**6.3 Closure of the Paleozoic Rheic ocean and Variscan orogeny**

The Variscan Belt is a segment of a mountain system that has existed all around the world because of a sequence of Paleozoic collisional orogenic events (e.g., the Appalachians in America, Mauritanides in Africa, the Caledonides in Scandinavia

#### **Figure 5.**

*Simplified conceptual geodynamic sketch of the Alpine orogeny after Candioti et al. [78]. (a) Passive margin geometry and embryonic oceans after the rifting phase. (b) Horizontally forced SZI on the Adriatic passive margin and subduction of the Sesia-Dent Blanche unit. (c) Possible scenarios for the collisional phase of Alpine orogeny with a slab that is continually subducting (left) or a slab that is separated (right).*

and Scotland, the Urals in Russia, the Tien Shan in Asia, and the Lachlan Fold Belt in Australia) that marked the amalgamation of the supercontinent Pangea [138, 139] (**Figure 8**). The Variscan belt extends across Europe, with the best exposure in central and western Europe and parts of Morocco and Algeria to the north of the West African Craton [138, 165]. It formed between 480 and 250 My after the collision of Gondwana to the south and Baltica-Laurentia to the north [164, 166–167]. The Variscan belt is a much more complex paleogeographic orogenic belt whose elements were not only shuffled together by collisional deformation but were also dismembered by strike-slip faults and the formation of oroclines [167]. Reviewing the evolution of the main tectonic units and their paleogeography position within the Variscan is beyond the scope of our work, and the reader may refer to [138, 167–169] for further details. However, the presence of suture zones characterized by ophiolites, subduction-related metamorphism and magmatism, accretionary prisms, and foreland basins with syn-orogenic clastic sediments within the

*The Ampferer-Type Subduction: A Case of Missing Arc Magmatism DOI: http://dx.doi.org/10.5772/intechopen.109406*

#### **Figure 6.**

*(a) Geological sketch map of the Pyrenees [150]. Blue line indicates ECORS seismic section shown in (b). White diamonds denote mantle peridotite bodies. NPZ, North Pyrenean Zone; NPF, North Pyrenean Fault; SPZ, Southern Pyrenean Zone; B, Boixols thrust. (b) ECORS crustal-scale cross-section Pyrenees [150].*

European Variscides confirms the existence of several microcontinents between Laurussia and Gondwana. These microcontinents include the blocks of Avalonia, North Armorica (Franconia + Thuringia, separated by the failed Vesser Rift), and South Armorica (southwestern central Iberia, north-central Armorican Massif, Bohemia, all probably united, and Paleo-Adria) (**Figure 9**) [138, 139, 166, 167, 170, 171]. Several authors [138, 170, 171] have proposed that the Variscan microcontinents separated from the north-Gondwana margin by back-arc spreading and southward subduction. Although this model may apply to the Avalonia microcontinent and the opening of the Rheic Ocean, it cannot explain the existence of other microcontinents and intervening rift/drift zones during the Cambrian and Ordovician [167]. Alternatively, a system of mantle plume activity beneath the North Gondwanan margin has been hypothesized to result in the opening of the Rheic and other peri-Gondwanan oceans [172–174]. Only the Rheic (between Avalonia and the Armorican microcontinents) evolved into a sizeable ocean documented by biogeography and paleomagnetism [167]. The other basins (i.e., the Saxo-Thuringian Ocean between north and South Armorica and the Galicia-Moldanubian Ocean between South Armorica and Palaeo-Adria) did not grow beyond the narrow ocean stage and did not pass through the complete Wilson Cycles [167]. Closure of the narrow oceans and their subduction

#### **Figure 7.**

*Scissor-type scenario [159], for the plate kinematic of the Late Mesozoic motion of the Iberian Peninsula to Europe, with the inferred position of the Iberian Peninsula at M0 times (left panel) and the onset of the Alpine collision (right panel). NA, North America; IB, Iberia; EUR, Europe; NGFZ, Newfoundland-Gibraltar Fracture Zone. Circles with crosses denote the poles of the overall reconstruction. Circles labeled M0-A33 denote the poles of the phase describing the opening of the Bay of Biscay.*

#### **Figure 8.**

*Permian (at 280 Ma) assembly of the continents showing the Paleozoic belts. Yellow, 400 ± 250 Ma; orange, 450 ± 400 Ma [164].*

beneath microcontinents in order from south to north, between the middle Devonian and the Tournaisian gave birth to orogenic belts with HP-UHP metamorphism with missing arc magmatism (i.e., Ampferer-type subduction).
