Slab detachment and mantle plume upwelling in subduction zones: An example from the Italian South-Eastern Alps

Abstract

The geochemical properties of the South-Eastern Alps volcanics (SEAV, Eocene age) call for a within-plate origin of the most primitive basalts, in contrast to the widespread calc-alkaline magmatism which developed some million years later northwestwards along the Periadriatic Lineament. The two contrasting magmatic suites that coexist in the Alpine area define binary mixing relationships in the Sr-Nd and Sr-Pb isotopic space, the end members of which being a crustal component (e.g. lower continental crust) and a HIMU-DMM component (e.g. the SEAV). The occurrence of a HIMU (high μ = high 238 U/ 204 Pb) component, which normally traces mantle plumes of deep mantle origin, in a tectonic regime dominated by collision tectonics (the tertiary convergence of European and Adriatic plates) can be explained by slab detachment and ensuing upwelling of mantle material through the lithospheric gap. We combine geochemical data and geophysical modelling to unravel the evolution of the Alpine slab after interaction with plume material and the genesis of the Alpine magmatism. The combination of changes in negative buoyancy caused by continental subduction and softening of a part of the slab caused by slab-plume interaction may act as a regulator for the time of slab breakoff and, consequently, for the variations of magmatism in the overriding lithosphere above a subduction zone. The thermal evolution of a subducting slab is modified by contact with the plume material which decreases significantly the total strength of the slab and favours slab detachment. Interactions between the HIMU component and the shallower depleted mantle can account for the geochemical characteristics of the SEAV. Counterflows of plume material towards the top of the subducting slab may also increase heating and partial melting of the overriding mantle wedge, giving rise to the calc-alkaline suite outcropping in the proximity of the Periadriatic Lineament.

Metasomatized lithosphere–asthenosphere interaction during slab roll-back: Evidence from Late Carboniferous gabbros in the Luotuogou area, Central Tianshan

“…The Luotuogou gabbros and calculated melts based on representative Cr-rich clinopyroxene cores all show weakly fractionated chondrite-normalized REE patterns, suggesting that their Loucks (1990), the arc cumulate area is after Zhou et al (2007). Geochemical discrimination diagrams of (b) Ti-Zr (Pearce, 1996) and (c) Zr/Nb-La/Nb (Macera et al, 2008) for the Luotuogou gabbros.…”

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

“…The failure also allows asthenosphere to upwell through the tear, melt adiabatically, and rise into the collision zone, where it interacts especially with subcontinental lithosphere and crust of the upper plate. The resulting magmas, which form linear arrays above tears in the descending slab, are upwellings flowing through the breach in the slab (Macera et al 2008). They commonly overlap the terminal stages of deformation.…”

“…The effects of slab failure are important, diverse, and may be responsible for features such as rapid uplift (Chatelain et al 1992), syncollisional magmatism (Davies and von Blanckenburg 1995;Keskin 2003;Macera et al 2008), tomographic gaps in the descending slab (Wortel and Spakman 1992), thick-skinned foreland deformation (Cloos et al 2005), seismic discontinuities (Wortel and Spakman 1992), crustal recycling (Hildebrand and Bowring 1999), transitory pulses of mafic magmatism (Ferrari 2004) doubly vergent orogens (Regard et al 2008), plateau uplift (Rodgers et al 2002), ultra-high pressure exhumation Babist et al 2006;Xu et al 2010), changes in plate motion (Austerman et al 2011); subhorizontal swarms of deep earthquakes (Chen and Brudzinski 2011), lateral shifts in foredeep sedimentation (van der Meulen et al 1998), opening of small ocean basins (Carminati et al 1998), switchover from foredeep flysch to orogenic molasse (Sinclair 1997;Wilmsen et al 2009), and porphyry copper and other mineralization (Solomon 1990;de Boorder et al 1998;Cloos et al 2005;Hildebrand 2009). …”

Magmatectonic Zonation of Italy: A Tool to Understanding Mediterranean Geodynamics

“…The origin of the late Eocene-early Miocene magmatic activity along the Periadriatic Lineament and along the Sardinia Trough can be interpreted as the result of melting due the presence of H 2 O and K-rich fluids during unloading processes. Such processes are commonly associated with the Ligurian-Provençal back-arc, extensional process in Sardinia and with the Alpine slab break-up in the case of the Periadriatic Lineament (Macera et al, 2008 and references therein). It is interesting to note that in the late Eocene-early Oligocene (that is before the opening of the Ligure-Provençal basin), the Periadriatic Lineament and the Sardinian Trough were nearly continuous along a common ENE-WNW direction.…”

“…2 and 3). The prevailingly Eocene Alpine collisional phase was characterized mostly by calc-alkaline and K-alkaline magmatism concentrated along the Periadriatic Lineament that extends across the entire Alpine belt in an approximate E-W direction (Macera et al, 2008) (Fig. 2).…”