Physical Sciences and Mathematics Commons^™

Bedrock Geologic Mapping And Structural Analysis Of The Western Half Of The Petersham Quadrangle, Central Massachusetts: Further Tests Of The Model For Middle To Late Paleozoic Ductile Transpression, Vertical Extrusion, And Lateral Escape In The Northern Appalachians, Lucas P. Rohrer

Theses and Dissertations--Earth and Environmental Sciences

Bedrock mapping, structural analysis, and geochronology reveal the distribution of lithologies and timing of metamorphism and deformation in the western half of the Petersham 7.5’ quadrangle, western Massachusetts. Underlying lithologies are: (from west to east) the Ordovician Monson granitic orthogneiss, Silurian Rangeley migmatitic paragneiss, and Late Devonian (357 Ma) Hardwick tonalitic orthogneiss. Their tightly folded contacts strike north to south. The 361 Ma, unfoliated, strike-parallel Nichewaug quartz-diorite (10-100 m wide) intrusion spans the map area within the Rangeley. Evidence for vertical and lateral extrusion/escape of the Monson orthogneiss, as observed in the Palmer MA area, is absent. Instead, petrofabrics (foliations …