Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.
It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.
Münker
Carsten
C
Institut für Mineralogie, Corrensstrasse 24, Universität Münster, 48149 Münster, Germany. muenker@nwz.uni-muenster.de
Pfänder
Jörg A
JA
Weyer
Stefan
S
Büchl
Anette
A
Kleine
Thorsten
T
Mezger
Klaus
K
D018534:Earth, Planet; D019419:Evolution, Planetary; D019015:Geologic Sediments / Q000737:chemistry; D006195:Hafnium / Q000032:analysis; D018535:Mars; D019110:Meteoroids; D018543:Minor Planets; D016081:Moon; D009556:Niobium / Q000032:analysis; D017640:Silicates; D013635:Tantalum / Q000032:analysis; D015040:Zirconium / Q000032:analysis
D017640:Silicates; D009556:Niobium; D013635:Tantalum; D015040:Zirconium; D006195:Hafnium