A NOTE ON THE NATURAL FUSION OF GRANITE Youv.q Ar.-RlwrlNo I.qN

Partial fusion of quartzo-feldspathic rocks as a result of high temperature thermal metamorphism is sometimes displayed at the contacts of basic intrusions; many of the accounts and results of this phenomenon have been summarized by Butler (1961) and Wyllie (1961) who also give an extensive bibliography on the subject. This data on natural fusion taken with the experimental results of Tuttle and Bowen (1958) and von Platen (1965) on synthetic granite systems, together with the implications of the results of the strontium isotope technique (Faure and Hurley 1963) provoke renewed interest in the interaction of crustal material with magma, particularly of basic composition. An example of natural fusion and accompanying thermal metamorphism described here is caused by the intrusion of a small Tertiary basalticandesite plug (200 feet in diameter) into granite, and is located east of the Sierra Nevada, in California.l The flow of magma through the plug, perhaps acting as a feeder to the associated basaltic-andesite lavas, has generated an extensive amounL of liquid (black glass) immediately at, and adjacent to, the contact. Beyond the zone of fusion, the effects of thermal metamorphism may be seen in the constituent minerals of the granite; this note considers the fusion paths of granitic rocks and the mineralogical response to the heat effect of the plug, the details of which are almost identical to those described by Butler (1961) for the thermal metamorphism of arkose.