Constraints on the Fate of Delaminated Lithosphere in the Upper and Mid‐Mantle.

Delamination of lower continental lithosphere is known to have occurred under different tectonic settings. However, its fate in the mantle is poorly understood. By analyzing global seismic models, we find that most of likely lithosphere that delaminated during the Cenozoic and Mesozoic is preserved in the mantle transition zone, especially beneath North America and Africa. Numerical experiments indicates that delaminated lithosphere can remain stagnant in the mantle transition zone for tens of millions of years, followed by its potential sinking into the lower mantle or re‐rising to shallower depths depending on its density, the Clapeyron slope of the spinel‐to‐post‐spinel phase change and increase in mantle viscosity at ∼660–1,000 km depths. Re‐ascent occurs when delaminated lithosphere is reheated so that its effective density becomes lower than its surrounding ambient mantle after ∼100 Myr. Delaminated fragments can also potentially be mobilized by underlying global mantle flow to move horizontally away from plume regions. Plain Language Summary: The phenomenon of lower lithospheric delamination has been recognized in various tectonic settings, but the ultimate fate of these delaminated fragments within the mantle remains poorly known. From global seismic tomographic models, we gain first‐order constraints on the potential locations of geologically recent (<250 Ma) delaminated lithosphere, particularly in regions distant from subduction zones. A significant portion of Cenozoic and Mesozoic delaminated lithosphere appears to still be sequestered within the mantle transition zone, with pronounced concentrations beneath the Mesozoic and Cenozoic locations of North America and Africa. Numerical simulations further corroborate the hypothesis that these fragments of delaminated lithosphere can remain stagnant within the mantle transition zone over these geologically interesting timescales. Delaminated lithosphere can also re‐rise or move horizontally depending on underlying global mantle flow. Key Points: Seismic tomographic models provide first‐order constraints on the location of recent delaminated lithosphere in the upper and mid‐mantleDelaminated lithosphere can remain stagnant in the mantle transition zone for tens to hundreds of millions of yearsDepending on underlying mantle flow, delaminated lithosphere can also eventually warm and rise, or even move horizontally [ABSTRACT FROM AUTHOR]