links between melting, rheology and the composition and structure of the upper mantle greg hirth,...
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Links between melting, rheology and the composition and structure of the upper mantle
Greg Hirth, Brown Univeristy
Marc Parmentier & Alberto Saal
Mark Behn, Jim Gaherty, John Collins, Dan Lizarralde
Kiyoshi Baba, Rob Evans, Alan Chave, Don Forsyth
Joerg Renner, Karen Viskupic, Brian deMartin & Brian Evans
Cagnioncle et al. 2007
Hirth & Kohlstedt, 2003
Zhao et al. 2007
Gaherty et al., 1999
Mei & Kohlstedt, 2000; Jung & Karato, 2001; Borch & Green, 1989;Chopra & Paterson, 1981; Karato et al., 1986
Hirth & Kohlstedt, 2003
Influence of water of rheology (Strain Rate [Viscosity]-1)
Evans et al., 2005
Resistive layer consistent withdry olivine
Conductive “asthenosphere” consistent with damp olivine
Magnitude of anisotropyconsistent with crystallographicdependence of H diffusion inOlivine
Anisotropy hard to preserve ifconductive layer controlled bypresence of melt
0.000 0.005 0.010 0.015 0.020
Melt Fraction
10-4
10-3
10-2
10-1
100
101
Bul
kC
ondu
ctiv
ity
(Sm
)
[100][010][001]
0.000 0.005 0.010 0.015 0.020
Melt Fraction
10-4
10-3
10-2
10-1
100
101
Bul
kC
ondu
ctiv
ity
(Sm
)[100][010][001]
Basaltic Melt: 10 S/m
Fictive Melt: 100 S/m
(S/m
)(S
/m)
0.000 0.005 0.010 0.015 0.020
melt fraction
0
500
1000
1500
2000
2500
3000
oliv
ine
wat
erco
nten
t(p
pmH
/Si)
Enriched (650 ppm)
Depleted (85 ppm)
Two Component Mantle with 125 ppm Bulk Water
Yang, Weeraratne & Forsyth
dehydratation
dehydratation
Faul & Jackson, 2005
0
100
200
300
400
Vs
Behn et al., 2009
Behn et al., 2009
Need constraints on permeability (k)and bulk viscosity ()
0.0 0.1 0.2 0.3 0.4
melt fraction
10-8
10-7
10-6
10-5
10-4
10-3
com
pact
ion
rate
(1/s
)Olivine + Melt1200oC, P = 10 MPagrain size = 20 m
rate 1
rate 2
Renner et al., 2003
Predicts > 1022 Pas
10-1 100 101 102 103
grain size (mm)
10-2
10-1
100
101
102
103
104
com
pact
ion
leng
th(k
m)
n =
1
n = 3.5
“shear”
= 1%
Compaction Rate Pn = P/Compaction RateP = g
g 7000 (SI)
= 300 km gives
P = 2.1 GPa!!NO WAY
deMartin, Hirth & Evans
S = Carbonate melt fluxS = Fcarb*Upwelling fluxUpwelling flux = volume/area/timeUpwelling flux = Slab Flux/Earth surface areaUpwelling Flux = 1km/yrFcarb = 10-4 to 10-3
0 20 40 60 80 100
time (My)
0.00
0.02
0.04
0.06
0.08
0.10
mel
tfr
acti
on
F = 0.01%
F = 0.1%
-2-1
Darcy Flux = 0.01%
Pond
ed M
elt F
ract
ion
t = (pond /3) ( )/S
Dasgupta et al., 2009
“Ponded” 2%
Crystallize
H20 400 ppm
