LASER ABLATION ICPMS GEOCHRONOLOGY OF MIDDLE-LATE ORDOVICIAN KINNIKINIC QUARTZITE

Middle-Late Ordovician quartzite and sandstone were deposited in a high energy, shallow-shelf marine environment along the periphery of the Transcontinental Arch. The Eureka Quartzite and its lateral equivalents along the western Laurentian Cordillera extend from the Peace River Arch, British Columbia to northern Mexico. Similar siliciclastic units (Simpson Sandstone, Cable Canyon Sandstone, and St. Peter Sandstone) were deposited along the eastern side of the Transcontinental Arch. These siliciclastic strata represent a unique episode of mature siliciclastic deposition during an otherwise carbonate-dominated depositional phase on Laurentia. The Kinnikinic Quartzite in Idaho differs from most of its coeval units along the Laurentian margin, in that many of its eastern exposures were deposited unconformably on Mesoproterozoic metasedimentary rocks or Ordovician plutons along the Lemhi Arch. Laser ablation ICP-MS U-Pb geochronology of 1439 individual detrital zircon grains from eleven samples (four locations) of Kinnikinic Quartzite provides a distinct spectrum of ages: ~0.9-1.3 Ga, 1.8-2.0 Ga, ~2.0-2.2 Ga, and ~2.4-2.9 Ga. This age spectrum suggests provenance links to sources east of the Paleozoic passive margin, rather than to the north (Peace River Arch). It is hypothesized that the Trans-Hudson Arch (and Saskatchewan craton), adjacent Paleoproterozoic-Archean provinces (Wyoming, Hearne, and Rea) were major contributors of sediment. Recycling of underlying metasedimentary units (Mesoproterozoic Belt Supergroup and lateral equivalents) was nominal. The detrital zircon populations of all Kinnikinic Quartzite samples are similar, but slight changes in populations occur spatially between sample locations and temporally within sample locations. Measures of overlap and similarity calculated for each sample of Kinnikinic Quartzite against each other provide a numerical evaluation of the spatial and temporal provenance variation. The average overlap is 0.665, and average similarity is 0.823. Spatial and temporal variations in provenance are suggested to be a result of long-term sea level fluctuations recorded in systems tracts, which are capable of covering (TST, HST), or uncovering (LST, FSST) broad areas of potential source rocks.