Abstract
The Devonian Deer Isle granite complex, Penobscot Bay, Maine, exhibits complex and highly diverse textures of minerals and rocks that are the result of thermal perturbations related to injections of new magma during the crystallization history of the pluton. The pluton-wide systematic spatial variation in the abundance of minerals, plagioclase-mantled alkali feldspar, schlieren, enclaves, and rock textures allows us to define four facies. Their spatial distribution across the Deer Isle granite complex reflects crystallization within a zoned magma-chamber. Lithological and textural variations were produced by a combination of the open-system behavior and crystal–melt fractionation during evolution of the magma chamber. The Flye Point and Oak Point facies are basal cumulates formed by crystal accumulation during emplacement and growth of the chamber. Both subsequently matured by compaction and filter pressing of residual melts. The transition from the relatively static cumulate-rich base into a dynamic magmatic flow regime is preserved by the texturally variable Settlement Quarry facies. The overlying leucocratic Crotch Island facies represents an evolved felsic cap that was modified by addition of low-density melts derived from the growing pile of cumulates. The decreasing abundance of mafic enclaves from the Flye Point facies toward the Crotch Island facies indicates that the importance of replenishments of mafic magma, in terms of adding heat and material to the chamber, waned during crystallization. As crystallization proceeded, convection ceased and texturally distinct granite domains were preserved.
Published Version
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