GEOLOGY AND PETROLOGY OF THE BERRY BROOK PLUTON, EASTERN MAINE

The Berry Brook pluton is a small (~2 mi2), epizonal body of intermediate and mafic rocks that intruded low-grade metasedimentary rocks of the Fredericton belt in easternmost Maine (Ludman and Idleman, 1998). The pluton intruded in late Silurian times, cutting upright folds attributed to an early (mid-Silurian) phase of the Acadian orogeny, and is the NW-most outlier of the Coastal Maine magmatic province. Mapping during the summer of 2000 has significantly reinterpreted the size and shape of the pluton from the picture initially described by Larrabee et al. (1965), and provided new information about lithic variations, cooling history, and tectonic relationships. Detailed mapping shows that several rock types are distributed non-systematically, commonly occurring within a few meters of one another throughout the body: cpx-hb-bi leucogabbro, cpx-hb and hb diorites and leucodiorite, quartz diorite. Steeply dipping phase layering occurs at many places, both near the contacts and within the core of the intrusion. Dikes of pyroxenite and leucodiorite parallel phase layering in some instances, but cross-cut it in others. Cumulate textures and layering suggest that the Berry Brook pluton is a fragment of a larger body that was dismembered by faulting in the Kellyland Fault Zone, which lies just south of the pluton. Major, trace, and rare-earth data are being collected in an attempt to determine whether the Berry Brook pluton is related to the nearest similar body -- Pocomoonshine gabbro-diorite--or to other slivers identified by Wang and Ludman (2000) to the southwest in the Norumbega fault zone.