Mantle Exhumation in an Early Paleozoic Passive Margin, Northern                     Cordillera, Yukon

Canil, Dante; Johnston, Stephen T.; Evers, K.; Shellnutt, J. Gregory; Creaser, Robert A.

doi:10.1086/373971

Cited by 25 publications

(5 citation statements)

References 53 publications

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“…data). The ophiolite and orogenic massif samples are variably serpentinized (0 -50%) but retain coherent major and trace element trends consistent with partial melt extraction (Canil et al 2003;2006;Babechuk et al, 2010). The alkali basalt hosted xenoliths are completely fresh except for one sample (TM53) containing olivine that was extensively hematized by Fe-oxyhydroxides during emplacement in the lava flow.…”

Section: Mantle Peridotitesmentioning

confidence: 80%

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Mercury in some arc crustal rocks and mantle peridotites and relevance to the moderately volatile element budget of the Earth

et al. 2015

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We measured Hg concentrations in 37 igneous rocks from an arc crustal section and in 30 mantle peridotites from ophiolite, orogenic massif and xenolith settings. Mercury is heterogeneously distributed in the igneous rocks and shows a 'nugget effect', suggesting it is concentrated in a trace phase, likely sulfide. The abundance of Hg in the crustal samples varies from 0.9-8 ppb and correlates with S and Cu but no other element indicative of differentiation. The average of our data produces 2.9±2.6 Hg for the bulk crust, a factor of 10 lower than previous estimates. The mantle peridotites contained 0.2-5 ppb Hg and a correlation of Hg with Al, Cu, S or loss on ignition (LOI) depending on sample type. Secondary uptake of Hg due to low-temperature alteration or mantle metasomatism is evident in the ophiolite and orogenic massif samples, respectively. The primitive upper mantle (PUM) contains 0.4-0.6 ppb Hg based on the depletion/enrichment trends in the fresh xenolith samples that demonstrably retained primary Cu/S during emplacement. During mantle melting to produce the crust, Hg behaves as a mildly incompatible element (D Hg residue/melt ~ 0.1), not unlike Cu. For a chondritic abundance of 310 ppb Hg, our estimate for Hg in the mantle requires this element has a similar depletion to Se, Te or S in the bulk silicate Earth.

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Section: Mantle Peridotitesmentioning

confidence: 80%

“…We measured Hg in 30 samples of mantle peridotites (Table 2) from two ophiolites and an orogenic massif exhumed in the northern Canadian Cordillera (Canil et al, 2003;2006) and in xenoliths hosted in a Quaternary alkali basalt lava flow in central British Columbia (Canil and Russell, unpubl. data).…”

Section: Mantle Peridotitesmentioning

confidence: 99%

Mercury in some arc crustal rocks and mantle peridotites and relevance to the moderately volatile element budget of the Earth

et al. 2015

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“…The Buffalo‐Pitts orogenic peridotite massif located ~50 km to the southeast of the locality of 00RAY231A was exhumed into the Snowcap assemblage at c . 262–261 Ma (Canil et al., 2003; Johnston et al., 2007), indicating a significant extensional episode. Emplacement of the orogenic peridotites into the upper crust may have provided an alternative source of heat for the LPHT event but it also pre‐dates the age of metamorphism by c .…”

Section: General Discussion and Conclusionmentioning

confidence: 99%

“…This event is thought to be related to either intra‐arc thickening of the YTT during the closure of the Slide Mountain Ocean (Berman et al., 2007) or to thickening related to the collision of the YTT with North America following the closure of the Slide Mountain Ocean (Beranek & Mortensen, 2011). However, the link with crustal thickening is difficult to ascertain as this event also coincides with a period of major extension that culminated in the exhumation of orogenic peridotite in the YTT (Canil, Johnston, Evers, Shellnutt, & Creaser, 2003; Johnston, Canil, & Heaman, 2007). The last metamorphic event peaked at ~7.8 kbar and 595°C at 195–187 Ma (Berman et al., 2007; Staples et al., 2014).…”

