Collaborative Research: A Record of the Timing, Nature and Geometry of the Rheic Ocean in the Appalachian Carolina and Avalon Zones

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The Rheic Ocean opened in the wake of crustal blocks rifted from the northern margin of Gondwana to form one of the most prominent Paleozoic global features; its closure is responsible for one of the major collisions that produced the supercontinent of Pangea. Despite its importance in the global evolution of the Paleozoic, there is little knowledge of it paleogeogaphy. Most of what is known is based on limited exposures found in Europe. Critical questions exist regarding such fundamental aspects of the Rheic Ocean, including its timing and mode of opening and its geometry with respect to Paleozoic continental elements. In North America, a 3000 km long belt of peri-Gondwanan crustal blocks along the eastern flank of the Appalachian orogen defined the leading edge of the Rheic during its opening, yet the history of the Rheic recorded in these rocks has been neglected. This study focuses on the two largest Rheic-related elements of the Appalachian peri-Gondwanan realm, the Carolina and Avalon zones. The primary objectives of this study are to 1) determine the time of opening of the Rheic Ocean, 2) identify the mode of Rheic opening, and 3) constrain the geometry of the Rheic during its evolution.These objectives are being addressed through the integration of several lines of study, including focused geologic field mapping, geochemistry, high precision U-Pb and detrital zircon provenance analysis. The character and timing of opening of the Rheic Ocean are being addressed by combined geochemical- high precision U-Pb geochronological studies on late stage mafic plutonic rocks in the Carolina zone. By comparison with the established time of rifting of Avalon from Gondwana, these data will better constrain the mode of opening of the Rheic. The detrital zircon study is elucidating the original paleogeographic relationship between Carolina and Avalon. These data are being used to test the hypothesis that Carolina and Avalon once constituted a single 'ribbon continent' rifted from Gondwana. Detrital zircon age spectra from time equivalent lithic assemblages throughout each zone are elucidating long term trends and changes in source areas that might arise from rifting, collision, or drift past other eroding crustal blocks. Trends and changes in detrital zircon age spectra, considered in conjunction with other available data, represent new constraints on the relative paleogeography of the two zones. Detrital zircon data are also being utilized with other extant data sets in an attempt to identify the source region(s) of Carolina and Avalon; the original location of these crustal blocks is a prerequisite to delineating the geometry of the Rheic at its birth. High precision U-Pb zircon dating is providing tight age constraints on rocks of particular significance. Finally, the most important aspect of any geochronological/geochemical study is confidence in the field relations of the sampled rocks. Focused field geologic mapping is being conducted in conjunction with all sampling.