GEOLOGIC MAP OF THE PROTEROZOIC ROCKS IN THE PUTNAM QUADRANGLE, EASTERN ADIRONDACKS, NEW YORK: AN EDMAP PROJECT

Three teams of undergraduate students mapped the bedrock geology of the Putnam quadrangle, located in the eastern Adirondack Mountains in New York, during the summer of 2010. Each team, consisting of a senior-level lead mapper and a field assistant, had a tablet PC with an integrated GPS, running GIS software. Students located, plotted, and edited contacts utilitzing the computers while in the field and recorded data in a digital field book.

The Putnam quadrangle is largely underlain by a diverse suite of Proterozoic igneous and metamorphic rocks. The following rock units were recognized in the field: paragneiss with interlayered calc-silicate gneiss and biotite-quartz-feldspar gneiss, granitic to granodioritic biotite +/- hornblende-quartz-feldspar gneiss, impure marbles, augen gneiss with potassium feldspar megacrysts, metagabbro, garnet-bearing charnockite, a ferrogabbro to gabbroic anorthosite complex, a sillimanite-rich, garnet-potassium feldspar-quartz gneiss (khondalite), a white to iron-stained pink, foliated, equigranular leucogranite, and possible tonalitic gneiss.

The rocks are structurally complex with evidence for multiple phases of folding and ductile and brittle faulting. Upright, gently east-plunging isoclinal folds with an axial planar foliation are observed in the northern portion of the map area. This foliation is subsequently deformed by a more open phase of folding. Mylonitic rocks are present throughout the area but to date we have not delineated a continuous high strain shear zone. The ferrogabbro-gabbroic anorthosite suite is variably mylonitic, locally forming an L-tectonite with a strong, gently plunging eastward lineation. Field relations of isolated, mappable bodies of deformed metagabbro found throughout the map area are consistent with post-emplacement shear and boudinage. Late north- to northeast-trending normal faults are present throughout the map area.