The composition and paragenesis of the biotites of the Carsphairn igneous complex

The Cairnsmore of Carsphalrn igneous complex (1) is the smallest of the larger Caledonian intrusions of the Southern Uplands of Scotland. The intrusion is composite, consisting of a central granite, followed by successive zones of granite-tonalite hybrid, tonalite, and basic hybrids. The complex began with the intrusion of a gabbro. When this was crystallized, but still at a high temperature, the tonalite was emplaced. This intrusion of tonalite produced a series of hornblende-hybrids. The hybridization of the original gabbro attendant on the injection of the tonalite is the result of a 'partial magma' of potash-felspar, quartz, and volatiles. The final intrusion of granite took place while the tonalite was still incompletely crystallized, and resulted in the formation of a zone of acid hybrid rocks. The three biotites that have been analysed occur in the granite, tonalite, and hornblende-hybrid respectively.