Considering Continental Drift Velocities in Deep-Earth Mineral Phase Transition Modeling

Introduction to Deep-Earth Mineral Phase Transitions

The Earth's lower mantle, extending from approximately 660 km to 2900 km depth, consists primarily of bridgmanite, ferropericlase, and davemaoite. These minerals undergo phase transitions under extreme pressures and temperatures, influencing mantle dynamics and global geophysical processes. Recent advances in high-pressure mineral physics have revealed that the kinetics of these transformations are sensitive to both thermodynamic conditions and mechanical deformation rates.

The Role of Plate Tectonics in Mantle Dynamics

Plate tectonic motions at the surface are intrinsically linked to mantle convection patterns. Current measurements from space geodesy indicate continental drift velocities ranging from:

• 1-10 cm/year for major plates (e.g., Pacific, Eurasian)
• Up to 15 cm/year for rapidly moving plates (e.g., Australian Plate)
• Less than 2 cm/year for cratonic regions

Mechanisms of Stress Propagation

These surface motions generate stress fields that propagate into the deep mantle through:

1. Slab pull from subducting oceanic lithosphere
2. Basal drag at the lithosphere-asthenosphere boundary
3. Mantle flow induced by plate motions

Kinetics of Mineral Phase Transitions

The transformation kinetics between mineral phases in the lower mantle are governed by the general relationship:

k = k₀ exp[-(E* + PV*)/RT]

Where mechanical deformation introduces additional complexity through:

• Enhanced nucleation rates due to defect generation
• Stress-induced modification of activation energies
• Deformation-assisted interface migration

Experimental Constraints

Diamond anvil cell experiments coupled with synchrotron X-ray diffraction have demonstrated:

• 30-50% acceleration of the olivine-wadsleyite transformation under shear stress
• Non-linear dependence of transformation rates on strain energy
• Anisotropic transformation textures under differential stress

Modeling Approaches

Contemporary modeling frameworks must integrate:

Multi-Scale Simulation Techniques

Effective modeling requires coupling across scales:

Scale	Method	Application
Atomic	Density Functional Theory	Activation energies, defect properties
Microscopic	Phase Field Models	Interface dynamics, microstructure evolution
Macroscopic	Finite Element Analysis	Bulk transformation kinetics, stress coupling

Continuum Mechanical Formulations

The coupled thermo-mechanical-chemical problem can be expressed as:

ρ(∂φ/∂t + v·∇φ) = ∇·(M∇μ) + S_mech

Where the mechanical source term S_mech incorporates:

• Deformation work contributions to driving force
• Stress-dependent mobility coefficients
• Plastic strain-induced nucleation sites

Tectonic Velocity Dependencies

The influence of plate velocities manifests through several mechanisms:

Strain Rate Effects

Higher plate velocities generate proportionally greater strain rates in the mantle, leading to:

• Increased dislocation densities in mineral grains
• Enhanced diffusion rates along fast diffusion paths
• Modified transformation hysteresis loops

Thermal Perturbations

Rapid plate motions induce thermal anomalies through:

1. Advective heat transport by subducting slabs
2. Shear heating in deformation zones
3. Altered geothermal gradients

Computational Implementation Challenges

Current limitations in modeling this coupled system include:

Temporal Scaling Issues

The disparity between:

• Nanosecond-scale atomic vibrations
• Year-scale plate motions
• Million-year mantle convection cycles

Spatial Resolution Requirements

Simultaneous resolution of:

• Ångstrom-scale defect structures
• Kilometer-scale mantle heterogeneities
• Global-scale flow patterns

Future Research Directions

Critical areas for advancement include:

High-Pressure Rheology Measurements

Development of new experimental capabilities for:

• In situ deformation at lower mantle conditions
• Time-resolved phase transformation studies
• Coupled stress-temperature-chemical measurements

Multi-Physics Simulation Frameworks

Integration of:

• Geodynamical models with mineral physics databases
• Machine learning potentials for defect energetics
• Adaptive mesh refinement techniques

Geodynamic Implications

Mantle Heterogeneity Patterns

Variable plate velocities may contribute to:

• Lateral variations in phase transition depths
• Asymmetric transformation front morphologies
• Regional differences in seismic discontinuity sharpness

Plate-Mantle Feedback Mechanisms

The coupled system exhibits:

1. Velocity-dependent phase buoyancy effects
2. Transformation-induced viscosity variations
3. Modified slab penetration behaviors