NEW OBSERVATIONS ON THE CHOPAWAMSIC FAULT, AN EARLY PALEOZOIC TERRANE BOUNDARY IN THE WESTERN PIEDMONT OF VIRGINIA
In the area south of Lake Anna, limited observations of winged sigma feldspar grains indicate a sinistral component of shear along the Chopawamsic fault. Nearby, the Ellisville granodiorite intrudes across the fault, providing a timing constraint on fault motion. New TIMS U-Pb zircon ages indicate that the latest movement on the fault was pre- c. 437 Ma.
Field studies to date confirm the existence of a successor basin atop the fault in the area of Storck, VA; we intend to use detrital zircon analysis of metasediments in the basin in order to further constrain the timing of fault motion. In the Wilderness, VA area, our mapping indicates that the other successor basin previously mapped to overlie the fault, does not exist and that rocks previously mapped as the basin are most likely metasedimentary rocks within the Chopawamsic terrane.
Our ‘in progress’ investigation will involve additional field and laboratory research along the Chopawamsic fault. We plan to assess the cratonic source of the Chopawamsic terrane with the use of Nd and Pb isotopic analyses as well as detrital zircon populations from each side of the Chopawamsic fault. The detrital zircon study should also provide supplementary constraints on the timing and nature of fault motion. High precision U-Pb TIMS data from previously undated intrusive bodies will also augment our understanding of the early Paleozoic evolution of the western Piedmont.