Results 1 - 10
of
30
Self-Consistent Generation of Tectonic Plates in Time-Dependent, Three-Dimensional Mantle Convection Simulations, Part 1: Pseudo-Plastic Yielding
, 1999
"... . Presented here are the fi g4 three-digH66869gi siee-digH6 of mantle convecti6] to dig8q88 self-consi5969gigi69gi6) plate tectoni9)qgH6 behavii whivi ii contii9)q io space and ti g4 Plate behavi;6 arivi through a reasonable materiab describle g of sig4)W8] deformati68W wifo a si598W yi598 stress be ..."
Abstract
-
Cited by 71 (11 self)
- Add to MetaCart
(Show Context)
. Presented here are the fi g4 three-digH66869gi siee-digH6 of mantle convecti6] to dig8q88 self-consi5969gigi69gi6) plate tectoni9)qgH6 behavii whivi ii contii9)q io space and ti g4 Plate behavi;6 arivi through a reasonable materiab describle g of sig4)W8] deformati68W wifo a si598W yi598 stress beiss suffi5W;65 to gig4 fi488W5gH69 plate-liH6 behaviiH ToroiiH69)69gi ratii are wi g85 geologi9gH5q]69giiW li5q]69 The sensi958gH5 of the system to yig5 strength and the form of strength envelope iv systemati;qW)g istemati;qW Optiema plate character ih obtaicte it a narrow range of yig;W strength, below whiwg diwg5W boundari9gH and above epie g4q behaviq;; and eventually a riW;5 liW; are observed. Models wiel mobis lii develop very long-wavelength horiwavele structure- the longest wavelength possieng is the domai85 Twodig5W; ]]gH5 models diels g much greater titer g;;W;]gH5 than threedie -g5W;]8gH5;969g INTRODUCTION Platetectoni)g wit attendant contintg8q driti i arguably the most istg...
The generation of plate tectonics from mantle convection, Earth Planet
- Sci. Lett
, 2003
"... In the last decade, significant progress has been made toward understanding how plate tectonics is generated from mantle dynamics. A primary goal of plate-generation studies has been the development of models that allow the top cold thermal boundary layer of mantle convection, i.e. the lithosphere, ..."
Abstract
-
Cited by 54 (9 self)
- Add to MetaCart
(Show Context)
In the last decade, significant progress has been made toward understanding how plate tectonics is generated from mantle dynamics. A primary goal of plate-generation studies has been the development of models that allow the top cold thermal boundary layer of mantle convection, i.e. the lithosphere, to develop broad and strong plate-like segments separated by narrow, weak and rapidly deforming boundaries; ideally, such models also permit significant strike-slip (toroidal) motion, passive ridges (i.e. pulled rather than pried apart), and self-consistent initiation of subduction. A major outcome of work so far is that nearly all aspects of plate generation require lithospheric rheologies and shear-localizing feedback mechanisms that are considerably more exotic than rheologies typically used in simple fluid-dynamical models of mantle flow. The search for plate-generating behavior has taken us through investigations of the effects of shear weakening (‘stick-slip’) and viscoplastic rheologies, of melting at ridges and low-viscosity asthenospheres, and of grain-size dependent rheologies and damage mechanics. Many such mechanisms, either by themselves or in combination, have led to self-consistent fluid-mechanical models of mantle flow that are remarkably plate-like, which is in itself a major accomplishment. However, many other important problems remain unsolved, such as subduction intiation and asymmetry, temporal evolution of plate geometry, rapid changes in plate motion, and the Archaean initiation of the plate-tectonic mode of convection. This paper presents a brief review of progress made in the plate-generation problem over the last decade, and discusses unresolved issues and future directions of research in this important area.
Energetics of a two-phase model of lithospheric damage, shear localization and plate-boundary formation
- GEOPHYS. J. INTL
, 2002
"... ..."
2005), Synthetic tomographic images of slabs from mineral physics, in Earth’s Deep Mantle
- Structure, Composition, and Evolution, Geophys. Monogr. Ser
"... Abstract. The mantle structures observed by seismic tomography can only be linked with convection models by assuming some relationships between tempera-ture, density and velocity. These relationships are complex and non linear even if the whole mantle has a uniform composition. For example, the dens ..."