Section: Regional Geologymentioning

confidence: 99%

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Gaidies

Morneau

Petts

et al. 2020

Journal Metamorphic Geology

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Garnet crystallization has been simulated in the MnNCKFMASHT model system using a simple nucleation and growth scenario, calibrated with three‐dimensional garnet crystal size distribution data as well as garnet compositional data obtained by electron probe micro‐analysis and laser ablation inductively coupled plasma mass spectrometry. Results indicate wide‐spread Barrovian‐type metamorphism for garnet‐zone rocks from the Snowcap assemblage along a hairpin‐shaped pressure–temperature loop with garnet growth from ~515°C and 4 kbar to metamorphic peak conditions of ~600°C and 6 kbar. Lu–Hf garnet‐whole geochronology points to initial garnet growth at c. 192.2 ± 4.7 Ma. Sm–Nd garnet–whole‐rock geochronology applied to a sample with garnet rims enriched in Sm indicates that the metamorphic peak conditions have been attained at c. 172.9 ± 2.4 Ma. Older garnet growth at c. 245.3 ± 0.8 Ma during a low‐P–high‐T event has been preserved as garnet cores separated from the Jurassic garnet rims by a sharp microstructural and compositional discontinuity. These polyphase garnets are restricted to Mn‐rich metapelitic lithologies. Trace element zoning in the outermost ~50 μm thin segments of the Early Triassic garnet cores reflects a short garnet growth episode in the presence of melt at peak conditions of ~710°C and 2.5 kbar, supported by phase equilibrium and diffusion geospeedometry calculations. Diffusion simulations across the interface between the Early Triassic garnet core and the Jurassic garnet rim indicate that the Barrovian‐type metamorphism during the Jurassic lasted for 20–25 Myr, in line with the radiometric data.

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“…At ca. 262 Ma, the Buffalo Pitts peridotite was emplaced within metasedimentary rocks of the Snowcap assemblage (Canil et al, 2003;Johnston et al, 2007) ~40 km SE of locality JR-140 ( Fig. 2A).…”

Section: Timing Constraints and Tectonic Significance Of The Yrsz: A mentioning

confidence: 99%

Structural evolution of a crustal-scale shear zone through a decreasing temperature regime: The Yukon River shear zone, Yukon-Tanana terrane, Northern Cordillera

et al. 2018

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We present the first detailed structural analysis of the Yukon River shear zone (YRSZ), which forms an important structural break within the Yukon-Tanana terrane of the Northern Cordillera in Yukon (Canada). The YRSZ is a NW-SE-striking shear zone that juxtaposes Mississippian orthogneiss hanging-wall rocks (Simpson Range suite) against preLate Devonian metasedimentary footwall rocks (Snowcap assemblage). Field and microstructural analyses, including quartz c-axis fabric investigation, indicate that the YRSZ initiated as a top-ESE mid-crustal shear zone active through a temperature range of ≥650-500 °C to ~540-440 °C. Constraints from the footwall associated with top-ESE shearing on the YRSZ at mid-crustal conditions record a decrease in deformation temperature toward the shear zone, coincident with a transition from coaxial to non-coaxial deformation and an increase in fabric intensity, strain rate, and differential stress estimates. Collectively, these spatial trends represent a classic example of a narrowing shear zone that progressively localizes and intensifies deformation as ambient temperature decreases. U-Pb zircon geochronometry of a deformed Permian orthogneiss from within the YRSZ combined with previously published thermochronometry bracket the timing of top-ESE mid-crustal shearing between 259 ± 2 Ma and 176-168 Ma, either during Late Permian-Middle Triassic metamorphism and lithospheric extension or latest Triassic-Early Jurassic metamorphism and crustal thickening. The YRSZ was subsequently reactivated as a top-WNW upper-crustal thrust fault zone during or after Early to Middle Jurassic cooling and exhumation at 176-168 Ma. This top-WNW thrusting within the YRSZ may be responsible for structural separation of Late Triassic and Early Jurassic plutonic rocks in the hanging wall of the YRSZ from Permian plutonic rocks in its footwall.

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Mantle Exhumation in an Early Paleozoic Passive Margin, Northern Cordillera, Yukon

Cited by 25 publications

References 53 publications

Mercury in some arc crustal rocks and mantle peridotites and relevance to the moderately volatile element budget of the Earth

Mercury in some arc crustal rocks and mantle peridotites and relevance to the moderately volatile element budget of the Earth

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Structural evolution of a crustal-scale shear zone through a decreasing temperature regime: The Yukon River shear zone, Yukon-Tanana terrane, Northern Cordillera

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