Abstract
The differences in FeO mantle contents and core masses between the terrestrial planets suggest the oxygen fugacity (fO2) during their differentiation likely varied significantly. The metal-silicate partitioning of siderophile (iron-loving) elements is a function of fO2 and of their valence state(s) in silicate melts. Silicon (Si) is known to partition into metal at low fO2 and has been proposed as a possible light element in the cores of Mercury and the aubrite parent body (AuPB). To systematically study the metal-silicate partitioning behavior of siderophile elements into Si-bearing metal, 69 high pressure (P) – temperature (T) metal-silicate partitioning experiments were performed under moderately to highly reducing conditions. Oxygen fugacities ranged between 1 and 7 units below the iron-wüstite buffer (ΔIW). Experimental pressures and temperatures ranged between 1 and 5 GPa and 1883 to 2273 K, respectively. A comparison of the ΔIW values and the fO2 based on the Si-SiO2 buffer (ΔSi-SiO2) indicates that the activity coefficient of FeO in silicate melts decreases significantly from reducing to highly reducing conditions under C-saturated conditions. It was found that at conditions more reducing than ΔIW = −3 to −4, the metal-silicate partitioning behavior of the majority of the siderophile elements deviates significantly from values corresponding to their expected valence state(s). These results indicate that the activity in metal of the elements considered, including that of Si itself, is decreased as a function of Si metal content, and a thermodynamic approach was used to quantify these effects. Interaction coefficients of trace elements in Si-bearing, Fe-rich alloys (εM Si) derived from the new experiments are in good agreement with previously proposed values at similar pressures below 5 GPa. However, εM Si values obtained for C-free systems decrease within the 1 to 11 GPa range, suggesting extrapolation of lower-pressure parameters may yield erroneous results at much higher pressures. Altogether, the new results provide an extensive experimental foundation for future studies of planetary differentiation under (highly) reduced conditions.
| Original language | English |
|---|---|
| Article number | 113391 |
| Pages (from-to) | 1-28 |
| Number of pages | 28 |
| Journal | Icarus |
| Volume | 335 |
| Early online date | 5 Aug 2019 |
| DOIs | |
| Publication status | Published - 1 Jan 2020 |
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Keywords
- Accretion
- Aubrites
- Core
- Mercury
- Metal-silicate
- Siderophile
Cite this
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Metal-silicate partitioning systematics of siderophile elements at reducing conditions : A new experimental database. / Steenstra, E. S.; Seegers, A. X.; Putter, R.; Berndt, J.; Klemme, S.; Matveev, S.; Bullock, E. S.; van Westrenen, W.
In: Icarus, Vol. 335, 113391, 01.01.2020, p. 1-28.Research output: Contribution to Journal › Article › Academic › peer-review
TY - JOUR
T1 - Metal-silicate partitioning systematics of siderophile elements at reducing conditions
T2 - A new experimental database
AU - Steenstra, E. S.
AU - Seegers, A. X.
AU - Putter, R.
AU - Berndt, J.
AU - Klemme, S.
AU - Matveev, S.
AU - Bullock, E. S.
AU - van Westrenen, W.
PY - 2020/1/1
Y1 - 2020/1/1
N2 - The differences in FeO mantle contents and core masses between the terrestrial planets suggest the oxygen fugacity (fO2) during their differentiation likely varied significantly. The metal-silicate partitioning of siderophile (iron-loving) elements is a function of fO2 and of their valence state(s) in silicate melts. Silicon (Si) is known to partition into metal at low fO2 and has been proposed as a possible light element in the cores of Mercury and the aubrite parent body (AuPB). To systematically study the metal-silicate partitioning behavior of siderophile elements into Si-bearing metal, 69 high pressure (P) – temperature (T) metal-silicate partitioning experiments were performed under moderately to highly reducing conditions. Oxygen fugacities ranged between 1 and 7 units below the iron-wüstite buffer (ΔIW). Experimental pressures and temperatures ranged between 1 and 5 GPa and 1883 to 2273 K, respectively. A comparison of the ΔIW values and the fO2 based on the Si-SiO2 buffer (ΔSi-SiO2) indicates that the activity coefficient of FeO in silicate melts decreases significantly from reducing to highly reducing conditions under C-saturated conditions. It was found that at conditions more reducing than ΔIW = −3 to −4, the metal-silicate partitioning behavior of the majority of the siderophile elements deviates significantly from values corresponding to their expected valence state(s). These results indicate that the activity in metal of the elements considered, including that of Si itself, is decreased as a function of Si metal content, and a thermodynamic approach was used to quantify these effects. Interaction coefficients of trace elements in Si-bearing, Fe-rich alloys (εM Si) derived from the new experiments are in good agreement with previously proposed values at similar pressures below 5 GPa. However, εM Si values obtained for C-free systems decrease within the 1 to 11 GPa range, suggesting extrapolation of lower-pressure parameters may yield erroneous results at much higher pressures. Altogether, the new results provide an extensive experimental foundation for future studies of planetary differentiation under (highly) reduced conditions.
AB - The differences in FeO mantle contents and core masses between the terrestrial planets suggest the oxygen fugacity (fO2) during their differentiation likely varied significantly. The metal-silicate partitioning of siderophile (iron-loving) elements is a function of fO2 and of their valence state(s) in silicate melts. Silicon (Si) is known to partition into metal at low fO2 and has been proposed as a possible light element in the cores of Mercury and the aubrite parent body (AuPB). To systematically study the metal-silicate partitioning behavior of siderophile elements into Si-bearing metal, 69 high pressure (P) – temperature (T) metal-silicate partitioning experiments were performed under moderately to highly reducing conditions. Oxygen fugacities ranged between 1 and 7 units below the iron-wüstite buffer (ΔIW). Experimental pressures and temperatures ranged between 1 and 5 GPa and 1883 to 2273 K, respectively. A comparison of the ΔIW values and the fO2 based on the Si-SiO2 buffer (ΔSi-SiO2) indicates that the activity coefficient of FeO in silicate melts decreases significantly from reducing to highly reducing conditions under C-saturated conditions. It was found that at conditions more reducing than ΔIW = −3 to −4, the metal-silicate partitioning behavior of the majority of the siderophile elements deviates significantly from values corresponding to their expected valence state(s). These results indicate that the activity in metal of the elements considered, including that of Si itself, is decreased as a function of Si metal content, and a thermodynamic approach was used to quantify these effects. Interaction coefficients of trace elements in Si-bearing, Fe-rich alloys (εM Si) derived from the new experiments are in good agreement with previously proposed values at similar pressures below 5 GPa. However, εM Si values obtained for C-free systems decrease within the 1 to 11 GPa range, suggesting extrapolation of lower-pressure parameters may yield erroneous results at much higher pressures. Altogether, the new results provide an extensive experimental foundation for future studies of planetary differentiation under (highly) reduced conditions.
KW - Accretion
KW - Aubrites
KW - Core
KW - Mercury
KW - Metal-silicate
KW - Siderophile
UR - http://www.scopus.com/inward/record.url?scp=85070408941&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85070408941&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2019.113391
DO - 10.1016/j.icarus.2019.113391
M3 - Article
VL - 335
SP - 1
EP - 28
JO - Icarus
JF - Icarus
SN - 0019-1035
M1 - 113391
ER -