PUTTING PHYSICS BACK INTO SEISMOLOGY

ANISOTROPY ADIABATICITY (not) ANHARMONICITY ANELASTICITY 2 nd Law If you have tears, prepare to shed them now. You all do know this mantle… …is not isotropic, adiabatic, well-stirred, homogeneous, heated from below, frequency independent…perfectly elastic or an ideal fluid. Thou must Honor

When Anisotropy is properly taken into account (not pseudo-anisotropy with 2 or 3 parameters) plus Absolute wavespeeds, Background model & subAdiabaticity, & if Artefacts & models that violate the 2 nd Law are eliminated (injection, constant CMB temperature, Maxwell demons)… ANISOTROPY, ABSOLUTE WAVESPEED, ADIABATICITY, ARTEFACTS THE ABCs of mantle structure “…whatever remains, however improbable, must be the truth.”

Proper accounting for anisotropy changes everything! The PREM Postscript!

This, plus the recognition that mantle potential temperatures at ~200 km depth (bump) are higher than between ~ km depth are the most significant & far-reaching developments in mantle petrology & geochemistry since Birch & Bullen* established the non-adiabaticity of the mantle (superadiabatic thermal gradient above 200 km, subadiabatic gradient below). T depth High Tp in the shallow mantle is consistent with petrology (Hirschmann, Presnell) [the BL is mainly buoyant refractory harzburgite, not fertile pyrolite] *Raymond Jeanloz of UCB reopened this long-dormant issue bump

*A.M. Dziewonski, D.L. Anderson, Preliminary reference Earth model, Phys. Earth Planet. Inter. 25 (1981) J.-P. Montagner, T. Tanimoto, Global upper mantle tomography of seismic velocities and anisotropies, J. Geophys.Res. 96 (B12) (1991) 20337^ Anderson, D. L., Elastic wave propagation in layered anisotropic media, J. geophys. Res., 66, Anderson, D. L., Recent evidence concerning the structure and composition of the Earth's mantle, Phys. Chem. Earth, 6, Anderson, D. L. & Dziewonski, A. M., Upper mantle anisotropy: evidence from free oscillations, Ceophys. J. R. astr. Regan, J. & Anderson, D. L., Anisotropic models of the upper mantle, Phys. Earth Planet. Int., 35, Nataf, H. C. et al Measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy, J. geophys. Res., 91, M. Panning and B. Romanowicz. Geophys. J. Int. (2006) 167, 361–379 J.-P. Montagner /Earth and Planetary Science Letters 202 (2002) C. Beghein, J. Trampert /Earth and Planetary Science Letters 217 (2003) 151^162 Few * regional & global models take anisotropy into account in a self-consistent (Woodhousean) way. Common errors; assume that Vp is not important in Rayleigh waves, use SH data alone to derive an SH model, invert for 1 parameter, invert P-SV & SH data independently, use isotropic perturbations & scaling relations… is this a big deal?

3.5 sec S-time variation due to angle of incidence alone ~1.3 sec between S & SKS Pseudo- Anisotropic (3 moduli) VpVSH & VSV No angular dependence (unrealizable; bad physics) Laminations plus xl orientation Holtzman & Kendall Physically realizable patterns Polar plots Unaccounted for anisotropy in Region B of the upper mantle gives plume-like artefacts in telesesimic travel-time tomography

Hawaii ABSOLUTE WAVESPEEDS; Hawaii is blue!...in all well constrained inversions with anisotropy Models with lots of modes Lots of rays Lots of data & anisotropy allowed for fast HAWAII For example…

Hawaii Pacific This is what PREM would have looked like if anisotropy (& Vp) had not been taken into account, properly, cf. Hawaii PREM Laske et al. Pseudo-anisotropy The most subtle artefact “VSV” !

