Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation

Abstract

Apatite (U-Th-Sm)/He ages from the Karawanken Mountains range between 12 and 5 Ma and indicate an episode of fault-related exhumation leading to the formation of a positive flower structure and an associated peripheral foreland basin. In the Southern Alps, apatite (U-Th-Sm)/He and fission-track data combined with previous data also indicate a pulse of mainly Late Miocene exhumation, which was maximized along thrust systems, with highly differential amounts of displacement along individual structures. Our data contribute to mounting evidence for widespread Late Miocene tectonic activity, which followed a phase of major exhumation during strain localization in the Tauern Window. We attribute this exhumational phase and more distributed deformation during Adriatic indentation to a major change in boundary conditions operating on the orogen, likely due to a shift from a decoupled to a coupled system, possibly enhanced by a shift in convergence direction.

Fragmentation of the Adriatic Promontory: New Chronological Constraints From Neogene Shortening Rates Across the Southern Alps (NE Italy)

“…Considering that additional back thrusting has been neglected in constructing our cross section, this should be considered as a minimum value, in agreement with the 46‐km value recorded in the western Southern Alps by Schmid et al (). Based on syntectonic sedimentation (Castellarin et al, ) and thermochronologic data (Heberer et al, ; Zattin et al, ), the preferred estimate for the onset of thrusting in the Southern Alps is about 14 Ma, thus yielding a long‐term shortening rate of about 3 mm/year, 2 times higher than the postglacial shortening rate. If assuming on the other hand that thrusting initiated as early as 21 Ma at the onset of Adria indentation (Pomella et al, ), then the long‐term mean shortening rate would be of 2 mm/year, which is still higher than the postglacial rate.…”

“…The remaining Neogene convergence has been essentially absorbed by eastward extrusion of the Eastern Alps (e.g., Frisch et al, ; Linzer et al, ; Ratschbacher et al, ). Crustal deformation in this sector of the Alps is probably older than that in the Southern Alps (Heberer et al, ) and accounts for 61–64 km of N‐S shortening (Linzer et al, ). The last source of Neogene shortening is represented by thrusting in the Northern Alps and accounts for about 10 km of N‐S shortening (Linzer et al, and references therein; Figure c).…”

The topography of a continental indenter: The interplay between crustal deformation, erosion, and base level changes in the eastern Southern Alps

“…(c) Vertical (filled circles) and horizontal (arrows) velocity field based on GPS time series indicating recent crustal motion and deformation in the ESA [ Grenerczy et al ., ; Weber et al ., ; Serpelloni et al ., ]. (d) Compilation of low‐temperature thermochronology data based on the distribution of apatite fission track ages (circles) [e.g., Luth and Willingshofer , and references therein; Fox et al ., , and references therein] and apatite (U–Th–Sm)/He ages (squares) [ Heberer et al ., ]. Solid black lines indicate the position of major faults.…”

“…However, the scarcity of suitable lithology limits the applicability of low‐temperature thermochronometers for the Adriatic indenter, and data are mainly focused along major thrust systems (e.g., Valsugana thrust). There, latest Middle Miocene to Late Miocene exhumation and unroofing of ~ 4 km has led to the exposure of crystalline basement [ Zattin et al ., ; Heberer et al ., ]. In contrast, apatite fission track ages to the north and immediately to the west of the Valsugana thrust are Mesozoic [ Zattin et al ., ; Emmerich et al ., ; Heberer et al ., ], corroborating that overall exhumation throughout most of the ESA is minor [ Emmerich et al ., ; Zattin et al ., ] (Figure d).…”

“…There, latest Middle Miocene to Late Miocene exhumation and unroofing of ~ 4 km has led to the exposure of crystalline basement [ Zattin et al ., ; Heberer et al ., ]. In contrast, apatite fission track ages to the north and immediately to the west of the Valsugana thrust are Mesozoic [ Zattin et al ., ; Emmerich et al ., ; Heberer et al ., ], corroborating that overall exhumation throughout most of the ESA is minor [ Emmerich et al ., ; Zattin et al ., ] (Figure d). Thin‐skinned tectonic shortening with fault‐propagation folding and fault‐bend folding prograded southward in the ESA, producing a pronounced relief, e.g., of 1200 m above the plain along the SE verging Bassano‐Valdobbiadene thrust [ Galadini et al ., ] (Figure ).…”