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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. [ABSTRACT FROM AUTHOR]

Stratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab rollback. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/ He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3-4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post--5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between <2 km in most areas and ≥3-4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab. [ABSTRACT FROM AUTHOR]

• Divergence of δ 18 O between high- and low-elevation basins starting 2.5 Ma. • Surface uplift of central Apennines of 1–2 km since the late Pliocene. • Surface uplift likely due to slab break-off beneath the central Apennines. The central Apennines, an accretionary wedge overlying an area of slab detachment, are characterized by prominent topography, active normal faulting, and high uplift rates. However, previous studies have failed to resolve the surface uplift history, complicating efforts to link the topographic evolution with underlying geodynamic processes. We aim to better quantify orographic changes by using stable oxygen isotope paleoaltimetry. Modern surface water δ 18 O are 5‰ lower at high elevation than at sea level, reflecting orographic rainout over the Apennines. We present 262 new lacustrine and paleosol carbonate δ 18 O measurements collected from ten extensional intermontane basins—spanning both high and low elevations—and combine these with 1,166 published δ 18 O data, permitting us to constrain changes in δ 18 O both spatially and temporally. Since the Pliocene, δ 18 O in present-day high-elevation basins has continuously decreased, even as δ 18 O in lowland basins has remained constant over time. We attribute this continuous 5‰ shift to increased orographic rainout as the central Apennines were uplifted. We estimate an increase in mean elevation of approximately 1–2 km since the late Pliocene, and these estimates match the suggested timing and expected amplitude of slab break-off related uplift. This supports the hypothesis that the opening of the Adriatic slab window and associated mantle flow contributed significantly to building topography in the central Apennines. [ABSTRACT FROM AUTHOR]

The inference of crustal temperature is limited by the scarcity of heat-flow measurements and their unreliability, especially in active regions where the assumption of pure heat conduction does not hold. We propose two alternative approaches for constraining the thermal structure at crustal depth, based on seismic observables and thermodynamics.We invert receiver functions and ambient-noise dispersion curves at 50 locations across the Italian peninsula. Beside the retrieval of a subsurface model in terms of Vs and Vp/Vs, the trans-dimensional, Monte Carlo Markov chain algorithm used for inversions allows a quantitative estimation of the likelihood of occurrence of a seismic interface within the crust. Sharp and well constrained seismic interface where the Vp/Vs ratio increases above 1.8 are interpreted as indicative of the transition of quartz from its α to β form. Such seismic interfaces are then used for the inference of the local geothermal gradient. As a comparison, we employ an alternative method that relies on the translation of shear wave velocities at depth into absolute temperature through thermodynamics, assuming that the chemical composition is known (we use the global estimate from Rudnick and Gao [2003]). The similarity of the outcomes from the two approaches is remarkable and coherent with the known tectonic and geodynamic setting of the Italian peninsula. Based on this premise, we produce the first quantitative estimation of Moho temperatures for this area. These are comprised between 800 and 900°C, approaching 1000°C in the thickest portion of the western Alps and central Apennines. A shallow and anomalously hot Moho (>800°C at 15 km depth) is found in the Tyrrhenian basin, coherent with its extensional regime, high heat-flow and volcanism (i.e. Vavilov and Marsili active seamounts). In the Tuscan magmatic province, we find Moho temperatures >800°C at 20-25 km that are compatible with the significant hydrothermal activity and known geothermal potential of the area. Our findings also unravel a significant thermal anomaly at the transition between the Alpine and Apennine orogens in NW Italy. The robustness of this feature is supported by independent geological and geophysical evidence. More in-depth studies are required for clarifying its cause, role and possible implications in the evolution of the Alps-Apennine transition.The proposed methods, relying on seismic observable and thermodynamics, can surpass heat-flow data for temperature inference in terms of coverage, resolution and data abundance, suggesting that these would be potentially employed in a variety of geological and tectonic complexes. [ABSTRACT FROM AUTHOR]

Estimates of surface uplift and exhumation are necessary to reconstruct the evolution ofmountain belts and quantify the contributions of shallow and deep processes to the underlyinggeodynamics. We focus on the Central Apennines, which formed as an accretionary wedgebefore undergoing post-orogenic extension. Since 3 Ma, it overlies an area of local slabdetachment. We aim to better relate surface observations to possible geodynamic processes.To do so, we combine low-temperature thermochronology to date exhumation and stableisotope paleoaltimetry to reconstruct surface topography, with samples collected from 13intermontane basins in the central Apennines that record both tectonic and climaticsyn-orogenic events. Today, meteoric waters in the Apennines show progressivelylower δ18O with elevation, with an approximately 5‰ difference between sea-leveland high-elevation sampling sites, suggesting that authigenic carbonates in thesebasins may preserve a measureable difference between sea-level and high-elevationlocalities. Our 34 new apatite (U-Th)/He ages from Miocene sandstones range from 7 Ma on theThyrrenean coast to 1.62 Ma in the Central-Eastern Apennines. This pattern reflectsmigrating extension due to Thyrrenian rifting, as well as a large scale uplift pulsearound 2 Ma (exhumation rates &#x003E;1mm/yr). We also present &#x003E;500 lacustrine andpaleosol carbonate δ18O measurements collected from various elevations alongthe mountain range. Since the Pliocene, the gradient in δ18O between basins nearsea-level today and those at high-elevation today has continuously increased. Weattribute this shift to increased orographic rainout, thereby causing progressively lowerδ18O in high-elevation basins as they are uplifted. Using this data and the modernmeteoric water δ18O lapse rate, we estimate that there has been approximately 1 km ofuplift since late Pliocene. Both our isotopic data and exhumation ages match thesuggested timing and expected amplitude of slab break-off. This supports the hypothesisthat the opening of the Adriatic slab window caused substantial uplift in the area. [ABSTRACT FROM AUTHOR]