NATIVE MESOZOIC SIERRA NEVADA ARC INDICATED BY DETRITAL ZIRCON GEOCHRONOLOGY OF PREBATHOLITHIC FRAMEWORK AND INTRA-ARC STRATA

The Mesozoic Sierra Nevada arc of California was built through pre-Mesozoic W Laurentian continental margin strata and Mesozoic intra-arc deposits exposed in isolated pendants. Pre-Mesozoic framework strata comprise terranes with distinct detrital zircon provenance and post-depositional histories, forming 3 broad groups: allochthonous Neoproterozoic-lower Paleozoic strata with interpreted W Laurentian sources; Neoproterozoic-Permian strata parautochthonous to SW Laurentia; and middle-upper Paleozoic deposits related to the McCloud Arc. The composite detrital age population of the pre-Mesozoic Sierran framework is indistinguishable from that of Mesoproterozoic to Permian inboard SW Laurentian margin strata, providing a strong provenance link to W Laurentia. The prebatholithic framework terranes were emplaced against the tectonically reorganized SW Laurentian margin in the Late Paleozoic, culminating with Permo-Triassic collapse of the fringing arc against SW Laurentia and initiation of Cordilleran arc activity.

Intra-arc sediments show consistent stratigraphic and detrital zircon provenance trends across the Sierra: Triassic strata show unimodal Triassic detrital ages and few pre-Mesozoic grains. Sierra-wide, westward prograding, Jurassic marine overlap deposits show Jurassic major age peaks, few Triassic ages, and a spread of pre-Mesozoic detrital ages. This trend continues in Early to Late Cretaceous sediments with progressively younger major peaks. Mesozoic sediments show Pre-Mesozoic detrital ages indistinguishable from prebatholithic framework and SW Laurentian margin detrital ages suggesting significant sediment recycling from older sources. Jurassic-Cretaceous sediments show no detrital zircon age shifts in response to proposed Late Jurassic arc/terrane collisions outboard of the Foothills Suture. Ages of pre, syn, and post-tectonic intrusions and strata are instead consistent with multiple episode of prolonged and heterogeneous Mesozoic tectonism.

Late Paleozoic assembly of displaced Sierran framework terranes with W Laurentian provenance and deposition of Permian-Mesozoic strata across the Sierra indicate that the Permo-Triassic to Cretaceous Sierran arc was native to the SW Cordillera with limited intrabatholithic displacements (<10s-100 km).