Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.v13d1594j&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #V13D-1594
Other
1012 Reactions And Phase Equilibria (3612, 8412), 3640 Igneous Petrology, 5410 Composition (1060, 3672), 8412 Reactions And Phase Equilibria (1012, 3612)
Scientific paper
Ni is of particular interest because it is the most compatible cation in olivine at basaltic conditions. However, models of lunar magma ocean petrogenesis have suggested that at high temperatures and pressures Ni behaves incompatibly (Longhi and Walker 2006). Their conclusions rely on a partitioning model that was developed mainly using terrestrial studies (Jones 1984). Therefore, this study addresses whether the partitioning model (Jones 1984) can be extrapolated into planetary compositions at high temperature and pressure. It also investigates the effect of Ni on phase relations of a Martian basalt. The Martian basalt, Humphrey, was chosen because it has been studied in the absence of Ni, providing a baseline for the addition of Ni (Filiberto and Treiman 2007). Experiments were conducted using a piston cylinder apparatus on a synthetic, anhydrous, Humphrey composition + NiO at near liquidus Martian mantle pressures and temperatures. Experimental run products were analyzed by EMP and partition coefficients between olivine and melt were calculated for all samples. Although DNiol-liq determined for the Humphrey composition is always >>1 (Ni is always strongly compatible with olivine), it does match predicted values by Jones' model. Additionally, as suggested by Jones (1984), this correlation is independent of temperature and pressure. The success of the model in predicting DNiol-liq values in a Martian system is evidence that Jones' model can be applied to other planetary systems, such as the Moon; however the validity of extrapolating into ultra-mafic systems has not been fully addressed. The addition of small amounts of NiO (<< 1wt %) to the Humphrey basalt has drastic effects on the liquidus phase relations raising the olivine saturated liquidus 25 degrees. Due to NiO's greater stability in olivine's crystal structure, NiO stabilizes olivine to higher temperatures. The addition of NiO did not, however, change the location of the pigeonite-in phase boundary. This result is consistent with the near neutral partitioning of Ni and Mg into pigeonite. Therefore, the implied multiple saturation point is shifted 3 kbar higher (15.5 kbar) when compared to a nickel free system as a result of the higher temperature liquidus and the unaltered slope of the pigeonite-in line.
Filiberto Justin
Jackson Charles
Le Linh
Treiman Allan
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