Gravitational Instability in Coexisting Layered Magmas: Isle au Haut, Maine

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This proposal seeks funding for an integrated field, geochemical and petrographic study of a granite-diorite-gabbro association on the island of Isle au Haut, Maine. These rocks are part of the more extensive Bays-of-Maine Igneous Complex. A major concern of this research will be to document and understand a spectacularly exposed sequence of layered gabbro and diorite units which we believe to be the frozen relics of a sequence of coexisting melts. Field relationships show clearly that several of these layers were gravitationally unstable, and were in the process of overturning and mixing. Recent theoretical studies applying fluid dynamics to magma chamber models predict that compositionally zone magma chambers, stratified magmatic layers, and mixing of distinct magma types play important roles in the petrogenesis of igneous rocks. On Isle au Haut we have, perhaps for the first time, an unprecedented opportunity to obtain systematic petrographic and geochemical data on coexisting magmas within a stratified magma chamber. From this data we will be able to evaluate many of the magmatic processes predicted to occur in magma reservoirs by recent fluid dynamics and experimental studies.