Melting and melts in the deep Earth€¦ · 14/07/2018 · – Stability of melts in the deep...
Transcript of Melting and melts in the deep Earth€¦ · 14/07/2018 · – Stability of melts in the deep...
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Zhicheng Jing
Case Western Reserve University
July 14, 2018 CIDER
(After CIDER: Southern University of Science and Technology)
Melting and melts in the deep Earth
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Kilauea volcano, Hawaii, Kent Nishimura/LA Times
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Earth’s internal fires, Athanasius Kircher
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Credit: Keelin Murphy Dziewonski and Anderson, PEPI, 1981
Molten layer inside? - Outer core
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Mercury Moon
MarsGanymede
Molten Fe cores in other planetary bodies
Weber et al., 2011Credit: Calvin J. Hamilton
https://www.jpl.nasa.gov/news/news.php?feature=60
https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00519
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No melting under normal mantle conditions
Temperature
Depth Solidus
T0 Tm0
Adiabaticgeotherm
Boundary layerConductive geotherm
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Mechanisms of mantle melting
Temperature
Depth Solidus
Adiabaticgeotherm
Boundary layerConductive geotherm
(1)
(2)
(3)
(1) Decompression melting
(2) Hydration melting(3) Melting by increasing
temperature
T0 Tm0
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Examples of mantle melting
Simkin et al., 2006
Melting at mid-ocean ridges, ocean islands, and subduction zones: CIDER 2018 lecture by Esteban Gazel
Asimow, 2017
Credit: S. Shawn Wei
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Primordial melting in the mantle
Labrosse, 2007
Early magma ocean
Basal magma ocean
https://www.extremetech.com/extreme/179768-the-moons-real-age-is-finally-revealed-but-the-mystery-of-earths-tardy-development-lives-on
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Volatile induced deep melting
Hirschmann, 2006
Leahy and Bercovici, 2007
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Metallic melts in the deep mantle
Smith et al, 2016
Early magma ocean
Basal magma ocean
Liu et al., 2016
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Why do we care about melts and melting (or solidification)?
• Understanding the chemical evolution of Earth– Core formation– Formation of crusts– Distribution of heat producing elements– Cycling of volatiles
• Understanding composition and heterogeneities of the deep Earth– Composition of the outer core– Stability of melts in the deep mantle– Interpretation of seismic velocity anomalies, attenuation, and
anisotropy
• Understanding the cooling of Earth– Magma ocean solidification– Solidification of the outer core and the generation of the intrinsic
magnetic field
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Past CIDER lectures related to melting and melts:
2010 Cin-Ty Lee, Melting of mantle2011 David Kohlstedt, Melt and rheology2013 Rajdeep Dasgupta, Melting in ridges, subduction zones2014 Paul Asimow, Melting in planetary interiors2015 Marc Hirschmann, Melting, deep Earth water and carbon2016 Frank Spera, Thermodynamics of melting2018 lectures by Esteban Gazel, Lars Stixrude, ChrysteleSanloup
This lecture will cover:
1. Physics of melting2. Equations of state of melts3. Solidification of melts
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What is melting?
Tabor, 1991
SolidCrystalline latticePeriodically ordered
LiquidShort range orderNo long range order
Melting http://www.nyu.edu/classes/tuckerman/pchem/extras/extras.html
Ice melting
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Structure of liquids from X-ray diffraction
Shen et al., 2004
Uchida et al, 2001
fcc-Fe Liquid Fe
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Short range order in liquids
http://www.globalsino.com/EM/page3097.html
Pair distribution function Liquid Fe
Morard et al., 2014
Wang et al., 2014
Liquid Di (CaMgSi2O6)
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Theories of melting
1. Melting theories based on the thermodynamic condition that the free energies of solids and liquids are equal.
Clausius-Clapeyron relation
2. Melting theories based on the stability of solids near its melting point.
Lindemann’s law of melting
3. Empirical relationsSimon-Glatzel equationKraut-Kennedy equation
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Richet & Neuville, 1992
Ø !" = $%$& "
= ' $($& "
) = ∫+& ,-&. /'′
Ø Crystals and glasses have similar Cp. However, liquids have higher Cp and entropy due to additional degrees of freedom, i.e., the freedom of having different spatial configurations.
Heat capacity and entropy of liquids
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One component system: Gibbs free energy
G
TTm
Solid
Liquid
! = − $%$& '
G
P
SolidLiquid
( = $%$) *
Melting is a first order phase transition. The first order derivatives of G are discontinuous across the transition.
