DECOUPLING OF WHOLE ROCK ND AND DETRITAL ZIRCON U-PB PROVENANCE DETERMINATIONS-AN EXAMPLE FROM THE CAMBRIAN WOOD CANYON FORMATION, SW NORTH AMERICA

New and existing whole rock Nd isotopic data and detrital zircon U-Pb age spectra from the Cambrian Wood Canyon Formation from various locations in SW North America were used to assess whether the two datasets necessarily yield similar inferences regarding the provenance of siliciclastic sediments. The subarkosic, fluvial middle member of the Wood Canyon Formation in both cratonal (Marble Mountains, CA) and off-craton (Nopah Range, CA) locations in the Mojave Desert region are dominated by high whole rock ε_Nd (0) values (>-10) that align along an ~1.1 Ga reference isochron. The high ε_Nd (0) sedimentary rocks all have detrital zircon U-Pb age spectra dominated by a ~1.1 Ga peak, suggesting that the bulk sediment and entrained detrital zircon were both derived from Mesoproterozoic sources. Possible sources include proximal, shallowly intruded but now eroded, granitic rocks related to the ~1.1 Ga mafic dikes that are widespread in southwestern North America and/or distal Grenvillian-age rocks eroded along the flanks of Cambrian southern Oklahoma aulacogen. Detailed Nd isotopic data the Wood Canyon Formation in Nopah and Marble Mountains, however, reveals that the bulk Wood Canyon Formation is not composed exclusively of high ε_Nd(0) sediment but instead is interbedded with lower ε_Nd(0) sediment clearly derived from the local Paleoproterozoic (Mojave Province) basement. Aside from sediment at the basal nonconformity on basement in the Marble Mountains, where detrital zircon are dominated by 1.7 Ga grains, the lower ε_Nd(0) sedimentary rocks still mainly contain ~1.1 Ga grains. In these rocks, the provenance of these bulk sediment based on whole rock Nd and the detrital zircon U-Pb are not equivalent. Exactly why ~1.1 Ga detrital zircon dominate even in bulk sediment derived from ~1.7 basement rocks is unclear, but our results demonstrate that detrital zircon U-Pb age spectra do not always faithfully reflect the sources of the bulk sediment in which the zircons are entrained.