Geophysical evidence of a missing lithospheric root beneath the Eastern Pyrenees: Consequences for post-orogenic uplift and associated geomorphic signatures

Abstract

When compared with other areas in western Europe with similar crustal thicknesses, or with the Central Pyrenees where the high topography is supported by thick crust, the Eastern Pyrenees are anomalously elevated. Furthermore, the distinctive plateau topography capping individual blocks at a wide range of elevations (0.25–2.9 km) suggests that a widespread erosional plain had formed by the end of the Pyrenean orogeny, and was differentially uplifted and dissected in more recent times. We present 2-D and 3-D geophysical images of the thermal lithosphere below the Central and Eastern Pyrenees and the Western Mediterranean based on an interpretation of topographic, geoid, free-air gravity and heat flow data. Results show that a lithospheric root still present beneath the Central Pyrenees is absent from the Eastern Pyrenees. Evidence for thinning of the mantle lithosphere is associated in this region with three surface signatures commonly recognized as symptomatic of this process: (i) crustal extension, which occurred in two stages, i.e. after ~ 28 Ma in relation to the opening of the Western Mediterranean back-arc basin; and more locally after ~ 12 Ma, when new clastic basins formed within the mountain belt; (ii) Late Neogene to Quaternary volcanism, which first occurred ca. 10 Ma; and (iii) crustal and topographic uplift. We suggest that the anomalously high elevation of East Pyrenean topography is related to uplift in Neogene times of the low-relief and low-elevation landscape that formed the eroded stumps of the Eastern Pyrenees. Preserved remnants of this now uplifted peneplain have survived at high elevations in this high-energy Mediterranean environment mostly because of the recent age of the vertical uplift, which has outpaced opportunities for denudation to erode all of the uplifting plateau.