EXPERIMENTAL CONSTRAINTS ON RECYCLING OF POTASSIUM FROM SUBDUCTED OCEANIC-CRUST

Petrological experiments on oceanic crust samples characterize the rec ycling of potassium from mid-ocean ridge basalts and sediments. Metaso matism could develop directly and continuously from subducted potassiu m-bearing crust from shallow levels to a maximum depth of 300 kilomete rs. Phengite (a potassium-rich mica) is the principal potassium host a t subsolidus conditions. It transports potassium and water to depths o f up to 300 kilometers and could yield over the entire depth range pot assium-rich fluids or melts (depending on the specific geotherm), whic h are likely to constitute one of the primary metasomatic agents for g eneration of calc-alkaline magmas.