Contributions of crystallography, mineralogy, and petrology to the geology of the Lucerne Pluton, Hancock County, Maine

Abstract

Mineralogical studies of the Lucerne pluton, Hancock County, Maine, have established the pre-intrusive geology and the intrusive nature of the pluton, contributed to the interpretation of gravity and magnetic anomalies, explained geomorphic features surrounding the pluton, and identified post-plutonic faulting. The pluton is a biotite granite, rich in alkali feldspar, containing both seriate and porphyritic facies. Post-intrusive faulting, followed by erosion, has exposed two levels ofthe pluton. The northern, or higher, level has a slightly greater Fe/ (Fe + Mg) but is lower in total Fe + Mg. Five percent of the alkali feldspars in both facies are mantled by Anrn plagioclase. The alkali feldspars are microcline perthites of Abto.*Or6o.o composition. Biotite, which varies in Ti and Al contents, was the primary major phase to crystallize from the magma, closely followed by the apparently simultaneous crystallization of plagioclase, qvattz, and alkali feldspar. Most of the magmatic crystallization took place at l-2 kilobars total pressure at temperatures between 650' and 700oC. Boron may have been a signifcant constituent. The source region for the magma may have been a previously metamorphosed graywacke containing quartz, plagioclase, alkali feldspar, and biotite.