Abstract
ABSTRACTStratigraphic 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 roll-back. 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.
Highlights
The elevated surface topography of mountain belts impacts the local and global climate and hosts biodiversity hotspots
We study the case of the central Apennines of Italy, one of the most elevated topographic barriers in the Mediterranean area, where surface topography is controlled tectonically by an intricate system of multiple subduction zones
Since the Pliocene, surface topography above sea level and denudation have become significant (e.g., Fellin et al, 2007; Thomson), and extensional deformation has extended on land with the formation of intermontane basins (e.g., Patacca et al, 1990; Boccaletti et al, 1990; Cipollari and Cosentino, 1995a, 1995b; Cosentino et al, 2010)
Summary
The elevated surface topography of mountain belts impacts the local and global climate and hosts biodiversity hotspots. Subduction can affect upper plate topography in a variety of ways: the pull exerted by the subducting slab and the induced return flow can depress the forearc regions by some hundreds of meters (Zhong and Gurnis, 1994), whereas the upwelling associated with return flow or small-scale convection can induce a positive signal in the backarc regions (Zhong and Gurnis,1994; Hyndman and Currie, 2011; Crameri et al, 2017; Faccenna and Becker, 2020) This scenario can change with a decrease in subduction pull and subduction rate as in, for example, the case of slab break-off (e.g., Duretz and Gerya, 2013).
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