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Clausius-Clapeyron relation
Pressure
Temperature
Solid
Liquid
!Δ# = %& − %( !) − *& − *( !+ = 0!+-!) = Δ%-
Δ*-with
Δ%- = %& − %(Δ*- = *& − *(
Gas
Triple point
Critical point
Supercritical fluid
Melting
Difficult to quantify the detailed atomic and electronic structures of the solid and liquid (Tallon, 1982)
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Negative volume of melting
!"#!$ = Δ'#
Δ(#Δ( is always larger than 0. A negative slope in the melting curve indicates the liquid is denser than the solid.
Li et al., 2017
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Lindemann’s law of melting
• Melting occurs when the vibration of atoms is at a critical fraction f of the distance r0 of nearest neighbors.
< "# > = &#'(#• From Debye’s approximation,
< "# > ≅ 9+,-./0#
= 9ℏ#-.+,2#
where 2 = ℏ3456
is Debye temperature
• Lindemann’s law
-7 = &# +,9ℏ# .2#8
#9
m – mean atomic massv – mean atomic volume
• Differential form: ln -7: ln = = 2 ? − 1
3where ? = C DE 3
C DE F =C DE GC DE F
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Lindemann factor f
Poirier, 1989
• The Lindemann’s melting law is supported by the observations that for many metals f is about 0.08, and for perovskite oxides f is about 0.13.
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Melting in super-earths: extrapolation using Lindemann’s law
Stixrude, 2014
f = 0.137 for MgSiO3 post-perovskite
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Kraut-Kennedy equation
Approximate Lindemann’s law! ln $%! ln & = 2 ) − 13
with a finite difference equationΔ$%$%
= $% − $%.$%
= 2 ) − 13Δ//.
That is
$% = $%. 1 + 2 ) − 13Δ//
Kraut-Kennedy equation (Kraut and Kennedy, 1966)
$% = $%1 1 + 2 Δ//Generally cannot be used at very high pressures.
Kennedy and Vaidya, 1970
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Simon-Glatzel equation
Combine Lindemann’s law and Murnaghan EOS! ln $%! ln & = 2 ) − 1
3and
-. = -./ + -./1 2where -. = 34
3 56 7 ., we have
$% = $%/ 1 + -./12
-./
8 9:;<
Simon’s law (Simon and Glatzel, 1929)
$% = $%= 1 + 2>
?
or2 − 2/
> = $%$/
@− 1
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Melting curve of Fe fitted by Simon-Glatzel equation
Anzellini et al. (2013):
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Gibbs free energy of binary ideal solutions
For ideal solution of two components A and B,! = #$!$ + #&!& − (Δ*+,-
where
Δ*+,- = −.& lnΩ = −.& ln2$ + 2& !2$!2&!
= −4(#$ ln#$ + #& ln#&)
Compare to the Euler form! = #$7$ + #&7&
We get7$ = 7$8 + 4( ln#$7& = 7&8 + 4( ln#&
Porter and Esterling, 1981, Phase transformations in metals and alloys
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Melting in the binary systems – Eutectic melting
Bowen, 1915
!"#$ = !"#$&!"#' = !"#'& + )* ln-"#'
During melting!"#$& = !"#'& + )* ln-"#'
Liquidus curve
ln -"#' =1)* !"#$& − !"#'&
= − 1RTΔ34
"# = Δ54"#
)1*4"#
− 1*Or
-"#' = 6789:;<=>
-?@' = 6789:AB=>
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Melting in the binary systems – Solid solution
Bowen and Chairer, 1935
!"#$ = !"#$& + () ln,"#$!"#- = !"#-& + () ln,"#-
During melting!"#$& + () ln,"#$ = !"#-& + () ln,"#-!".$& + () ln,".$ = !".-& + () ln,".-
Also,"#$ + ,".$ = 1,"#- + ,".- = 1
We have
,"#$ = 1 − 1234567
1234568 − 1234567
,"#- =1234568 1 − 1234567
1234568 − 1234567with
Δ:; = Δ<; − )Δ=;
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Mg-Fe distribution between olivine and melts
Agee and Walker, 1988 Mibe et al., 2006
Fe-Mg distribution constant between olivine and melt is defined as
!"#$/&' =⁄(+, -.)01⁄(+, -.)2$13
Smaller KD means more Fe in the melt and the melt is denser.
