EarthRef.org Reference Database (ERR) -- Concei\c{c}\~{a}o & Green 2000

The system leucite-olivine (Fo90)-quartz has been experimentally studied from 0.5 to 2.0 GPa under dry conditions, and the position of the invariant point involving olivine, enstatite, K-rich phase (leucite or sanidine), and liquid has been determined. We find that at 0.5 GPa the olivine (Ol) + liquid (Liq1) enstatite (En) + leucite (Lc) + liquid (Liq2) peritectic occurs at 1205?C and Lc31.7Qz66.5Ol1.8, while at 1.0 GPa, at 1265?C, it has moved to Lc38Qz58Ol4 as the leucite field contracts. A second peritectic reaction, Lc + Liq3 Sa + En + Liq4, occurs at 1.0 GPa and ~1260?C (Lc37Qz60Ol3). With increasing pressure from 1.0 GPa the stability field of sanidine increases such that at 1.5 GPa the subsolidus reaction En + Lc = Ol + San intersects the solidus, defining an invariant point at 1290?C (Lc46Qz47.5Ol6.5). At 2.0 GPa the leucite field contracts farther toward the leucite corner, and the peritectic reaction En + Liq6 Ol + Sa + Liq7 takes place at 1350?C (Lc50Qz43Ol7). The Ol + En + Liq boundary moves from the silica-oversaturated field at 0.5 and 1.0 GPa into the silica-saturated field at 1.5 GPa and to the silica-undersaturated field at 2.0 GPa. Our new data, together with earlier studies of anhydrous and hydrous Lc-Ol-Qz systems for 2.8 GPa, suggest that highly potassic (i.e., with very low Na2O contents), silica-oversaturated magmas with minor contents of water could be direct partial melts of a potassic-harzburgite or phlogopite-bearing lherzolite mantle at pressures of nearly 1.5 GPa and temperatures of about 1200?-1300?C. Generation of strongly undersaturated K-rich magmas requires higher pressures (>2.0 GPa) and is favored by the presence of dissolved carbon as CO3= and/or fluorine.