DETRITAL AGE CONSTRAINTS ON THE AGE OF DEPOSITION AND PROVENANCE OF THE METASEDIMENTARY COVER SEQUENCE OF THE THOR-ODIN DOME, BRITISH COLUMBIA, CANADA

U-Pb LA – ICP-MS zircon analysis was carried out on six metasedimentary units of the cover sequence of Monashee Complex, a metamorphic complex within the Omineca Belt of the Canadian Cordillera, in order to constrain the ages of deposition and provenance areas. The samples were taken from northwest Thor-Odin dome, the southern dome of the Monashee Complex, along a transect from the basal quartzite unit to the structurally (and stratigraphically?) highest unit of the Monashee Complex. The cover sequence overlies a Paleoproterozoic basement of orthogneiss and paragneiss that can be correlated with the Canadian Shield. It contains quartzite, orthogneiss, paragneiss, pelitic schist, calcsilicate gneiss and marble.

The Monashee cover sequence of northwest Thor-Odin dome can be separated into three groups, 1 to 3 from lowest to highest structural level, based on age and provenance of our samples combined with existing ID-TIMS data. Group 1 includes the basal quartzite and is characterized by ~2.70-2.36 Ga and ~2.08-1.80 Ga zircon populations, with a 1802 ± 18 Ma youngest detrital zircon age. Group 2 includes the similar populations as Group 1 (~2.70-2.36 Ga and ~2.08-1.64 Ga), but also a ~560 Ma zircon. Group 3 received most zircons from 1.88-1.64 Ga and 1.48-1.30 Ga sources and significantly less zircons from the ~2.70-2.36 Ga source than Groups 1 and 2. It also contains rare ~600-560 Ma zircons.

Groups 1 and 2 had source areas in the Canadian Shield, with Group 2 having a potentially much younger age of deposition than Group 1 units. Group 1 may be correlative with units of the northeastern part of the Mesoproterozoic Belt-Purcell Supergroup. Alternatively, it could be a Paleoproterozoic passive margin sequence. Group 2 may be correlative with Lower Paleozoic units of the Kootenay Arc. Group 3 units occur exclusively west of Eocene brittle faults, such as the Victor Creek Fault, that show evidence for significant dextral motion. While Group 3 may have been deposited at the same time as Group 2 and may also be correlative with Lower Paleozoic units of the Kootenay Arc, the provenance areas were likely farther to the south, perhaps including sedimentary and igneous units in the Belt-Purcell basin and igneous and metamorphic rocks of the Mazatzal orogenic belt. Group 3 units were later juxtaposed with Group 2 units along the Eocene faults.