Date of Award
Program or Major
Earth Sciences - Geology
Doctor of Philosophy
Wallace A Bothner
The seacoast region of New Hampshire is underlain by two lithotectonic belts: the Rye Complex (RC), and the eastern portion of the Merrimack Group (MG). The Rye Formation and the Breakfast Hill member constitute the RC; the Kittery, Eliot, and Berwick Formations, the MG. The stratigraphic order interpreted in this study places the Kittery Formation transitionally above the Eliot, and identifies the contact between the Berwick and the Eliot Formations as a fault.
Study of folds using a variant of the Fourier series analysis indicates that the degree of asymmetry and shape of folds in the MG and the RC are similar. Besides documenting the folding event that affected the RC and the MG simultaneously (Acadian Orogeny), the method has proven its effectiveness as an educational tool.
Occurrence of pyrite crystals in MG rocks permitted the application of Finite Element Analysis. It consisted of numerical simulation of a set of controlled load cases applied to models of distorted pyrite crystals to reconstruct their assumed regular square shape. Results suggest that deformation of the crystals is related to folding that affected the host rock and not to the emplacement of a nearby Mesozoic dike.
Fieldwork, microstructural analysis, and digital elevation models, provide refinement of the traces of the Calef, Nannie Island, Portsmouth, and Great Common Fault Zones; and the identification of the brittle "Exeter Fault". Petrographic and microstructural analyses document the temperature of deformation in the south block of the Great Common Fault Zone, and support the correlation of these rocks with outcrops on New Castle Island and to the northeast on Gerrish Island, ME.
A proposed transpressional tectonic model involving a continuum from the late Silurian through early Paleozoic suggests that folding, magmatic intrusion(s), and ductile followed by brittle faulting affected the seacoast. In this model, after juxtaposition, simultaneous folding of the MG and RC was followed by northeast-trending, right lateral ductile shear. Later, right lateral, normal, northeast-trending, and east-west trending brittle faulting occurred affecting most Paleozoic plutons. The emplacement of Mesozoic mafic dikes is associated to the opening of the Atlantic Ocean.
Escamilla-Casas, Jose Cruz, "Bedrock geology of the seacoast region of New Hampshire, United States" (2003). Doctoral Dissertations. 190.