The 410- and 520-km Discontinuities in the Earth's Mantle ...

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Fiorenza Deon, Maria Mrosko, Monika Koch-Müller
Deutsches GeoForschungsZentum, GFZ, Department 3, Telegrafenberg, 14473, Potsdam
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
(Mg, Fe) 2 SiO 4
olivine, wadsleyite, ringwoodite
H incorporation in the range of wt%
if expressed as H 2 O

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
d410-km:
olivine to wadsleyite
Seismology: Wide range of
thicknesses from about 4 km
to 35 km
Related to water
incorporation in the
coexisting minerals ol and
wads?
Experiments indicate shift of
the transformation to lower
P in the presence of water.
Experimental studies: Frost
and Dolejs, 2007; Chen et
al., 2002; Frost and
McCammon, 2009
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
No clear picture
(Mg, Fe) 2 SiO 4
d520-km:
wadsleyite to ringwoodite
Seismology: large variation
in the depth and very sharp
Related to water
incorporation in the
coexisting minerals ol and
wads?
Experiments indicate shift of
the transformation to
higher P in the presence of
water.
Contrary to the d410 the
reason for this variation is
thermodynamically
completely unclear.

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Experiments in a rotating/rocking multi-anvil press in the system (Mg,Fe) 2 SiO 4 - H 2 O,
buffered with opx and water in excess under reducing conditions using multi-anvil
sets 14/8 and 10/5.
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Experiments in a rotating/rocking multi-anvil press in the system (Mg,Fe) 2 SiO 4 - H 2 O,
buffered with opx and water in excess using multi-anvil sets 14/8 and 10/5.
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Reducing conditions: Fe/FeO buffer

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
static rocking
Experiments in a rotating/rocking multi-anvil press in the system (Mg,Fe) 2 SiO 4 - H 2 O,
buffered with opx and water in excess using multi-anvil sets 14/8 and 10/5.
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
water in excess

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
JEOL JXA 8500 F:
chemical composition
Horiba Jobin Yvon Laser Raman,
Water quantification
Phase identification, chemical analyses,
quantification of water and Fe 3+
Synchrotron FIR: vibrational mod.
SIMS,
Water quantification
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Bruker, NIR and MIR
Fei TEM and FIB:
EELS for Fe 3+
Co-operation with
Dr. Alexandra Friedrich for X-RDA

The 410-km Discontinuity in the Earth’s Mantle:
Results - Mg2SiO4 +/- H2O Mg 2 SiO 4
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Systematic occurrence of hydrous
Wadsleyite in the stability field of dry
olivine.
In the presence of water the
olivine-wadsleyite phase boundary
is shifted 0.6 GPa to lower P.
This is due to a stronger fractionation
of water into wadsleyite rather than
olivine - increase of the
configurational entropy of hydrous
wadsleyite.

The 410-km Discontinuity in the Earth’s Mantle:
Results - (Mg, Fe) 2SiO 4
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
P-x projection
1200 °C

The 410-km Discontinuity in the Earth’s Mantle:
Results - (Mg, Fe) 2SiO 4 + H 2O
Triple point at 12.2 GPa, 1200°C
ol: 2700 wt ppm H 2 O
wad:10000 wt ppm H 2 O
ring: 4000 wt ppm H 2 O
BSE image
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
EEL-Spectra
FIB-Foil
Coexisting
ol-wad-ring
Fe 3+ pfu:
Wad:
0.07(2)
Ring:
0.02(1)

The 410-km Discontinuity in the Earth’s Mantle:
Results - (Mg, Fe) 2SiO4 +/- H2O P-x projections
dry
Extension of the stability field of hydrous wadsleyite to lower and
to higher pressures
which brings us to the new project on:
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
hydrous

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Modelling the stability of wadsleyite and ringwoodite
in dependence of the water content
Experimental part:
quenched Multi-Anvil-runs
- effect of P, T, x
- fractionation of water
between wads and ring
- structural and crystalchemical
analyses
- vibrational spectroscopy
- calorimetry
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Different approach:
Thermodynamic modelling
- calculate vibrational spectra
(DFPT)
- calculate thermodynamic
properties on basis of
vibrational DOS
- model phase stabilities as
f(H 2 O)

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Modelling of phase stabilities
Determine thermodynamic data
Calorimetry at University of Salzburg (E. Dachs)
PPMS-System of Quantum Design
PPMS (5-303K):
- Sample and measuring probe in liquid-Hebath
- Resonance of sample to a heat-pulse is
determined at different temperatures
- non-linear curve-fitting of data produces
heat-capacities

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Modelling of phase stabilities
Determine thermodynamic data
Calorimetry at University of Salzburg (E. Dachs)
PPMS-System of Quantum Design
PPMS and DSC-measurements of
anhydrous wadsleyite:
C p (298) = 115.43 J/(mol*K)
S (298) = 86.67 J/(mol*K)
Cp (298) = 116.3 J/(mol*K) Akaogi et al 2007
Cp (298) = 117.3 J/(mol*K) Ottonello et al 2009
Values for hydrous wads differ clearly

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
» use vDOS (determined by vibrational spectroscopy) and
its pressure dependence to compute thermodynamic data
» the more modes can be characterized the better the
modelling
» complicate in the FAR-IR-region (loss of light due to
diffraction)
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Modelling of phase stabilities
Determine thermodynamic data
BUT: Calorimetric measurements not feasible for hydrous
syntheses (impurities of other phases)

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
High brilliance of IR synchrotron light maintains
enough intensity
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Therefore we constructed a microscope to take pressure-depending
FAR-IR-spectra in DAC at the Berlin Synchrotron source BESSY.
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
synchrotron
IR light
from
interferometer

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Merged spectrum (FAR and MID-IR) of anhydrous wadsleyite
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Merged spectrum (FAR and MID-IR) of anhydrous wadsleyite
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
1
2
3 4 5 6 78
9
10
11
12
1 ν as (SiO 3 )
2 ν s (SiO 3 )
3 ν s (SiOSi)
4 ρ(Si 2 O 7 )
5 ν(M3-O1)
6 ν(M3-O1)
7 ν(M3-O1)
8 T(M)
9 T(M)
10 R
11 T
12 R

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Pressure-depending FAR-IR spectra
of hydrous wadsleyite
» the more modes one can
observe the better one can
compute thermodynamic data
using the vibrational modelling
» correct assignment of modes is
essential (substitution experiments,
pressure-dependence)

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Pressure-depending FAR-IR spectra
of hydrous wadsleyite
Vibrational modelling after Kieffer
(1979, 1980)
#
"
0
x
e
CV = 3Nk
x
( e $ 1)
Cp = C V + TV a 2 K T
2
x
2
g(
! ) d!
» compare with experimental data

The 520-km Discontinuity in the Earth’s Mantle:
Experiments and Thermodynamic modelling
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
Pressure-depending FAR-IR spectra
of hydrous wadsleyite
Changes in pressure-depending
behaviour of FAR-IR-bands
» indicate phase transition between
7 and 8 GPa
» transition in dry wadsleyite seems
to appear at app. 10 GPa

The 410- and 520-km Discontinuities in the Earth’s Mantle:
Experiments and Thermodynamic modelling
Fiorenza Deon, Maria Mrosko, Monika Koch-Müller
Deutsches GeoForschungsZentum, GFZ, Department 3, Telegrafenberg, 14473, Potsdam
3. Berichtskolloquium SPP 1236 10. - 12. 03.2010 Oberursel
We thank you for your attention!