Lithospheric domains and controls on kimberlite emplacement, Slave Province, Canada: Evidence from elastic thickness and upper mantle composition

The observed density distribution of the lower mantle is compared with density measurements of the (M g,Fe)SiO 3 perovskite and (Mg,Fe)O magnesiowtistite highpressure phases as functions of pressure, tem perature and composition. We find that for plausible bounds on the composition of the upper mantle (ratio of magnesium to iron + magnesium components x M g ^ 0.88) and the temperature in the lower mantle ( T ^ 2000 K), the high-pressure mineral assemblage of upper-mantle composition is at least 2 .6 ( ± 1 ) % less dense than the lower m antle over the depth range 1000-2000 km. Thus, we find that a model of uniform m antle composition is incompatible with the existing mineralogical and geophysical data. Instead, we expect that the mantle is stratified, with the upper and lower m antle convecting separately, and we estimate that the compositional density difference between these regions is about 5 ( + 2) %. The stratification may not be perfect (‘leaky layering’), but significant intermixing and homogenization of the upper and lower m antle over geological timescales are precluded.

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Experimental melting studies on a model upper mantle composition at high pressure under water-saturated and water-undersaturated conditions

Earth and Planetary Science Letters ◽

10.1016/0012-821x(73)90176-3 ◽

1973 ◽

Vol 19 (1) ◽

pp. 37-53 ◽

Cited By ~ 505

Author(s):

D.H. Green

Keyword(s):

High Pressure ◽

Upper Mantle ◽

Mantle Composition ◽

Water Saturated ◽

Experimental Melting

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Surface-wave images of western Canada: lithospheric variations across the Cordillera–craton boundary

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2017-0277 ◽

2018 ◽

Vol 55 (8) ◽

pp. 887-896 ◽

Cited By ~ 4

Author(s):

Taras Zaporozan ◽

Andrew W. Frederiksen ◽

Alexey Bryksin ◽

Fiona Darbyshire

Keyword(s):

Surface Wave ◽

Phase Velocity ◽

Upper Mantle ◽

High Velocity ◽

Western Canada ◽

Low Velocity ◽

Phase Velocities ◽

Slave Province ◽

Upper Mantle Structure ◽

Tectonically Active

Two-station surface-wave analysis was used to measure Rayleigh-wave phase velocities between 105 station pairs in western Canada, straddling the boundary between the tectonically active Cordillera and the adjacent stable craton. Major variations in phase velocity are seen across the boundary at periods from 15 to 200 s, periods primarily sensitive to upper mantle structure. Tomographic inversion of these phase velocities was used to generate phase velocity maps at these periods, indicating a sharp contrast between low-velocity Cordilleran upper mantle and high-velocity cratonic lithosphere. Depth inversion along selected transects indicates that the Cordillera–craton upper mantle contact varies in dip along the deformation front, with cratonic lithosphere of the Taltson province overthrusting Cordilleran asthenosphere in the northern Cordillera, and Cordilleran asthenosphere overthrusting Wopmay lithosphere further south. Localized high-velocity features at sub-lithospheric depths beneath the Cordillera are interpreted as Farallon slab fragments, with the gap between these features indicating a slab window. A high-velocity feature in the lower lithosphere of the Slave province may be related to Proterozic or Archean subduction.

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