TY - JOUR
T1 - Experimental and computational study of trace element distribution between orthopyroxene and anhydrous silicate melt: substitution mechanisms and the effect of iron
AU - van Kan Parker, Mirjam
AU - Liebscher, Axel
AU - Frei, Dirk
AU - van Sijl, Jelle
AU - van Westrenen, Wim
AU - Blundy, Jon
AU - Franz, Gerhard
N1 - Funding Information:
Acknowledgments We would like to thank Alex Corgne and Tre-vor Green for their comments and suggestions, which significantly improved the manuscript. We thank Stu Parker for useful comments. This work was supported by a EURYI award to WvW. DF and GF thank the DFG for supporting this work by grant number FR 557/17-1 to GF. All experimental work presented here was carried out at the University of Bristol at the Large Scale Geochemical Facility supported by the European Community—Access to Research Infrastructure Action of Improving Human Potential Programme (contract number HPRI-CT-1999-00008 awarded to Prof. B.J. Wood) which is gratefully acknowledged. DF and JB greatly acknowledge access to the NSS Edinburgh ion microprobe facility granted by NERC. We are indebted to John Craven and Richard Hinton for their efforts and help with ion microprobe analysis, and to Oona Appelt (GFZ Potsdam) and Berit Wenzel (University of Copenhagen) for their help with the EMPA. This paper is published with the permission of the Geological Survey of Denmark and Greenland.
PY - 2010/4
Y1 - 2010/4
N2 - Although orthopyroxene (Opx) is present during a wide range of magmatic
differentiation processes in the terrestrial and lunar mantle, its
effect on melt trace element contents is not well quantified. We present
results of a combined experimental and computational study of trace
element partitioning between Opx and anhydrous silicate melts.
Experiments were performed in air at atmospheric pressure and
temperatures ranging from 1,326 to 1,420°C in the system CaO–MgO–Al2O3–SiO2 and subsystem CaO–MgO–SiO2.
We provide experimental partition coefficients for a wide range of
trace elements (large ion lithophile: Li, Be, B, K, Rb, Sr, Cs, Ba, Th,
U; rare earth elements, REE: La, Ce, Nd, Sm, Y, Yb, Lu; high field
strength: Zr, Nb, Hf, Ta, Ti; transition metals: Sc, V, Cr, Co) for use
in petrogenetic modelling. REE partition coefficients increase from DOpx-meltLa∼0.0005 to DOpx-meltLu∼0.109, D values for highly charged elements vary from DOpx-meltTh∼0.0026 through DOpx-meltNb∼0.0033 and DOpx-meltU∼0.0066 to DOpx-meltTi∼0.058,
and are all virtually independent of temperature. Cr and Co are the
only compatible trace elements at the studied conditions. To elucidate
charge-balancing mechanisms for incorporation of REE into Opx and to
assess the possible influence of Fe on Opx-melt partitioning, we compare
our experimental results with computer simulations. In these
simulations, we examine major and minor trace element incorporation into
the end-members enstatite (Mg2Si2O6) and ferrosilite (Fe2Si2O6). Calculated solution energies show that R2+ cations are more soluble in Opx than R3+ cations of similar size, consistent with experimental partitioning data. In addition, simulations show charge balancing of R3+ cations by coupled substitution with Li+
on the M1 site that is energetically favoured over coupled substitution
involving Al–Si exchange on the tetrahedrally coordinated site. We
derived best-fit values for ideal ionic radii r
0, maximum partition coefficients D
0, and apparent Young’s moduli E for substitutions onto the Opx M1 and M2 sites. Experimental r
0 values for R3+ substitutions are 0.66–0.67 Å for M1 and 0.82–0.87 Å for M2. Simulations for enstatite result in r
0 = 0.71–0.73 Å for M1 and ~0.79–0.87 Å for M2. Ferrosilite r
0 values are systematically larger by
~0.05 Å for both M1 and M2. The latter is opposite to experimental
literature data, which appear to show a slight decrease in rM20
in the presence of Fe. Additional systematic studies in Fe-bearing
systems are required to resolve this inconsistency and to develop
predictive Opx-melt partitioning models for use in terrestrial and lunar
magmatic differentiation models.
AB - Although orthopyroxene (Opx) is present during a wide range of magmatic
differentiation processes in the terrestrial and lunar mantle, its
effect on melt trace element contents is not well quantified. We present
results of a combined experimental and computational study of trace
element partitioning between Opx and anhydrous silicate melts.
Experiments were performed in air at atmospheric pressure and
temperatures ranging from 1,326 to 1,420°C in the system CaO–MgO–Al2O3–SiO2 and subsystem CaO–MgO–SiO2.
We provide experimental partition coefficients for a wide range of
trace elements (large ion lithophile: Li, Be, B, K, Rb, Sr, Cs, Ba, Th,
U; rare earth elements, REE: La, Ce, Nd, Sm, Y, Yb, Lu; high field
strength: Zr, Nb, Hf, Ta, Ti; transition metals: Sc, V, Cr, Co) for use
in petrogenetic modelling. REE partition coefficients increase from DOpx-meltLa∼0.0005 to DOpx-meltLu∼0.109, D values for highly charged elements vary from DOpx-meltTh∼0.0026 through DOpx-meltNb∼0.0033 and DOpx-meltU∼0.0066 to DOpx-meltTi∼0.058,
and are all virtually independent of temperature. Cr and Co are the
only compatible trace elements at the studied conditions. To elucidate
charge-balancing mechanisms for incorporation of REE into Opx and to
assess the possible influence of Fe on Opx-melt partitioning, we compare
our experimental results with computer simulations. In these
simulations, we examine major and minor trace element incorporation into
the end-members enstatite (Mg2Si2O6) and ferrosilite (Fe2Si2O6). Calculated solution energies show that R2+ cations are more soluble in Opx than R3+ cations of similar size, consistent with experimental partitioning data. In addition, simulations show charge balancing of R3+ cations by coupled substitution with Li+
on the M1 site that is energetically favoured over coupled substitution
involving Al–Si exchange on the tetrahedrally coordinated site. We
derived best-fit values for ideal ionic radii r
0, maximum partition coefficients D
0, and apparent Young’s moduli E for substitutions onto the Opx M1 and M2 sites. Experimental r
0 values for R3+ substitutions are 0.66–0.67 Å for M1 and 0.82–0.87 Å for M2. Simulations for enstatite result in r
0 = 0.71–0.73 Å for M1 and ~0.79–0.87 Å for M2. Ferrosilite r
0 values are systematically larger by
~0.05 Å for both M1 and M2. The latter is opposite to experimental
literature data, which appear to show a slight decrease in rM20
in the presence of Fe. Additional systematic studies in Fe-bearing
systems are required to resolve this inconsistency and to develop
predictive Opx-melt partitioning models for use in terrestrial and lunar
magmatic differentiation models.
KW - Computer simulations
KW - Experimental determination
KW - Orthopyroxene
KW - Partition coefficient
KW - Substitution mechanisms
UR - http://www.scopus.com/inward/record.url?scp=77952240740&partnerID=8YFLogxK
U2 - 10.1007/s00410-009-0435-0
DO - 10.1007/s00410-009-0435-0
M3 - Article
SN - 0010-7999
VL - 159
SP - 459
EP - 473
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 4
ER -