zircon solubility in alkaline aqueous fluids at upper - Vanderbilt

22 Pages·2013·1.85 MB·English

by  John C. Ayers

ZIRCON SOLUBILITY IN ALKALINE
AQUEOUS FLUIDS AT UPPER
CRUSTAL CONDITIONS
Ayers J.C.1, Zhang L.1,2, Luo Y.1,3, Peters T.1
1. Dept. of Earth & Environmental Sciences, Vanderbilt University
2. Division of Geological and Planetary Sciences, California Institute
of Technology
3. Department of Earth Sciences, The University of New Brunswick,
Canada
Zircon Solubility Diagram
In alkaline solution: ZrSiO (xt) + 2H O + OH- = SiO (aq) + Zr(OH) -
4 2 2 5
-4
)
y We measured the solubilities
Baddeleyite
t -6
i
al Zircon
l of the assemblages
o
m
a
( “a” and “b.”
n -8 n
o o
ati ati
tr ur
n t
e a
c -10 s
n z
co Zr(OH)5- b art
r u
Z Q
g -12
o
l
-14
-4 -3 -2 -1 0 1 2
log Si concentration (molality)
Solubility diagram for the system ZrO -SiO -H O at 200°C and 1m NaOH calc. using
2 2 2
LLNL.dat of GWB (Bethke, 1996) and the stability constants of Adair et al. (1997).
pH Dependence of Solubility of Zircon + Baddeleyite
The solubility of the assemblage baddeleyite + zircon at 200°C as a function of pH,
calculated using LLNL.dat of GWB (Bethke, 1996) and stability constants of Adair et al.
(1997).
Zircon Solubility In Quartz-saturated Fluid
–8
25°C and 1 bar
–10
pressure,
thermodynamic
–12
Zircon
data from Adair
+
+2
)
H –14 et al. (1997)
O
(
r
Z
a –16

g
o +++
Zr(OH)
l

–18

-
Zr(OH)
5
++
Zr(OH)
2
–20
+
Zr(OH)
Zr3(OH) (aq)
4
25°C
–22
0 2 4 6 8 10 12 14
pH
ayersj Thu Apr 24 2003
Zircon Solubility In Quartz-saturated Fluid
0
–2
–4 25°C and 1 bar
–6
Zircon
pressure, default
–8
–10
LLNL thermodynamic
+
+2 –12
)
H
data from Naumov et
O –14
(
r
Z –16
al. (1974)
log a –––––––32222210864208 ZZZrrr((OOOHHH+))+++23++ Zr(OH)4(aq) 25°C ++, T = 25 °C , P = 1.013 bars, a [HO] = 1, a [Quartz] = 1Diagram Zr(OH)22
0 2 4 6 8 10 12 14
pH
berrios Mon Apr 28 2003
Methods
Quench Zr and Si leached from outer
capsule; leachate analyzed by ICP-MS.
Zir-003 (Z + B) Run Product Zircons
Zir-001 (Z + Q) Run Product Zircon
SM CL
SM BE
Zircon grains
250-500
microns in
diameter.
RP BE RP CL
Baddeleyite Crystals on Surface of Run
Product Zircon Grain