SICILIAN Orogen -

Geodynamic and Tectono-Stratigraphy of the Sicilian Orogen

By Maxime HENRIQUET

In Central Mediterranean, Sicily is known for its strong historical earthquakes (Noto – 1693, M 7.4; Messina – 1908, M 7.1) and its intense volcanic activity (Mount Etna, Aeolian Islands). Such events are the result of an active converging plate boundary between Europe and Africa, a long-lived geodynamic context that shaped Sicily during the Neogene-Quaternary (Figure 1). The Sicilian Chain is a central piece of the Apennines-Maghrebian subduction orogen. This mobile belt originated from the Alpine Tethys subduction and rollback that vanished with the collision of drifted continental blocks against the African paleomargins. From North to South, the Sicilian Fold-and-Thrust Belt (SFTB) is structured in four main tectono-stratigraphic domains: (1) subduction-dragged relics of the continental European margin, the Calabro-Peloritani block; (2) remnants of the Alpine Tethys accretionary Wedge (ATW) that define the oceanic inner-belt suture zone; (3) folded and thrusted platform (Panormide) and deep-water (Imerese-Sicanian) units of the offscrapped Meso-Cenozoic African margin sedimentary cover; (4) a relatively undeformed African foreland, the thick Hyblean platform. Nevertheless, scarce quality seismic lines and outcrops of key tectono-stratigraphic units make the structure and dynamic evolution of the central-eastern part of the SFTB controversial. In particular, the major remaining issues concerns: the occurrence of inferred Alpine Tethys units far from the inner suture zone, both in a forearc position above the Peloritani backstop and at the present-day front of the belt; the diverging tectonic styles, from stacked large-scale tectonic nappes to foreland imbricated thrust systems and duplexes.

Figure 1: Tectonic map of the Central Mediterranean and present-day kinematics recorded by seismic moment tensors (Mw > 4.5) and GPS data. From Henriquet et al., (2020).

New constraints are provided here using analog models to test mechanically the structural and tectono-stratigraphic evolution of the SFTB (figure 2). The experiments simulate the orogenic evolution at the upper crustal-scale, from the Oligocene Tethys subduction, to the Middle Miocene-Late Pliocene continental collision between the drifted Calabro-Peloritani continental blocks and the African paleomargin. The first-order mechanical stratigraphy and architecture of the paleo-margin simulated in the analog models are inferred from a critical review of the extensive literature, complemented by new field observations. We performed 2D experiments including syntectonic erosion and sedimentation, structural and stratigraphic regional inheritance as well as syn-kinematic flexure. These analog models (figure 2) provide experimental constraints evaluating the paleogeography of the African margin, as well as the evolution of the main tectono-stratigraphic units forming the backbone of the orogenic wedge through scaled tectonic-erosion-sedimentation processes (figure 3).

Figure 2: Modeled tectono-stratigraphic evolution of Sicilian Fold and Thrust Belt. The main steps are illustrated with a picture of the experiment (a) and the corresponding stratigraphic and structural interpretation (b). Thick and thin black lines represent major and minor active faults. The syntectonic sediments and their equivalent formation names in nature are indicated. The Alpine Tethys wedge front (ATF) and the deformation front (DF) are marked by the red and black arrows. From Henriquet et al., (2020)

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Figure 3: Snapshot at an advanced state of experience. The orogenic prism is overthrusting the African continental margin where the Meso-Cenozoic units are progressively accreted at the front and under the Alpine Tethys wedge. From Henriquet et al., (2020)

For instance, we show that unlike previous interpretations suggesting a shortening accommodation by large-scale nappe thrusting, frontal accretion, and duplexing of the Sicilian tectonic units is supported by the experiments (figure 2, 3, and 4b). In particular, we demonstrate that reworking of Alpine Tethys units by gravity-driven and erosional processes could explain the occurrence of similar formations in anomalous locations within the forearc and foreland syntectonic sequences away from the suture zone (figure 1, t25, t31, and t37). Moreover, the comparison between the modeled and the real orogenic wedge allows us to validate a paleogeographic reconstruction of the African paleomargin (figure 4a) where the Panormide platform was in an external position relative to the Imerese-Sicanian basinal units.

Figure 4: Reconstruction of the African margin (a), outcomes from experiment (b), and interpreted present-day structure of the Sicilian Fold and Thrust Belt (c-d). From Henriquet et al., (2020)

Finally, such experiments not only give insights into key processes concerning the Sicilian Fold-and Thrust Belt evolution and its paleogeographic context but also provides deformation mechanisms applicable to other subduction-related orogens such as the nearby Apenninic or Maghrebian belts.

Learn more:

-> Henriquet, M., Dominguez, S., Barreca, G., Malavieille, J., Monaco, C., 2020. Structural and tectono-stratigraphic review of the Sicilian orogen and new insights from analog modeling, Earth-Science Reviews, 208, 103257, ISSN 0012-8252, https://doi.org/10.1016/j.earscirev.2020.103257

See also:

-> Henriquet, M., Dominguez, S., Giovanni, B., Malavieille, J., Cadio, C., Monaco, C., 2019. Deep Origin of the Dome‐Shaped Hyblean Plateau, Southeastern Sicily: A New Tectono‐Magmatic Model. Tectonics, 38, https://doi.org/10.1029/2019TC005548