HR: 0800h
AN: V41C-1410    [Abstracts]
TI: Extending Fe-Mg Olivine-liquid Partitioning to Picritic Compositions at One Atmosphere
AU: * Matzen, A
EM: andrew-matzen@tulsa.edu
AF: Dept. of Geosciences, Univ. of Tulsa 600 S. College Ave., Tulsa, OK 74104 United States
AU: Baker, M
EM: mikeb@gps.caltech.edu
AF: Div. of Geol. & Planet. Sci., Caltech, Pasadena, CA 91125 United States
AU: Beckett, J
EM: john@gps.caltech.edu
AF: Div. of Geol. & Planet. Sci., Caltech, Pasadena, CA 91125 United States
AB: Iron-magnesium partitioning between olivine and silicate melt exerts a fundamental control on the FeO and MgO contents of olivine-saturated liquids undergoing low-pressure fractionation as well as the compositions of liquids produced during partial melting of peridotite. Surprisingly, very little low-pressure olivine-liquid experimental data has been published on natural melt compositions with $>$ 16 wt% MgO. Results from high-pressure experiments [1] are scattered but they hint at an increasing value of the exchange coefficient, K$_{D}$=(FeO/MgO)$^{ol}$/(FeO/MgO)$^{liq}$, as melt MgO contents increase from 20 to 30 wt%; the K$_{D}$ values increase by as much as 30% relative over this range. Whether one uses K$_{D}$ = 0.30 or 0.38 has a dramatic effect on the compositions of reconstructed primary magmas, and it is therefore of interest to better determine the appropriate value(s). We conducted one-atmosphere experiments on a synthetic, alkali-free, Hawaiian picrite composition (25.7 wt% MgO, 45.7 wt% SiO$_{2}$) at QFM and temperatures ranging from $1300\deg$-$1500\deg$C. Samples were suspended on pre-saturated Pt-Fe wire loops and quenched after $\sim$12 to 72 hours. Time series experiments were conducted at $1300\deg$ and $1450\deg$C. Melt and olivine are present in all experiments; chrome spinel occurs in the $1300\deg$ and $1350\deg$C experiments. Over the temperature range investigated, wt% MgO in the glass varies from 13.4 to 23.8, while olivine forsterite contents increases from 88 to 92 (mole%). The weight fraction of glass shows a strong positive linear correlation with temperature, while the weight fraction of olivine is inversely correlated with temperature. The K$_{D}$ values calculated from the olivine-liquid pairs (after first calculating liquid FeO/Fe$_{2}$O$_{3}$ using [2]), are independent of temperature and melt composition (the mean value is 0.32$\pm$0.01, 1 sigma). Our mean value is the same as that calculated by [3] from a large body of lower temperature one-atmosphere experiments from the literature, and supports the results of the olivine-addition calculations on Mauna Kea glasses reported in [3]. [1] Kushiro & Walter (1998) Geophys. Res. Letters 25, 2337-2340. [2] Kress & Carmichael (1991) Contrib. Mineral. Petrol. 108, 82-92. [3] Stolper et al. (2004) GGG 5, doi 10.1029/2003GC000553.
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 3655 Major element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting