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