Early exhumation of underthrust units near the toe of an ancient erosive subduction zone: A case study from the Northern Apennines of Italy

Abstract

Apatite fi ssion-track (AFT) analyses were performed on 16 sandstone samples from a tectonic mélange unit exposed in three tectonic windows located near the inferred front of the early Miocene subduction system of the Northern Apennines of Italy. The tectonic windows display a block-on-block tectonic mélange present under the Ligurian Units. The mélange is formed by portions of the upper plate incorporated in the plate boundary shear zone as a consequence of a mechanism of frontal tectonic erosion during the Aquitanian (early Miocene). AFT and structural data, together with stratigraphic constraints, allow the reconstruction of a complete deformation cycle with a phase of underthrusting followed by underplating and early exhumation of the tectonic mélange. The exhumation, in particular, took place at ~10-20 km from the original subduction front. Moreover, the analysis suggests that multiple faults were active at the same time in the frontal part of the subduction zone.

Crustal and upper mantle responses to lithospheric segmentation in the northern Apennines

“…[], the thermochronological data are consistent with the suggestion that the two domains separated by the LSL have experienced different modes of wedge kinematics, with the southeastern segment dominated by frontal accretion [e.g., Batt and Brandon , ] that gave rise to a ~20 km offset between the AFT front and the AHe front (see diverging diagrams in Figure c). Northwest of the LSL, the two fronts overlap (Figure c), indicating that at least until the middle Miocene (~15 Ma), frontal accretion was not the primary mode of wedge kinematics in this segment of the orogenic belt, which was more likely dominated by underplating [ Vannucchi et al ., ; Remitti et al ., ].…”

“…Constraints on the exhumation history of the northern Apennines are available from low‐temperature thermochronology [e.g., Zattin et al ., ; Balestrieri et al ., ; Fellin et al ., ; Thomson et al ., ; Remitti et al ., ]. Thomson et al .…”

“…Constraints on the exhumation history of the northern Apennines are available from low-temperature thermochronology [e.g., Zattin et al, 2002;Balestrieri et al, 2003;Fellin et al, 2007;Thomson et al, 2010;Remitti et al, 2013]. Thomson et al [2010] have shown that the spatial distribution of apatite fission track (AFT) and apatite U-Th/He (AHe) ages in the northern Apennines is characterized by a rapid decrease in ages close to the core of the orogen.…”

Development of an Intrawedge Tectonic Mélange by Out‐of‐Sequence Thrusting, Buttressing, and Intraformational Rheological Contrast, Mt. Massico Ridge, Apennines, Italy

“…Whereas the development and evolution of tectonic mélanges along subduction channels has been the subject of many studies (e.g., Meneghini et al, ; Meneghini & Moore ; Platt, ; Remitti et al, , ), mechanisms leading to the generation of intrawedge tectonic mélanges and to the related deformation structures accommodating the tectonic activity are still poorly investigated (e.g., Vannucchi & Bettelli, ).…”

From soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue: the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)

“…The SVU is formed of different tectonically superposed units, which are hundreds of meters to kilometers wide and were derived from the Ligurian accretionary complex (Late Jurassic – middle Eocene) and the slope deposits emplaced at the toe and atop of its frontal part (late Eocene – middle Miocene) (Bettelli & Panini, 1992; Remitti, Bettelli & Vannucchi, 2007; Remitti et al . 2013; Lucente & Pini, 2008). The SVU is bounded and cut by several anastomosing thrust faults (Vannucchi, Remitti & Bettelli, 2008; Vannucchi et al .…”