Cambro-Ordovician palaeogeography and fragmentation of the North Gondwana margin is still not very well understood. Here we address this question using isotopic data to consider the crustal evolution and palaeogeographic position of the, North Gondwana, Iberian Massif Ossa–Morena Zone (OMZ). The OMZ preserves a complex tectonomagmatic history: late Neoproterozoic Cadomian orogenesis (ca. 650–550 Ma); Cambro-Ordovician rifting (ca. 540–450 Ma); and Variscan orogenesis (ca. 390–305 Ma). We place this evolution in the context of recent North Gondwana Cambro-Ordovician palaeogeographic reconstructions that suggest more easterly positions, adjacent to the Sahara Metacraton, for other Iberian Massif zones. To do this we compiled an extensive new database of published late Proterozoic–Palaeozoic Nd model ages and detrital and magmatic zircon age data for (i) the Iberian Massif and (ii) North Gondwana Anti-Atlas West African Craton, Tuareg Shield, and Sahara Metacraton. The Nd model ages of OMZ Cambro-Ordovician crustal-derived magmatism and Ediacaran-Ordovician sedimentary rocks range from ca. 1.9 to 1.6 Ga, with a mode ca. 1.7 Ga. They show the greatest affinity with the Tuareg Shield, with limited contribution of more juvenile material from the Anti-Atlas West African Craton. This association is supported by detrital zircons that have Archaean, Palaeoproterozic, and Neoproterozoic radiometric ages similar to the aforementioned Iberian Massif zones. However, an OMZ Mesoproterozoic gap, with no ca. 1.0 Ga cluster, is different from other zones but, once more, similar to the westerly Tuareg Shield distribution. This places the OMZ in a more easterly position than previously thought but still further west than other Iberian zones. It has been proposed that in the Cambro-Ordovician the North Gondwana margin rifted as the Rheic Ocean opened diachronously from west to east. Thus, the more extensive rift-related magmatism in the westerly OMZ than in other, more easterly, Iberian Massif zones fits our new proposed palaeogeographic reconstruction.

The ophiolitic Villa Clara serpentinite-matrix mélange, central Cuba, forms part of the large ophiolitic belt of the Greater Antilles. The composition of ultramafic and mafic rocks allows classifying them into two main groups, revealing a complex multi-stage formation of oceanic lithosphere in varied tectonic settings: i) group 1 matches fertile MORB-like mantle typical of abyssal/transform fault peridotites, while ii) group 2 shows characteristics of refractory mantle-wedge forearc peridotites. These features are consistent with moderate extent of partial melting (4–8%) of depleted mantle at a mid-ocean ridge setting that created residual abyssal peridotite (group 1) and intense remelting (14–18%) of the latter in a forearc setting that created highly refractory peridotite (group 2). The elemental and isotopic characteristics of groups 1 and 2 serpentinites denote the influx of fluids evolved from the subducting slab. Mafic rocks appear as variably sized tectonic blocks within serpentinite that underwent variable alteration at low pressure. Immobile element concentrations allow identifying two main groups: i) group 1 is consistent with forearc basalts formed during the second stage of melting of (abyssal) peridotite, while ii) group 2 has a compositional pattern like island-arc tholeiitic basalts. A geodynamic evolution from abyssal to forearc settings is presented to explain the nature of the oceanic lithosphere of the Villa Clara ophiolitic bodies and ensuing serpentinization and mélange formation. This model may explain other ophiolitic bodies of the Caribbean arc in Cuba, Dominican Republic and Puerto Rico and elsewhere formed in abyssal/transform fault or forearc settings.

