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enriched mantle component (probably the subcontinental mantle of Gondwana) and as an important
contamination of DM-derived melts with continental crust material, respectively. The metasedimen-
tary rocks were partially melted at around 485–495 Ma. After the magmatic activity finished, the
Upper Allochthon did not drift away opening the Rheic Ocean, as it has been proposed by other au-
thors for the Avalonian terranes, but formed part of the extended passive margin of Gondwana until
the Devonian. The high-grade metamorphism attained by the Upper Allochthon was driven by the
subduction of the margin of Gondwana under the colliding retro-continent. Taking into account the
paleogeographic reconstructions proposed by other authors for the Devonian, this retro-continent
should be Laurrusia, but it is likely to be another continental fragment of Gondwana. In the context
of this high-grade metamorphic event (D1 event) zircon recrystallised at
c.
395 Ma in the acidic rocks.
The basic rocks were transformed into eclogites, which was recorded by a zircon recrystallisation cli-
max at
c.
393 Ma, most probably near the metamorphic P–T path temperature peak. The high-grade
metamorphic event re-melted the leucosomes at high-T conditions between 379 and 403 Ma, with a
climax at
c.
388 Ma. During this subduction event the Upper Allochthon was exhumed as an ultra-HP
buoyant plume (D2 event). The progression of the deformational history of the upper units entails the
development of large recumbent folds and an important basal thrust (D3 structures). The mentioned
subduction event was the first one attained by the margin of Gondwana in the complex history of the
early stages of supercontinent assembly.
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