DID THE APPALACHIAN DETRITAL ZIRCON SIGNAL CHANGE THROUGH THE PHANEROZOIC EON?

The detrital zircon (DZ) U-Pb signature of the Appalachian-Ouachita orogenic system is dominated by Grenville (ca. 1250–950 Ma) and Appalachian (ca. 500–275 Ma) age groups and, in many ways, dictates the Phanerozoic DZ record of North America. The Appalachian orogenic system extends >5000 km from eastern Canada to West Texas and northern Mexico and formed after Neoproterozoic rifting of the post-Grenville Iapetus Ocean. Arc magmatism was common in the Ordovician Taconic (ca. 480–440 Ma) and Devonian to Mississippian Acadian phases (ca. 400–350 Ma), whereas during the Mississippian through early Permian (ca. 320–275 Ma), the Alleghenian and Ouachita-Marathon collisional belts formed on Laurentia during the assembly of Pangea. The provincial “Appalachian” DZ U-Pb signature initially accumulated in clastic wedges of the Appalachian foredeep and represents the integrated record of sediment sources within the Appalachian cordillera. This signature is dominated by what we refer to as the Appalachian-peri-Gondwanan-Grenville (APG) age group, composed of (a) Paleozoic DZ U-Pb ages that reflect the different phases of Appalachian orogenesis (10–15% of the total); (b) small (<5%) contributions from Neoproterozoic to Cambrian peri-Gondwanan terranes (ca. 850–510 Ma) that accreted to, or formed in, eastern and southern Laurentia prior to and during the assembly of Pangea; and (c) Mesoproterozoic Grenville age groups that reflect erosion of Grenville inliers within the Appalachians (40–60%).

This study compares Paleozoic, Mesozoic, and Cenozoic DZ U-Pb data from the eastern United States and demonstrates a persistent sediment supply laced with the Appalachian DZ signature, even throughout the Cenozoic Era. During the height of the Appalachian orogeny, Lower Pennsylvanian deposits proximal to the Appalachian orogen are 50–75% Appalachian- and Grenville-age DZ, representing the key component in the primary Appalachian signature. Some 300 million years later, 70–85% of the DZ U-Pb ages in rivers that drain the Appalachians still belong to this very provincial primary APG age group, demonstrating that this eon-long signal persists due to the rejuvenation of an ancient orogeny.