Syn‐convergence exhumation of continental crust: evidence from structural and metamorphic analysis of the Monte Cecu area, Alpine Corsica (Northern Corsica, France)

Abstract

In the Corsica Island, a stack of metamorphic continental units derived from the European continental margin is thrust over a pre‐Alpine basement during the convergence‐related processes in the Late Eocene–Early Miocene time span. The Piedigriggio‐Prato Unit is representative of these units. Its tectono‐metamorphic history has been reconstructed by an integrated approach, ranging from map‐ to meso‐ and microscopic scale analyses. This unit is characterized by a polyphase deformation history that consists of three deformation phases developed under retrograde metamorphism ranging from blueschist to sub‐greenschist facies metamorphic conditions. At the map‐scale, the Piedigriggio‐Prato Unit is characterized by km‐size isoclinal folds deformed by open to closed recumbent folds producing Type 3 fold interference pattern. The features of the deformations and the P–T conditions suggest that the first two phases were acquired during the ductile extrusion of the Piedigriggio‐Prato Unit. Before the Early Miocene, the gravitational collapse of over‐thickened continental crust produced vertical shortening and the consequently recumbent F3 folds. The exhumation history of the Piedigriggio‐Prato Unit can be viewed as representative for the exhumation of a continental crust fragment during the transition from the continental subduction to the continental collision. Copyright © 2016 John Wiley & Sons, Ltd.

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

“…Blueschist assemblages in the unit have been described by regional studies (Bezert and Caby, 1988;Malasoma et al, 2006;Molli, 2008;Di Rosa et al, 2016) and are observed in all suitable rock types, such as in metapelites from cover rocks, metabasic dykes, and in some of the granitoid suites from the basement. Peak metamorphism has been initially constrained to 250-350 • C and 0.4-0.55 GPa (Bezert and Caby, 1988) or more recently more closely bracketed at 325-370 • C and 0.75-0.85 GPa (Malasoma et al, 2006;Di Rosa et al, 2016).…”

“…1), each of them corresponding to different peak metamorphic con- These occurrences document the progressive underthrusting of these units down to different depths and their insequence contractional exhumation within an Alpine-age, east-dipping subduction system (Mattauer et al, 1981;Bezert and Caby, 1988;Jolivet et al, 1990;Garfagnoli et al, 2009;Molli and Malavieille, 2011;Maggi et al, 2012;Di Rosa et al, 2016;Guyedan et al, 2017;Beaudoin et al, 2017).…”

“…The studied samples come from the external continental units (Molli, 2008;Molli and Malavieille, 2011;Vitale Brovarone et al, 2013) of Alpine Corsica, more specifically from the Popolasca unit (Bezert and Caby, 1988;Malasoma et al, 2006;Di Rosa et al, 2016). This unit is characterized by a pre-Mesozoic basement mainly formed by granitoids, a Permo-Mesozoic metasedimentary sequence and an early Eocene flysch (Fig.…”

“…Peak metamorphism has been initially constrained to 250-350 • C and 0.4-0.55 GPa (Bezert and Caby, 1988) or more recently more closely bracketed at 325-370 • C and 0.75-0.85 GPa (Malasoma et al, 2006;Di Rosa et al, 2016). The prograde to peak pressure assemblage has been recently dated with 40 Ar / 39 Ar at 45-36 Ma by Di Vincenzo et al (2016).…”

“…The contributions of Malasoma et al (2006) and Di Rosa et al (2016) analysed the cartographic to mesoscopic-scale structural geometries of deformation in the area of the studied sample. Superimposed foliations and fold structures are typical of the metasedimentary cover, with blueschist assemblages as relict fabrics.…”