Big Mantle Wedge in Europe

Big Mantle Wedge in Europe#

Intra-continental volcanoes differ significantly from their oceanic counterparts (e.g., Hawaii and Iceland) because: (1) their eruptions are sporadic (every few thousand years), (2) they do not display the classic age progression associated with a hot spot, and (3) their eruption products are more alkaline and silica-undersaturated compared to oceanic island basalts. Moreover, seismic tomography beneath these regions reveals that the low-velocity anomalies commonly associated with warm mantle plumes are interrupted in the mantle transition zone (MTZ) by high-velocity anomalies [21]. These anomalies have been interpreted as a cold, stagnant slab in the MTZ.

In the Big Mantle Wedge (BMW) hypothesis [22], intra-continental volcanism is either induced by the bulldozing action of a subducting slab pushing hydrous material out of the MTZ [8], or by the dehydration of the slab itself once it stagnates in the MTZ and warms up [9].

In the Mediterranean region there are several volcanic provinces which are not related to either converging or diverging margin, and are collectively referred to as the Circum-Mediterranean Anorogenic Cenozoic Igneous Province (CiMACI) [13]. Within the CiMACI, there are four volcanic provinces located north of the Alps: (1) Massif Central (France), (2) Eifel (Germany), (3) Eger Rift (Czech Republic), and (4) the Pannonian Basin (Hungary). These four regions together constitute the European Cenozoic Rift system (ECRiS) [23].

Seismic tomography of Europe reveals slow-velocity anomalies in the upper mantle beneath the volcanic provinces of the ECRiS and fast-velocity anomalies in the underlying MTZ [4], which have been interpreted as different generations of Mediterranean slabs now stagnating on top of the 660 km discontinuity [4]. Potentially, the four volcanic regions of the ECRiS are fed by a common mantle reservoir [12], represented by the recycling (i.e., flux melting) of subducted oceanic crust (meta-sediments and meta-basalts) [6], induced by the dehydration of the inner portions of slab [9]. This process may lead to the formation of secondary mantle plumes driven by the chemical buoyancy of low-density, water-rich melt [15] that ascends toward the surface and may be responsible for the slow-velocity anomaly observed in the upper mantle beneath ECRiS.

The Big Mantle Wedge hypothesis was originally proposed to explain the intra-continental volcanism in the Changbaishan volcanic province (NE China), located more than 1000 km away from the Japan Trench [21], and may also explain the intra-continental volcanism of the ECRiS.

This cookbook can be used to set up the initial conditions of a regional-scale mantle convection model to investigate the Big Mantle Wedge hypothesis or to visualize its geometry in 3D.

The region is 4000 x 3000 x 660 km Cartesian box (x,y,z) representing continental Europe and the underlying upper mantle and transition zone (Figure 1-3). In total there are 15 features, divided as:

  1. Mantle Layer: uniform composition [0]; no distinction between upper mantle and MTZ

  2. Oceanic Plate: relatively thin lithosphere (100 km), uniform composition [1]; it represents the ocean and seas surrounding Europe

  3. Continental Plates

    3a. Continental Europe: relatively thick lithosphere (200 km), uniform composition [2]

    3b. Alps: mountain chain, thick lithosphere (250 km), uniform composition [3]

    3c. Appennines: mountain chain, thick lithosphere (250 km), uniform composition [3]

    3d. Pyrenees: mountain chain, thick lithosphere (250 km), uniform composition [3]

    3e. Massif Central: ECRiS volcanic province; thinned continental lithosphere (100 km), uniform composition [4]

    3f. Eifel: ECRiS volcanic province; thinned continental lithosphere (100 km), uniform composition [4]

    3g. Bohemian Massif: ECRiS volcanic province; thinned continental lithosphere (100 km), uniform composition [4]

    3h. Pannonian Basin: ECRiS volcanic province; thinned continental lithosphere (100 km), uniform composition [4]

  4. Subducting Slab (Alpine): defined by 5 segments to represent the steep descent toward the MTZ and the horizontal flattening of the slab along the 660 km discontinuity. The final segment stretches north-ward to reach the four ECRiS regions. Uniform composition [4]. The coordinates of the linear feature are taken in the middle of the Alps polygon.

  5. Mantle Plumes: the [x,y] coordinates of the four plumes are defined by the centroids of the polygons created to represent the ECRiS regions. Uniform composition [5]. The maximum depth of each plume has been limited to < 600 km to represent the secondary plumes generated in the MTZ by slab dehydration.

    5a. Massif Central Plume

    5b. Eifel Plume

    5c. Boehmian Massif Plume

    5d. Pannonian Plume

European continental plate including the Alps, Appennines, Pyrenees and the ECRiS regions.

Figure (1): different colours represent different features: oceanic plate (dark blue), continental plate (dark green), mountain ranges (light green), intra-continental volcanic provinces (orange)#

Alpine slab subducting beneath Central Europe

Figure (2): different colours represent different features: oceanic plate (dark blue), continental plate (dark green), mountain ranges (light green), and subducted slab (orange)#

Mantle plumes feeding the ECRiS intra-continental volcanic regions

Figure (3): different colours represent different features: oceanic plate (dark blue), continental plate (dark green), mountain ranges (light green), subducted slab (orange), intra-continental volcanic provinces and ascending plumes (red)#