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Minor Crystalline Solids and Elements: Minor Crystalline Solids and Elements: Physicochemical Behavior and Geologic Physicochemical Behavior and Geologic
SignificanceSignificance
• Ti4+, P5+ associate with (silica) network-modifying cations, e.g., Mg, Fe
• Strong effect on melt composition and structure, mineral-melt equilibria, liquid line of descent
TiO2-enrichment in silicate melts
Ol+Opx+Ox - saturated liquidsLunar glasses
TiO2 (wt% ) in silicate melt
0 5 10 15 20 25
SiO
2 (
wt%
) in
silic
ate
melt
30
35
40
45
50
55
SiO
2 in m
elt
0.2
0.4
0.6
0.8
1633 K, 1.2 GPa
1803 K, 2.8 GPa
XSiO
2 in m
elt
0.3
0.4
0.5
1633 K, 1.2 GPa
1803 K, 2.8 GPa
XTiO2 in melt
0.00 0.04 0.08 0.12 0.16
aSiO
2 in m
elt
0.2
0.3
1633 K, 1.2 GPa
1803 K, 2.8 GPa
Xirouchakis et al (2001)
TiO2-enrichment in silicate melts
Ol + Px + Ox saturated Liquids
TiO2 (wt.% ) in liquid
(0 - 2 wt.% Na2O + K2O in liquid)
0 5 10 15 20 250.20
0.24
0.28
0.32
0.36
0.40
Ol/
Liq F
eO
-MgO
KD
Longhi et al (1978): 0.5 - 1.5 GPa, 1568 - 1648 K
Longhi et al (1978): in vacuo, 1423 - 1603 K
Wagner & Grove (1997): 1.4 - 1.7 GPa, 1643 - 1693 K
Baker & Stolper (1994): 1.0 GPa, 1543 - 1663 K
Longhi & Pan (1988): in vacuo, 1423 - 1523 K
Xirouchakis et al (2000): 1.2 GPa, 1633 K
Xirouchakis et al (2000): 2.8 GPa, 1803 K
Xirouchakis et al (2000)
aoxi
de
0.2
0.4
0.6MgO: 1633 K, 1.2 GPa
FeO: 1633 K, 1.2 GPa
MgO: 1803 K, 2.8 GPa
FeO: 1803 K, 2.8 GPa
Ol+Opx-saturated liquids
Xoxi
de
0.1
0.2
0.3
XTiO2 in liquid
0.00 0.04 0.08 0.12 0.16 0.20
oxi
de
2
3
4
P5+, geochemical significanceLess of a phosphate mineral may be needed to account for the bulk P2O5 of Solid Earth & Planetary systems (e.g., mantle) as silicate minerals may host P5+
In the absence or prior to saturation with a phosphate mineral, mafic silicate melts may become enriched in P2O5, especially in the geochemically important low melt fraction regime
Interactions between P5+-hosting silicates and accessory phosphates may affect the stability of the latter
P5+-bearing silicates as a source of phosphorus for microorganisms in nutrient-limited, sub-surface environments.
Reports of extreme enrichment in Olivine and Pyroxenes:
2-4 wt.% P2O5 in olivine and pyroxene in Pallasites [Buseck &
Clark 1984]
and in reduced terrestrial basalts [Goodrich 1984]
17 wt.% P2O5 in zoned olivine crystals from ancient slags [Kresten et al. 1998]
Poorly characterized silico-phosphates in Angrites [Mittlefehldt 2002]
Isostructural solid solutions of silicates and phosphates are not common; Si4+, P5+ and Al3+ have similar radii but also different EN
The higher the degree of SiO4-polymerization, the lower the P2O5 content, e.g., Gt > Ol >> Px (Koritnig 1965; Henderson
1968; Anderson & Greenland 1969; Thompson 1975; Bishop et al. 1978; Brunet & Chazot 2001)
Al3+
0.39Å
EN=1.5
P5+
0.31Å
EN=2.1
Si4+
