Transcript Estimating temperature and composition in the

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 km
S40RTS 300 km
Kustowski et al. (2008)
Ritsema et al. (2010)
QRFSI12 300 km
Transition Zone Thickness
Dalton et al. (2008)
Lawrence & 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 from
Langmuir & Forsyth 2007
Definition of Ridge Segments
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
MORB Composition
Humler et al. (1993)
This study
Ridge Depth vs. S-Velocity
Calculation of Water Depth:
Isostasy
P = Dwwg+Dccg+Drrg+Dmmg
Calculation of Water Depth and Seismic Velocity
1250oC
1370oC
Comparison of Na8 and Seismic Velocity
Effect of Composition on VS
3 GPa (~90 km) and 800oC
garnet facies
spinel facies
pyrolite
Mg# = Mg / (Mg + Fe)
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
Seismological Models
Parameter
Velocity
Attenuation
Temperature
Composition
?
Melt
Water
?
Transition zone
thickness
Previous Studies
Wiens et al. (2006)
Zhang et al. (1994)
Na8.0
Previous Studies
Courtier et al. (2007)
Velocity variation (%)
Humler et al. (1993)
Definition of Ridge Segments
median = -3246 m
Resolution of Seismic Models
MAR
SEIR
EPR
Resolution of Seismic Models
SEIR
SWIR
longitude
longitude
MAR
latitude