Experimental Studies on K-Rich Rocks - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 413

They observed that clinopyroxene crystallizes over a temperature interval of

50 C, at pressures between 3.1 and 3.3 GPa below which spinel is the accom-

panying phase. At lower pressures (below 2.3 GPa) olivine is the liquidus phase
followed by the appearance of spinel. They observed that with 6 % water in the
coexisting melt phlogopitef is stable. These results indicate that the magma was
derived from a hydrous source at greater than 100 km depth.
Xenoliths carried by other young Pliocene lavas in the vicinity of WC-1 have
yielded temperatures of equilibrium from 700 to 900

°

° C, with one outlier at

1,060 C. These xenoliths are consistent with the hypothesis that the lower litho-

sphere under the Sierra Navada lamproites the mantle got metasomatized prior to
the Pliocene, then got partially melted to produce the highly K-rich lavas. They
suggested that subduction-derived

°

fluids were derived by a reaction that consumed
garnet + orthopyroxene to create clinopyroxene + phlogopite, and that the high-
potassium Sierran magmas were generated by melting phlogopite-clinopyroxene
metasomatized peridotite.