A petrochronological approach for the detrital record: Tracking mm-sized eclogite clasts in the northern Canadian Cordillera

• Published in: Earth and Planetary Science Letters
• Main Authors: Kellett, Dawn A., Weller, Owen M., Zagorevski, Alex, Regis, Daniele
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2018
• Subjects: 05 - Petrology - Igneous; Metamorphic and Volcanic Studies; Yukon; Whitehorse
• Online Access: http://eprints.esc.cam.ac.uk/4287/; http://eprints.esc.cam.ac.uk/4287/1/1-s2.0-S0012821X18302395-main.pdf; https://doi.org/10.1016/j.epsl.2018.04.036

Sutures recording the accretion history of the Canadian Cordillera terranes are poorly preserved. The Whitehorse trough syn-orogenic basin formed during early Mesozoic terrane accretion at the western margin of Laurentia and contains a ∼300 m thick horizon that includes eclogite clasts possibly sourced from a suture zone. By applying petrochronological micro-analytical techniques to the mm-diameter eclogite clasts, including thermobarometry and in situ rutile thermochronology, as well as detrital zircon geochronology and thermal diffusion modeling, we constrain a source-to-sink path for the clasts. The eclogite clasts likely reached peak metamorphic conditions of 2.2–2.9 GPa and ≥800 °C, cooled through Pb closure in rutile during Early Jurassic at ≥610 °C and were deposited into the basin by latest Pliensbachian/earliest Toarcian. This history implies minimum mean cooling and exhumation rates on the order of ∼38 °C/myr and ∼4.1 km/myr, respectively, consistent with rates reported for subduction-related eclogite worldwide. We suggest the most likely source for the clasts is the suture between the Yukon–Tanana and Stikinia terranes, involving a latest Triassic collision, followed by rapid Early Jurassic exhumation of the lower plate Yukon–Tanana terrane, either by buoyant extrusion or in a plate boundary zone metamorphic core complex. Our study demonstrates that micro-analytical techniques used for petrochronology can be applied to very small lithic clasts in the sedimentary record towards the tectonic reconstruction of accretionary orogens.