A Revised Subduction Inception Model to Explain the Late Cretaceous, Double‐Vergent Orogen in the Precollisional Western Tethys: Evidence From the Northern Apennines

Abstract

The Meso‐Cenozoic alpine belts of the Mediterranean area are characterized by complex architectures, result of a complex subduction and collision evolution that preserve also a legacy of the rifting‐related configuration of the continental margins. The Northern Apennines is a segment of these belts originated during closure of the Ligure‐Piemontese ocean and collision between the Europe and Adria plates. The different configuration of the Adria and Europe margins, inherited from asymmetric rifting, is recorded in the Ligurian Units that preserve incorporation into the subduction factory of fragments of the oceanic domain (Internal Ligurian Units) and portions of the Ocean‐Continent Transition Zone (OCTZ) toward Adria (External Ligurian Units). We provide here unpublished data on the stratigraphy and sedimentology of these units, together with a review of what is already established in literature. Both data sets combined testify that at 80 Ma, an accretionary prism was growing between the deposition basins of the two groups of units and fed both basins with clasts from the ocean realm, the continental crust, and the subcontinental mantle. We propose that closure of the Ligure‐Piemontese ocean occurred through subduction that nucleated at the transition from the oceanic plate and the thinned Adria margin and developed a double‐vergent prism by accreting oceanic material and continental extensional allochthons from the OCTZ. We believe the revised site of subduction initiation, and the precollisional architecture, inherited from the rifting and spreading phases, allows reconciling most of the discrepancies between the various interpretations proposed in literature for the precollisional evolution of the Apennines.

A reconstruction of Iberia accounting for W-Tethys/N-Atlantic kinematics since the late Permian-Triassic

“…Major dynamic changes occurred with the CAMP event (Olsen, 1997;Marzoli et al, 1999;McHone, 2000;Leleu et al, 2016;Peace et al, 2019) that led to breakup in the Central Atlantic Ocean during the 190-175 Ma interval (Pliensbachian-Toarcian) ( 2017, respectively. The propagation of the Central Atlantic rift northwards caused extension to propagate in the southern North Atlantic (Murillas et al, 1990;Leleu et al, 2016) and laterally, eastward in the Alpine Tethys (Schmid et al, 2008;Marroni et al, 2017) by some reactivation of Triassic Neotethyan rift structures. Evidence for nearly synchronous intrusions of MORB-type gabbro, in a western branch of the Alpine Tethys, is described at 180 Ma in the internal zones of eastern Betics (Puga et al, 2011), associated with the rapid subsidence in the Betics (Fig.…”

“…Continental rifting 270 to 220 Stampfli and Borel, 2002;Schmid et al, 2008;Scisciani andEsestime, 2017 Breakup 180 Schmid et al, 2008;Puga et al, 2011;Marroni et al, 2017 N Alpine Tethys…”

A reconstruction of Iberia accounting for Western Tethys–North Atlantic kinematics since the late-Permian–Triassic

“…An expression of the continued lithospheric thinning and thermal instability associated with high heat flow during the Permian (McKenzie et al, 2015) and the Triassic (Peace et al, 2019a, and references therein) is recorded in the central and southern North Atlantic. Lithospheric extension prior to (or associated with the premises of the subsequent) Early Jurassic continental breakup in the central Atlantic then favored the drainage of mantle melt reservoir (Silver et al, 2006;Peace et al, 2019a), attested by the very rapid emergence of the widespread tholeiitic magmatic CAMP (Central Atlantic Magmatic Province) event at the Triassic-Jurassic boundary (200 Ma) in the central Atlantic (Olsen, 1997;Marzoli et al, 1999;McHone, 2000). The CAMP extends to Iberia as large-scale volcanic intrusions such as the Messejana-Plasencia dyke (Cerbiá et al, 2003) in Iberia and the Late Triassic-Early Jurassic ophitic magmatism in the Pyrenees (e.g., Azambre et al, 1987).…”

New Constraints on the Evolution of the Inner Northern Apennines by K‐Ar Dating of Late Miocene‐Early Pliocene Compression on the Island of Elba, Italy

“…The Italian inner Northern Apennines (NA; Figure a) are an orogenic wedge formed in response to the Upper Cretaceous‐Eocene closure of the Ligurian‐Piedmont ocean (Marroni et al, , and references therein, for a comprehensive review) and the subsequent Oligocene‐Miocene convergence and collision between the Adriatic Promontory and the Sardinia‐Corsica Block, of African and European origin, respectively (e.g., Boccaletti et al, ; Vai & Martini, and references therein). Alternative models of subduction polarity exist (see Molli, for a review).…”