A general mixing equation with applications to Icelandic basalts

The ultrapotassic rocks: Characteristics, classification, and constraints for petrogenetic models

The effects of assimilation of country rocks by magmas on 18O/16O and 87Sr/86Sr systematics in igneous rocks

Erosion of lithospheric mantle beneath the East African Rift system: geochemical evidence from the Kivu volcanic province

The rare earth content of alkali-rich, silica-undersaturated basalts erupted onto oceanic and continental plates is consistent with their derivation by slight amounts of partial melting of hydrous garnet peridotite at the top of the asthenosphere, within the low-velocity, low-Q zone of the mantle. The rare earths are fractionated during partial melting by retention of heavy rare earths relative to light rare earths in garnet and clinopyroxene in the mantle residue. We conclude from a melting model that the amount of melting of hydrous peridotite at the top of the asthenosphere and its clinopyroxene-garnet ratio increase with decreasing thickness of the overlying dry lithospheric plate. Thus, potassic basalts derived by 0.5% melting of peridotite with a clinopyroxene-garnet ratio of 0.3 come from deeper than nephelinites (1% melting, ratio of 1), and alkali basalts (2% melting, ratio of 5). Convection within the partly molten asthenosphere establishes an adiabatic geothermal gradient and localizes renewabl...

J. L. Powell

Papers

Strontium Isotopic Studies of Alkalic Rocks: The Potassium-rich Lavas of the Birunga and Toro—Ankole Regions, East and Central Equatorial Africa