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

Wei‐Qiang Ji,Antonio Langone,Liang Zhao,Massimo Tiepolo,Marco G Malusà,Fu‐Yuan Wu

doi:10.1111/ter.12377

Abstract

AbstractPeriadriatic 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.

Highlights

The long-lasting debate on the origin of Periadriatic magmatism in the European Alps (Laubscher, 1983; Rosenberg, Berger, & Schmid, 1995) has led to the formulation of one of the most successful theories of modern geology, the slab breakoff model (Davies & von Blanckenburg, 1995; von Blanckenburg & Davies, 1995) that is extensively adopted worldwide (Garzanti, Radeff, & Malusà, 2018 and references therein)
This process is more effective in the Central Alps because of (i) the free boundary represented by the slab edge, (ii) the anchoring of the Dinaric slab that may have pushed back the European slab, and (iii) a minor amount of buoyant continental crust subducted at the trench
Zircon U–Pb data demonstrate that magmatism started synchronously in the Western and Central Alps when subduction was still active

Summary

Introduction

The long-lasting debate on the origin of Periadriatic magmatism in the European Alps (Laubscher, 1983; Rosenberg, Berger, & Schmid, 1995) has led to the formulation of one of the most successful theories of modern geology, the slab breakoff model (Davies & von Blanckenburg, 1995; von Blanckenburg & Davies, 1995) that is extensively adopted worldwide (Garzanti, Radeff, & Malusà, 2018 and references therein). According to Davies and von Blanckenburg (1995), slab breakoff magmatism would be induced by the passive asthenosphere upwelling along the breakoff gap Such magmatism should exhibit a mantle parentage, should be extremely localized, its trace should be nearly linear, its duration very short, and intrusions may display symmetrically younging trends with distance away from the breakoff gap (Davies & von Blanckenburg, 1995). Part of these features are observed in the Alpine region: the Periadriatic plutons are clustered along the Insubric Fault (Figure 1a,b), which probably favoured magma ascent (Rosenberg, 2004), but the widespread Periadriatic dykes (Bergomi, Zanchetta, & Tunesi, 2015; D'Adda et al, 2011) form a much wider belt parallel to the European slab (Figure 1b)

Methods

Discussion

Conclusion