Dynamic Earth: Plates, Plumes and Mantle Convection

by Geoffrey F. Davies

• ISBN13: 9780521599337
• ISBN10: 0521599334
• Format: Paperback
• Copyright: 2000-01-28
• Publisher: Cambridge University Press

Summary

Dynamic Earth presents the principles of convection in the earth’s mantle in an accessible style. Mantle convection is the process underlying plate tectonics, volcanic hotspots and, hence, most geological processes. The book summarises key observations and presents the relevant physics starting from basic principles. The main concepts and arguments are presented with minimal mathematics, although more mathematical versions of important aspects are included for those who desire them. The book also surveys geochemical constraints and mantle evolution. The audience for Geoff Davies’ book will be the broad range of geologists who desire a better understanding of the earth’s internal dynamics, as well as graduate students and researchers working on the many aspects of mantle dynamics and its implications for geological processes. It is also suitable as a text or supplementary text for upper undergraduate and postgraduate courses in geophysics, geochemistry, and tectonics.

Table of Contents

Part 1 Origins	1	(70)
Introduction	3	(5)
Objectives	3	(3)
Scope	6	(1)
Audience	6	(1)
Reference	7	(1)
Emergence	8	(14)
Time	8	(4)
Catastrophes and increments	12	(3)
Heat	15	(1)
Cooling age of earth	16	(3)
Flowing rocks	19	(1)
References	20	(2)
Mobility	22	(49)
Drifting continents	23	(4)
Creeping mantle	27	(6)
A mobile surface -- re-emergence of the concept	33	(5)
Wilson's plates	38	(5)
Strong evidence for plates in motion	43	(6)
Magnetism	43	(4)
Seismology	47	(2)
Sediments	49	(1)
Completing the picture -- poles and trenches	49	(6)
Euler rotations	50	(3)
Subduction zones	53	(2)
Plumes	55	(3)
Mantle convection	58	(5)
Afterthoughts	63	(2)
References	65	(6)
Part 2 Foundations	71	(138)
Surface	73	(16)
Plates	73	(4)
Topography	77	(3)
Continents	77	(1)
Sea floor	78	(2)
Seafloorr depth versus age	80	(1)
Heat flow	80	(5)
Sea floor	80	(3)
Continents	83	(2)
Gravity	85	(2)
References	87	(2)
Interior	89	(33)
Primary structure	90	(7)
Main layers	90	(2)
Internal structure of the mantle	92	(1)
Layer names	93	(2)
Pressure, gravity, bulk sound speed	95	(2)
Layer compositions and nature of the transition zone	97	(8)
Peridotite zone	97	(1)
Transition zone and perovskite zone	98	(7)
Phase transformations and dynamical implications	105	(7)
Pressure-induced phase transformations	105	(1)
Dynamical implications of phase transformations	106	(1)
Thermal deflections of phase boundaries	107	(2)
Compositional deflections and effects on density	109	(3)
Three-dimensional seismic structure	112	(6)
Seismic detection of subducted lithosphere	112	(3)
Global deep structure	115	(1)
Spatial variations in the lithosphere	116	(2)
References	118	(4)
Flow	122	(56)
Simple viscous flow	124	(4)
Stress [Intermediate]	128	(6)
Subscript notation and summation convention	131	(2)
Hydrostatic pressure and deviatoric stress	133	(1)
Strain [Intermediate]	134	(3)
Strain rate [Intermediate]	137	(1)
Viscosity [Intermediate]	138	(2)
Equations governing viscous fluid flow [Intermediate]	140	(7)
Conservation of mass	140	(1)
Force balance	141	(1)
Stream function (incompressible, two-dimensional flow)	142	(2)
Stream function and force balance in cylindrical coordinates [Advanced]	144	(3)
Some simple viscous flow solutions	147	(2)
Flow between plates	147	(1)
Flow down a pipe	148	(1)
Rise of a buoyant sphere	149	(7)
Simple dimensional estimate	150	(2)
Flow solution [Advanced]	152	(4)
Stresses on a no-slip boundary	156	(1)
Viscosity of the mantle	156	(10)
Simple rebound estimates	157	(4)
Recent rebound estimates	161	(2)
Subduction zone geoids	163	(3)
Rotation	166	(1)
Rheology of rocks	166	(9)
Brittle regime	167	(4)
Ductile or plastic rheology	171	(2)
Brittle--ductile transition	173	(2)
References	175	(1)
Exercises	176	(2)
Heat	178	(31)
Heat conduction and thermal diffusion	178	(2)
Thermal diffusion time scales	180	(4)
Crude estimate of cooling time	181	(1)
Spatially periodic temperature [Intermediate]	182	(1)
Why is cooling time proportional to the square of length scale?	183	(1)
Heat loss through the sea floor	184	(5)
Rough estimate of heat flux	185	(1)
The cooling halfspace model [Intermediate]	186	(2)
The error function solution [Advanced]	188	(1)
Seafloor subsidence and midocean rises	189	(3)
Radioactive heating	192	(1)
Continents	193	(5)
Heat transport by fluid flow (Advection)	198	(1)
Advection and diffusion of heat	199	(3)
General equation for advection and diffusion of heat	199	(1)
An advective--diffusive thermal boundary layer	200	(2)
Thermal properties of materials and adiabatic gradients	202	(4)
Thermal properties and depth dependence	202	(1)
Thermodynamic Gruneisen parameter	203	(1)
Adiabatic temperature gradient	204	(1)
The super-adiabatic approximation in convection	205	(1)
References	206	(1)
Exercises	207	(2)
Part 3 Essence	209	(144)
Convection	211	(28)
Buoyancy	212	(2)
