinge. At realistic Earth parameters, we show that viscoelastic stresses have a minor effect on morphology yet are less dissipative at depth and result in an energy transfer between the energy stored during bending and the energy released during unbending. We conclude that elasticity is important during both bending and unbending within the slab hinge with the resulting stress loading and energy profile indicating that slabs maintain larger deformation rates at smaller stresses during bending and retain their strength during unbending at depth.

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Modeling of craton stability using a viscoelastic rheology

Cited by 14 publications

References 114 publications

Ephemeral isopycnicity of cratonic mantle keels

Ephemeral isopycnicity of cratonic mantle keels

Craton stability and longevity: The roles of composition-dependent rheology and buoyancy

The role of viscoelasticity in subducting plates

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