An isolated cooling planet with internal heating is characterized by broad upwellings*. An accreting proto- planet & fluids heated from below are characterized by narrow ‘ heat pipes ’ aka ‘mantle plumes’ Physics Preliminaries * Mimics a cooling planet; broad ‘passive’ upwellings

Realizable forms of anisotropy Anisotropic & transition zone artefacts Regions B, C, D’ & D” are chemically distinct Passive & slab-driven broad upwellings Subadiabaticity (derives from Kelvin, Rutherford & Bullen) Thermal bump (thermal max at 200 km) Overlooked physics

VSV Single parameter (VSV) inversion of fundamental mode Rayleigh waves (essentially isotropic) HAWAIIAN SWELL Multimode anisotropic inversion (e.g. Maggi, Katzman, Jordan…) Hawaiian swell versus Causes bleeding artefacts Bleeding artefact Pseudo-

LIL Sheared mélange ridge UPPER MANTLE Tp km Ancient eclogite cumulates Modern slab fragments LVZ TZ LIL Athermal Anisotropy (NOT just SV or SH data, or isotropic perturbations) Advection-Shearing (driven from the top) Artefacts (streaking, smearing, bleeding, neglect of Vp in “shear wave” data) Absolute wavespeeds Boundary Layers Bullen Parameter (Adiabaticity–NOT) Conservation Laws (2 nd Law violations constant T boundaries (CMB, thin plate, whole mantle convection) B Honor thy ABC’s…

eclogite harzburgite cold The plate tectonic bi-cycle Eclogite is intrinsically dense & stays at the base of the TZ Harzburgite (lithosphere) is intrinsically light & returns to surface They both displace older material (MORB source) up & cool off top of lower mantle

Laske, Phipps Morgan & Orcutt HAWAII Based on fundamental model Rayleigh waves using isotropic shear-wave perturbations to isotropic starting model. Nominally an SV model (Vp ignored). This model disagrees with electrical conductivity, travel time, shear wave splitting & heat flow data. Reason: 1. Bleeding Artefact. Vp is important in anisotropic structures. 2. Perturbation kernals are small in shallow mantle but actual variations are large (Hawaii is blue in other studies; different reference model) Anisotropy & reference model artefacts

Improperly allowing for anisotropy The pseudo- anisotropy artefact Pseudo-isotropic wavespeed VP VSH VSV 3 moduli No angular dependency Two shear moduli X Afar PREM Pre-PREM & “Hawaii”

TRADE OFFS 3-parameter inversion (density, Vp, VSV) 6-parameter anisotropic inversion (density, VSV,VSH, VPH, VPV, ETA) The same data & starting model are used in both inversions artefact High wavespeed LID & ultra-LVZ artefacts

TRADE OFFS Isotropic 1-parameter inversion (VSV) 6-parameter anisotropic inversion (density, VSV,VSH, VPH, VPV, ETA) The same data & starting model are used in both inversions artefacts HAWAII

isotropic Anisotropic inversions Neglect of anisotropy or use of Love-ScS-SS (SH) or Rayleigh-PSV (SV) data, alone or separately, has led to many conundrumes & false conclusions; 1.Deep (>>400-km) continents 2.No melt in LVZ (Stixrude) 3.Deep & hot roots to ‘hotspots’, e.g.Hawaii (Wolfe, Montelli, Solomon) 4.Ultra-thick & fast lids (Knopoff,Laske) In contrast to isotropic theory, Rayleigh waves are sensitive to Vp THICK SEISMIC LID ARTEFACT

earthquake Seismic waves Teleseismic Transmission Travel Time Tomography Why concentrate on the deepest mantle (D”) rather than on Gutenberg’s heterogeneous region B, which explains most teleseismic delays & surface wave data? (streaking, smearing, bleeding, vertical exaggeration, color palette, relative wavespeeds, parallax, cropping, saturation) Other Artefacts

Plato’s Cave … In Plato's cave people see only shadows and these are the only reality there is … they kill the informed outsider … When you have eliminated the impossible*, whatever remains, however improbable, must be the truth. Seismology is “A Game of Shadows” *In science The 2 nd Law defines ‘impossible’… geodynamic simulations violate The Law.