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Binary phase diagram – Solvus and immiscibility
Karato, Deformation of Earth materials
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Silicate – H2O pseudo-binary phase diagrams
Mibe et al., 2007
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Binary phase diagram – Incongruent melting
Bowen, 1914de Koker et al., 2013
1 atm
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Binary phase diagram – Incongruent melting
Bowen, 1914
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Zhang & Herzberg, 1994
Melting relation in a multi-component system
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Melting of the upper mantle
Sarafian et al., 2017
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Melting of the lower mantle
Nomura et al., 2014
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Melting of Fe under core conditions
Anzellini et al., 2013 Zhang et al., 2016
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2. Equations of state of melts
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Stolper et al, 1981
Stability of a melt layer in the mantle
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Silicate liquids are less dense but more compressible than solids at 1-bar.
Silicate melts vs silicate solids
Jing and Karato, 2011
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Ø Birch Murnaghan EOS
! = 32%&'
(('
)* − (
('
,* 1 + 34 %&'0 − 4 (
('
1* − 1
Ø (' and %&' are calculated by ideal mixing model (e.g., Lange, 1997; Ai and Lange, 2008; Ghiorso and Kress, 2004).
Ø %&'0 is constrained by high-pressure density measurements.
Applying Birch-Murnaghan equation of state to melts
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Up
Jing and Karato, 2012
Sink/float method to determine density of melts at high pressures
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Effect of composition on K’T
Jing and Karato, 2008
K’ has a large uncertainty due to the trade-off between K and K’
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Ultrasonic sound velocity measurements to determine K and K’ at high P
Xu and Jing et al., submitted
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Sound velocity of liquid diopside
Xu and Jing et al., submitted
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Problems with the Birch-Murnaghan EOS
1. For each melt composition, at least one density or sound velocity data point at high pressure to is required to constrain K’.
2. Cannot be used to explain many distinct properties of melts because the EOS is not based on the physics of liquids.
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• Helmholtz free energy of a system! = # − %&
• Equation of state is given by taking volume derivative of F
' = ' (, % = − *!*( +
= − *#*( +
+ % *&*( +
Equation of state
Energycontribution
Entropycontribution
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• Free energy has two parts! = #$%& + !()
• For solids, Fth mainly comes from lattice vibration!() = !*+, = #*+, − ./*+,
• Mie-Grüneisen EOS of solids
0 = − 1#$%&12 $
− 1!()12 $
0 = 0$%& + 0() = 0$%& + 3#()2
Entropic contribution is small.
Mie-Grüneisen equation of state for solids
Böer and Pohl, 2014
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Birch’s law: Velocity of a solid material is a linear function of its density, regardless of the specific pressure and temperature conditions. That is,
where a(M) is a constant depending on the mean atomic number
Birch, 1961
Birch’s law of correspondence state
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Ø Solids and glasses have the similar compression mechanism. But liquids have additional mechanisms.
Ø Entropic contribution is likely important for the compression of liquids.
Ø Liquids and glasses are fundamentally different in compressional properties. Glasses cannot be used as an analogy for liquids when studying compressional properties.
Silicate melts do not follow Birch’s law
Xu, Jing, et al., submitted
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Mosenfelder et al., JGR, 2009
Ø Grüneisen parameter is defined as
Ø For materials that follow Birch's lawor
Ø But Grüneisen parameter increases with pressure for liquids (q<0).
Ø Liquids do not follow Birch's law.
Ø Entropic contribution to compression must be important.
Pressure dependence of Grüneisen parameter
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Equation of state based on hard sphere mixtures
Jing and Karato, 2011
Kinetic energy(entropy)
Attractive force
Repulsive force
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Ø The correlation between sphere diameters and bond lengths suggests that the short-range order of liquids is correctly represented in the hard sphere model.
Room pressure Compress to V=0.5V0
Comparison of sphere diameters with bond lengths in solids
Jing and Karato, 2011
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Coordinated hard sphere mixture model
• Coordination of cations is explicitly modeled.• Currently only available to MgO melt
Wolf et al., 2015
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3. Solidification of melts
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adiabat
liquidus
Pressure (Depth)
outer coreFe-rich liquid
inner coresolid Fe
dTad/dP < dTliq/dPbottom-up solidification
adiabat
liquidus
Pressure (Depth)
outer coreFe-rich liquid
inner coresolid Fe
dTad/dP > dTliq/dP: top-down solidification
The adiabatic temperature gradient is related to the temperature dependence of sound velocity of the liquid
Solidification of a melt layer in planetary interiors
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Solidification of a silicate magma ocean
Stixrude et al., 2009 Mosenfelder et al., 2009
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Double snowing core in Mercury
Chen et al., 2008
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Solidification of the Martian core
Stewart et al., 2008
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