Synchronous Periadriatic magmatism in the Western and Central Alps in the absence of slab breakoff

Abstract

Periadriatic Alpine magmatism has long been attributed to slab breakoff after Adria-Europe continental collision, but this interpretation is challenged by geophysical data suggesting the existence of a continuous slab. Here, we shed light on this issue based on a comprehensive dataset of zircon U-Pb ages and Hf isotopic compositions from the main western Periadriatic intrusives (from Traversella to Adamello). Our zircon U-Pb data provide the first evidence of Eocene magmatism in the Western Alps (42-41 Ma in Traversella), and demonstrate that magmatism started synchronously in different segments of the Alpine belt, when subduction was still active. Zircon U-Pb ages define younging trends perpendicular to the strike of the European slab, suggesting a progressive Eocene-Oligocene slab steepening. We propose that slab steepening enhanced the corner flow. This process was more effective near the torn edge of the European slab, and triggered Periadriatic magmatism in the absence of slab breakoff.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Slab break-offs in the Alpine subduction zone

“…Lippitsch et al (2003). Tectonic units and major lineaments simplified from Schmid et al (2004Schmid et al ( , 2008; Handy et al (2010); ages of Periadriatic magmatism: Del Moro et al (1983); Barth et al (1989); Bigioggero and Colombo (1994); Romer et al (1996); Müller et al (2000); Oberli et al (2004); Fodor et al (2008); Berger et al (2012); Bergomi et al (2015); Ji et al (2019); shorten-ing estimates: Schmid et al (1996); Frisch et al (1998); Schönborn (1999); Nussbaum (2000); Schmid et al (2004); Bellahsen et al (2014); Rosenberg et al (2015); Schmid et al (2017); Rosenberg et al (2019); rotation of Adria: Ustaszewski et al (2008); Le Breton et al (2017); GPS horizontal: Metois et al (2015); GPS vertical: Serpelloni et al (2013). AF Alpine Front, ApF Apenninic Front, DF Dinaric Front, PF Periadriatic Fault, GF Giudicarie Fault, SEMP Salzach-Ennstal-Mariazell-Puchberg fault, TW Tauern Window…”

The Role of Crustal Buoyancy in the Generation and Emplacement of Magmatism During Continental Collision

“…More synchronous mantle melting (Rosenberg, , and references therein) occurred sporadically along the strike of the whole Alpine orogen, roughly parallel to the original suture and no more than 100 km perpendicular to the former trench (Blanckenburg & Davies, ). Formerly suggested sources of mantle melting, such as hot upwelling of asthenosphere after slab breakoff (Blanckenburg & Davies, ), seem not to match observations (Ji et al, ) or numerical models (Freeburn et al, ), unless breakoff depths occur at very shallow depths (<100 km). We thus suggest crustal exhumation along the subduction channel to have caused melting in the Alps.…”

“…In this work, syncollisional magmatism refers to melting generated after onset of collision and during the entire collisional process that can continue for tens of millions of years (e.g., van Hunen & Allen, ). The Alps have very little syncollisional magmatism (e.g., Blanckenburg & Davies, ), which is most likely derived from a lithospheric mantle source (Rosenberg, , and references therein) and could be linked to slab steepening (Ji et al, ). Magmatism in the India‐Eurasia collision is scattered across the central Tibetan Plateau (Figure ).…”

Response to reviewer's comments

“…1) has been related to post-20 Ma extension resulting from slab roll back, rather than slab break-off (Fodor et al 2008). Recently, the hypothesis of the Periadriatic magmatism being related to a slab break-off has been questioned, because of ambiguities in the origin of the magmatic intrusions and the timing of emplacement of the first plutons when subduction may still have been active (Bergomi et al 2015;Garzanti et al 2018;Ji et al 2019). For the current study, we do not take the presence or absence of magmatic activity as argument in favor or against slab break-off, as the research on the topic is not conclusive enough.…”

“…Lippitsch et al (2003). Tectonic units and major lineaments simplified from Schmid et al (2004Schmid et al ( , 2008; Handy et al (2010); ages of Periadriatic magmatism: Del Moro et al (1983); Barth et al (1989); Bigioggero and Colombo (1994); Romer et al (1996); Müller et al (2000); Oberli et al (2004); Fodor et al (2008); Berger et al (2012); Bergomi et al (2015); Ji et al (2019); shorten-ing estimates: Schmid et al (1996) ;Frisch et al (1998); Schönborn (1999); Nussbaum (2000); Schmid et al (2004); Bellahsen et al (2014); Rosenberg et al (2015); Schmid et al (2017); Rosenberg et al (2019); rotation of Adria: Ustaszewski et al (2008); Le Breton et al (2017); GPS horizontal: Metois et al (2015); GPS vertical: Serpelloni et al (2013). AF Alpine Front, ApF Apenninic Front, DF Dinaric Front, PF Periadriatic Fault, GF Giudicarie Fault, SEMP Salzach-Ennstal-Mariazell-Puchberg fault, TW Tauern Window…”