An Overview
Program: RESESS Boulder
Major: Earth and Environmental Science
Academic Affiliation: University of North Carolina at Charlotte
Biography
Jonese Pipkin is a senior undergraduate student at the University of North Carolina at Charlotte. The degree she is pursuing is an Earth and Environmental Science bachelors, and plans to continue her educational career by enrolling into a grad school program with a focus in water processes and management. This summer she worked as a RESESS intern at the Colorado School of Mines under the UNAVCO program for students. She conducted structural analysis of the southeastern New England Appalachian Mountains by digitalizing structures from pre-existing bedrock geology quadrangle maps and compiling data on bedding, schistosity/gneissosity and cleavage.
Abstract
Structural analysis of planar structural data from the Nashoba-Putnam terrane, and adjacent western Avalon terrane and eastern Merrimack Terrane, southeastern New England Appalachians, USA
Bedding, schistosity/gneissosity and cleavage orientation data (n = 18,912) from 36 7.5’ bedrock geological quadrangle maps from the Nashoba-Putnam terrane (NPT), western Avalon terrane and eastern Merrimack belt in the southeastern New England Appalachians were compiled and analyzed. Data were digitized using ArcMap, structural domains were defined based on map patterns, and structural analysis was conducted using the open-source software Orient. The NPT is a Cambrian-Ordovician arc-backarc complex, on the trailing edge of Ganderia. Ganderia, and the Avalon terrane that exists east of the NPT, are terranes that rifted from Gondwana in the early Paleozoic and accreted to Laurentia in the middle Paleozoic. The Merrimack belt to the west of the NPT is a Silurian to earliest Devonian metasedimentary belt with Ganderian and Laurentian sources, and is interpreted to overlie Ganderian basement. The NPT shows a narrow region or ‘impingement’ between the Nashoba terrane in the north and the Putnam terrane in the south. The NPT was metamorphosed under upper amphibolite facies conditions, while most adjacent rocks of the Merrimack belt and Avalon terrane reached only greenschist facies conditions. The southwestern part of the Avalon terrane reached upper amphibolite facies conditions.
Planar structures of the Nashoba terrane generally vary from steeply NW dipping in the north to moderately WNW dipping in the south. In the Putnam terrane they dip WNW and show a systematic alternation between shallower and steeper dips across the terrane, suggesting map-scale folds. These, and isoclinal folds that are known to exist throughout the NPT, are interpreted as a result of the middle Paleozoic Acadian orogeny or accretion of the Avalon terrane to the east, based on previous geochronology data. In the eastern Merrimack belt, planar structures dip moderately to shallowly WNW. In the Avalon terrane, both near the impingement in the NPT and south of the Putnam terrane, structures generally dip northerly, but also show complex folds. The northerly dip is unlike the general WNW dip along the NPT boundary and may be due to local or regional indentations. Existing geochronology data suggest that deformation and metamorphism in the southern Avalon terrane is at least in part a result of the late Paleozoic Alleghanian orogeny or formation of Pangea.