Abstract
-
Cited by 14 (1 self)
- Add to MetaCart
Abstract. The mantle structures observed by seismic tomography can only be linked with convection models by assuming some relationships between tempera-ture, density and velocity. These relationships are complex and non linear even if the whole mantle has a uniform composition. For example, the density variations are not only related to the depth dependent thermal expansivity and incompress-ibility, but also to the distribution of the mineralogical phases that are themselves evolving with temperature and pressure. In this paper, we present a stoichiometric iterative method to compute the equilibrium mineralogy of mantle assemblages by Gibbs energy minimization. The numerical code can handle arbitrary elemental composition in the system MgO, FeO, CaO, Al2O3 and SiO2 and reaches the thermodynamic equilibrium by choosing the abundances of 31 minerals belonging to 14 possible phases. The code can deal with complex chemical activities for min-erals belonging to solid state solutions. We illustrate our approach by computing the phase diagrams of various compositions with geodynamical interest (pyrolite, harzburgite and oceanic basalt). Our simulations are in reasonable agreement with
Subduction Zones: Observations and Geodynamic Models
, 2001
"... This review of subduction and geodynamic models is organized around three central questions: (1) Why is subduction asymmetric? (2) Are subducted slabs strong or weak? (3) How do subducted slabs interact with phase transformations, changes in mantle rheology, and possibly chemical boundaries in the m ..."
Abstract
-
Cited by 13 (0 self)
- Add to MetaCart
This review of subduction and geodynamic models is organized around three central questions: (1) Why is subduction asymmetric? (2) Are subducted slabs strong or weak? (3) How do subducted slabs interact with phase transformations, changes in mantle rheology, and possibly chemical boundaries in the mantle? Based on laboratory measurements of the temperature dependence of olivine, one would conclude that the core of a subducting slab is at least 10,000 times more viscous than ambient mantle; however, there are a number of complementary but independent observations that suggest that slabs are much weaker than this. Slabs undergo significant deformation in the upper mantle and may thicken to twice their original width by the time they reach the base of the transition zone. The lack of a clear correlation between the observed dip angle of deep slabs and plate velocity, rate of trench migration, and slab age in modern subduction zones is consistent with hypothesis that subduction is a time-dependent phenomenon. Both tank and numerical convection experiments with plates conclude that subduction is not a steady phenomenon, but that slabs bend, thicken, stretch, and change dip through time. This is at odds with the assumptions used in steady-state slab thermal models, where slab deformation is not considered. 2001 Elsevier Science B.V. All rights reserved.
Tectonic plate generation and two-phase damage: Void growth versus grain size reduction
- Journal of Geophysical Research
"... Abstract. The two-phase theory for compaction and damage employs a nonequi-librium relation between interfacial surface energy, pressure, and viscous defor-mation, thereby providing a model for damage (void generation and microcrack-ing) and a continuum description of weakening, failure, and shear l ..."
Abstract
-
Cited by 12 (8 self)
- Add to MetaCart
Abstract. The two-phase theory for compaction and damage employs a nonequi-librium relation between interfacial surface energy, pressure, and viscous defor-mation, thereby providing a model for damage (void generation and microcrack-ing) and a continuum description of weakening, failure, and shear localization. Here we examine the application of this theory to the problem of generating plate-like behavior from convective-type divergent (poloidal) motion through a source-sink formulation. We extend the previous damage theory to consider two pos-sible damage effects: (1) growth and nucleation of voids associated with dila-tion of the host matrix, and (2) increasing fineness (i.e., reducing coarseness) of the mixture by, for example, grainsize reduction. Void-generating damage is found to be poor at plate generation because of the predominance of dilational motion that is adverse to the development of plate-like flow. Fineness-generating damage is found to be very efficient at generating plate-like behavior if we as-sume that the matrix viscosity is a simple function of grain/void size, as is typ-ical for diffusion creep. The implied grainsize reduction mechanism is differ-ent than that of dynamic recrystallization, and appears more capable of gener-ating the requisite shear-localization for forming tectonic plates from mantle flow.
Constraints on subducting plate strength within the Kermadec trench
- J. geophys. Res
, 2005
"... [1] Four specially designed surveys parallel to the Kermadec trench allow localized estimates of plate strength within the subducting Pacific plate to be made. The transfer function between topography and gravity is estimated for five trench-parallel ship tracks at distances of 25–110 km from the tr ..."
Abstract
-
Cited by 11 (0 self)
- Add to MetaCart
[1] Four specially designed surveys parallel to the Kermadec trench allow localized estimates of plate strength within the subducting Pacific plate to be made. The transfer function between topography and gravity is estimated for five trench-parallel ship tracks at distances of 25–110 km from the trench axis. We find a clear reduction in the magnitude and peak wavelength of the transfer function from the outer rise to the trench axis. The change in the transfer function indicates a decrease in plate strength and is consistent with a reduction in flexural rigidity by 3–5 orders of magnitude or a decrease in effective elastic thickness by more than 15 km. Such a large-magnitude decrease in the effective elastic strength suggests that the plate has little or no elastic strength within the trench and that viscous stresses play an important role in transferring slab-pull forces to the subducting plate and regulating plate speeds in subduction zones.