4 DECEMBER 2009 VOL 326 SCIENCE

…color pictures, intended to help in visualizing tomographic models, can be misinterpreted (by ourselves &) by non-specialists & editors of Science & Nature. We have a responsibility, as scientists, to do more than present laterally truncated color-saturated 2D images. “The first principle is that you must not fool yourself and you are the easiest person to fool.” ― Richard P. FeynmanRichard P. Feynman

Color graphics have become very sophisticated & there is no mistaking what authors want you to see Filtering, smoothing, interpolating, color pallet, orientation, vertical exaggeration, truncation, parameterization, reference model, contour cutoffs… No power Or two unrelated BLs ?

Passive upwellings are broad & sluggish, to compensate for narrow fast downwellings Ridge crests occur above ~2000 km broad 3D passive upwellings…’hotspots’ are secondary or satellite shear- driven upwellings km Near-ridge ‘hotspots’ sample deep & are coolish compared to midplate volcanoes Similar features occur intraplate

Passive upwellings are broad & balance subduction flux & are captured by spreading ridges but some are midplate active passive Upwellings are associated with plate tectonics even if there is no heating from below

LLAMA Transition Zone Ridge source Ridge crests can move around Ritsema, King 6% Gondwana site Atlantic & Indian Oc. hotspots & still be above the passive upwelling L Region D

Velocity anomalies & anisotropy change abruptly at 220 km Ritsema et al., 2004 EPR Deep (TZ) ridge feeders ? Maggi et al. Broad passive upwellings Region B

Top-Down Plate-Slab Driven Upwellings Ridges capture upwellings (Marquart) Broad passive upwellings

French et al. SCIENCE 2013 Off-ridge “p lumes” are also >1000 km broad, therefore PASSIVE UCB thanks, Barbara Similar features occur under & near ridges

MOVING PLATE For all practical purposes any magma source below about 150 km depth can be regarded as “fixed”. This is within the surface boundary layer as defined by anisotropy & heterogeneity. On the other hand, sources near the core-mantle free-slip boundary are highly mobile. 220 km LID LVZ REGION B Upper boundary layer of mantle fixed

2% LVZ OIB components Non-MORB components are in the sheared boundary layer Magma is “squeezed” out of the mantle

PLATE Low-velocity zone Intra-plate magmas (e.g.Hawaiian tholeiites) are derived from the low-velocity zone (LVZ) part of the sheared surface boundary layer (LLAMA*). They are shear-driven not buoyancy-driven. The upper 220 km of the mantle (REGION B) is a thermal, shear & lithologic boundary layer & the source of midplate magmas. 200 km FOZO 1600°C (OIB components) *LLAMA=laminated lithologies & magma accumulations

3.5 sec S-time variation due to angle of incidence alone ~1.3 sec between S & SKS Pseudo- Anisotropic (3 moduli) VpVSH & VSV No angular dependence (unrealizable) Laminations plus xl orientation Holtzman & Kendall Physically realizable patterns Polar plots

Cold warm TZ Through-going slabs Though-going plumes Stagnant slabs Ridge adiabat Midplate geotherm surface volatiles TEMPERATURE 200 “The transition region is the key to a number of geophysical problems…” Francis Birch 1952

Intraplate volcanoes in China & Korea, inboard of the Japan Trench (JT) Yellowstone, Snake River Plains, Karoo, Deccan… occur in similar terranes (essentially, Back-Arc Basins). Slab graveyard fixed

RIDGETRENCH OIB BAB Slabs displace ancient depleted materials out of TZ that become Ridge Feeding Upwellings (RFUs) Contaminated MORB OIB MORB OIB Slab fluids

Slide 2 Flat slabs at 650 km cool off the mantle & thicken the TZ Blue is thick, cold Flat slabs are the rule Slabs & possible locations of material displaced upwards by slabs

