Basaltic Macadam-breccias In The Girvan-ballantrae Complex, Ayrshire

Abstract

Many supposed “volcanic agglomerates and tuffs” in the Girvan-Ballantrae complex of southern Ayrshire are considered to be non-pyroclastic in origin. These macadam breccias are accumulations of lava breccia derived mainly from the autoclastic disintegration of pillow basalts during, or shortly after, extrusion. The breccia-forming process is considered to be mainly a function of supercooling, glass formation and retention of volatiles, all of-which are directly related to external hydrostatic pressure.