Abstract
Abstract. Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern and Southern Alps. The Giudicarie Belt is a prime example of this, as it offsets the entire Alpine orogenic edifice; its activity has been kinematically linked to strike-slip faulting and lateral extrusion of the Eastern Alps. Remaining questions on the exact role of this fold-and-thrust belt in the structure of the Alpine orogen at depth necessitate a quantitative analysis of the shortening, kinematics, and depth of decoupling beneath the Giudicarie Belt and adjacent parts of the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local NNW–SSE shortening direction reveals that this belt comprises two kinematic domains that accommodated different amounts of shortening during overlapping times. These two domains are separated by the NW–SE-oriented strike-slip Trento-Cles–Schio-Vicenza fault system, which offsets the Southern Alpine orogenic front in the south and merges with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ∼ 18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, this domain experienced at least ∼ 12–22 km shortening, whereas the NE kinematic domain accommodated at least ∼ 25–35 km shortening. Together, these domains contributed an estimated minimum of ∼ 40–47 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that most offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ∼ 15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and are responsible for N–S shortening and eastward, orogen-parallel escape of deeply exhumed units in the Tauern Window. Finally, the E–W lateral variation of shortening across the Giudicarie Belt indicates internal deformation and lateral variation in strength of the Adriatic indenter related to Permian–Mesozoic tectonic structures and paleogeographic zones.
Highlights
Based on the calculated amount of shortening, we propose a kinematic sub-division of the Giudicarie Belt (Sect. 6) and discuss the relationship between Neogene shortening along the Giudicarie Belt and Neogene motion along the Northern Giudicarie Fault (NGF), a topic which has fascinated many researchers in the past (Castellarin and Vai, 1981; Picotti et al, 1995; Prosser, 1998, 2000; Müller et al, 2001; Viola et al, 2001; Linzer et al, 2002; Stipp et al, 2004; Pomella et al, 2011, 2012)
We interpret the TC-SV fault system to act as a major sinistral transfer zone (Fig. 11), accommodating the largest variation of shortening along the Giudicarie Belt (between profiles 5 (11 km) and 6 (25 km); Fig. 6) and subdividing the area into two kinematic domains (1) and (2), west and east of the TC-SV fault system, respectively (Fig. 11)
We argue that these local variations in shortening in the eastern Southern Alps are related to inherited paleogeographic features from Permian to Jurassic times with the majority of the deformation focused within the Lombardian Basin and the Atesina Volcanic Complex, which have a thicker sedimentary cover than the Trento Platform, which is composed of mainly competent carbonate platforms
Summary
The fold-and-thrust belt of the eastern Southern Alps formed due to indentation of the Adriatic plate into the Eastern Alps (Schönborn, 1992, 1999; Picotti et al, 1995; Frisch et al, 1998, 2000; Castellarin and Cantelli, 2000; Linzer et al, 2002; Rosenberg et al, 2007; Pomella et al, 2011, 2012; Favaro et al, 2017). Previous studies have established a direct kinematic link between sinistral motion along the NGF and Neogene exhumation in the Tauern Window (Ratschbacher et al, 1989; Frisch et al, 1998, 2000; Linzer et al, 2002; Rosenberg et al, 2007; Scharf et al, 2013; Schmid et al, 2013; Handy et al, 2015; Favaro et al, 2015, 2017; Hülscher et al, 2021) This complex response of the orogenic crust to indentation calls for detachment of both sedimentary cover and metamorphic units above one or more detachments located at or above the Moho Discontinuity (Oldow et al, 1990). The kinematic link of this belt to the northern and southern segments of the Giudicarie Fault remains poorly constrained and is the focus of this study
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