Some candidates for broad passive off-ridge upwellings RITSEMA Midplate upwellings interact with the surface boundary layer

French et al. SCIENCE “ Plumes” are >1000 km broad, therefore PASSIVE

Plate (conducting) Depth 1600 ToCToC GEOTHERMS illustrating the thermal bump and subadiabaticity UPPER MANTLE -The highest potential temperature in the mantle is near 200 km -Tectonic processes (shear, delamination) are required to access this B LLAMA (shearing) Ridge adiabat D”D” CMB Depth LOWER MANTLE UPPER MANTLE TZ Midplate (& backarc) T ridge midplate Boundary layer (lithosphere) bump 200 km

COLD WARM REGION B TZ Ridges & near- ridge hotspots COOL SLABS DISPLACE ANCIENT DEPLETED MATTER OUT OF TZ Reheated harzburgite (‘lithosphere’) also rises MORB

Cool 650, warm 410 Houser, Masters, Flanagan, Shearer (20008)

 T(CMB) Ts It may be hotter than the CMB! T(CMB)<3570 K (Nomura et al 2014) geotherms

Schuberth et al. (2009) Representative geotherms for whole mantle convection with hot core & constant CMB Temperature CMB superadiabatic subadiabatic adiabat A subadiabatic mantle is stable and will not convect unless sinking material displaces it. Free-slip boundary SUBADIABATICITY HOT COLD

Slab cooling Thermal bump & subadiabatic gradient; Keys to mantle petrology ‘deep’ passive upwellings are cold geotherms

K Canonical 1600 K adiabat Geotherm from seismic gradients SUBADIABATIC REGION Thermal bump region (OIB source) seismic gradients imply subadiabaticity over most of the mantle… Passive upwellings can be cold! Modified after Xu et al. 2011, GJI T Depth km CONDUCTION REGION Vs Dry lherzolite solidus 50 ppm H 2 O Tp Any point on a geotherm can be assigned a Tp (the surface projection of a hypothetical adiabat)

Internal boundaries allow for a fixed reference system

TAKE AWAY MESSAGE Tomographic features called “plumes” are ~1000-km broad & must therefore be mainly passive & not heated-from-below active upwellings They feed ridges If they come up under mature plates, they get contaminated & pick up ancient trapped 3 He The so-called “plume reservoir” is actually in the surface boundary layer (B not D”)

Broad depleted Ridge-feeding upwellings Fractionation & contamination km 650 km [low 3 He/ 4 He] High 3 He/ 4 He Volcanic islands are interactions of passive upwellings with the boundary layer Ridges migrate

RIDGE Darwin R. Villagómez1(, Douglas R. Toomey1*, Dennis J. Geist2, Emilie E. E. Hooft & Sean C. Solomon NATURE Geoscience 2014 ‘high’ 3 He/ 4 He High & variable 3 He/ 4 He is picked up in boundary layer No He anomaly

Cold ridge source hot

Slab graveyard Slab reference frame TZ No-slip boundary

slabs volatiles SpainItaly Slabs, a fixed mantle reference system

Both the top and lower boundary layers are rapidly moving in any whole mantle convection scheme However, slabs at 650 lie on a viscid boundary and provide a fixed reference frame Free-slip boundary Mantle reference frame

Free-slip Slip-free 60 Myr later start Non-fixed non- vertical upwellings

CAN BOTH UPPER MANTLE & LOWER MANTLE BE COOLED BY LONG-LIVED FLAT (STAGNANT) SLABS? Cold slab European, African, Asian (Changbai), Yellowstone & most continental “hotspots” are underlain by slabs Cooled mantle

COLD WARM REGION B TZ Ridges & hotspots COOL No hotspots LVA STAGNANT SLABS–A FIXED REFERENCE FRAME SLIP-FREE BOUNDARY

In whole mantle convection simulations, both the surface & the core-mantle boundary move rapidly. Neither provides a stable reference system FREE-SLIP BOUNDARY HEATED FROM BELOW

No physics!