A simple quantitative convention model	214	(3)
Scaling and the Rayleigh number	217	(3)
Marginal stability	220	(4)
Flow patterns	224	(1)
Heating modes and thermal boundary layers	225	(5)
Other Rayleigh numbers [Advanced]	228	(2)
Dimensionless equations [Advanced]	230	(3)
Topography generated by convection	233	(4)
References	237	(1)
Exercises	237	(2)
Plates	239	(22)
The mechanical lithosphere	239	(2)
Describing plate motions	241	(1)
Rules of plate motion on a plane	242	(11)
Three margins	242	(1)
Relative velocity vectors	243	(2)
Plate margin migration	245	(2)
Plate evolution sequences	247	(2)
Triple junctions	249	(4)
Rules on a sphere	253	(2)
The power of the rules of plate motion	255	(1)
Sudden changes in the plate system	256	(1)
Implications for mantle convection	257	(2)
References	259	(1)
Exercises	259	(2)
The plate mode	261	(32)
The role of the lithosphere	262	(2)
The plate-scale flow	264	(11)
Influence of plates on mantle flow	264	(4)
Influence of high viscosity in the lower mantle	268	(2)
Influence of spherical, three-dimensional geometry	270	(3)
Heat transported by plate-scale flow	273	(2)
Summary	275	(1)
Effect of phase transformations	275	(3)
Topography and heat flow	278	(7)
Topography from numerical models	279	(2)
Geoids from numerical models	281	(1)
Heat flow from numerical models	282	(1)
General relationship	283	(2)
Comparisons with seismic tomography	285	(5)
Global structure	285	(2)
Subduction zones	287	(3)
The plate mode of mantle convection	290	(1)
References	291	(2)
The plume mode	293	(31)
Volcanic hotspots and hotspot swells	293	(3)
Heat transported by plumes	296	(3)
Volume flow rates and eruption rates of plumes	299	(1)
The dynamics and form of mantle plumes	300	(11)
Experimental forms	300	(4)
Heads and tails	304	(1)
Thermal entrainment into plumes	305	(4)
Effects of a viscosity step and the phase changes	309	(2)
Flood basalt eruptions and the plume head model	311	(3)
Some alternative theories	314	(3)
Rifting model of flood basalts	314	(1)
Mantle wetspots	315	(1)
Melt residue buoyancy under hotspot swells	316	(1)
Inevitability of mantle plumes	317	(2)
The Plume mode of mantle convection	319	(1)
References	320	(4)
Synthesis	324	(29)
The mantle as a dynamical system	324	(7)
Heat transport and heat generation	325	(1)
Role of the plates: a driving boundary layer	326	(1)
Passive upwelling at ridges	326	(2)
Plate shapes and kinematics	328	(1)
Forces on plates	328	(2)
A decoupling layer?	330	(1)
Plume driving forces?	330	(1)
Other observable effects	331	(6)
Superswells and Cretaceous volcanism	331	(4)
Plume head topography	335	(2)
Layered mantle convection	337	(6)
Review of evidence	338	(1)
The topographic constraint	339	(2)
A numerical test	341	(2)
Some alternative interpretations	343	(4)
`Flattening' of the old sea floor	343	(2)
Small-scale convection	345	(2)
A stocktaking	347	(1)
References	348	(5)
Part 4 Implications	353	(95)
Chemistry	355	(52)
Overview -- a current picture of the mantle	356	(2)
Some important concepts and terms	358	(3)
Major elements and trace elements	358	(1)
Incompatibility and related concepts	358	(2)
Isotopic tracers and isotopic dating	360	(1)
MORB and other acronyms	361	(1)
Observations	361	(13)
Trace elements	362	(2)
Refractory element isotopes	364	(4)
Noble gas isotopes	368	(6)
Direct inferences from observations	374	(12)
Depths and geometry of the MORB and OIB sources	374	(1)
Ages of heterogeneities	375	(1)
Primitive mantle?	376	(3)
The mantle--oceanic lithosphere system	379	(1)
Mass balances	379	(7)
Generation of mantle heterogeneity	386	(2)
Homogenising processes	388	(10)
Stirring and mixing	389	(1)
Sampling -- magma flow and preferential melting	390	(1)
Stirring in viscous flows	391	(3)
Sensitivity of stirring to flow details	394	(2)
Separation of denser components	396	(1)
Summary of influences on stirring and heterogeneity	397	(1)
Implications of chemistry for mantle dynamics	398	(4)
References	402	(5)
Evolution	407	(41)
Tectonics and heat	407	(1)
Review of heat budget, radioactivity and the age of earth	408	(3)
Convective heat transport	411	(4)
Plate mode	411	(1)
Effect of temperature dependence of viscosity	412	(1)
Plume mode [Intermediate]	413	(2)
Thermal evolution equation	415	(1)
Smooth thermal evolution models	416	(2)
Age distribution of the continental crust	418	(1)
Episodic thermal evolution models	419	(6)
Compositional effects on buoyancy and convection	425	(11)
Buoyancy of continental crust	426	(2)
Interaction of oceanic crust with the transition zone	428	(1)
The D" layer	428	(1)
Buoyancy of oceanic crust	429	(3)
Alterrrnatives to plates	432	(2)
Foundering melt residue	434	(2)
Heat transport by melt	436	(1)
Tectonic evolution	437	(7)
Plumes	438	(1)
Mantle overturns	439	(1)
Alternatives to plates and consequences for thermal evolution	440	(3)
Possible role of the basalt--eclogite transformation	443	(1)
Discriminating among the possibilities	444	(1)
References	444	(4)
Appendix 1 Units and multiples	448	(2)
Appendix 2 Specifications of numerical models	450	(5)
Index	455