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Mantle xenoliths in within-plate alkaline mafic lavas from NE Spain are mainly anhydrous spinel lherzolites and harzburgites, grading into each other, and subordinate pyroxenites. Peridotites followed an earlier melt depletion caused by mantle decompression and subsequent metasomatism. Two main types of metasomatism are differentiated affecting mainly the harzburgites: a silicate-melt metasomatism of Fe–Ti type and a carbonatite metasomatism. Both types are recognized in the nearby Pyrenean peridotite massifs, but the presence of hydrous minerals is less frequent in the xenoliths. The two metasomatic styles could have been generated by the intrusion of Cretaceous alkaline magmas, if a chromatographic fractionation–reaction process at decreasing melt mass took place. This would account for the evolution of the original alkaline silicate percolating melt towards a carbonatite-rich melt, allowing the coexistence in both space and time of the two metasomatic styles. Metasomatism in lherzolites could be explained in the same way. The pyroxenite xenoliths are interpreted as cumulates from these alkaline basic magmas that crop out in the area as rare camptonite dykes. Interaction with host lavas is minor and could explain the partial melting, enrichment and disequilibrium observed in a deformed composite xenolith and sporadic veins filled with glass.

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The Cabo Ortegal Complex is a composite allochthonous terrane that was thrust onto the western edge of Gondwana during the Variscan orogeny. It is formed of two main tectonic units: the Upper Tectonic unit, comprising rocks affected by highpressure (P)-high-temperature (T) metamorphism, and the Lower Tectonic unit, which represents the resulting suture of the Variscan collision. The suture preserves remnants of strongly deformed and metamorphosed ophiolitic rocks overriding the parautochthon, and the lower Paleozoic sequence of the Ollo de Sapo antiform, regarded as the autochthonous sequence of the Iberian plate. The Upper Tectonic unit is formed by layered ultramaµc, maµc, and quartzo-felspathic rocks that were buried at levels in excess of 50 km (~1.56 GPa) before the Variscan collision in a convergent plate boundary within the Rheic ocean domain ca. 490-480 Ma (Early Ordovician). They have been interpreted either (1) as an earlier thinned continental crust, underlain by a lithospheric mantle and oceanic spreading, or (2) as independent terranes, formed in different geodynamic settings (island arc, oceanic). Most structures observed in these rocks are ductile and are associated to their exhumation process. It started with the development of a persistent horizontal foliation in granulite facies conditions, which equilibrated in amphibolite facies conditions ca. 385 Ma, and ended in higher crustal levels with the progressive development of noncoaxial structures, such as eastverging asymmetrical isoclinal folds and thrusts, leading to the emplacement of the Upper Tectonic unit over the Lower Tectonic unit ca. 365 Ma (Late Devonian).

The Cabo Ortegal complex (northwestern Iberian massif ) is a klippen formed of several structural units stacked during the Hercynian collision. All these units include ultramafic rocks, metabasites and quartzfeldspathic gneisses affected by different metamorphic conditions. The Bacariza formation is heterogeneous showing a conspicuous layering mainly defined by alternate high-pressure ultrabasic-to-basic granulites, retrogressed garnet amphibolites of intermediate composition and rare acid rocks forming garnet trondhjemitic gneisses. This layering is inherited from a gabbroic protolith showing a composition rich in Fe and Ti. Major and trace elements of these rocks can be correlated to continental tholeiitic series of extensional settings. These high-pressure granulites are situated in normal contact between$serpentinised ultramafic rocks and other high-grade metabasites with lessevolved and more-depleted composition comparable to T-type and N-type MORB. It is suggested that the layered gabbro-type protolith was part of a continuous mafic crust. This crust was initially formed during Early Ordovician in a continental extensional setting and progressively evolved to oceanic spreading.