RECYCLING THE APPALACHIANS: PERSISTENCE OF APPALACHIAN SIGNATURES IN DETRITAL ZIRCON U-PB PROVENANCE RECORDS OF MESOZOIC AND CENOZOIC NORTH AMERICA

The primary DZ U-Pb signature of Appalachian-derived rivers for the last ~300 Myrs has consisted of a ~700-275 Ma population associated with Appalachian orogenesis (20-40% of the total), and a ~1250-950 Ma population associated with Mesoproterozoic Grenville rocks that were incorporated into the Appalachians (60-80% of the total). This presentation discusses how this primary “Appalachian-Grenville” signature has been recycled over time.

The primary “Appalachian-Grenville” DZ U-Pb signature first appears in Carboniferous sedimentary rocks of Western Laurentia, which indicates transcontinental sediment transfer, but the actual fluvial routing systems are difficult to identify: during the Pennsylvanian, there were north-south oriented paleovalleys in the US Midcontinent, as well as the Ouachita and Marathon Basin deepwater sinks, which would have limited transcontinental sediment transfer. However, beginning in the Late Triassic, the Chinle Formation in Utah displays the primary “Appalachian-Grenville” signature, with minor populations accrued along the way.

Development of the Mesozoic Western Cordillera changed the western US Laurentian margin from a sink to a source. Beginning in the Middle Jurassic, western US fluvial systems flowed to the east, across the Sevier foreland, and merged with Appalachian-derived rivers to flow north to the Boreal Sea, or discharged to the Western Interior Seaway. Accordingly, recycled “Appalachian-Grenville” signatures dominate Late Jurassic through Late Cretaceous strata of the Sevier foreland basin from Utah through Alberta.

Late Cretaceous to Paleogene continental-scale drainage reorganization resulted in southern North America river systems flowing to the Gulf of Mexico. Today, primary “Appalachian-Grenville” signatures are delivered to the Gulf from the Ohio, Tennessee and other river systems, whereas a dilute recycled “Appalachian-Grenville” signature is delivered by the Mississippi River’s Rocky Mountain tributaries.