EXPERIMENTAL PARTITIONING OF ZR, NB, AND TI BETWEEN PLATINUM-GROUP METALS AND SILICATE LIQUIDIMPLICATIONS FOR THE ORIGIN OF REFRACTORY-METAL NUGGETS IN CARBONACEOUS CHONDRITES
Reports of percent level concentrations of normally lithophile elements
such as Zr, Nb, and Ta in some refractory noble metal nuggets in
CAIs raise important questions about the redox state of the early
solar nebula. Consequently, we have determined the metal/silicate
liquid partition coefficients for Zr, Nb, and Ti at 1548 K and solar
oxygen fugacity (fo(2) similar to 10(-16) bar). In most experiments,
these elements formed intermetallic compounds with Pt-metal. Even
though our partition coefficients for Zr (2.06-4.55) were substantially
greater than previously determined values, they are still too small
to account for percent levels of Zr in a refractory metal nugget
from an average CAI. In addition, partition coefficient values obtained
for Nb and Ti show an extremely strong affinity for the metal phase.
Yet, Nb, is rarely observed in refractory metal nuggets and Ti has
never been observed. Given the abundance of Ti in CAIs, substantial
concentrations of Ti should be present in refractory metal nuggets.
This discrepancy is attributed to either: (1) the solar fo(2) was
too oxidizing during condensation to form the predicted intermetallic
compounds; or (2) the lithophile elements originally formed intermetallic
compounds with Pt-metals during condensation in the solar nebula
but were subsequently oxidized in a latter heating event. Whereas
our experiments suggest that conditions were never reducing enough
for Ti to alloy with Pt metal, other redox determinations (e.g. Ti3+/Ti4+
ratios in CAI) imply approximately solar oxygen fugacities. Our experiments
serve to emphasize the range in redox states implied by metal and
silicate assemblages in CAI.
%0 Journal Article
%1 JUREWICZ1995
%A JUREWICZ, S. R.
%A JONES, J. H.
%A FEGLEY, B.
%D 1995
%J Earth and Planetary Science Letters
%K ALLENDE ASSEMBLAGES; CA,AL-RICH CHEMISTRY; CONDENSATION; ELEMENTS INCLUSION; INCLUSIONS; METEORITE; NEBULA; OPAQUE PROPERTIES; RICH SOLAR SYSTEMS; TEMPERATURE THERMODYNAMIC
%N 1-4
%P 183--198
%T EXPERIMENTAL PARTITIONING OF ZR, NB, AND TI BETWEEN PLATINUM-GROUP METALS AND SILICATE LIQUIDIMPLICATIONS FOR THE ORIGIN OF REFRACTORY-METAL NUGGETS IN CARBONACEOUS CHONDRITES
%V 132
%X Reports of percent level concentrations of normally lithophile elements
such as Zr, Nb, and Ta in some refractory noble metal nuggets in
CAIs raise important questions about the redox state of the early
solar nebula. Consequently, we have determined the metal/silicate
liquid partition coefficients for Zr, Nb, and Ti at 1548 K and solar
oxygen fugacity (fo(2) similar to 10(-16) bar). In most experiments,
these elements formed intermetallic compounds with Pt-metal. Even
though our partition coefficients for Zr (2.06-4.55) were substantially
greater than previously determined values, they are still too small
to account for percent levels of Zr in a refractory metal nugget
from an average CAI. In addition, partition coefficient values obtained
for Nb and Ti show an extremely strong affinity for the metal phase.
Yet, Nb, is rarely observed in refractory metal nuggets and Ti has
never been observed. Given the abundance of Ti in CAIs, substantial
concentrations of Ti should be present in refractory metal nuggets.
This discrepancy is attributed to either: (1) the solar fo(2) was
too oxidizing during condensation to form the predicted intermetallic
compounds; or (2) the lithophile elements originally formed intermetallic
compounds with Pt-metals during condensation in the solar nebula
but were subsequently oxidized in a latter heating event. Whereas
our experiments suggest that conditions were never reducing enough
for Ti to alloy with Pt metal, other redox determinations (e.g. Ti3+/Ti4+
ratios in CAI) imply approximately solar oxygen fugacities. Our experiments
serve to emphasize the range in redox states implied by metal and
silicate assemblages in CAI.
@article{JUREWICZ1995,
abstract = {Reports of percent level concentrations of normally lithophile elements
such as Zr, Nb, and Ta in some refractory noble metal nuggets in
CAIs raise important questions about the redox state of the early
solar nebula. Consequently, we have determined the metal/silicate
liquid partition coefficients for Zr, Nb, and Ti at 1548 K and solar
oxygen fugacity (fo(2) similar to 10(-16) bar). In most experiments,
these elements formed intermetallic compounds with Pt-metal. Even
though our partition coefficients for Zr (2.06-4.55) were substantially
greater than previously determined values, they are still too small
to account for percent levels of Zr in a refractory metal nugget
from an average CAI. In addition, partition coefficient values obtained
for Nb and Ti show an extremely strong affinity for the metal phase.
Yet, Nb, is rarely observed in refractory metal nuggets and Ti has
never been observed. Given the abundance of Ti in CAIs, substantial
concentrations of Ti should be present in refractory metal nuggets.
This discrepancy is attributed to either: (1) the solar fo(2) was
too oxidizing during condensation to form the predicted intermetallic
compounds; or (2) the lithophile elements originally formed intermetallic
compounds with Pt-metals during condensation in the solar nebula
but were subsequently oxidized in a latter heating event. Whereas
our experiments suggest that conditions were never reducing enough
for Ti to alloy with Pt metal, other redox determinations (e.g. Ti3+/Ti4+
ratios in CAI) imply approximately solar oxygen fugacities. Our experiments
serve to emphasize the range in redox states implied by metal and
silicate assemblages in CAI.},
added-at = {2009-11-03T20:21:25.000+0100},
author = {JUREWICZ, S. R. and JONES, J. H. and FEGLEY, B.},
biburl = {https://www.bibsonomy.org/bibtex/29d3ee062e29ebc477af66efc8bb08090/svance},
interhash = {49602484783ce4d10826d9f0d869a9b4},
intrahash = {9d3ee062e29ebc477af66efc8bb08090},
journal = {Earth and Planetary Science Letters},
keywords = {ALLENDE ASSEMBLAGES; CA,AL-RICH CHEMISTRY; CONDENSATION; ELEMENTS INCLUSION; INCLUSIONS; METEORITE; NEBULA; OPAQUE PROPERTIES; RICH SOLAR SYSTEMS; TEMPERATURE THERMODYNAMIC},
number = {1-4},
owner = {svance},
pages = {183--198},
timestamp = {2009-11-03T20:21:53.000+0100},
title = {EXPERIMENTAL PARTITIONING OF ZR, NB, AND TI BETWEEN PLATINUM-GROUP METALS AND SILICATE LIQUIDIMPLICATIONS FOR THE ORIGIN OF REFRACTORY-METAL NUGGETS IN CARBONACEOUS CHONDRITES},
volume = 132,
year = 1995
}