Age and provenance of a Paleoproterozoic to Devonian Canadian Cordilleran sequence of metasedimentary rocks, Thor-Odin dome, southeastern British Columbia

Abstract

We present a U-Pb detrital zircon age and provenance study of a sequence of metasedimentary rocks in the northwestern Thor–Odin high-grade gneiss dome within the Omineca crystalline belt of the Canadian Cordillera. Despite strong overprint by deformation and metamorphism, we successfully analyzed the age and provenance of six samples collected at various structural levels, using U-Pb detrital zircon laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis. The Thor–Odin dome consists of Paleoproterozoic basement and a metasedimentary cover sequence of previously unknown age and tectonic significance. Our results indicate that the oldest units of this sequence may be Paleoproterozoic, and some of the oldest known metasedimentary rocks in the Canadian Cordillera, originally deposited on top of Laurentian basement rocks. The youngest rocks are Devonian and deposited shortly before the onset of widespread Late Devonian to early Mississippian igneous activity in the Selkirk Domain or Kootenay arc. The cover sequence of the Thor–Odin dome thus preserves some of both the oldest and the youngest (meta)sedimentary rocks deposited between the formation of supercontinent Columbia and the onset of igneous activity and convergence that marked the beginning of Cordilleran deformation and metamorphism. Parts of as many as ∼1.4 b.y. of sedimentary history are preserved in the Thor–Odin dome, implying that much information on the sedimentary history of the Canadian Cordillera may be hidden in other Cordilleran gneiss domes.