Nova Terra 52

the generation of the mafic protoliths of this ensemble (Bandrés et al . 2004). Combining our new interpretation for the regional geology of this massif with these data allows us to propose an Ediacaran suprasubduction zone marginal basin setting for the generation of the Mérida Ophiolite that, as commonly observed in suprasubduc- tion zone ophiolites (Pearce et al . 1984), has the geo- chemical features of island arcs (note negative anomalies in Ti, Nb and Ta relative to REE and other distinctive arc signatures such as those observed in ele- mental ratios like Zr/Nb and Ba/Nb; Bandrés et al . 2004) but the structure of oceanic crust (layered structure made of ultramafics, massive gabbros, banded gabbros, dikes, etc.; see description in this work). Should the current upper boundary of the Mérida Ophiolite be a pre-Ordovician extensional fault (Trujillanos detachment), the suture zone this mafic- ultramafic unit represents must be Cadomian in age. The current juxtaposition of tectonostratigraphic units in the Mérida Massif suggests a large-scale nappe struc- ture affecting this suture, where the Lower Gneiss Unit would represent the lower plate, and the Mérida Ophiolite would account for oceanic or transitional litho- sphere located at the base of the upper plate, here represented by the Upper Schist-Metagranitoid Unit. This way, the primary upper and lower boundaries of the Mérida Ophiolite could be Cadomian accretionary thrusts, the current nappe structure being the result of a late Cadomian extensional event that affected pre- viously thickened crust built at the expense of basal tectonic accretion (peak metamorphic conditions for the Mérida Ophiolite suggest lower crust depth). The root of the suture zone represented by the Mérida Ophiolite is not exposed in the study area, as its lower plate (Lower Gneiss Unit) occurs in a tectonic window. This supports a pre-Variscan low-dipping geometry for the thrust sheets involved in the suture zone (e.g. Magdalena thrust; Figure 4(b)), some of the tectonostra- tigraphic units being allochthonous terranes. The pri- mary geometry of the main accretionary thrusts (e.g. imbricates in the Merida Ophiolite) can be inferred from the distribution of cut-offs along the SE-dipping Trujillanos detachment. Cut-offs for the same thrust seem to be aligned to a trend that ranges between E-W and NE-SW. Crosscutting relationships between the trace of the Trujillanos detachment and the trace of Cadomian thrusts indicate that the primary geometry of the thrusts was less inclined to the S and SE than the detachment. Overall, a primary S-directed component of dip can be deduced for the Cadomian thrusts. The number of peri-Gondwanan, Cadomian ophio- lites described in northern Africa and Europe is limited, and include the Bou Azzer Ophiolite in the Anti-Atlas of Morocco (El Hadi et al . 2010), the Frolosh Ophiolite in Kraishte zone, Bulgaria (Kounov et al . 2012), and the Calzadilla Ophiolite in SW Iberia (Arenas et al . 2018). The Mérida Ophiolite described here adds to this short list, and given its geographical proximity with the Calzadilla Ophiolite, located 75 km to the S, some rela- tionships between them can be discussed. The Cadomian metamorphic evolution of these two ophio- lites is different. While the Mérida Ophiolite was buried and heated close to or at granulite facies conditions (1.2 GPa and 750°C; Bandrés et al . 2000), the Calzadilla Ophiolite experienced peak-metamorphic conditions at the (garnet-free) epidote amphibolite facies (Díez Fernández et al . 2019), reflecting a contrasting tecto- nothermal evolution. Without ruling out erosion, the Cadomian post-metamorphic peak exhumation in the Mérida Ophiolite was driven by doming and extension (Trujillanos and Carija detachments), whereas inland- directed obduction (and associated erosion) was the main exhumation mechanism for the Calzadilla Ophiolite (Díez Fernández et al . 2019). The Mérida Ophiolite rests under a metasedimentary rock sequence of the Serie Negra Group (Montemolín Formation) (Figures 3 and 4), while the Calzadilla Ophiolite thrusts onto it (Díez Fernández et al . 2019). Thrusting related to the Cadomian obduction of the Mérida Ophiolite is directed to the N s.l . (Cadomian thrusts are inferred to have a dip component to the S), which is equivalent to the N-directed Cadomian thrusting experienced by the Calzadilla Ophiolite (Díez Fernández et al . 2019). Accordingly, the different structural position relative to similar sedimentary series and the southern location of the Calzadilla Ophiolite relative to the Mérida Ophiolite suggest these ophiolites represent different tracts of (marginal) oceanic basins (Figure 10(a)) emplaced one (Calzadilla Ophiolite) on top of the other (Mérida Ophiolite) (Figure 10(b)). Therefore, the Cadomian record of the Mérida Massif should be framed in an inboard position across the margin of Gondwana relative to the fore-arc sections of the Cadomian arc system that are preserved to the S of the Mérida Massif (Sánchez Lorda et al . 2014), for instance around the Calzadilla Ophiolite (Arenas et al . 2018). The sequence and broad timing of tectonic events recognized for the building of the Mérida Massif fit well into the regional geology of SW Iberia. The Cadomian suture zone and nappe structure identified in the Mérida Massif add to the evidence of Cadomian tectonics in southern Europe (Pieren et al . 1987; Quesada 1990; Eguíluz et al ., 2001; Bandres et al . 2002; Simancas et al . 2004; Díaz García 2006; Pereira et al . 2012; Díez Fernández et al . 2019), which is tightly connected to subduction-accretion processes in the periphery of the 14 R. D. FERNÁNDEZ ET AL. &KDSWHU