Fig. 4
From: Platinum-bearing chromite layers are caused by pressure reduction during magma ascent
Thermodynamic modelling indicating the mechanism via which basaltic melts become saturated in chromite alone by pressure reduction. The basaltic liquid that is saturated in orthopyroxene and chromite at high pressures (along the interval from 10 to 6 kbar) becomes saturated in chromite alone, which is the first liquidus phase, followed by orthopyroxene, at low pressures (P < 6kbar). This case is analogous to path C–D in Fig. 3b, c. Note that adiabatic ascent of the crystal-free melts from a deep-seated storage region located at pressure of ~10 kbar towards the Earth’s surface may result at 1–3 kbar in up to 80–95 °C of magma superheating relative to their liquidus temperature. Crystallisation of the basaltic liquid (Table 1) was modelled at FMQ oxygen buffer and a low water content (0.45 wt.%) using alphaMELTS software, version 1.4.118, 19. The results are summarised in the electronic appendix (Supplementary Data 1 and 2)
