Nova Terra 52

and a model for its evolution. The new results also provide for more detailed correlations with existing Ediacaran units in other regions of the Variscan Orogen. 2 . Geo l ogica l setting 2.1. The Ossa-Morena Complex In the SW Iberian Massif, the Ossa Morena Complex contains several peri-Gondwanan terranes emplaced onto an Autochthonous Domain, initially located inboard towards the Gondwanan mainland (Díez Fernández and Arenas 2015; Arenas et al . 2016a,b; Díez Fernández et al . 2016; Fuenlabrada et al . 2020, 2021). The lower part of the complex is represented by a Basal Allochthonous Terrane that can be recognized at the scale of the entire Iberian Massif and consists of a sequence with continental affinity affected by high-P Variscan metamorphism dated at 377–370 Ma (Díez Fernández and Arenas 2015; Abati et al . 2018; Novo- Fernández et al . 2021; Arenas et al . 2021a). The Badajoz – Córdoba Unit (or Central Unit) and the Cubito- Moura Unit define the Basal Units in SW Iberia (Figure 1b). The Basal Allochthonous Terrane has been interpreted as a section of the outer margin of Gondwana, subducted under Laurussia during the ear- liest stages of Pangea assembly (Martínez Catalán et al . 1996; Díez Fernández et al . 2011; Arenas et al . 2016b). At the top of the Ossa-Morena Complex, the Upper Allochthonous Terrane represents a thick composite ter- rane containing several units with continental and ocea- nic affinities. Units with continental affinity mainly comprise a thick sedimentary sequence that includes deposits with ages ranging from Ediacaran to Carboniferous. The oldest metasedimentary rocks are represented by the so-called Serie Negra Group (Black Series Group; Carvalhosa 1965; Eguiluz 1988; Cambeses et al . 2017, and references therein), which includes a lower formation consisting of metagreywackes, meta- sandstones, schists, micaschists, quartzschists, and black quartzites, with abundant greenschist and amphibolite horizons (Montemolín Formation), and an upper forma- tion that consists of metasandstones, volcanogenic metagreywackes, slates and phyllites, black quartzites, metacherts and layers of micaschists and limestones (Tentudía Formation). The precise age of this series is unknown, but its maximum depositional age has been estimated using detrital zircons at c . 600–590 Ma for the Montemolín Formation (Ordóñez Casado 1998) and c . 565–541 Ma for the Tentudía Formation (Schäfer et al . 1993; Linnemann et al . 2008; Pereira 2015). Whole-rock geochemistry and Nd isotopic sources of the Serie Negra Group are compatible with an arc-related setting built on a thinned older continental margin. The Ediacaran series shares almost identical isotopic (Nd) compositions with other Neoproterozoic series described in the Variscan Belt, such as those from the Bohemian Massif (Linnemann et al . 2000; Linnemann and Romer 2002), suggesting a common crustal provenance and similar palaeo-position along the northern Gondwanan margin (Pereira 2015; Rojo-Pérez et al . 2021). The Serie Negra is affected by Cadomian deformation and metamorphism that ranges between the chlorite zone and regional migmatization. However, the age of Cadomian deforma- tion and metamorphism is loosely constrained. The Cadomian tectonothermal event affecting the Serie Negra Group has been dated at c . 550–560 Ma in the northern sector of the Ossa Morena Complex (Obejo – Valsequillo Domain; Blatrix and Burg 1981; Dallmeyer and Quesada 1992). The Serie Negra is unconformably overlain by the Malcocinado Formation (Fricke 1941), which is characterized by less intense deformation and low-grade metamorphism. It is composed of andesitic tuffs, rhyolites, granitoids, phyllites, sandstones, grey- wackes, and polygenic conglomerates with pebbles of the Serie Negra (Pereira et al . 2006; Cambeses et al . 2017). The Malcocinado Formation probably crosses the Ediacaran-Cambrian boundary (Pereira 2015), since the youngest lavas in this series have been dated at c . 534 Ma (Sarrionandia et al . 2020). The overlying Torreárboles Formation (Liñán 1984) is considered the lowest Cambrian series. It is composed of fluvial to shal- low marine shelf deposits comprising slates, sandstones, conglomerates, and breccias, with suggested maximum depositional ages in the range c . 567–532 Ma (Linnemann et al . 2008; Pereira et al . 2011). The Torreárboles Formation shows clear unconformable rela- tionships with the Serie Negra Group and Malcocinado Formation, which confirms the existence of a penetrative deformation, metamorphism, and effective exhumation processes of Cadomian age in SW Iberia (Díez Fernández et al . 2019, 2022). The Ediacaran and Early-Middle Cambrian series of the Ossa-Morena Complex are affected by extensive magmatism ranging in age from Late Proterozoic to Ordovician. This magmatism occurred on the Gondwanan margin allegedly during a switch from a subduction-related environment (Ediacaran-Early Cambrian) to a rift setting (Middle Cambrian-Early Ordovician) (Linnemann et al . 2008; Pereira et al . 2012; Sánchez-García et al . 2013; Sánchez- Lorda et al . 2014, 2016; Díez Fernández et al . 2015; Henriques et al . 2015; Von Raumer et al . 2015; Cambeses et al . 2017; Rojo-Pérez et al . 2022). In the NW Iberian Massif, equivalent units to the Basal and Upper allochthonous terranes of the Ossa Morena Complex are separated by various ophiolitic units with 4 R. ARENAS ET AL. &KDSWHU