Layered convection mimics whole mantle convection at long wavelengths Visual interpretations of color tomograms of such models led some to infer whole mantle convection (e.g. Grand, van der Hilst, van DeCar, Solomon, Montelli…). Later models (e.g. Ritsema) cannot be so interpreted.

HOT *Laminated Lithologies & Aligned Melt Accumulations Seismology of LLAMA* teleseismic rays Large lateral variation in relative delay times due to plate & LVZ structure & subplate anisotropy (can bleed into deep mantle giving plume-like artefacts) SKS very lateS early S late explains large relative delay times = comparable to crustal delays underplate

200 km Non fixed boundary track No physics!

Tomographic View on Western Mediterranean Geodynamics W. Spakman and M.J.R. Wortel

TZ cold warm cold warm SLAB GRAVEYARD IN TZ & EXPLANATION OF CORRELATED 410 & 650 DEPTHS Slabs in the TZ; a stable reference system

EXTENSIONAL STRESS EXTENSIONAL STRESS Surface hotspots correlate with ridges & ridge-like mantle structure & with extensionanal stress

Only ~3 hotspots are not near yellow/red. All LIPs backtrack to red. STATISTICS ~100% of hotspots fall in LVAs of the upper mantle, mostly those associated with ridges, & in regions of extension

50% of hotspots & 25% of LIPs formed >1000 km away from CMB “plume generation zone” Most of these are over ridge-related or ridge-like LVAs, are on active or abandoned ridges, or are underlain by slabs or are on tectonic shears or rifts Most hotpots formed on or near ridges Distance of hotspots from Plume Generation Zones at CMB (-1% contour) Evidence that ‘most’ (1/2) hotspots are from plumes from the CMB 1000 km 2000 km

TZ Statistics It has been argued that “correlations” of seismic and petrologic thermometers suggests deep thermal anomalies beneath hotspots” *Correlation coefficient A ‘significant correlation’ is negative & > 0.5 Ambient subplate mantle Sub-ridge mantle (subadiabat) theor y ? ? None of the “correlations” are statistically significant.

MORGAN PHIPPS MORGAN (MPM) MPM; MODIFIED PLUME MODEL (Plumes feed hotspots & ridges) …but passive upwellings may feed both ridges & hotspots. e.g. CMB BAM MORB=PLUME-OIB subtraction 2700 km

Modified Plume Model (Morgan Phipps Morgan) PGZ [MORB & OIB] =PLUME-OIB Minus OIB PLUM PUDDING PLUMS Plum removal

RIDGE FEEDING UPWELLINGS (RFUs) RFU LLAMA TZ 650 km OIB=MORB+LLAMA (e.g. contamination) addition 220 km MORB source

slabs Future ridges & hotspots

slabs Slabs Over- ridden oceanic plates, mantle fluxed by slab volatiles Pacific plateaux formed at boundaries & triple junctions of new plates

There are remarkable correlations of present LVAs in the upper mantle and the original sites of breakup of Pangea and the locations of triple junctions and new plate boundaries in the Pacific hemisphere. Ridges, hotspots, LIPs, kimberlites….all backtrack to plate tectonic features associated with plate boundaries and spreading. These features correlate with upper mantle tomography with much higher statistical significance than with D”.

Steep gradients are indications of subadiabatic gradients

Along-ridge profile Ridge-normal profile ridge R i d g e Ridge adiabat T RIDGE FEEDERS True intra-plate hotspots do not need deep feeders for their T & isotopes, but they may be near passive upwellings

Plato showed that shadows can be deceiving * & differences from ‘the background’

Republished in GSAToday,Geotimes, Science, EOS etc. & referred to in most mantle geochemical papers “the Farallon slab” (times 10) This picture caused mantle geochemists & modelers to drop layered models in favor of simple whole mantle convection “It is… well established that oceanic plates sink into the lowermantle …” The evidence

extension compression freezingmelting Seismic waves interact with partially molten solids Spetzler & Anderson (1968) Li & Weidner (2013) melt freeze

