The age and provenance of the Lay Range assemblage provides an indirect record of basement to north-central Quesnellia, British Columbia

The Lay Range assemblage, the lowest exposed lithostratigraphic unit of north-central Quesnellia, is separated into lower sedimentary and upper mafi c tuff divisions. Fossil and fi eld evidence indicates deposition of the lower sedimentary division during the Late Mississippian to Middle Pennsylvanian and of the upper mafi c tuff division during the Middle Pennsylvanian to early Permian. A quartz sandstone and polymictic pebble conglomerate from the lower part of the lower sedimentary division yield detrital zircon U-Pb ages between 360 and 290 Ma (Carboniferous to early Permian), with a range of older detrital zircons from ca. 3600 to 890 Ma (Archean and Proterozoic). A small population of zircons ranges from 450 to 390 Ma (n=4; Ordovician to Devonian). The Carboniferous detrital zircons have mostly juvenile εHf(t), indicating that the parental magmas did not interact with older crust. Few zircons are more evolved and were derived from parental magmas that interacted with or melted from crust as old as middle Mesoproterozoic. The combined εHf(t) and trace element compositions of detrital zircon are consistent with formation in a juvenile arc during the Carboniferous. Comparison of Lay Range detrital zircon U-Pb, Hf, and trace element systematics indicate a similar timing of arc magmatism with eastern Stikinia and Wrangellia, but little relationship to ancient North America or Yukon-Tanana terrane. The older detrital zircons (Archean through Paleozoic) were sourced from a fringing landmass, possibly a continental oceanic plateau, that had little to no role in the petrogenesis of the Carboniferous magmas. The spread of ages in the Lay Range assemblage zircon distributions likely records multiple cycles of deposition, uplift, erosion, transport, and sedimentation. One possibility is that the fringing landmass was calved from the Neoproterozoic through Cambrian western North American passive margin.