Partitioning of samarium and nickel between olivine, orthopyroxene, and liquid; preliminary data at 20 kbar and 1025°C

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Olivine (ol) and aluminous enstatite (opx) coexist with a hydrous liquid (liq) of haplobasaltic composition in the system Fo An 50Ab 50 SiO 2 H 2O at 20 kbar and 1025°C. Concentrations of Ni and Sm in these three phases have been determined by mapping β tracks in nuclear emulsions using 63Ni and 151Sm as sources of β particles. Partition coefficients defined as K i α−β = C i α/C i β (concentrations in ppm of i =Ni or Sm in phases α and β) have been determined for total Sm content of the system (ΣSm) ranging from 1.27 to about 100 ppm and for total Ni content (ΣNi) ranging from 10 to 3000 ppm. The K Sm ol-liq ranges from 0.027 ± 0.002 at ΣSm = 1.27 ppm (∼0.8 ppm Sm in ol) to 0.024 ± 0.001 at ΣSm = 20 ppm. At higher samarium concentrations, K Sm ol-liq decreases to about 0.016 ± 0.001atΣSm ≥ 100 ppm. The K Sm opx-liq equals 0.056 ± 0.002 at ΣSm ≤ 20 ppm. The partition coefficient decreases rapid to less than 0.020 at higher samarium contents. The K Ni ol-liq equals about 19 at ΣNi ≤ 200 ppm (≲1000 ppm in olivine) and then decreases to less than 5 at higher nickel contents of the system. The K Ni opx-liq behaves similarly, equaling ∼1.3 in the low-Ni range and 0.6 in the high-Ni range. The data demonstrate that the concentration range over which the partition coefficient is constant is wider for nickel than for samarium. Furthermore, for nickel the range is wider for the ol-liq pair than for the opx-liq pair. With samarium as the trace element, the range of the constant partition coefficient is approximately the same for both the ol-liq and the opx-liq pairs.