Maggi et al., 2006, GJI Some ridge segments are underlain by “feeders” that can be traced to >400 km depth, particularly with anisotropic tomography (upwelling fabric) Ridges cannot represent ambient midplate or back-arc mantle WHERE DOES MORB COME FROM? RIDGES MAY HAVE DEEPER FEEDERS THAN OIB (still upper mantle) 6:1 vertical exaggeration Only ridge-related swells have such deep roots

200 Myr of oceanic crust accumulation TRANSITION ZONE (TZ) REGION B Super- adiabatic boundary layer Thermal max 600 km 300 km Tp decreases with depth 600 km Physics-Based Paradigm* (RIP) (* actually due to Birch, Tatsumoto, J. Tuzo Wilson) Shear strain “fixed” Hawaii source MORB source Shear-driven magma segregation Sources deeper than ~ km can be regarded as effectively fixed

Density is too low to be able to sink into lower mantle even when cold STABLE STRATIFICATION Transition Zone is source of midocean ridge basalts Region B is source of OIB chemistry

Crust & upper mantle eclogite: garnet & pyroxene-rich fertile rock Seismic LID

All hotspots, ridges & backtracked LIPs occur in red & yellow regions LVZ Near base of thermal boundary layer (Region B) Schaeffer 2013

Upper (B) & Lower (D”) Boundary Layers of the Mantle Hypothesis test Null Hypothesis: Region D” (the Core-Mantle Boundary) correlates better with hotspots & backtracked LIPs than any other region of the mantle. D” therefore contains Plume Generation Zones, e.g. fixed points above the core (Burke, Torsvik). Result: the hypothesis fails

LVZ CMB Excellent correlations with hotspots & LIPs D” boundary layer

CMB (D”) Region D” exhibits little correlation with upper mantle, surface tectonics or hotspots

slabs Slabs Over- ridden oceanic plates, mantle fluxed by slab volatiles Pacific plateaux formed at boundaries & triple junctions of new plates

The low velocity zones (LVAs) associated with present day ridges are in the same places as they were when Pangea broke up & the antipodal Pacific plates reorganized & oceanic plateaus erupted. The surface expressions of ridges migrate but only within the confines of the ~2000-km wide LVAs associated with ridges at km depth. Hotspots & LIPs backtrack to these same ridge-related regions. Plates & D” are highly mobile since they are next to inviscid boundaries. Why is there apparently a fixed reference frame in the “convecting mantle”?

Plate reconstructions show that subduction repeatedly occurs along the same bands. Regions that are warmed from above by the insulating effects of large plates and not cooled from below by stagnant slabs tend the control the locations of divergence of plates; the colder regions control the locations of convergence and subduction. These effects also control the boundary conditions at the top of the lower mantle, topography and temperature. …much of the long-wavelength geoid originates in the deep mantle, the dynamic topography appears to originate from density variations in the upper mantle… More than 1600 spherical harmonic coefficients are used in modern global tomography but only one has any degree of correlation between the top and the bottom of the mantle (Adam’s Anchor)…most of the power is in degree 2 & 3.

About 32 of the world’s active non-arc volcanoes or volcano clusters in the oceans occur in region O1 (19% of area) which roughly corresponds to the 20 Ma age contour. Only about 7 occur well away from the LVAs associated with spreading ridges and most of these are in oceanic region O2 (27% of area). (Leki´c et al., 2010).

