Evidence from olivine/melt element partitioning that nonbridging oxygen in silicate melts are not equivalent

Partitioning of Ca, Mn, Mg, and Fe2+ between olivine and melt has been used to examine the influence of energetically nonequivalent nonbridging oxygen in silicate melts. Partitioning experiments were conducted at ambient pressure in air and 1400 degrees C with melts in equilibrium with forsterite-rich olivine (Fo > 95 mol%). The main compositional variables of the melts were NBO/T and Na/(Na+Ca). In all melts, the main structural units were of Q(4), Q(3), and Q(2) type with nonbridging oxygen, therefore, in the Q(3) and Q(2) units.