0.26Å
EN=1.8
Phosphorus in silicate minerals
5-9 GPa supersolidus 5-9 GPa supersolidus experimentsexperiments
Sample in graphite capsule
“hard” Al2O3 sleeve
crushable Al2O3
sample
WC cubes
9 GPa, 1775°C
Ol Gt
Opx
All JSC data for P2O5 wt% in orthopyroxene [0.011(6) wt.%], olivine [0.07(3) wt%], and garnet [0.24(5) wt.%] in equilibrium with liquid [0.7-1.5 wt%]
0.15
0.2
0.25
0.3
0.35
0.4
P2O
5 w
t%
Gt
mean P2O
5 wt%
Ol0.02
0.04
0.06
0.08
0.1
0.12
0
0.005
0.01
0.015
0.02
0.025
OpxP
2O
5 wt% in Gt
0.1 0.2 0.3 0.40
5
10
15
20
25
30
35
P2O
5 wt% in Ol
0 0.05 0.10
2
4
6
8
10
12
P2O
5 wt% in Opx
0 0.01 0.020
2
4
6
8
10
12
72 78 84 90 96
Ol mg#
0.0
0.2
P2O
5 w
t%
DX & DSD (2002)Brunet & Chazot (2001)This study
Al2O3 wt% in Ol
0.0 0.2 0.4 0.6
0.0
0.2
P2O
5 w
t%
Na2O wt% in Ol
0.00 0.06 0.120.0
0.2
P2O
5 w
t%
78 84 90
Opx mg#
0.00
0.02
Al2O3 wt% in Opx
1 2 3
0.00
0.02
Na2O wt% in Opx
0.0 0.3 0.60.00
0.02
a b
c d
e f
0 4 8
P (GPa)
0.0
0.2
0.4
0.6
DX & DSD (2002)Thompson (1975)Bishop et al. (1978)
This study
T (oC)
1000 15000.0
0.2
0.4
0.6
P2O
5 w
t% in G
t
mg# in Gt
20 40 60 800.0
0.2
0.4
0.6
P2O
5 w
t% in G
t
SiO2 wt% in Gt
36 40 44 48
0.0
0.2
0.4
0.6
Al2O3 wt% in Gt
16 20 240.0
0.2
0.4
0.6
Na2O wt% in Gt
0.0 0.2 0.40.0
0.2
0.4
0.6
a b
dc
e f
….Partitioning coefficients….
• depend on ionic size and charge of the element
• may depend on the composition and structure of the involved crystalline and liquid phases phase
• may depend on intensive parameters
<< 1
1
liqxlD /
liqxlD /
incompatible element:
compatible element:
phosphorus behaves incompatibly in pyroxenes (chain silicate) and becomes more compatible in olivine and garnet (orthosilicates)
Dxl/ liqP2O5
0.0 0.1 0.2 0.3 0.4
Opx
Ol
GtAll JSC data
Dxl/liq = Cixl/Ci
liq
SiO2 wt% in gl
DP
2O
5
Gt/
Liq
0.0
0.2
0.4
DX & DSD (2002)Thompson (1975a, b)This study
P2O5 wt% in gl
0 1 2
0.0
0.2
0.4
36 42 48 54D
P2O
5 O
l/Li
q
0.0
0.1
0.2
DX & DSD (2002)Libourel et al. (1994)Brunet & Chazot (2001)This study
SiO2 wt% in gl
36 42 48 54
DP
2O
5 O
px/L
iq
0.00
0.02
0.04
0 1 2
0.0
0.1
0.2
ba
dc
P2O5 wt% in gl
0 1 2
0.00
0.02
0.04e f
Si pfu (12 O)
2.9 3.0 3.1 3.2 3.3
Dgt/
liq P
2O
5
0.0
0.2
0.4
This studyDX & DSD (2002)Thompson (1975)
liqOpxOPD
/
52liqGt
OPD/
52
P (GPa)
3 4 5 6 7 8 90.0
0.2
0.4
Dgt/
liq P
2O
5
This studyDX & DSD (2002)Thompson (1975)
2.2 2.4 2.6 2.8 3.2 3.43.0
P (GPa)0.08
0.12
0.16
0.20
0.24
DGt/Liq P2O5: Thompson (1975)
1300oC
1300oC 1325oC
1350oC
1385oC1450oC
1250oC
• Common silicates (Opx, Ol, Gt) can host phosphorus (P)
• Possible positive correlation between P and Na in Gt, but no apparent correlation between P and other elements in Ol and Opx
• P2O5 (wt%) in Gt > Ol > Cpx > Opx > Plag: P incorporation more structure than site specific(?)
• Ol/Liq, Opx/Liq DP2O5 probably constant
• Gt/Liq, Cpx/Liq, Plag/Liq DP2O5 may vary with P and/or T, and liquid and garnet composition