Isostasy, dynamic topography, and the elevation of the Apennines of Italy

a r t i c l e i n f o a b s t r a c t The elevation of an orogenic belt is commonly related to crustal/lithosphere thickening. Here, we discuss the Apennines as an example to show that topography at a plate margin may be controlled not only by isostatic adjustment but also by dynamic, mantle-driven processes. Using recent structural constraints for the crust and mantle we find that the expected crustal isostatic component explains only a fraction of the topography of the belt, indicating positive residual topography in the central Apennines and negative residual topography in the northern Apennines and Calabria. The trend of the residual topography matches the mantle flow induced dynamic topography estimated from regional tomography models. We infer that a large fraction of the Apennines topography is related to mantle dynamics, producing relative upwellings in the central Apennines and downwellings in the northern Apennines and Calabria where subduction is still ongoing. Comparison between geodetic and geological data on vertical motions indicates that this dynamic process started in the early Pleistocene and the resulting uplift appears related to the formation and enlargement of a slab window below the central Apennines. The case of the Apennines shows that at convergent margins the elevation of a mountain belt may be significantly different from that predicted solely by crustal isostasy and that a large fraction of the elevation and its rate of change are dynamically controlled by mantle convection. The Apennine Mountains of Italy comprise an active orogenic belt, with a high-relief, but moderate topographic expression that has formed as a consequence of subduction of the Adriatic plate Although the tectonic setting is well understood, the actual mechanisms of the formation of topography are complex and still debated. Subduction leads to crustal thickening and isostatic uplift (Bally et al., 1986; Casero et al., 1991; Mele et al., 2006) but also produces a complex mantle dynamic response including up-Subduction also induces an isostatic effect due to the subduct-ing lithosphere. This effect is not accounted for by simple local isostasy of the crust. Stresses associated with the negative buoyancy of the dense slab are transmitted up the slab and into both the forearc of the overlying plate and the foreland on the sub-ducting plate (Mitrovica et al. This leads to an isostatic depression of the over-lying regions and changes in the slab load or geometry can lead to …