Transcript Document 7687424

Variations in alkali feldspar/melt
trace-element partitioning during
fractionation of peralkalic quartz
trachyte-rhyolite suites
John C. White1, Don F. Parker, and
Minghua Ren2
Baylor University
Waco, Texas 76798
1Current
address: Elizabeth City State University,
Elizabeth City, NC 27909
2Current address: University of Texas at El Paso,
El
Paso, TX 79968
18
Comenditic
Trachyte
14
2
wt% Al O
3
16
Pantelleritic
Trachyte
Comendite
12
10
8
6
Pantelleria
Baitoushan
TPMP, Texas
HMVC, Oregon
Oregon Plateau
2
Pantellerite
4
6
wt% FeO*
8
10
Rb
Rb
-0.75
-1.00
-1.25
ln DRb Predicted
• ln D(Rb) = -2.2122 +
0.0273(SiO2) –
0.6396(A.I.)
• R2 = 0.90
• p < 0.0001
• 64.8 to 76% SiO2
• 0.97 to 1.75 A.I.
WHPR
MS90
M81
DBN83
N70/71
95% CI
-1.50
Rb(M)
-0.75
-1.00
-1.25
-1.50
-1.50 -1.25 -1.00 -0.75
ln DRb Expected
Rb
Rb(M)
-0.75
-1.00
-1.25
ln DRb Predicted
• ln D(Rb) = -2.1370 +
0.0354(Or) –
0.3071(A.I.)
• R2 = 0.85
• p < 0.0001
• 28.3 to 47.7 mol% Or
• 0.97 to 1.95 A.I.
WHPR
MS90
M81
DBN83
N70/71
95% CI
-1.50
Rb(M)
-0.75
-1.00
-1.25
-1.50
-1.50 -1.25 -1.00 -0.75
ln DRb Expected
Eu
1
Eu
0
-1
ln DEu Predicted
• ln D(Eu) = 20.3729 –
0.2119(SiO2) –
4.0374(A.I.) –
1.1188(Na2O/K2O)
• R2 = 0.91
• p = 0.0001
• ~66 to 74% SiO2
• 0.99 to 1.75 A.I.
-2
WHPR
MS90
M81
DBN83
N70/71
95% CI
-3
-4
1
Eu(A)
0
-1
-2
-3
-4
-4
-3
-2
-1
0
1
ln DEu Expected
Eu
1
Eu(A)
0
-1
ln DEu Predicted
• ln D(Eu) = 5.2871 –
4.8100(A.I.) +
0.0830(Na2O/K2O)
• R2 = 0.85
• p < 0.0001
• 0.90 to 1.95 A.I.
-2
WHPR
MS90
M81
DBN83
N70/71
95% CI
-3
-4
1
Eu(A)
0
-1
-2
-3
-4
-4
-3
-2
-1
0
1
ln DEu Expected
Zr
HFSE
-3
ln DHFSE Predicted
• ln D(Zr) = -13.4268 +
0.1554(SiO2) –
0.3997(A.I.)
• ln D(Nb) = -14.9113 +
0.1793(SiO2) –
0.6432(A.I.)
• R2 = 0.84(Zr),
0.91(Nb)
• P < 0.0001
-2
-4
This study
95% CI
Nb
-2
-3
-4
-4
-3
-2
ln DHFSE Expected
DRb
0.40
DZr
0.08
0.35
0.06
0.30
0.04
0.25
0.20
0.02
Buckhorn Caldera
Star Mountain Fm
Pantelleria
DEu
DNb
0.08
1
0.06
0.1
0.04
0.01
0.02
0.001
500
1000
1500
2000
500
ppm Zr
1000
1500
2000
Pantelleria: Major-Element FC Model
Opl361i (64.86% SiO2) to Sic172 (70.88% SiO2)
• 66.1% (86.3%) Alkali Feldspar (AF-20-13)
• 4.4% (5.7%) Sodic Hedenbergite (CPX-20-41)
• 2.2% (2.9%) Fayalite (OL-20-21)
• 3.5% (4.5%) Cossyrite (Aenigmatite, COS-22-23)
• 0.3% (0.4%) Ilmenite (IL-31-22)
• 0.2% (0.2%) Apatite (#32, Mahood and Stimac, 1990)
• 23.3% Daughter Magma (76.6% Crystallization)
• SSR = 0.005
Trace-Element Partitioning Models
• F = COZr / CLZr (Allegre et al., 1977)
• F = COpl361iZr / CSic172Zr = 480 ppm / 2314 ppm
= 0.207
• Major-element model: F = 0.233 (76.6%
crystallization)
• Allegre et al. (1977) model: F = 0.207 (79.3%
crystallization)
% fractional crystallization
D(Eu)
0
60
40
20
80
100
Model Parent
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
D(Eu) = -0.46 + 2.32(F)
Model Daughter
0.34
0.32
Model Daughter
D(Rb)
0.30
0.28
D(Rb) = 0.32 - 0.11(F)
0.26
0.24
0.22
Model Parent
0.20
1.0
0.8
0.6
0.4
0.2
F (x 100 = % liquid remaining)
0.0
FC Model (Greenland, 1970)
• dC = (D – 1) d[ln F]
• ln (CL/CO) = (D – 1) ln F
• CL/CO = F (D – 1)
• D = a + bF
• dC = (a + bF – 1) d[ln F]
• ln CL/CO = (a – 1) ln F + b(F – 1)
35
D(Eu) = 0.02
30
5
25
4
3
15
D(Eu) = -0.46 + 2.32(F)
10
ppm Eu
ppm Eu
20
2
5
1
D(Eu) = 1.86
0
1000
2000
3000
ppm Zr
4000
500
1000
1500
2000
2500
ppm Zr
Data: White et al. (2003), Civetta et al. (1998), Mahood and Stimac (1990)
500
D(Rb) = 0.32 - 0.11(F)
400
200
300
D(Rb) = 0.34
150
ppm Rb
ppm Rb
D(Rb) = 0.21
200
100
100
1000
2000
3000
ppm Zr
4000
500
1000
1500
2000
2500
ppm Zr
Data: White et al. (2003), Civetta et al. (1998), Mahood and Stimac (1990)
Concluding Remarks
• In addition to being strongly incompatible, traceelements used as fractionation indices should also
have nearly constant partition coefficients.
• Other trace-elements (e.g., Rb and Eu) may
demonstrate considerable variability in
partitioning behavior.
• The Greenland (1970) fractional crystallization
model, which can incorporate variable D’s, may
be a more realistic model of FC processes.