BEDROCK GEOLOGIC MAP OF THE MT. WASHINGTON EAST AND CARTER DOME 7.5 MINUTE QUADRANGLES, PRESIDENTIAL RANGE, NEW HAMPSHIRE

With support from the New Hampshire Geological Survey and the U.S.G.S. EdMap program, a bedrock mapping project of the Mt. Washington East and Carter Dome 7.5’ Quadrangles has been completed. Providing undergraduates a geologic mapping experience and furthering our understanding of the Early Devonian Acadian orogeny were other goals of the project. The geology is composed of Silurian and Devonian metasedimentary rocks located on the west flank of the Central Maine Terrane and Ordovician metavolcanic rocks on the east flank of the Bronson Hill anticlinorium. The Devonian Littleton Formation has been divided into 16 members, the Silurian Madrid and Smalls Falls Formations serve as important marker horizons, and the Silurian Rangeley Formation has been divided into 9 members. The Ordovician Ammonoosuc volcanics have been divided into 8 different members and mylonites have been mapped within it. The Pinkham Notch and Graham Trail pre-metamorphic normal faults cut out the Madrid and Smalls Falls Formations. D1 and associated fabrics are found throughout the region and are characterized by east verging isoclinal nappes. D2 is characterized by the stratigraphic and metamorphic discontinuities that are interpreted to be thrusts: e.g. the Greenough Spring, Snyder Brook, Mahoosuc and Glen Boulder thrusts. D3 is localized macroscopic refolding of the D2 thrusts in the Great Gulf region. D4 folds are ubiquitous and characterized by asymmetric, moderately inclined folds. D5 is a crenulation that is restricted to the Pinkham Notch region. Mesozoic deformation is restricted to joints and a few silicified faults: e.g. the Glen Ellis and Pine Peak faults. The Wamsutta diorite (408 Ma) and Wildcat (401 Ma), Slide Peak (400 Ma), Bigelow Lawn (399 Ma), Bretton Woods (368 Ma), Bickford (363 Ma) and Peabody River (355 Ma) granites define a spectrum of early Devonian to early Carboniferous plutonism in the region. Metamorphism began with an early low pressure event characterized by pseudomorphed andalusite that grew during D1 nappe-stage folding. The peak of metamorphism reached the lower and upper sillimanite zones in the Littleton and Rangeley Formations. Complex zones of migmatization are found within the Rangeley. Various retrograde events produced scattered occurrences of staurolite, chlorite and/or sericite.