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TitleHygrometric control on the lithosphere-asthenosphere boundary: a 28 million year record from the Canadian Cordillera
AuthorCanil, D; Hyndman, R DORCID logo; Fode, D
SourceGeophysical Research Letters vol. 48, issue 9, e2020GL091957, 2021 p. 1-9,
Alt SeriesNatural Resources Canada, Contribution Series 20210119
PublisherBlackwell Publishing Ltd.
Mediapaper; on-line; digital
File formatpdf; html
ProvinceAlberta; British Columbia
Lat/Long WENS-141.0000 -118.0000 65.0000 49.0000
SubjectsScience and Technology; tectonics; mantle; plate margins; lithosphere; Water
Illustrationslocation maps; diagrams; cross-plots; charts
Released2021 04 30
AbstractThe depth to the lithosphere-asthenopshere boundary (LAB) provides a strong control on the temperature and strength of the lithosphere and its susceptibility to tectonic deformation. We probe the nature of the LAB by deriving the depth and source of mantle-xenolith bearing alkaline lavas aged 28 Ma to 8 ka in the Canadian Cordillera (CC). We document a striking coincidence of the average depth of equilibration of these lavas (65 ± 5 km) with the seismically observed LAB both in the CC and in western USA, and the change in H2O storage capacity at the spinel-garnet transition of fertile peridotite under the geothermal gradient of hot thin back arc regions. The convergence of these factors show the LAB of hot back arcs is hygrometrically controlled at this phase boundary, limiting the H2O to <150 ppm in the mantle lithosphere. Intraplate regions with a shallower LAB require more H2O and/or less fertile lithosphere.
Summary(Plain Language Summary, not published)
The surface of the earth is made of tectonic plates that vary in thickness and temperature, and governs how they deform under the forces of plate tectonics. The base of the plate is marked by a change in the speeds of seismic waves in the mantle indicates small amounts of melt below certain depths. We show a narrow depth range at which magmas stall en route to the surface beneath British Columbia and Yukon that correlates with the base of the plate in this region. In this and other continental margins, the depth to the base of the plate is controlled by the combined effects of a change in mineralogy and H2O storage capacity of mantle peridotite that determines whether or not melts are stable under a certain temperature.

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