What’s under the youngest volcanism on the US eastern Coast?

Byrnes et al., 2019 in EPSL - Thin lithosphere beneath the central Appalachian Mountains: Constraints from seismic attenuation beneath the MAGIC array

See Evans et al., 2019 in EPSL for a companion study that came to similar conclusions with independent data.

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Measuring seismic attenuation

This study relies on the relative degree to which the high frequency data in seismograms is “attenuated” - lost while propagating through the imperfectly elastic Earth. This is quantified as “Δt*” and an example is on the left. A synthetic source-time function is made an attenuated into the traces. The most attenuated the traces, the smoother and less complex the trace appears.

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Lithospheric loss and upwelling

We conclude that attenuation in the mantle is too strong to be consistent with much remaining lithosphere beneath this section of the Appalachian Mountains. Further, attenuation is so strong that melting must be occurring (though we can’t say if any melt is present, just that the solidus is likely reached). If you are maining the solidus in a sharply bounded lithospheric hole, you probably have edge-driven convection occuring.

Remarkably, this site lies beneath the youngest volcanism in the region - 48 Ma, which wasn’t yesterday, but rifting ceased over 200 Ma. We speculate that lithospheric loss, possibly due to delamination, occured in the Eocene and sparked edge-driven convection that has continued until the present.