Related Experiment Video
Updated: Mar 28, 2026
11:03
An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
9.1K
Grain-size dynamics beneath mid-ocean ridges: Implications for permeability and melt extraction
Andrew J Turner1, Richard F Katz1, Mark D Behn2
1Department of Earth Sciences, University of Oxford Oxford, UK.
Geochemistry, Geophysics, Geosystems : G(3)
|December 23, 2015
Summary
Mantle grain size significantly impacts asthenosphere properties and melt transport beneath mid-ocean ridges. Our model reveals how grain size variations create permeability structures that focus melt toward the ridge axis.
Area of Science:
- * Geophysics
- * Petrology
- * Tectonics
Background:
- * Grain size is a key factor influencing mantle viscosity and permeability, crucial for understanding mid-ocean ridge (MOR) processes.
- * Direct in situ measurement of grain size beneath MORs is currently infeasible.
- * Mantle rheology is complex, involving multiple deformation mechanisms like diffusion creep and dislocation creep.
Purpose of the Study:
- * To construct a numerical model simulating the steady-state mean grain size beneath a mid-ocean ridge.
- * To investigate the sensitivity of grain size distribution to variations in global parameters such as grain growth exponent, potential temperature, spreading rate, and mantle hydration.
- * To interpret the resulting grain-size field in terms of its influence on melt transport and permeability structure.
Main Methods:
- * Development of a two-dimensional, single-phase model for steady-state mean grain size.
- * Incorporation of a composite mantle rheology including diffusion creep, dislocation creep, and grain boundary sliding.
- * Calculation of mean grain size using the paleowattmeter relationship (Austin and Evans, 2007).
Main Results:
- * The model predicts a mean grain-size field beneath MORs that can vary significantly (orders of magnitude).
- * This grain-size field establishes a permeability structure characterized by a high-permeability region beneath a low-permeability region.
- * A steeply inclined boundary separates these permeability zones, oriented towards the ridge axis.
Conclusions:
- * The grain-size field beneath MORs is highly variable and significantly affects asthenospheric rheology and permeability.
- * This grain-size-driven permeability structure may focus melt towards the ridge axis, analogous to established focusing mechanisms.
- * Such melt focusing is consistent with geophysical observations (e.g., magnetotellurics) of the asthenosphere beneath features like the East Pacific Rise.
Related Concept Videos
01:20Porosity and Absorption of Aggregate
938
Aggregates contain pores of varying sizes; while some are completely enclosed within the particles, others open onto the surface, allowing water to penetrate. The porosity of aggregates is a major factor contributing to the overall porosity of concrete, given that aggregates constitute about three-quarters of concrete's volume.
When all pores in an aggregate are filled with water, the aggregate is considered saturated and surface-dry. If left in dry air, water will evaporate until the...
When all pores in an aggregate are filled with water, the aggregate is considered saturated and surface-dry. If left in dry air, water will evaporate until the...
938
01:23Pore Size Distribution
602
In concrete, the pore size distribution significantly influences the material's properties. Capillary pores, markedly larger than gel pores, form a vast network within partially hydrated cement paste, reducing the concrete's strength and increasing its permeability. This heightened permeability leads to a greater risk of damage from environmental factors like freeze-thaw cycles and chemical attacks, with the extent of vulnerability also being tied to the water-to-cement ratio.
Adequate...
Adequate...
602
01:23Factors Affecting Dissolution: Particle Size and Effective Surface Area
2.0K
Dissolution kinetics, an essential aspect of oral drug delivery, is significantly influenced by the drug's particle size. According to the Noyes-Whitney dissolution model, the dissolution rate correlates directly with the drug's surface area. The larger the surface area, the higher the drug's solubility in water, leading to a faster drug dissolution rate. Reducing particle size increases the effective surface area, enhancing the dissolution process. Micronization and nanosizing are...
2.0K
01:09Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
908
Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the...
908
01:31Magnetic Susceptibility and Permeability
2.7K
In linear magnetic materials, like paramagnets and diamagnets, magnetization is proportional to the magnetic field intensity. The constant of proportionality, a dimensionless number, is called magnetic susceptibility. The value of the susceptibility depends on the type of material.
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
2.7K
01:15Theories of Dissolution: Diffusion Layer Model
2.2K
Dissolution, the process by which drug particles dissolve in a solvent, is explained by the diffusion layer model, a theoretical framework that simulates the absorption of oral drugs and allows us to analyze experimental data.
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
2.2K