RUI: Motion History and Tectonic Significance of Major Faults in Southeastern New England

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The goals of this project are to define the thermal history, direction, sense and timing of motion(s) on potential terrane-bounding faults in the northern Appalachians. The regional geology is reasonably well known with the exception of fault motions. The fault system to be studied marks the western boundary of the Avalon zone in southeastern New England and may be a segment of a fault system which spans the northern Appalachians. Although the faults have been proposed as marking a Permian collisional suture, preliminary results suggest that various segments have experience different motion histories. The entire system of faults may have experienced Silurian (430-400 Ma.) left-lateral motion with a thrust component and some segments were reactivated in Permian time as low-angle normal faults. Additional work is required to define the motion histories of fault segments not yet studied, to establish relationships between segments with different motion histories, to investigate possible relationships between fault motion and deformation in isolated occurrences of Pennsylvanian metasedimetary rocks and to integrate these results with the regional geology. Techniques to be used will be standard detailed structural analysis in the field and microstructural analysis on oriented thin sections. Thermal histories will be established by characterization of temperature dependent microstrutures corroborated by phase equilibria where applicable. Timing of motions will be established by structural analysis of dated igneous rocks. Student involvement will take the form of two undergraduate field assistants for each of the two field seasons and several "senior honors theses". Results are expected to help constrain the tectonic history of some of the terranes in New England.