About 32 of the world’s active non-arc volcanoes or volcano clusters in the oceans occur in region O1 (19% of area) which roughly corresponds to the 20 Ma age contour. Only about 7 occur well away from the LVAs associated with spreading ridges and most of these are in oceanic region O2 (27% of area). (Leki´c et al., 2010)

200 Myr of oceanic crust accumulation TRANSITION ZONE (TZ) REGION B Super- adiabatic boundary layer Thermal max 600 km 300 km Tp decreases with depth 600 km (RIP) (* actually due to Birch, Tatsumoto, J. Tuzo Wilson) “fixed” Hawaii source MORB source Shear-driven magma segregation Plate vs Plume

…you ought to have done a better job! -Ernest Rutherford “ The probability that 18…out of 24 randomly chosen points lie within the belts (23.5% of the CMB area) is about 1 in 7 million” ( p =1.47 ·10−7 ) …considered by authors to be “remarkable” CMB & backtracked LIPs 69

VS

Ambient mantle heat & temperature Huge volume changes with little  T Cools off mantle THE ECLOGITE ENGINE Working fluid:basalt/eclogite/magma Lubricant: carbonatites Paired volcanic provinces CONTINENT or CONTINENTAL DRIP THEORY 650

temperature Vs Passive upwellings from below 200 km are cold ! adiabats Vs

MORB LVZ LITHOSPHERE Ocean Island 220 km OIB UPDATE OF CLASSICAL PHYSICS-BASED PLATE MODELS (Birch, Hales, Elsasser, Uyeda, Hager…)* after Hirschmann 2010 Pepi *not Morgan, Schilling, Hart, DePaolo, Campbell… -200 C INSULATING LID 650

Actual anomalies are ~2.5 times larger; therefore, not thermal

Saturated images showing slab-like features Modern mantle geochemistry & geodynamics are based on these images & cartoons Geochemists at Lyon, Paris, Yale, Berkeley, Mainz…are particularly impressed by these cartoons Whole-mantle convection, hole- in-the-floor, water filter…

Do these picture prove whole mantle convection, thermal coupling, barriers at 650 or ~1000 km…or do they map ray bundles?

The pale yellow areas become slightly positive when a background reference model with slabs at 650 km is added back in and the blue regions above 650 become bluer. In contrast to global reference models, the actual Earth has a global LVZ between 600 and 650 km. Correcting to this new reference turns the red patches above 650 into pale blue or neutral patches & blue regions into flat slab like anomalies km

Whole mantle convection? [color pictures have made everyone a geodynamicist!]

Different color schemes

Farallon Slab ? Van der Lee & Nolet Trapped at 650 or CMB?

Relative wavespeeds

Transition zone is oblivious to surface “hotspots” Garnero et al ridge slab hotspot 410 is cold under ridges

Thermal convection is a far-from-equilibrium self-organized system. It is inordinately sensitive to changes in initial & boundary conditions. No continents with continents Internal heating

BLUE REGIONS ARE SLAB GRAVEYARDS (FARALLON,TETHYS) 1100 km depth 600 km Stagnant slab Secondary downwelling

Zhao et al. (1997) Science 278, P-wave tomography in Tonga-Fiji region Slow anomalies in the mantle wedge extend down to 500* km depth: eclogite, water, CO 2 ? High 3 He/ 4 He means low 4 He & low U/He High 3He/4He Slower than hotspot mantle Wedge becomes part of ambient mantle (non- MORB) *more than many hotspots!

Unexpected behavior of TZ; not thermal, not peridotite Garnero and others

Fixity? The Low Velocity Zone (LVZ) decouples plate motions from deep mantle The Transition Zone (TZ) is a high viscosity region & contains stagnant slabs; it is a source of fertile depleted passive upwellings D” is next to the inviscid core & is not fixed; it may be colder than Region B

Sheared, anisotropic boundary layer

Cartoon interpretations No physics!

