U-Pb detrital-zircon geochronology of northern Salinian basement and cover rocks

Abstract

Salinia is an out-of-place granitic ter-rane in central coastal California whose debated origin is critical to understanding the tectonic history of southwestern North America. Salinian metasedimentary and sedimentary rocks that respectively host and cover its predominant arc rocks should contribute important data about its origin and kinematic history, but pervasive intrusion, high-grade metamorphism and Cenozoic erosion of the Salinian block have inhibited their widespread characterization and correlation. To further address these problems, we report 605 U-Pb detrital-zircon geo-chronologic ages collected by laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) from seven Salinian metasedimentary framework (Sur Series) and sedimentary cover samples. Samples collected from the Sur Series contain Late Archean (2.5–2.9 Ga), late Paleo-proterozoic (1.6–1.9 Ga), Mesoproterozoic (0.9–1.5 Ga), Neoproterozoic (0.65–0.8 Ga), Paleozoic (250–450 Ma), and possibly Mesozoic U-Pb detritalzircon ages. Samples collected from Upper Cretaceous cover units have various age-peak distributions, which collectively include late Paleoproterozoic (1.6–1.8 Ga), early Mesoproterozoic (1.35–1.55 Ga), Permo-Triassic (220–290 Ma), and Jurassic-Cretaceous (80–190 Ma) peaks. From these data, several interpretations are made. (1) Maximum depositional ages of the Sur Series and cover intervals are 280–360 Ma and 78–90 Ma, respectively. (2) The presence of Late Archean, early Paleoproterozoic, and Neoproterozoic zircons in Salinian metasedimentary rocks suggest that uplift and erosion of adjacent basins recycled sediment onto Salinia. (3) The abundant pre-Mesoproterozoic detritalzircon ages in Sur Series and cover units preclude the possibility that Salinia originated in southern Mexico, as has been previously suggested. (4) Five of six key detritalzircon age peaks identified in Salinian basement and cover units are nowhere more closely arranged than in the Mojave Desert–Peninsular Ranges region of Baja and southern Alta California. (5) Paleozoic and early Mesozoic detrital zircons in Sur Series and cover units match the ages of several plutonic events that occurred along the western margin of North America—however, Permian ages favor a Mojave Desert origin over other candidates. Collectively, these and other data suggest that Salinia resided in the Mojave Desert–Peninsular Ranges region from the late Paleozoic until the Late Cretaceous, after which it was rapidly exhumed, deposited upon, and then translated outboard and northward to its current position.

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