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

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 similar to 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 degrees C, cooled through Pb closure in rutile during Early Jurassic at >= 610 degrees 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 similar to 38 degrees C/myr and similar to 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. Crown Copyright (C) 2018 Published by Elsevier B.V. All rights reserved.