REGIONAL – SCALE DETRITAL ZIRCON PROVENANCE STUDY OF THE MIDDLE TO LATE ORDOVICIAN EUREKA QUARTZITE, EAST-CENTRAL IDAHO

The Middle to Late Ordovician Eureka Quartzite (and its equivalents) is a unique orthoquartzite deposited along a carbonate-dominated Lower Paleozoic passive margin of the western North American Cordillera. Previous detrital zircon provenance studies indicate that the sole source of sediment is the Peace River Arch, British Columbia (Gehrels et al., 1995; Gehrels and Dickinson, 1998; Gehrels, 2000). This model, which is supported by a north to south decrease in grain size and increase in sediment sorting (Ketner, 1968), is referred to as the long-distance transport model. According to this model sediment was transported over 2000 km by southerly long-shore currents along the passive margin, and that potentially exposed basement source areas on the Transcontinental Arch east of the passive margin, as well as recycling of underlying Mesoproterozoic to Lower Paleozoic siliciclastic rocks supplied little or no detritus, even though these potential sources would have been positioned near the equator during the Ordovician and subject to intense equatorial weathering. A method for testing the long-distance transport model is a regional study of provenance at a high-resolution scale, to provide insights into local sediment source inputs, as well as their spatial and temporal variations.

New U-Pb geochronologic analyses of Middle to Late Ordovician Kinnikinc Quartzite detrital zircons by the LA-ICPMS, coupled with paleocurrent measurements provide a test for the single-source long-distance transport model. The Middle-Late Ordovician Kinnikinic Quartzite in east-central Idaho was deposited directly on Early Ordovician plutons and Mesoproterozoic metasedimentary rocks. A high-resolution, 3-dimensional data set is being assembled by sampling the tops and bottoms of Kinnikinic Quartzite measured sections, which are 10's of km apart, along depositional strike and dip for detrital zircons and coeval paleocurrents. Preliminary detrital zircon data and paleocurrent measurements that provide an important test of the long-distance transport model will be presented.