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 defor mation and metamorphism, we successfully analyzed the age and provenance of six samples collected at various structural levels, using U-Pb detrital zircon laser-ablationinductively 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 signifi cance. 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 Cordi lleran gneiss domes.

Effects of Paleogene faults on the reconstruction of the metamorphic history of the northwestern Thor-Odin culmination of the Monashee complex, southeastern British Columbia

“…The four samples analyzed were collected from a part of the Monashee cover sequence (Fig. 2) that is interpreted as latest Neoproterozoic or younger, and at least in part Devonian, based on the presence of sparse latest Proterozoic or earliest Cambrian zircon grains and one Devonian (396 Ma) zircon grain in those samples (Kuiper et al, 2014). Samples lie along a transect from lowest to highest structural level, generally from east to west, in the following order: 30, 54, 70, and 92/97.…”

“…For samples 91 and 97, zircon ID-TIMS data for single and multigrain fractions are included because both samples contain predominantly metamorphic zircon (as opposed to predominantly detrital zircon in the other samples; cf. Kuiper et al, 2014). ID-TIMS monazite analyses showed a potential for multiple monazite ages per sample, possibly also within individual grains.…”

“…The geological significance of the Victor Creek fault has been alluded to earlier by Lorencak et al (2001), Kuiper et al (2014), and (Toraman et al, 2014). Kuiper et al (2014) noted that detrital zircon in Neoproterozoic and younger metasedimentary units west of the Victor Creek fault (samples 30 and 54; same as used in this study) yielded fewer Archean and Paleoproterozoic ages and more Mesoproterozoic ages than those east of the Victor Creek fault (samples 70, 92, and 97; same as used in this study), possibly because they were deposited in different regions and later juxtaposed by the fault. Data by Gilley (1999) andVan Rooyen et al (2011) show the same trends across the Victor Creek fault, and data by Crowley (1997) show the same trends across the Ratchford Creek-Perry River normal fault (Kuiper et al, 2014).…”

“…Rocks of the Selkirk domain (cf. Kuiper et al, 2014) west of the Monashee complex structurally overlie the Monashee complex. They consist of Neoproterozoic and younger quartzite, marble, paragneiss, and orthogneiss (Parrish, 1995, and references therein).…”

“…In this contribution, we consider the effects of one such fault, the Paleogene Victor Creek fault of the western Monashee complex, to explain at least part of the complex distribution of ages of deformation and metamorphism. This fault is known to at least locally display discon-tinuity in geology on either side of the fault (Kruse and Williams, 2005) and in detrital zircon signatures (Kuiper et al, 2014), and some offset has been inferred from this (see following). In this contribution, we investigate the differences in metamorphic history across the fault.…”