Experimental determination of ferric iron partitioning between pyroxene and melt at 100 kPa

Pyroxene is the principal host of Fe 3+ in basalt source regions, hosting 79 and 81% spinel garnet lherzolite, respectively. In peridotite, orthopyroxene (opx) clinopyroxene (cpx) 48% 31%, respectively, total . Yet relationship between mantle mineralogy, pyroxene chemistry, oxygen fugacity ( f O2 ) recorded by mantle-derived basalts remains unclear. To better understand partitioning melt we conducted experiments at 100 kPa with controlled CO-CO 2 gas mixes ∆QFM −1.19 to +2.06 a system containing andesitic saturated opx or cpx only. produce large (100–150 μm), homogeneous pyroxenes, employed dynamic cooling technique 5–10 °C/h rate, initial final dwell temperatures °C 20–30 super sub-liquidus, Resulting crystals have absolute variation Al O 3 TiO < 0.05 wt% 0.02 wt%, /Fe T pyroxenes quenched glass were measured K -edge XANES. We used newly developed XANES calibration for selecting spectra X-rays vibrating on optic axial plane 45 ± 5° crystallographic c axis. Values D Fe3+ cpx/melt increase from 0.03 0.53 as increases −0.44 +2.06, while opx/melt unchanged 0.26 +1.37. comparison natural peridotitic crystallized this study are lower similar , presumably owing contents. Comparison thermodynamic models implemented pMELTS Perple_X suggest that these over-predict stability causing underpredict peridotites under conditions genesis.