TY - JOUR
T1 - High Pressure Experiments on Metal-Silicate Partitioning of Chlorine in a Magma Ocean
T2 - Implications for Terrestrial Chlorine Depletion
AU - Kuwahara, Hideharu
AU - Gotou, Hirotada
AU - Shinmei, Toru
AU - Ogawa, Nobuhiro
AU - Yamaguchi, Asuka
AU - Takahata, Naoto
AU - Sano, Yuji
AU - Yagi, Takehiko
AU - Sugita, Seiji
N1 - Funding Information:
The data for this study are available in Tables within the manuscript. H.K. is grateful to the members of Geodynamics Research Center at Ehime University for their technical assistance on high-pressure experiments and helpful discussions of the results, and Hajime Hiyagon and Takanori Kagoshima for their helpful comments on NanoSIMS analysis. We are also grateful to K. P. Jochum for providing terrestrial basaltic glass standards. The part of the research was carried out under the Visiting Researcher’s Program of Geodynamics Research Center, Ehime University. We would like to thank Renbiao Tao and an anonymous reviewer for helpful comments. The research was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant 26247092, 15J06330, and 15H05830) and Core-to-Core program ‘‘International Network of Planetary Sciences.’’
Publisher Copyright:
© 2017. American Geophysical Union. All Rights Reserved.
PY - 2017/11
Y1 - 2017/11
N2 - In the bulk silicate Earth, chlorine is more depleted than other elements with similar volatilities; however, the cause of terrestrial chlorine depletion is not well understood. Two major hypotheses have been proposed to explain this depletion: Incorporation into the Earth's metallic core and escape to space. The former hypothesis can be tested by investigating the partitioning of chlorine between iron-rich metallic liquids and silicate melts. In this study, we investigated the experimental partitioning of chlorine between iron-rich metallic liquids and silicate melts at pressures from 4 to 23 GPa and temperatures from 1,650 to 2,400°C using multi-anvil presses. The results demonstrate that chlorine is moderately to highly lithophile under the experimental conditions. In sulfur-free experiments, chlorine becomes slightly more siderophile as temperature increases and less siderophile as pressure increases. For sulfur-bearing experiments, no significant effects of pressure or temperature were observed. Based on these data and thermodynamic considerations, we obtained empirical laws to estimate chlorine partition coefficients between iron-rich metallic liquids and silicate melts. Under the P-T conditions that would have controlled metal-silicate equilibration during core segregation in the Earth, the calculated metal-silicate partition coefficients for chlorine are much lower than unity. This result suggests that terrestrial chlorine that may have been present in the accreting Earth was not partitioned into its core, supporting that escape to space is the more likely hypothesis. If terrestrial chlorine was lost to space, chlorine depletion may have resulted from the loss of the primordial hydrosphere during the formation of the Earth.
AB - In the bulk silicate Earth, chlorine is more depleted than other elements with similar volatilities; however, the cause of terrestrial chlorine depletion is not well understood. Two major hypotheses have been proposed to explain this depletion: Incorporation into the Earth's metallic core and escape to space. The former hypothesis can be tested by investigating the partitioning of chlorine between iron-rich metallic liquids and silicate melts. In this study, we investigated the experimental partitioning of chlorine between iron-rich metallic liquids and silicate melts at pressures from 4 to 23 GPa and temperatures from 1,650 to 2,400°C using multi-anvil presses. The results demonstrate that chlorine is moderately to highly lithophile under the experimental conditions. In sulfur-free experiments, chlorine becomes slightly more siderophile as temperature increases and less siderophile as pressure increases. For sulfur-bearing experiments, no significant effects of pressure or temperature were observed. Based on these data and thermodynamic considerations, we obtained empirical laws to estimate chlorine partition coefficients between iron-rich metallic liquids and silicate melts. Under the P-T conditions that would have controlled metal-silicate equilibration during core segregation in the Earth, the calculated metal-silicate partition coefficients for chlorine are much lower than unity. This result suggests that terrestrial chlorine that may have been present in the accreting Earth was not partitioned into its core, supporting that escape to space is the more likely hypothesis. If terrestrial chlorine was lost to space, chlorine depletion may have resulted from the loss of the primordial hydrosphere during the formation of the Earth.
KW - chlorine
KW - core
KW - magma ocean
UR - http://www.scopus.com/inward/record.url?scp=85038370830&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85038370830&partnerID=8YFLogxK
U2 - 10.1002/2017GC007159
DO - 10.1002/2017GC007159
M3 - Article
AN - SCOPUS:85038370830
VL - 18
SP - 3929
EP - 3945
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
SN - 1525-2027
IS - 11
ER -