GPS Imaging of Mantle Driven Uplift of the Apennines, Italy

One way for the continental lithosphere to extend is to increase its regional elevation, yet the mechanism for the formation of high-topography in actively extending continental settings (e.g., Tibet, Basin and Range, southwestern Balkans, Apennines) is still uncertain. It has been suggested that active extension in the Apennines Mountain chain in Italy is intimately related with regional topographic elevation. We use a newly updated GPS dataset and the GPS Imaging technique to show that the dynamic relief of the Apennines is currently increasing along its entire length by ~1 mm/yr. We image positive uplift along the entire length of the Apennine crest including the northern Apennines, Calabria and northern Sicily. The maximum rate is geographically aligned with the highest elevations and the topographic drainage divide. Relief is increasing in a ~120 km wide zone with a profile similar to the long wavelength topography, but not similar to the shorter wavelength topography generated by active faulting and erosion. A zone of minor active uplift is aligned with areas having restive volcanic fields and high geothermal potential west of the Apennines: e.g., Campi Flegrei, Alban Hills, and Lago Bolsena. However, the primary uplift axis aligns with the topography and zone of extension accommodating east-northeast translation of the Adriatic microplate relative to the Tyrrhenian Basin. Broad uplift occurs despite that the expected consequence of extension is crustal thinning and subsidence.   Anomalies in free-air gravity and deep seismic wavespeed suggest that elevation gain is driven by forces originating in the mantle. We use these results to address the hypothesis that these forces result from upward flow of asthenospheric mantle beneath the Apennines, possibly related to a sinking and detached slab previously attached to the Adriatic microplate, or from extensional flank flexure across the axis of the Apennine rift.