Geochronology and tectonics of the northern Wolverine Complex, British Columbia

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Abstract
The Wolverine Complex is a metamorphosed and polydeformed sequence of Hadrynian clastic rocks that forms part of the Omineca Crystalline Belt in north-central British Columbia. Twenty-six Rb–Sr and K–Ar dates from an area at the north end of the complex are presented. Rb–Sr muscovite dates are the oldest, 70–166 Ma, and constrain the main metamorphic–deformational event to the Middle to Late Jurassic or earlier. K–Ar dates on muscovite and biotite are highly discordant and the dates of the minerals vary in the order Rb–Sr muscovite > K–Ar muscovite > K–Ar biotite. Many rocks show partial or complete homogenization of the isotopes during an early Tertiary thermal event, which has extensively reset K–Ar dates in part of the complex.The blocking temperatures of the isotopic systems when combined with the isotopic dates, other published dates, and estimated geothermal gradients, allow inference of thermal history and paleo-uplift rates. In the Chase Mountain area where the influence of Eocene resetting is either small or minimal, the rocks had cooled to 220 ± 40 °C by about 80 Ma ago or earlier. During their cooling from metamorphic temperatures of about 500 °C, they cooled at rates between 3 and 10 °C/Ma with an average minimum cooling rate of 4 °C/Ma. Using estimated geothermal gradients, corresponding uplift rates were 0.1–0.3 km/Ma or more.Because cooling of these rocks probably took place dominantly by advection resulting from uplift and erosion, a significant portion of the total uplift of these rocks was complete by the time they reached the biotite blocking temperature, 220 °C, at least 80 Ma ago. The predominantly Late Jurassic to Early Cretaceous uplift of the complex implied by these dates has important implications for regional tectonics and models of evolution for the Omineca Crystalline Belt and adjacent areas.

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