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TitleA petrochronological approach for the detrital record: tracking mm-sized eclogite clasts in the northern Canadian Cordillera
AuthorKellett, D A; Weller, O M; Zagorevski, A; Regis, D
SourceEarth and Planetary Science Letters vol. 494, 2018 p. 23-31,
Alt SeriesEarth Sciences Sector, Contribution Series 20160167
Mediapaper; on-line; digital
File formatpdf; html; docx; png; xlsx; xls
ProvinceBritish Columbia
AreaAtlin Lake
Lat/Long WENS-133.5000 -133.0000 59.2500 59.0000
Subjectstectonics; geochronology; tectonic history; accretion; sutures; terranes; basin evolution; thermal history; diffusion; metamorphism; depositional history; subduction; plate boundaries; orogenies; erosion; pressure-temperature conditions; sedimentary basins; clasts; eclogites; rutile; thermobarometry; radiometric dating; uranium lead dating; zircon dates; modelling; provenance; source areas; source rocks; bedrock geology; lithology; sedimentary rocks; conglomerates; electron microscope analyses; electron probe analyses; mass spectrometer analysis; spectroscopic analyses; Canadian Cordillera; Intermontane Belt; Whitehorse Trough; Laberge Group; Eclogite Ridge Member; Laurentia; Yukon-Tanana Terrane; Stikinia Terrane; suture zones; petrochronological analyses; thermochronological analyses; thermal diffusion; exhumation; plate collisions; sensitive high resolution ion microprobe (SHRIMP) analyses; Phanerozoic; Mesozoic; Jurassic; Triassic
Illustrationslocation maps; geoscientific sketch maps; photomicrographs; profiles; tables; spectra; phase diagrams; Concordia diagrams; models
ProgramWestern Cordillera, Regional porphyry transitions, GEM2: Geo-mapping for Energy and Minerals
AbstractSutures 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 ~300m 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 2.2-2.9GPa and greater than or equal to 800°C, cooled through Pb closure in rutile during Early Jurassic at greater than or equal to 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 ~4.1km/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.
Summary(Plain Language Summary, not published)
The Canadian Cordillera mountain belt was formed by the amalgamation of several independent blocks of crust, each containing particular rock types of particular ages and resource potential. This study looks at a part of the amalgamation history of these blocks, or 'terranes', that has been recorded in distinctive sediments that were shed off of the mountains and into a basin during amalgamation. The pebbles we study were transformed into a rock called eclogite while hot (>750 °C) and deep (~80 km) in the crust. Using a range of laboratory methods, we determine when and how quickly the rocks reached the Earth's surface, were eroded, and deposited into a sedimentary basin. The rapid cooling and exhumation rates we constrain are typical of plate boundary collision zones. We use the results to propose a collision between two terranes, Stikinia and Yukon-Tanana, during the latest Triassic, about 200 million years ago.