A Note on Rhythmic Layering in Hornblende-rich Picrite and Dolerite Intrusions, near Rhiw, Caernarvonshire

Abstract

AbstractBanding, recorded by previous workers in hornblende picrite and dolerite intrusions near Rhiw, is found to be rhythmic layering. At least three major units (200 to 250 feet in thickness) have been recognized, and intermediate and minor scale units also occur, predominantly within the basal major unit. The majority of the rocks display cumulate textures, and crystallization appears to have been completed by heteradcumulus or adcumulus growth. Thin coarser-grained sheets, rich in plagioclase, and slightly discordant to the layering, are considered to be contemporaneous segregation veins.