A NEW MODERN RIVER DETRITAL RECORD OF SOUTHERN APPALACHIAN GEO- AND THERMOCHRONOLOGICAL EVENTS: IMPLICATIONS FOR TECTONICS AND SEDIMENTARY PROVENANCE

Geo- and thermochronology data from the southern Appalachian Mountains are sparse compared to the northern U.S. extent of the range, and as a result, the provenance signature has largely been inferred from Paleozoic foreland basin proxies. In this study, we survey the Appalachian orogenic belt using detrital zircon (DZ) and detrital apatite (DA) U-Pb and low-temperature fission track (FT) double dates from the sediment of eighteen modern rivers. Sand was collected from fourteen east- and four west-flowing rivers, upstream of the Atlantic and Gulf Coastal Plain. The contiguous river catchments span ~1800 km from New York to Alabama and in total cover ~78% of the presently exposed southern Appalachian hinterland (Piedmont and Blue Ridge) and foreland basin (Valley-and-Ridge and Appalachian Plateau). DZ U-Pb ages (n=1600) match bedrock map distributions, with Grenville-age zircon dominant in southwestern and northern rivers but relatively rare in eastern rivers. Conversely, Paleozoic Taconic-, Alleghanian-, and Acadian-age zircon are most abundant east of the drainage divide. Whereas zircon is subject to recycling from multiple orogenies, DA U-Pb ages (n=1125) record cooling through mid-crustal temperatures (375–570°C) and thus serve as indicators of recent orogenic provenance. Dominant DA U-Pb age components include 1) post-Grenville (ca. 800–950 Ma) ages restricted to Appalachian foreland basin sediments; and 2) ubiquitous Paleozoic ages with a broad 250–350 Ma mode, which likely represent peak crustal thickening and exhumation during magma-poor late-stages of the Grenville and Paleozoic orogenies, respectively. DZ FT cooling ages (n=1600) are variable, with unique Precambrian (>800 Ma) components in western rivers, Cenozoic (ca. 21–66 Ma) age components in eastern rivers, and common major components between 200–500 Ma. DA FT age components (n=1543) range from 45–615 Ma, with the majority of ages between 105–175 Ma. FT trends indicate that significant exhumation occurred in the southern Appalachians during the Jurassic–Cretaceous post-orogenic breakup of the Gondwana-Laurasia margin, followed by periods of Cenozoic rejuvenation. In aggregate, these data record the spatial extents of geo-thermochronologic events and refine the provenance signature of the southern Appalachian orogenic belt.