lecture n3: thermal modeling conduction versus advection … · 2020. 8. 31. · geologically...

Enabling Technologies

Thermal Modelling

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predictive mineral discovery*Cooperative Research Centre

A legacy for mineral exploration science

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A. Gradient inhydraulicpotential

B. Permeability

C. Solubilitysensitivity to P, T, C

D. Spatialgradient of P, T, C

E. Time (duration)

Key Parameter

is reflected in

ExplorationMineral System

scale-dependent translation

5 Questions1. Geodynamics2. Architecture3. Fluid

reservoirs4. Flow drivers &

pathways5. Deposition

Terrain Selection

Area Selection

Drill Targeting

Heat Transfer

Geologically relevant are only conduction and advection

Conduction is a diffusive process: ‘‘heat will flow from hot tocold’’

Advection is a transport process, whereby heat is transportedby a solid, fluid or gas

Advection is faster than diffusion

Normal geothermal gradient generally too small for convection(requires local heat source or high permeability)

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Heat Transfer

Convection

Density-driven flow

Density varies with P, T, and chemistry

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HEAT( )gPkq fρµ

−∇−=

Convection in geological systems

Critical Rayleigh number

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KTgkHc

Ra pf

µαρ ∆

=2

Permeability

Height of systemTemperature difference

Convection occurs when Ra > critical valueRa critical = 4p2 ~ 39.5 (fixed T boundaries)

Heat Transfer

Is thermal convectionpossible?

Average crustal permeabilitiestoo low for convection

Convection may occur wherepermeability is abnormally high(e.g. faults), or wheregeothermal gradient isabnormally high (e.g. intrusions)

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Modelling Convection

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Convection cells and temperature contours


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Gold concentration

(g/tonne)

Heat Transfer

Intrusions and hydrothermal ore depositsHeat from intrusions drives convection

Collect (“scavenge”) metals fromwide source areaDeposit metals in the narrow,upwelling regionBut flux is rather small

Heat drives dehydration reactions in thewall rocksCooling magma releases volatiles (fluids)

Dehydration and magmatic fluids areprobably more important for generatingore deposits.

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Sebastian Geiger (http://n.ethz.ch/student/sgeiger/)

Heat Transfer

Precipitation and dissolution due to convection

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CR ∇⋅≈ qx gradient in solubilityFluid fluxReaction rate =

… due to gradients in T, P, rock composition etc.

Reactions within thermal gradients

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Thermal Rock Properties

Specific heat capacity (c)

Thermal conductivity (λ)

Thermal diffusivity (κ)

Thermal capacity (ρ c)

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Thermodynamics of Folding

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Thermo-dynamic Simulation

Manuscript Geology (in press) available

Folded meta-quartz vein in Challenger Deposit: courtesy of Andy Tomkins (Monash)


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Coupled thermal-mechanical models

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Temperature development with thrusting


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Shear strain

Displacement vectors

Pink: tensile-failed areas

Thermal Modelling

CAN BE USED TO UNDERSTAND THE HEAT DISTRIBUTION IN THE LITHOSPHERE, AND BY INFERENCE ASPECTS OF ITS MECHANICAL AND HYDRAULIC ARCHITECTURE.

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lecture n3: thermal modeling conduction versus advection … · 2020. 8. 31. · geologically...

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