The geochemical features of the SE Alps volcanics (SEAV, Tertiary age) are comparable to the numerous volcanic eruptions of Tertiary-Quaternary age from the western Mediterranean area for which a plume-related origin has been assessed, and contrast to the widespread calcalkaline magmatism which developed northwestwards along the Periadriatic Lineament. The occurrence of a HIMU component, which is the hallmark of hotspot basalts, in a collision environment (the Tertiary convergence of Europe and Africa plates) is here explained in terms of slab breakoff. Evidence for the European slab breakoff comes from seismic tomography which shows that the present-day fast velocity material, interpreted as the European slab subducted below the Alpine chain, is shorter by about 300 km than the total length of the subducted slab estimated by paleotectonic reconstructions. Other piece of evidence comes from a kinematical model consisting in evaluating the time evolution of buoyancy of oceanic and continental lithosphere during subduction with both constant and time-varying convergence rates. If the subducted slab intercepts a rising plume from below the corresponding part of the slab is heated and therefore softened. The softening effect is enhanced if the slab includes continental material. 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 time and type variations of magmatism in the overriding lithosphere above a subduction zone. In the Alpine region, we assume that the plume material interacted with the subducting slab causing its heating, softening, and finally its detachment. Ensuing upwelling of plume material through the resulting plate window is supposed to be the responsible for partial melting in the lithospheric mantle wedge and/or decompression melting of the ascending plume material. On the basis of geological, geophysical and geochemical data we conclude that both magmatic suites originated from a common and primary deep mantle plume the root of which was located beneath the Cape Verde-Madeira-Canary Islands region, while the head was dragged and frayed by the northeastward motion of the Eurasian plate.

HIMU-OIB magmatism in subduction zones: An example from the Italian south-eastern Alps

MACERA, PATRIZIA;
2004-01-01

Abstract

The geochemical features of the SE Alps volcanics (SEAV, Tertiary age) are comparable to the numerous volcanic eruptions of Tertiary-Quaternary age from the western Mediterranean area for which a plume-related origin has been assessed, and contrast to the widespread calcalkaline magmatism which developed northwestwards along the Periadriatic Lineament. The occurrence of a HIMU component, which is the hallmark of hotspot basalts, in a collision environment (the Tertiary convergence of Europe and Africa plates) is here explained in terms of slab breakoff. Evidence for the European slab breakoff comes from seismic tomography which shows that the present-day fast velocity material, interpreted as the European slab subducted below the Alpine chain, is shorter by about 300 km than the total length of the subducted slab estimated by paleotectonic reconstructions. Other piece of evidence comes from a kinematical model consisting in evaluating the time evolution of buoyancy of oceanic and continental lithosphere during subduction with both constant and time-varying convergence rates. If the subducted slab intercepts a rising plume from below the corresponding part of the slab is heated and therefore softened. The softening effect is enhanced if the slab includes continental material. 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 time and type variations of magmatism in the overriding lithosphere above a subduction zone. In the Alpine region, we assume that the plume material interacted with the subducting slab causing its heating, softening, and finally its detachment. Ensuing upwelling of plume material through the resulting plate window is supposed to be the responsible for partial melting in the lithospheric mantle wedge and/or decompression melting of the ascending plume material. On the basis of geological, geophysical and geochemical data we conclude that both magmatic suites originated from a common and primary deep mantle plume the root of which was located beneath the Cape Verde-Madeira-Canary Islands region, while the head was dragged and frayed by the northeastward motion of the Eurasian plate.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/90746
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