Paleomagnetism and Detrital Zircon Geochronology of the Skeena Group, British Columbia

The mid-Cretaceous Skeena Group of British Columbia is a sedimentary continental margin deposit that overlies the lower Jurassic Hazelton Group of the Stikine Terrane. Nine paleomagnetic sites were collected in 2006 and 2007, demagnetized thermally in 50-15°C steps, and high temperature components fit using principal component analysis. A new Ar40/Ar39 age of 93.9 ± 0.6 Ma for a flow of the Rocky Ridge Formation was also collected. Three volcanic sites of the Rocky Ridge Volcanics possess coherent magnetizations, but did not prove useful. Five of six sedimentary sites from the Rocher de Boule and Bulkley Canyon Formations appear more likely to retain a primary magnetization. Curie temperature analysis indicates the primary carrier of magnetic remanence is magnetite. Hysteresis and direct field demagnetization data indicate the magnetite is primarily multi-domain in the volcanic sites and possess a mix of single and multi-domain grains in the sedimentary rocks, which may account for the more likely primary remanence from the sedimentary formations When subjected to a bootstrap fold test, the sedimentary sites have maximum grouping at 40% untilting, but the hypotheses that the magnetization was acquired either before or after tilting cannot be rejected at the 95% confidence level. An inclination-only paleolatitude analysis was used to estimate paleolatitude as different declinations between sites suggest rotation between sites. The resulting paleolatitude for the Skeena Group is ~57°± 21°. This is equivalent to a location ~1150 ± 2000 km south of the expected latitude with respect to North America. Uranium-lead ages of detrital zircons from a sample of the Rocher de Boule Formation were obtained using laser ablation inductively coupled mass spectrometry. These ages form several Mesozoic peaks indicating that the majority of zircons came from Stikine terrane units and Mesozoic arc volcanism. A Mississippian peak with some Proterozoic aged grains suggests a source from the Yukon-Tanana terrane. No Archean-aged grains were found