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

Abstract

Continental-scale recycling of detrital zircon (DZ) grains and associated sediment across North American is not well understood. We trace a through line following the DZ proxy for the detritus originally sourced from Grenville and Appalachian orogens. This paper lays out an antecedent framework for one of the greatest sedimentation episodes of the Phanerozoic: the initial dispersal of Appalachian- and Grenville-age DZ grains to the western passive margin of Laurentia and the subsequent paleodrainage reorganization and sediment remobilization back to the east. The 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 dominates the Phanerozoic record of North America. This study juxtaposes Pennsylvanian to modern DZ U-Pb data from across North America and demonstrates a persistent Appalachian signature, including a recycled Appalachian signature across Western North America. Lower Pennsylvanian deposits proximal to the Appalachian orogen are 50%–75% Appalachian- and Grenville-age DZ grains, representing the key component in the primary Appalachian signature. It remains unclear how the Appalachian signal was propagated to the west, but the Appalachian DZ signature was clearly present across the late Paleozoic passive margin of Laurentia and thus antecedent to potential DZ recycling throughout the Mesozoic and Cenozoic Eras. Triassic DZ samples document transcontinental fluvial systems that reached the western Laurentian margin, but subsequent Jurassic-Cretaceous samples indicate drainage reversal due to the rise of the Mesozoic Western Cordillera. A persistent Appalachian signature exists in these western-sourced, eastward-flowing systems—a phenomenon that continues to the present: samples are frequently composed of >40% Appalachian- and Grenville-age DZ. However, none of these systems are interpreted to be sourced by primary Appalachian or Grenville terranes, suggesting a recycled Appalachian signature. The persistent Appalachian signature, originally sourced by the linking of two orogenic terranes, continues to dominate the Phanerozoic record of much of North America to this day.