A gravitationally stable rock column These can only become buoyant if they partially melt These can eclogitize below 60 km Helium-rich carbonatites degas above 60 km, not deeper (e.g. SCLM)

Material displaced out of TZ by slabs is not the same as modern subducted material; it can be cold & ancient (e.g. high 3 He/ 4 He)

Why is there a strong bias of volcanoes, both plate boundary and intraplate to equatorial & southern latitudes…& volcanism, tomography, gravity field…to degree 2 patterns (C20)…& alignment of most continents & geoid lows to a polar band? The non-hydostatic geoid, the ellipticity of the Earth, rotation, tidal breaking, tomography, at all levels distribution of volcanoes all are dominated by C 20 (Ray, DLA). Fluid dynamic & self compression effects force the mantle to convect at the longest possible wavelengths– the long wavelength parts of these features control the moments of inertia & the rotation axis of the Earth..regions of extension, including ridges, concentrate in low & southern latitudes…+30 to -45 degrees latitude…& hug the boundaries of large geoid highs. Plate reconstructions show that subduction repeatedly occurs along the same bands. Regions that are warmed from above by the insulating effects of large plates & not cooled from below by stagnant slabs tend the control the locations of divergence of plates; the colder regions control the locations of convergence & subduction. These effects also control the boundary conditions at the top of the lower mantle, topography & temperature. much of the long-wavelength geoid originates in the deep mantle, the dynamic topography appears to originate from density variations in the upper mantle… There are more than 1600 spherical harmonic coefficients used in modern global tomography but only one has any degree of correlation between the top & the bottom of the mantle (Anchor)…& most of the power is in degree 2 and 3.

The issue arises, why is there a strong concentration of volcanism in equatorial and southern latitudes…and of geoid lows, continents, island arc volcanism and subduction zones in a narrow polar band? [NewTOE FIG. 6.1]. Most of the power in the geoid and in tomographic models at all depths is in degree 2. This does not imply whole mantle convection since shorter waveslength features are not correlated but it does imply thermal, rotationall or gravitational control on long wavelength fetures in both the upper and lower mantles…volcanism, tomography, gravity field…to degree 2 patterns (C20)…and alignment of most continents and geoid lows to a polar band? The non-hydostatic geoid, the ellipticity of the Earth, rotation, tidal braking, tomography, at all levels distribution of volcanoes all are dominated by C20 (Ray, DLA). Fluid dynamic and self compression effects all force the mantle to convect at the longest possible wavelengths and the long wavelength parts of these features control the moments of inertia and the rotation axis of the Earth.. regions of extension, including ridges, concentrate in low and southern latitudes…+30 to -45 degrees latitude…and hug the boundaries of large geoid highs.

Ultra-refractory harzburgite (stable) Eclogite (unstable) lherzolite SiO 2 -poor eclogite MORB-st eclogite (stable) LID TZ coldhot An oscillating rock group Oceanic crust Lower arc crust (metastable) 650 (cold) 410 (warm) subadiabatic LID

Cooled cooled + + Cold slab Maximum lateral density & thickness differences, thermal & lithological, at level of neutral buoyancy! Runaway ascent + (-) density excess (deficit) Large blobs of mafic low-melting materials, containing much of the mantle LIL (U, Th…) transiting between crust & TZ ECLOGITE ENGINE THE BLOB MODEL

Kelvin’s Revenge Earth’s thermal history is a top-down cooling process The upper boundary layer (B) is thick & traps heat …resulting in a Thermal Bump …& a subadadiatic geotherm …& a relatively thin, cold & cooling CMB (D”)

Nature

Woodhouse, JH (1981) 'A note on the calculation of travel times in a transversely isotropic Earth model', Physics of the Earth and Planetary Interiors. Vol. 25, pp Physics of the Earth and Planetary Interiors, 25 (1981) 357— Elsevier Scientific Publishing Company. Amsterdam — Printed in The Netherlands A note on the calculation of travel times in a transversely isotropic Earth model J.H. Woodhouse

Improperly allowing for anisotropy (Vp ignored) The pseudo- anisotropy artefact Pseudo-isotropic wavespeed VP VSH VSV 3 moduli No angular dependency

Region D” is the smallest & least accessible boundary layer It has received an inordinate amount of attention from seismologists & geochemists It has been claimed to be the largest plausible source for Hawaii & Yellowstone It is next to the fluid core, meaning that it is a free-slip (moving) boundary Seismologists have become fascinated with D” Let’s take it from the top (Region B)