Double-verging collisional orogens record the superposition of subduction, collision, and post-collisional extension acting at different crustal levels over long timescales. The Alps-Apennines orogen preserves evidence of Late Cretaceous-Paleocene subduction of oceanic lithosphere, Eocene continental subduction, and a subsequent polarity reversal that led to west-dipping continental subduction during the Oligocene-Miocene. The core of this orogen was dismantled during the Middle Miocene, first by syn-collisional extension and later by subsequent post-collisional extension, related to the opening of the Tyrrhenian Basin during the Late Miocene-Pliocene period. As a result of this dismantling, fragments of deep crustal domains remain discontinuously exposed in the Tyrrhenian region. We present new structural, petrographic and geochronological data from Gorgona Island, which has been interpreted up to now as consisting of metamorphosed ophiolites tectonically overlaying their metasedimentary cover. However, our results support the reinterpretation of the metasediments as deriving from the Adria continental crust, which was involved in west-dipping continental subduction. The pressure peak metamorphism associated to the maximum burial is in this paper documented at 1.0-1.05 GPa and ~300 °C, then followed by a temperature peak at 0.80-0.95 GPa and 360-380 °C. These new findings suggest that during syn-collisional extension, deep structural levels belonging to distinct segments of the former collisional orogen were juxtaposed. Gorgona Island therefore preserves part of the deep core of the Alps-Apennines system, providing new insights into the tectonic configuration resulting from the interplay of continental subduction, polarity reversal, and extension in double-verging collisional orogens that have evolved over time and in different locations.
A glimpse into the core of the dismantled Alps-Apennines double-verging collisional orogen: The Gorgona Island case study (Italy)
Saccani, Emilio;
2026
Abstract
Double-verging collisional orogens record the superposition of subduction, collision, and post-collisional extension acting at different crustal levels over long timescales. The Alps-Apennines orogen preserves evidence of Late Cretaceous-Paleocene subduction of oceanic lithosphere, Eocene continental subduction, and a subsequent polarity reversal that led to west-dipping continental subduction during the Oligocene-Miocene. The core of this orogen was dismantled during the Middle Miocene, first by syn-collisional extension and later by subsequent post-collisional extension, related to the opening of the Tyrrhenian Basin during the Late Miocene-Pliocene period. As a result of this dismantling, fragments of deep crustal domains remain discontinuously exposed in the Tyrrhenian region. We present new structural, petrographic and geochronological data from Gorgona Island, which has been interpreted up to now as consisting of metamorphosed ophiolites tectonically overlaying their metasedimentary cover. However, our results support the reinterpretation of the metasediments as deriving from the Adria continental crust, which was involved in west-dipping continental subduction. The pressure peak metamorphism associated to the maximum burial is in this paper documented at 1.0-1.05 GPa and ~300 °C, then followed by a temperature peak at 0.80-0.95 GPa and 360-380 °C. These new findings suggest that during syn-collisional extension, deep structural levels belonging to distinct segments of the former collisional orogen were juxtaposed. Gorgona Island therefore preserves part of the deep core of the Alps-Apennines system, providing new insights into the tectonic configuration resulting from the interplay of continental subduction, polarity reversal, and extension in double-verging collisional orogens that have evolved over time and in different locations.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
