terrestrial magmatism covers 8 orders of magnitude oxygen fugacity
DESCRIPTION
Terrestrial magmatism covers 8 orders of magnitude oxygen fugacity. from Carmichael (1991). Compiled from work of O’Neill, Pownceby, Holzheid and others. Chondritic metals become Co- and Ni-poor and Fe-rich Chondritic silicates become Fe-, Ni-, Co-poor. from Arculus et al. (1990). - PowerPoint PPT PresentationTRANSCRIPT
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0.0005 0.0006 0.0007 0.0008 0.0009 0.0011/T (K)
Pd-PdOIr-IrO2Rh-Rh2O3Os-OsO2Ru-RuO2HMCu-Cu2OMnO-Mn3O4Re-ReO2Ni-NiOFMQCo-CoOW-WO2Fe-FeOFQICr-Cr2O3
1400 130012001100 1000 900 800
Compiled from work of O’Neill, Pownceby, Holzheid and others
Chondritic metals become Co- and Ni-poor and Fe-richChondritic silicates become Fe-, Ni-, Co-poor
from Arculus et al. (1990)
Olivine composition changes with oxygen fugacity such that it has an enormous stability field that depends upon equilibria with Fe metal and Fe oxide
2Fe3O4 + 3SiO2 = 3Fe2SiO4 + O2
FeSiO3 + Fe + ½ O2 = Fe2SiO4
from Nitsan (1974)
from Buening and Buseck (1973) from Chakraborty et al. (2004)
Diffusion of major, minor and trace elements in crystalline solids is strongly dependent upon oxygen fugacity
Five different approaches in high pressure research
A) Sliding sensors (Taylor et al. 1992; Rubie et al., 1993)
B) Sample composition helps to set fO2 (Rubie, 1999)
C) Fluid or buffer in capsule (King et al. 2000)
D) Capsule imposes fO2 (Frost et al. 2004)
E) Assembly imposed (COMPRES development?) (Dobson and Brodholt, 1999)
Respond to fO2 of environment and record in either metal or oxide solid solution
Problems:Cannot really control fO2 using this approach, but at least it can be known
from Taylor et al. (1992)
A) Sliding sensors
A) Sliding sensors
Fe2SiO4 = 2Fe + SiO2 + O2
Ni2SiO4 = 2Ni + SiO2 + O2
Mg2SiO4 + SiO2 = Mg2Si2O6
from Rubie et al. (1993)
fO2 calculated from td and a-x data.
B) Sample composition participates
from Rubie (1999)
Si:Fe ratio in metal of metal/silicate experiments was varied to vary the fO2 imposed upon sample
Problems: Si in metal causes non-ideal behavior and therefore potentially not natural
C) Fluid or buffer in capsule
from Holloway et al. (1992); Pawley et al. (1992); King et al. (2000)
CO2 or O2 sources have been used to fix fO2 in capsules
Problems: -C migration into Pt and reduction over time- fluids dissolve into other phases
C) Fluid or buffer in capsule
from Rubie (1999)
Ni-NiO mix has been used to fix fO2 in capsules
Problems: NiPt alloying
D) Capsule imposed
Re capsules have been used to carry out experiments at higher fO2, because Re-ReO2 buffer is much higher than IW or QFM
Problems: buffer never verified and buffer can react with sample
from Frost et al. (2004)
D) Capsule imposed
from Arculus et al. (1990)
Graphite capsules can be used to buffer oxygen fugacity
C-CO-CO2 is below IW at 1 bar, but is very pressure sensitive
At 10 kb 3 log units higher…..
D) Capsule imposed
from LaTourette and Holloway (1994)
……by 80 kb, oxygen fugacity is buffered about 6 log fO2 units above that of 1 bar
from Luth (1993)
Diamond can also participate in buffering equilibria, but its hardness becomes a problem for later sample preparation –
grinding and polishing
Best approach?
Buffer is in pressure medium
Advantages:- Long lasting- Doesn’t react with sample
from Dobson and Brodholt (1999)
E) Pressure medium imposed
Castable octahedragasket and pressure medium are the same
(Dobson and Brodholt, 1999)=> high failure rate
Ni-, Fe-, Re-doped pressure medium – cast or injection molded?
Pre-cast with spacersgasket and pressure medium are different
(maybe an area for COMPRES development??)=> lower failure rate ?
3 short 1 short, 2 long 3 long2 short, 1 long
4 cubes with teflon and pyrophyllite spacers
4 cubes with balsa wood spacers
strips ofteflon tape
Hybrid ?