Quantifying relationships between basalt geochemistry, shear wave velocity and asthenospheric temperature beneath western North America.

Klöcking, M. and White, N. J. and Maclennan, J. and McKenzie, D. P. and Fitton, J. G. (2018) Quantifying relationships between basalt geochemistry, shear wave velocity and asthenospheric temperature beneath western North America. Geochemistry, Geophysics, Geosystems, 19 (9). pp. 3376-3404. ISSN 15252027 DOI https://doi.org/10.1029/2018GC007559

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Western North America has an average elevation that is ∼2 km higher than cratonic North America. This difference coincides with a westward decrease in average lithospheric thickness from ∼240 to <100 km. Tomographic models show that slow shear wave velocity anomalies lie beneath this region, coinciding with the pattern of basaltic magmatism. To investigate relationships between magmatism, shear wave velocity, and temperature, we analyzed a suite of >260 basaltic samples. Forward and inverse modeling of carefully selected major, trace, and rare earth elements were used to determine melt fraction as a function of depth. Basaltic melt appears to have been generated by adiabatic decompression of dry peridotite with asthenospheric potential temperatures of 1340 ± 20 °C. Potential temperatures as high as 1365 °C were obtained for the Snake River Plain. For the youngest (i.e., <5 Ma) basalts with a subplate geochemical signature, there is a positive correlation between shear wave velocities and trace element ratios such as La/Yb. The significance of this correlation is explored by converting shear wave velocity into temperature using a global empirical parameterization. Calculated temperatures agree with those determined by inverse modeling of rare earth elements. We propose that regional epeirogenic uplift of western North America is principally maintained by widespread asthenospheric temperature anomalies lying beneath a lithospheric plate, which is considerably thinner than it was in Late Cretaceous times. Our proposal accounts for the distribution and composition of basaltic magmatism and is consistent with regional heat flow anomalies.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA73
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
12 - PhD
Journal or Publication Title: Geochemistry, Geophysics, Geosystems
Volume: 19
Page Range: pp. 3376-3404
Identification Number: https://doi.org/10.1029/2018GC007559
Depositing User: Sarah Humbert
Date Deposited: 08 Aug 2018 09:59
Last Modified: 12 Sep 2019 09:41
URI: http://eprints.esc.cam.ac.uk/id/eprint/4312

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