Estimating mantle temperature and composition

from seismic models (and other data)

Colleen Dalton, Boston University

with Allie Gale, Charlie Langmuir, Uli Faul, Mollie Celnick, and others

Seismological Models

S362ANI 300 kmKustowski et al. (2008)

S40RTS 300 kmRitsema et al. (2010)

QRFSI12 300 kmDalton et al. (2008)

Transition Zone ThicknessLawrence & Shearer (2008)

MORB Composition

Hotter mantle:•melting initiates deeper•larger extent of melting•lower Na in MORB•higher Fe in MORB•thicker oceanic crust•shallow ridge depths

modified fromLangmuir & Forsyth 2007

540 segments without “8 values”

RIDGE nseg Length (km)

Mid-Atlantic 255 16,594

SE Indian 79 7,268

E. Pacific Rise 76 7,326

SW Indian 67 4,624

Central Indian 61 3,860

Pac-Ant Ridge 46 5,454

Afar 36 3,483

Chile Rise 27 1,462

Gakkel 18 1,907

Juan de Fuca 17 1,003

Galap. Ridge 17 2,127

AAR 10 514

Back Arcs 62 5,242

TOTAL 771 60,864

Definition of Ridge Segments

Humler et al. (1993)

This study

MORB Composition

Ridge Depth vs. S-Velocity

P = Dwwg+Dccg+Drrg+Dmmg

Calculation of Water Depth: Isostasy

1250oC

1370oC

Calculation of Water Depth and Seismic Velocity

Comparison of Na8 and Seismic Velocity

Effect of Composition on VS

3 GPa (~90 km) and 800oC

Mg# = Mg / (Mg + Fe)

garnet faciesspinel faciespyrolite 0.1 km/s ~ 2%

Cratonic Temperature & Composition

150 km

Lee et al. (2010)

CIDER

1. Possible themes:tectonic settings: cratons; ridges; transform faults; hotspots

no theme? research projects based on who is there

2. Other things to consider: more time for research: start research projects right away

some research lectures in addition to overview lectures

opportunity to make progress with collaborators

support for meetings in person after summer crucial

Parameter Velocity AttenuationTemperatureComposition ?Melt Water ?

Transition zone thickness

Seismological Models

Zhang et al. (1994)

Wiens et al. (2006)

Previous Studies

Courtier et al. (2007)

Velocity variation (%)

Na 8

.0

Humler et al. (1993)

Previous Studies

median = -3246 m

Definition of Ridge Segments

MAR SEIRResolution of Seismic Models

EPR

Resolution of Seismic Models

SWIR SEIR

MAR

longitude

longitudelatitude