Dr. David Kimbrough’s new paper published using the California forearc to provide a case study of the utility of detrital zircon geochronology in resolving landscape evolution in an active margin setting. Particularly true where the source regions are segments of a volcano-plutonic arc complex with distinct and well-documented spatial variations in crystallization age.
Detrital zircon provenance of the Late Cretaceous–Eocene California forearc: Influence of Laramide low-angle subduction on sediment dispersal and paleogeography
Glenn R. Sharman1, Stephan A. Graham1, Marty Grove1, David L. Kimbrough2 and James E. Wright3
1Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
2Department of Geological Sciences, San Diego State University, San Diego, California 92182, USA
3Department of Geology, University of Georgia, Athens, Georgia 30602, USA
Abstract
Upper Cretaceous–Eocene forearc strata deposited along the California continental margin record a complex history of plate convergence that shaped the tectonic development of the U.S. Cordillera. Synthesis of new and published detrital zircon U-Pb ages over a 2000 km length of the southern Oregon–California–northern Baja forearc clearly demonstrates spatial and temporal changes in sandstone provenance that reflect evolving sediment dispersal patterns associated with the extinction of continental margin arc magmatism and transfer of deformation to the continental interior during latest Cretaceous–early Cenozoic Laramide low-angle subduction.
Measured age distributions from Cenomanian to Campanian forearc strata indicate the existence of a drainage divide formed by a high-standing mid-Cretaceous Cordilleran arc that crosscut older, Late Permian–Jurassic arc segments. Progressive influx of 125–85 Ma detrital zircon in the Great Valley forearc reflects ongoing denudation of the Sierra Nevada batholith throughout Late Cretaceous–early Paleogene time. In contrast, age distributions in the Peninsular Ranges forearc indicate early denudation of the Peninsular Ranges batholith that is hypothesized to have resulted from the initial collision of an oceanic plateau with the southern California margin; as a result, these age distributions exhibit little change over time until delivery of extraregional detritus to the margin in Eocene time. Maastrichtian through middle Eocene strata preserved south of the Sierra Nevada record a pronounced shift from local to extraregional provenance caused by the development of drainages that extended across the breached mid-Cretaceous continental margin batholith to tap the continental interior. This geomorphic breaching of the mid-Cretaceous arc, and associated inland drainage migration, represents the culminating influence of Laramide low-angle subduction on the continental margin and likely occurred following subduction of the Shatsky conjugate plateau beneath the western United States.
