DETRITAL ZIRCON INVESTIGATIONS OF EARLY CRETACEOUS SEDIMENT PROVENANCE AND TRANSPORT ASSOCIATED WITH THE SIERRA NEVADA ARC, CA

Detrital zircon data from metamorphic pendants exposed in the southwestern Sierra Nevada batholith and from the western margin of the Great Valley (all sites approx. modern 36°N latitude) provide incomplete records of (1) late Paleozoic to early Mesozoic modification of the southwestern margin of North America, and (2) proximal depositional environments associated with the Mesozoic Cordilleran arc. The newly defined Goldstein Peak Formation provides a rare record of nonmarine sedimentation and volcanism within an Early Cretaceous intra-arc basin. Nonmarine basin sedimentation was grossly synchronous with initiation of marine deposition within the nascent Great Valley forearc basin, which at that time was composed of isolated depocenters. U-Pb zircon dates demonstrate a similar depositional age and provenance for Goldstein Peak fluvial deposits and lowermost Gravelly Flat forearc deposits, each comprising subequal contributions from the Mesozoic arc and pre-Mesozoic sources. Preliminary investigations of local metamorphic pendants suggest correlations that support recent reconstructions of pre-arc modification of the North American margin, including recognition of rocks of the Snow Lake block and of the Golconda allochthon. Current data indicates that all major detrital zircon populations present in the intra-arc and forearc basins at 36°N could have been derived from erosion of the arc and its metamorphic framework, thus not requiring arc-traversing fluvial systems in the Early Cretaceous. Metamorphic records of younger, mid-Cretaceous sedimentation suggest that future detrital zircon investigations of Sierra Nevada pendants may extend the record of proximal arc sedimentation further through the Mesozoic.