SEQUENTIAL REGULARITY OF DETRITAL ZIRCON U-PB AGES IN WESTERN NORTH AMERICAN TERRANES: SECOND-ORDER TECTONIC CONTROL ON SEDIMENT PROVENANCE

On a time-integrated global scale, detrital zircon U-Pb age distributions reflect periodic magmatic accretion of juvenile continental crust. At a finer temporal and spatial scale, (i.e., second-order, 10⁷–10⁸ yr, Km's of rock), sediment provenance should be controlled by the distribution of continental orogenic belts, long-lived Cordilleran-style magmatic arcs, and associated continental sediment-dispersal systems. Supporting detrital zircon U-Pb age evidence for this type of long-term control in the ancient rock record exists, but is generally sparse and typically documents a single stage of paleogeography-paleotectonics. Detrital zircon U-Pb data from Paleozoic–early Mesozoic clastic sedimentary successions in terranes of western North America record the dynamic interplay of orogenic, erosion, and sediment-transport systems during phases of the super-continent cycle. I identify sequential regularity at a scale of 10⁷–10⁸ yr in detrital zircon U-Pb ages and suggest that this records the stepwise shift from a complex, marginal-basin regime during most of Paleozoic and early Mesozoic time, to a cordilleran-type integrated margin during Late Mesozoic time. At the plate-margin scale, the detrital zircon record reflects sediment dispersal pathways that were initially connected to the craton, and were subsequently cut off as new, arc-front drainage became established along the rising plate margin. Despite a shift from a regional pericratonic-arc setting to a continental margin-arc setting, associated basins reflect a decrease in continental signature. Counter intuitively, continental growth via arc accretion and tectonic stabilization of an active plate margin may be regionally manifest as a decrease of continental influence in the sedimentary record.