The Rocciavrè massif is a large eclogitized ophiolitic fragment exposed in the Western Alps (Piemonte, Italy) exhibiting an almost complete sequence of the subducted Liguro‐Piemont lithosphere. Raman spectroscopy on carbonaceous material in metasediments from Rocciavrè and the juxtaposed Orsiera massif indicates maximum temperatures in the range ~510°C–550°C, whereas thermodynamic modelling in mafic lithologies reveals peak burial metamorphic conditions of 550°C–590°C/2.2–3.0 GPa for both units, suggesting the absence of a metamorphic gap between them. Late Jurassic (ca. 151–158 Ma) zircons extracted from Rocciavrè metagabbros reflect the crystallization age near the seafloor, and no alpine metamorphic rims have been detected. The garnet‐omphacite‐rutile–dominated Fe‐Ti metagabbros are crosscut by a variety of high‐pressure vein systems, including garnet‐rich, omphacite‐rich, omphacite‐quartz–rich, glaucophane‐quartz–rich and winchite‐actinolite‐talc veins. Vein textures, mineral assemblages and mineral compositions suggest the formation of garnet‐rich and omphacite‐rich veins at conditions close to peak burial and the successive formation of omphacite‐quartz–rich and glaucophane‐quartz–rich types by reopening former omphacite‐rich veins at eclogite‐ to epidote‐blueschist‐facies conditions along the exhumation path. In contrast, winchite‐actinolite‐talc veins are interpreted as retrograde greenschist‐facies features. In situ U‐Pb dating of monazite constrains the age omphacite‐quartz–rich veining at 40.4 ± 0.2 Ma. Major and trace element mapping of vein assemblages shows various zoning patterns of omphacite and rutile crystals for a large variety of elements (e.g., Fe, Mg, Mn, Sr, Li, U and Cr). Aqueous primary fluid inclusions trapped in vein‐filling and host‐rock minerals have intermediate to high salinity values, interpreted to reflect the partial signature of hydrothermal alteration preserved up to eclogite‐facies conditions. High fluid inclusion salinity values associated with the presence of N₂ (± CO₂) suggest the presence of fluids produced by local dehydration reactions at peak burial. In contrast, some inclusions from glaucophane‐quartz–rich veins contain a low to intermediate salinity CO₂‐CH₄–bearing fluid interpreted as reflecting a sedimentary contribution and a larger scale of fluid circulation. In addition, the mineralogy of winchite‐actinolite‐talc veins associated with high‐salinity values suggests an ultramafic signature. The successive steps of vein formation are interpreted to record the evolution from a closed to open chemical system during exhumation, with late sedimentary and ultramafic fluid contributions that witness the mobility of fluids within the mafic sequence and transport distances likely reaching the kilometre scale. The Rocciavrè massif, which shares a similar metamorphic history to the Monviso Lago Superiore Unit further south, enables a precise characterization of fluid–rock interaction processes in subduction from eclogite‐facies to greenschist‐facies conditions.

The Ossa-Morena Zone (OMZ), SW Iberia, has numerous Lower Carboniferous compositionally zoned plutons that formed in a Variscan intra-orogenic extensional setting. This magmatism shows a wide compositional variation comprising alkaline, transitional, and calc-alkaline suites. The calc-alkaline suite was produced by hybridization of alkaline magmas with felsic melts generated by crustal anatexis related to the intrusion of mafic magmas in the middle crust. In this work, we present a textural and mineralogical study of the Variscan Valencia del Ventoso main pluton from the OMZ to track the compositional evolution of magmas during hybridization using constraints from amphibole compositions and to determine the P-T conditions of emplacement using amphibole-based thermobarometry. This pluton exhibits reverse zoning with an inner facies containing alkaline dolerites, gabbros, and quartz diorites, an intermediate facies with transitional diorites, and an outer facies with calc-alkaline quartz diorites to monzogranites. Magmas from the intermediate and border facies crystallized under oxidizing conditions at relatively low temperatures (range: 640–760 °C) and ca. 280–300 MPa, implying near H₂O-saturated conditions. These rock facies show mineralogical evidence of hybridization between alkaline to mildly alkalic and calc-alkaline magmas. The former is inferred from the occurrence of antecrysts of labradorite-andesine, high-Ti pargasite-hastingsite, and biotite with deficiency in tetrahedral-site occupancy, a distinctive feature of biotite from the inner facies alkaline dolerites. This contrasts with later crystallization from the calc-alkaline magma of andesine-oligoclase, low-Ti magnesiohornblende-edenite, and biotite with full tetrahedral-site occupancy. Constraints from amphibole-melt compositional relationships in antecrystic high-Ti amphibole suggest that the alkaline magmatic component could have a high- to ultra-K affinity.