On Some Early Dyke-Like Bodies in the Tonigala Granite, Ceylon

Several dyke-like bodies of uniform width (called "purple dykes" in the field) are found within the Tonigala Granite in north-west Ceylon. These are shown to be true dykes and comparable in some respects to the "relict dykes" of the Cornucopia and the Vancouver regions (Goodspeed, 1955; Roddick and Armstrong, 1959) and to the "early dykes" in the Main Donegal Granite (Pitcher and Read, 1960). The complex relations of the purple dykes to such elements in the Tonigala Granite as pegmatites, granitic veinlets, and biotite-rich foliae indicate that the dykes were intruded early in the history of the granite, after tensional stresses had been set up and during a long period of pegmatisation. Little evidence is however available to show the original composition and the actual mode of emplacement of the dykes. Petrographical and petrochemical similarities between the dyke rock and the surrounding granite suggest that the dykes underwent the same metasomatic changes viz. granitisation, as affected the granite in the later stages of its history.