Variations in planetary convection via the effect of climate on damage
- Earth Planet. Sci. Lett
, 2009
"... A new model for the generation of plate tectonics suggests an important interaction between a planet's climate and its lithospheric damage behavior; and thus provides a simple explanation for the tectonic difference between Earth and Venus. We propose that high surface temperatures will lead t ..."
Abstract
-
Cited by 5 (2 self)
- Add to MetaCart
(Show Context)
A new model for the generation of plate tectonics suggests an important interaction between a planet's climate and its lithospheric damage behavior; and thus provides a simple explanation for the tectonic difference between Earth and Venus. We propose that high surface temperatures will lead to higher healing rates (e.g. grain growth) in the lithosphere that will act to suppress localization, plate boundary formation, and subduction. This leads to episodic or stagnant lid convection on Venus because of its hotter climate. In contrast, Earth's cooler climate promotes damage and plate boundary formation. The damage rheology presented in this paper attempts to describe the evolution of grain size by allowing for grain reduction via deformational work input and grain growth via surface tension-driven coarsening. We explore the interaction of damage and healing in two-dimensional numerical convection simulations. We also develop a simple "drip-instability" model to test the hypothesis that the competition between damage and healing controls convective and plate tectonic style by modulating episodicity at subduction zones. At small values of damage, f A , (or large values of healing, k A ) the lithosphere remains strong enough to resist subduction on time scales of billions of years. At intermediate values of f A and k A the lithosphere may become mobilized and allow for short bursts of tectonic behavior followed by periods of quiescence. At large (small) values of f A (k A ) the fineness is increased so that the viscosity of the plate boundary is reduced to allow for continuous, unimpeded subduction of lithosphere and plate-like deformation. The results suggest the feasibility of our proposed hypothesis that the interplay of climate and damage control the mode of tectonics on a planet.
Two-dimensional convection with a self-lubricating, simple-damage rheology, Geophys
- J. Int
, 2003
"... We present 2-D simulations of convection in the Earth’s mantle with temperature and damage-dependent viscosity in a basally heated system. The equation governing the temporal evolution of damage includes a source term for damage, a healing term and an advection term. A systematic study of the influe ..."
Abstract
-
Cited by 5 (5 self)
- Add to MetaCart
(Show Context)
We present 2-D simulations of convection in the Earth’s mantle with temperature and damage-dependent viscosity in a basally heated system. The equation governing the temporal evolution of damage includes a source term for damage, a healing term and an advection term. A systematic study of the influence of the different damage terms on the convection pattern shows that: (1) at least four different convective regimes can be distinguished depending on the size of the damage source term and (2) self-lubricating behaviour is possible only if the advection term in the damage equation is small enough compared with the other terms. We also demonstrate, that good plate-like behaviour in terms of (a) focused low-viscosity bands (LVB), (b) homogeneous surface velocities within the plates and abrupt velocity jumps across the plate boundaries and (c) asymmetric subduction, can be obtainedwith this kind of rheology, although an increase in subduction asymmetry tends to make convection highly time-dependent. Key words: lithospheric deformation, mantle convection, plate tectonics. 1 INTRODUCT ION Understanding the driving mechanisms associated with the motions of the Earth’s major tectonic plates remains one of the fundamen-
Tectonic velocities, dynamic topography, and relative sea
, 2006
"... [1] A simple dynamic model based on boundary layer theory shows that dynamic topography is unlikely to vary significantly in response to short term (20 Myr) variations in the mean tectonic velocity. Tectonic velocities essentially mirror variations in mantle viscosity, but are not indicative of subs ..."
Abstract
-
Cited by 3 (1 self)
- Add to MetaCart
[1] A simple dynamic model based on boundary layer theory shows that dynamic topography is unlikely to vary significantly in response to short term (20 Myr) variations in the mean tectonic velocity. Tectonic velocities essentially mirror variations in mantle viscosity, but are not indicative of substantial modification of dynamic topography, which primarily reflects mass anomalies in the mantle. This implies that relative sea level is unlikely to be affected by ‘‘tectonic pulses’ ’ and also that observed tilting of cratonic margins cannot result from a pulse of increased tectonic velocities. Thus, relative sea level is primarily controlled by the seafloor age distribution, although long term (100 Myrs) changes in tectonic velocity will produce dynamic topography that reinforces sea level changes associated with changing ridge
