THERE AND BACK AGAIN: THE RECYCLING OF APPALACHIAN AND GRENVILLE SIGNATURES IN DZ U-PB RECORDS OF PHANEROZOIC NORTH AMERICA

The detrital zircon (DZ) U-Pb signature of the Appalachian-Ouachita orogenic system, which includes the Grenville (1250–950 Ma) and Appalachian (500–275 Ma) age groups, dominates the entire Phanerozoic record of North America. An east-to-west comparison of DZ samples across North America (late Paleozoic to present), demonstrates a persistent Appalachian signature for samples, including a “recycled” Appalachian signature in the West. Lower Pennsylvanian deposits proximal to the Appalachian orogen are composed of ~50–75% Appalachian- and Grenville-age DZ, representing a “primary” Appalachian signature. The Ouachita Basin received contributions from the Appalachians and the midcontinent, resulting in a “diluted” primary Appalachian signature. By the Triassic the DZ record out West displays a primary Appalachian signature and represents rivers sourced from the Appalachian-Ouachita-Marathon highlands.

DZ sampled from Mesozoic fluvial sandstones, such as along the Front Range, indicate drainage reversal due to the rise of the Western Cordillera; yet a persistent Appalachian signature exists in these western-sourced, eastward-flowing systems—a phenomenon that continues to the present. None of these systems are interpreted to be sourced by primary Appalachian or Grenville terranes, suggesting a recycled Appalachian signature. These western samples frequently are composed of >40% Appalachian- and Grenville-age DZ and accompanied by “western” age groups (e.g., Yavapai-Mazatzal and Western Cordillera). This is representative of west-to-east flowing Jurassic to Holocene rivers of western North America. Although western drainage reorganization reversed the trajectory of sediment routing sourced by the Appalachian-Ouachita orogen, Western Cordillera-age DZ are underrepresented across the continent, even in the West. The persistent Appalachian signature continues to have an outsized presence in the DZ record of North America.