A mantle convection perspective on global tectonics

Mantle convection shapes Earth's surface by generating dynamic topography. Observational constraints and regional convection models suggest that surface topography could be sensitive to mantle flow for wavelengths as short as 1,000 and 250 km, respectively. At these spatial scales, surface processes including sedimentation and relative sea‐level change occur on million‐year timescales. However, time‐dependent global mantle flow models do not predict small‐scale dynamic topography yet. Here we present 2‐D spherical annulus numerical models of mantle convection with large radial and lateral viscosity contrasts. We first identify the range of Rayleigh number, internal heat production rate and yield stress for which models generate plate‐like behavior, surface heat flow, surface velocities, and topography distribution comparable to Earth's. These models produce both whole‐mantle convection and small‐scale convection in the upper mantle, which results in small‐scale (<500 km) to large‐scale (>104 km) dynamic topography, with a spectral power for intermediate scales (500 to 104 km) comparable to estimates of present‐day residual topography. Timescales of convection and the associated dynamic topography vary from five to several hundreds of millions of years. For a Rayleigh number of 107, we investigate how lithosphere yield stress variations (10–50 MPa) and the presence of deep thermochemical heterogeneities favor small‐scale (200–500 km) and intermediate‐scale (500–104 km) dynamic topography by controlling the formation of small‐scale convection and the number and distribution of subduction zones, respectively. The interplay between mantle convection and lithosphere dynamics generates a complex spatial and temporal pattern of dynamic topography consistent with constraints for Earth.

Section: Temporal Evolution Of Dynamic Topographymentioning

confidence: 99%

Section: Model Limitationsmentioning

confidence: 99%

On the Scales of Dynamic Topography in Whole‐Mantle Convection Models

Arnould

Coltice

Flament

et al. 2018

“…These 3‐D spherical convection models are produced with the code StagYY, solving for the nondimensional equations of mass, momentum, and heat conservation on an Yin‐Yang grid [ Tackley , ]. The pseudo‐plastic rheology is an empirical approximation of the mechanical behavior of the mantle‐lithosphere system [see Coltice et al ., for a review]. It is designed to generate plates self‐consistently.…”

Section: Testing Adopt Against Detection By Visual Inspectionmentioning

confidence: 99%

ADOPT: A tool for automatic detection of tectonic plates at the surface of convection models

Mallard

Jacquet²,

Coltice

2017

Mantle convection models with plate‐like behavior produce surface structures comparable to Earth's plate boundaries. However, analyzing those structures is a difficult task, since convection models produce, as on Earth, diffuse deformation and elusive plate boundaries. Therefore we present here and share a quantitative tool to identify plate boundaries and produce plate polygon layouts from results of numerical models of convection: Automatic Detection Of Plate Tectonics (ADOPT). This digital tool operates within the free open‐source visualization software Paraview. It is based on image segmentation techniques to detect objects. The fundamental algorithm used in ADOPT is the watershed transform. We transform the output of convection models into a topographic map, the crest lines being the regions of deformation (plate boundaries) and the catchment basins being the plate interiors. We propose two generic protocols (the field and the distance methods) that we test against an independent visual detection of plate polygons. We show that ADOPT is effective to identify the smaller plates and to close plate polygons in areas where boundaries are diffuse or elusive. ADOPT allows the export of plate polygons in the standard OGR‐GMT format for visualization, modification, and analysis under generic softwares like GMT or GPlates.

“…Plate tectonics, along with quantum mechanics and general relativity, is one the foundational scientific theories developed during the twentieth century. As formulated, it is a kinematic theory (Cox, 1973;Morgan, 1968), and developing a dynamic theory of plate tectonics remains an intensely active area of research (e.g., Bercovici et al, 2000Bercovici et al, , 2015Coltice et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

The Cathles Parameter (Ct): A Geodynamic Definition of the Asthenosphere and Implications for the Nature of Plate Tectonics

Richards

Lenardic

2018

A weak asthenosphere, or low‐viscosity zone (LVZ), underlying Earth's lithosphere has played an important role in interpreting isostasy, postglacial rebound (PGR), and the seismic LVZ, as well as proposed mechanisms for continental drift, plate tectonics, and postseismic relaxation. Consideration of the resolving power of PGR, postseismic relaxation, and geoid modeling studies suggests a sublithospheric LVZ perhaps ~100–200 km thick with a viscosity contrast of ~100–1,000. Ab initio numerical models of plate‐like boundary layer motions in mantle convection also suggest a key role for the LVZ. Paradoxically, a thinner LVZ with a strong viscosity contrast is most effective in promoting plate‐like surface motions. These numerical results are explained in terms of the reduction in horizontal shear dissipation due to an LVZ, and a simple scaling theory leads to somewhat nonintuitive model predictions. For example, an LVZ causes stress magnification at the base of the lithosphere, enhancing plate boundary formation. Also, flow within the LVZ may be driven by the plates (Couette flow), or pressure‐driven from within the mantle (Poiseuille flow), depending upon the degree to which plates locally inhibit or drive underlying mantle convection. For studies of the long‐wavelength geoid, PGR, and mantle convection, a simple dimensionless parameter controls the effect of the LVZ. This “Cathles parameter” is given by Ct = η*(D/λ)3, where η* is the viscosity contrast, D is the thickness of the LVZ, and λ is the flow wavelength, emphasizing the tightly coupled trade‐off between LVZ thickness and viscosity contrast.