DETERMINING P-T PATHS AND RELATIVE TIMING OF METAMORPHISM BASED ON MINERAL TEXTURES AND PSEUDOSECTION ANALYSES IN SMALL POINT, MAINE

The bedrock geology of Small Point, Maine was mapped at 1:10,000 using digital methods in 2011 as part of an USGS EDMAP grant. Previous work on the metamorphism at Small Point focused on regional studies throughout Casco Bay (Hussey and Marvinney, 2002; Lang and Dunn, 1990). This study reconstructs the detailed metamorphic history of Small Point and directly links it to related stratigraphic and structural studies in the same region using standard petrographic analyses to identify varying mineral assemblages and the sequence of syn-kinematic metamorphic textures. X-ray fluorescence analyses will be used to construct pseudosections for the study area. The bedrock consists of the Ordovician Cape Elizabeth, Spring Point, Diamond Island, and Scarboro Formations, a diverse collection of metapelitic schists interbedded with quartz-rich layers, rusty weathered schists, thin layers of calc-silicate granofels, amphibolites, marble, and graphitic phyllites. Meso and macro-scale granite/pegmatite intrusions are common throughout the study area, with increased size/density to the north. Small Point has experienced four tectonometamorphic events related to the Salinic (D1?), Acadian (D2, D3), and Alleghenian orogenies (Phippsburg Shear Zone, D4). Preliminary results from the metapelites (bt + msc + qtz + plg + grt ± sil ± and ± str) show at least two metamorphic events of Buchan-style metamorphism. The first of these metamorphic events at Small Point (M2?) occurred during D2 isoclinal folding and developed the dominant biotite + muscovite S2 foliation, muscovite pseudomorphs of andalusite, the staurolite out reaction to andalusite, and inclusion-rich, poikioblastic garnet cores. The next event (M3?) was syn to post D3 open folding (Small Point synform), and shows a second generation of less to non-foliated biotite and muscovite, clear garnet rims, fresh staurolite showing a later staurolite out reaction, hinge parallel fibrolitic sillimanite filling between boudined andalusite, and fibrolite pseudomorphic lenses of staurolite or andalusite. M3 shows three metamorphic zones including a staurolite zone, an andalusite zone, and a sillimanite zone, that increase in grade from the SW to the NE, towards map-scale granite intrusions in northern Small Point.