E&PS 400

‘Topics in Earth and Planetary Sciences: Processes in the Earth’s Deep Interior’

3 credits - prerequisites are Petrology EPS 303

Fall 2000

Instructor - Dr Adrian Brearley, Associate Professor, Earth and Planetary Sciences

Section I- Geophysics

Geophysical constraints on the internal structure of the Earth.

Stress and strain, elastic moduli. Characteristics of P, S, Love and Rayleigh waves.

Velocities of P and S waves. Refraction and reflection of P and S waves at discontinuities in the Earth’s interior.

Determination of travel-time vs depth curves for P and S waves – Jeffreys and Gutenberg.

Derivation of ray parameter and extraction of velocity-depth relations.

Free oscillations

Density Distribution within the Earth.

Determination of the mass and moment inertia of the Earth

Simple Self compression model – Adams-Williamson equation

Reasons for failure of WA equation.

Section II – Cosmochemistry – Origin of the Earth

Cosmochemical classification of the elements

Definition of cosmic abundance of the elements. Chondritic abundance of the elements.

Cosmochemical classification of the elements and comparison with geochemical classification.

Definition of refractory, moderately volatile, siderophile, highly volatile elements.

Condensation benchmarks for classification.

Origin of the solar system

Models for origin of the solar system.

Collapse of part of molecular cloud to form accretion disk.

Nebular models

Formation of protosun, accretion of planets.

Composition of the bulk silicate Earth (BSE).

Importance of knowledge of bulk silicate Earth.

Determination of composition of bulk silicate Earth – appraisal of different methods.

Meteoritic constraints on the composition of BSE.

Composition determined from mantle xenoliths.

Section III – From Moho to Core – Mineralogy and Composition

Structure of the upper mantle - Geophysical and geochemical constraints.

Nature of the Moho – velocity variations

Gabbro to eclogite transition vs compositional heterogeneity.

Constraints from geophysics, geochemistry and experimental petrology.

Mantle xenoliths – upper mantle sample suite

Geochemical characteristics and origin of upper mantle.

Classification, petrology and mineralogy of mantle peridotites

Geochemistry of mantle peridotites – restites from melt extraction.

Kimberlites.

Ringwood pyrolite model.

Origin of MORBS by melting of depleted upper mantle.

High pressure experimental techniques.

Piston cylinder apparatus

Multianvil press

Diamond anvil cells

Mantle transition zone

Historical perspective of the mantle transition zone.

Birch Murnaghan equation of state – inferences for mantle transition zone. Explanation for failure of WA equation. High pressure phase transformations.

Compositional vs isochemical phase boundary for the mantle transition zone.

Experimental petrology of mantle transition zone:

Phase relations in pyrolitic mantle – olivine –spinel-modified spinel transformation.

Pyroxene to perovskite transition.

The lower mantle.

Mineralogy of lower mantle- geophysical and geochemical constraints.

Stability of perovskite.

Section IV – The Dynamic Mantle

Mantle Convection

Basics of convection, the Rayleigh Number. Factors that influence convection.

Experimental studies of convection.

Style of mantle convection: hole mantle vs layered mantle convection.

Seismic tomography constraints on the behavior of subducting oceanic slabs.

Geochemical Constraints on Mantle convection. Geochemical evidence for mantle heterogeneity.

Sr isotope systematics, Nd isotope systematics. The mantle array. Origin of MORBS and OIBS.

Mantle plumes

Possible origins of mantle plumes – geochemical characteristics, mechanism of formation.

Heat flux from plumes. Plumes from core-mantle boundary.

Magmatic products of mantle plumes.

Source material for plumes.