Fold Dating in the Central Appalachian Valley-and-Ridge.

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Folded rocks are common, highly aesthetic features of mountain belts and their ages constrain the timing of mountain building events, regional patterns of deformation, continental evolution and (economic) mineralization of the Earth?s crust. This geochronological study will improve and test a novel fold dating method based on the dating of illite clays, determine timing of folding in the central Appalachian Mountains of the eastern United States, and demonstrate the method?s potential for other locations around the world. In addition to the scientific goals of the project, it is providing support for the research of a doctoral scientist and is providing research experiences for undergraduate students, thus contributing to educational work force development in an important STEM (science, technology, engineering and mathematics) discipline. In addition, the principal investigators research and educational outreach will be broadly distributed through professional publications and by presentations at professional meetings and public presentations. The research will also be feature in an online textbook, and will be used in class and field experiences for undergraduate students. Illite dating also has direct application for industry and societal resource needs, as fossil fuel and mineral industries typically involve the same geologic setting and conditions that are examined in this study. The Principal investigators have recently developed a method for fold dating using argon geochronology of neocrystallized illite and tested its application in a case study of the Mexican Fold-Thrust Belt. The method relies on the quantification of illite in grain-size fractions of a single sample, and their respective ages; extrapolation of dated grain size fractions determines the ages of deformation and their errors. The Appalachian Valley-and-Ridge project has two primary goals: (1) improve the illite dating method by developing better clay quantification approaches that also reduce error estimates; (2) determine fold ages in the well-known central Appalachians, where forward fold progression has been hypothesized; currently, fold ages are stratigraphically bracketed as Upper Paleozoic; (3) directly constrain the timing of regional paleomagnetic remagnetization, mineralization and economic deposits in the eastern United States.