The Eifel Anomaly: 3D Present-Day Surface Deformation Caused by a Buoyant Mantle Plume

Abstract:

The Eifel hotspot is one of the few known active continental hotspots. The evidence is based on volcanism as recent as 11ka and a seismic velocity anomaly that shows a plume-like feature downward to at least the upper transition zone. However, the volcanism lacks a clear space-time progression and evidence for surface deformation has been ambiguous. We show that the greater area above the Eifel plume shows a distinct and significant surface deformation anomaly not seen anywhere else in intraplate Europe. We use GPS data of thousands of stations in western Europe to image contemporary vertical land motion (VLM) and horizontal strain rates. We show significant surface uplift rates with a maximum of ~1.0 mm/yr (after correcting for glacial isostatic adjustment) roughly centered on the Eifel Volcanic Field, and above the mantle plume. The same area that uplifts also undergoes significant N-S-oriented extension of ~3 nanostrain/yr, and this area is surrounded by a radial pattern of shortening. River terrace data have revealed tectonic uplift of ~150–250 m of the Eifel since 800 ka, when recent volcanism and uplift reactivated, which would imply an average VLM of 0.1–0.3 mm/yr since that time. Our VLM results suggest that the uplift may have accelerated since Quaternary volcanism commenced. The remarkable superimposition of uplift, horizontal extension, and volcanism strongly suggests a causal relationship with the underlying mantle plume. We model the plume buoyancy as a half-space vertical force applied to a bi-modal Gaussian areal distribution exerted on a plane at 50 km depth. Our modeling shows a good regional fit to the long-wavelength aspects of the surface deformation by applying buoyancy forces related to the plume head at the bottom of the lithosphere. From our spatially integrated force and some first-order assumptions on the extent and rate of uplift, we estimate that a 360 km high plume requires density reduction of 57-184 kg m^-3 (i.e., ~0.7-5.6% of a 3300 kg m^-3 dense reference mantle), We note that the highest extension rates are centered on the Lower Rhine Embayment (LRE), where intraplate seismicity rates are high, and where paleoseismic events increased since 800 ka. We suggest that the surface uplift imposed by the Eifel plume explains the relatively high activity rate of the LRE.