Ionprobe investigation of rare earth element distributions and partial melting of metasedimentary granulites

The rare earth element (REE) characteristics of feldspars and garnet in two metasedimentary xenoliths from Kilbourne Hole, New Mexico, have been determined by secondary ion mass spectrometry. Mass balance considerations show that the majority of the REE reside in the major mineral phases of these xenoliths. High concentrations of light (L)-REE are observed in the feldspars. The activity of REE-rich accessory phases in the Kilbourne Hole metasediments is inferred to be low. Melts in equilibrium with the observed major mineral assemblage and inferred accessory phase assemblage are strongly LREE-enriched, and a good fit to the REE characteristics of the Kilbourne Hole metapelites is attained by extraction of <25% of this melt from a protolith whose REE concentrations are elevated with respect to average shales. -from Author