Trace Element Partitioning between CAI-Type Melts and Grossite, Melilite, Hibonite, and Olivine

1,2Gokce Ustunisik,2,3Denton S.Ebel,3,2David Walker,4,1Roger L.Nielsen,3,2Marina Gemma
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.038]
1Department of Geology and Geological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, 57701
2Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, 10024-5192
3Department of Earth and Environmental Sciences, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY, 10964-8000
4104 CEOAS Admin, College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331
Copyright Elsevier

We determined the mineral-melt partition coefficients (Di’s) and the compositional and/or temperature dependency between grossite, melilite, hibonite, olivine and Ca-, Al-inclusion (CAI)-type liquids for a number of light (LE), high field strength (HFSE), large ion lithophile (LILE), and rare earth (REE) elements including Li, Be, B, Sr, Zr, Nb, Ba, La, Ce, Eu, Dy, Ho, Yb, Hf, Ta, Th. A series of isothermal crystallization experiments was conducted at 5 kbar pressure and IW+1 in graphite capsules. The starting compositions were selected based on the calculated and experimentally confirmed phase relations during condensation in CI dust-enriched systems (Ebel and Grossman, 2000, Ebel, 2006, Ustunisik et al., 2014).

The partition coefficients between melt and gehlenite, hibonite, and grossite show that the trace element budget of igneous CAIs is controlled by these three major Al-bearing phases in addition to pyroxene. In general, LE, LILE, REE, and HFSE partition coefficients (by mass) decrease in the order of Gehlenite-MeltDi > Hibonite-MeltDi > Grossite-MeltDi. The partition coefficients between gehlenitic melilite and CAI melt are approximately Be:0.14, B:0.07, Sr:0.79, Zr:0.02, Nb:0.01-0.02, Ba:0.05, La:1.03-3.44, Ce:1.2-3.86, Eu:1.19-2.88, Dy:1.14-3.23, Ho:1.04-2.91, Yb:0.7-1.70, Hf:0.02, Ta:0.01-0.02, Th:0.31-1.71. These results suggest that Gehlenite-MeltDi vary by a factor of 2-3 in different melt compositions at the same T (∼1500 oC). Hibonite-MeltDi exhibit a range as Be:0.02-0.04, B:0.01, Sr:0.21-0.66, Zr:0.02-0.18, Nb:0.03-0.05, Ba:0.02-0.06, La:0.56-4.38, Ce:0.52-3.54, Eu: 0.33-0.84, Dy: 0.25-0.32, Ho:0.17-0.29, Yb:0.05-0.19, Hf:0.05-0.38, Ta:0.02, Th:0.31-1.71. Increased Al and Ca, relative to earlier work, increases the compatibility of Gehlenite-MeltDi , and also the compatibility of Hibonite-MeltDi, especially for La and Ce.Grossite-MeltDi of individual mineral-melt pairs are Be:0.43, Sr:0.31, Zr:0.09, Nb:0.01, Ba:0.03, La:0.06, Ce:0.07, Eu:0.13, Dy:0.04, Ho:0.04, Yb:0.03, Hf:0.01, Ta:0.01, Th:0.01 for #18 at 1550 oC and as Sr:0.29, Nb:0.03, La:0.07, Ce:0.09, Eu:0.10, Dy:0.05, Ho:0.04, Yb:0.02, Hf:0.003, Ta:0.02, Th:0.02 for #7 at 1490 oC.

Olivine partitioning experiments confirm that olivine contribution to the trace element budget of CAIs is small due to the low Olivine-MeltDi at a range of temperatures while Olivine-MeltDEu, Yb are sensitive to changes in T and fO2. The development of a predictive model for partitioning in CAI-type systems would require more experimental data and use of analytical instruments capable of obtaining single phase analyses for crystals < 5µm.

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