Unravelling the Origin of European Cenozoic Rift System (ECRiS) Intra-Continental Volcanism

There are three main types of volcanism on Earth: rifting volcanism at diverging plate margins (e.g. mid-ocean ridges), arc volcanism at converging plate margins (e.g. Japan and the Andes), and intraplate volcanism occurring relatively far from plate boundaries. Identifying the source of intraplate volcanism, however, remains one of the most challenging problems in geoscience.

Intra-oceanic volcanoes (e.g. Hawaii) are generally attributed to the ascent of hot and buoyant mantle material (plumes) rising from the core–mantle boundary (CMB). These volcanoes are characterised by frequent eruptions (every few years), a clear age progression (volcanic landforms are older away from the active eruption centre), sub-alkaline tholeiitic magmas, and high 3He/4He ratios, indicating a deep mantle source.

In contrast, intraplate continental volcanoes are more enigmatic. They typically display sporadic eruptions (every few thousand years), no systematic age progression, alkaline and SiO2-undersaturated magmas, and low 3He/4He ratios, which exclude a deep mantle reservoir. Several volcanic provinces in the Mediterranean region exhibit these features.

Among them, a group of provinces located north of the Alps constitutes the European Cenozoic Rift System (ECRiS): (1) Massif Central (France), (2) Eifel (Germany), (3) Eger Rift (Czech Republic), and (4) Pannonian Basin (Hungary). Seismic tomography beneath these regions reveals slow seismic velocity anomalies in the upper mantle, interpreted as warm or partially molten material, overlying fast velocity anomalies in the mantle transition zone (MTZ). These fast anomalies are commonly interpreted as cold, stagnant slabs subducted during the closure of the Tethys Ocean.

Plumes rising from the MTZ differ fundamentally from those originating at the CMB. Their ascent is thought to be driven primarily by the chemical buoyancy of relatively light and possibly volatile-rich material, whereas CMB plumes (e.g. Hawaii and Iceland) are driven by the thermal buoyancy of very hot mantle material (>3000 K). A recent hypothesis proposes that intraplate volcanism within the ECRiS is caused by hydrous plumes generated by flux melting of the subducted Tethyan oceanic crust, now stagnating in the MTZ beneath Europe. This geodynamic setting is referred to as a Big Mantle Wedge (BMW).