A parameterization of experimental data in the 0.2-7.0 GPa pressure range constrains both forward models of potential primary magma compositions that exit the melting regime in the mantle and inverse models for computing the effects of olivine fractionation for any olivine-phyric lava suite. This is used to infer the MgO contents of primary magmas from Gorgona, Hawaii, Baffin Island and West Greenland. They typically contain 18-20% MgO for wide variations in assumed peridotite source compositions, but MgO can drop to 14-17% for Fe-enriched sources, and increase to 24-26% for fractional melts from Gorgona. Primary magmas with 18-20% MgO have potential temperatures of 1520-1570°C. For Gorgona picrites with 24% MgO, the potential temperature and initial melting pressure were about 1700°C and 8.0 GPa, respectively; melting was hot and deep, consistent with the plume model. There are important restrictions to magma mixing in mantle plumes. Primary magmas that exist the melting regime are both well-mixed aggregate fractional melts and isolated fractional melts. The latter can originate from a hot plume axis and be in equilibrium with olivines having mg-numbers of 93.0-93.6, but they have MgO contents and thermal characteristics that are difficult to constrain.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Accumulated fractional melting
- Equilibrium melting
- Mantle plumes
- Primary magmas