Geological and geophysical study of a thin-skinned tectonic wedge formed during an early collisional stage: the Trasimeno Tectonic Wedge (Northern Apennines, Italy)

Abstract

The presence of a set of well-known turbidite successions, deposited in progressively E-migrating foredeep basins and subsequently piled up with east vergence, makes the Northern Apennines of Italy paradigmatic of the evolution of deepwater fold-and-thrust belts. This study focuses on the early Apenninic collisional stage, early Miocene in age, which led to the accretion of the turbidites of the Trasimeno Tectonic Wedge (TTW), in the central part of the Northern Apennines. Based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing, we present a detailed tectonic reconstruction of the TTW. In the study area, the TTW is characterized by a W-dipping shaly basal décollement located at a depth of 1–5 km. The tectonic wedge is c. 5 km thick at its central-western part and tapers progressively eastwards to c. 1 km. The total shortening, balanced along a 33 km long cross-section, is c. 60 km, including 20 km (40%) of internal imbrication, c. 23 km of horizontal ENE-wards translation along the basal décollement and c. 17 km of passive translation caused by the later shortening of footwall units. Deformation balancing, constrained through upper Aquitanian – upper Burdigalian (c. 21–16 Ma) biostratigraphy, provides an average shortening rate of c. 8.6 mm a–1. Internal shortening of the TTW shows an average shortening rate of c. 4 mm a–1 for this period.

Regional-scale paleofluid system across the Tuscan Nappe–Umbria–Marche Apennine Ridge (northern Apennines) as revealed by mesostructural and isotopic analyses of stylolite–vein networks

“…(B) Stratigraphic column based on stratigraphic and well data from the central part of the UMAR, after Centamore et al (1979). (C) Crustal-scale composite cross section based on published seismic data interpretations; A-A' modified after Carboni et al (2020); B-B' and C-C' after Scisciani et al (2014). Note that both tectonic style (thick skinned and thin skinned) are represented by question marks for the UMAR.…”

“…23-20.43 Ma) and lasted until the Langhian (ca. 16 to 13.8 Ma;Carboni et al, 2020). The UMAR is an arcuate ridge exhibiting an eastward convex shape, with a line connecting Perugia and Ancona separating a northern part where structural trends are oriented NW-SE, from a southern part where structure trends are oriented N-S (Calamita and Deiana, 1988).…”

Regional-scale paleofluid system across the Tuscan Nappe – Umbria Marche Arcuate Ridge (northern Apennines) as revealed by mesostructural and isotopic analyses of stylolite-vein networks

“…1c). In these last views, the style of deformation of the UMAR strongly contrasts with the style of deformation of the TN where shortening is accommodated by allochtonous, far-travelled duplex nappes (Carboni et al, 2020) (Fig. 1c).…”

“…In the western part of the area, the belt is a thin-skinned assembly of piggy back duplex folds (Fig. 1c), the so-called Tuscan Nappe (TN), the folding and thrusting of which started by the Late Aquitanian and lasted until the Langhian (Carboni et al, 2020). The UMAR is an arcuate ridge exhibiting an eastward convexity, with a line connecting Perugia and Ancona separating a northern part where structural trends are oriented NW-SE, from a southern part where structure trends are oriented N-S (Calamita and Deiana, 1988).…”

“…In the eastern part (now UMAR), the foreland was progressively folded and thrusted from the Lower Miocene in the westernmost part of the current ridge to the Messinian in the foreland of the ridge (Mazzoli et al, 2002). UMAR has been considered for long as a thin-skinned thrust belt where shortening was accommodated by stacking and duplexing of sedimentary units detached above a décollement level located in the Triassic evaporites (Conti and Gelmini, 1994;Carboni et al, 2020). The seismic profile of the CROsta Profonda (CROP) project led authors to interpret the UMAR as resulting from thick-skinned tectonics, where the basement is involved in shortening (Barchi et al, 1998) through the positive inversion of normal faults inherited from the Jurassic Tethyan rifting (Fig.…”