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oceanic crust, we advocate for an ocean to transitional crust affinity (see further discussion about its ophiolitic nature in section 5). 3.3. Upper Schist-Metagranitoid Unit: Serie Negra Group (Montemolín Formation) This unit comprises metasedimentary and metaigneous rocks, in which mafic, intermediate, and felsic compo- nents are recognized. The metasedimentary series includes schists (Figure 6(b)), grey metagreywackes, black quartzites (Figure 6(c)), and black schists. Black schists and quartzites occur as decimetre- to metre- scale lenses within the other schists and metagrey- wackes, while the latter are featured by cm- to mm- scale compositional layering that alternates finer and coarser-grained rocks (relict of sedimentary bedding). Metabasites can be found as fine-grained, lens-shaped (metre-scale) bodies dispersed over the metasedimen- tary series (Figure 6(d)). Former regional studies identi- fied this series as a correlative to a section of the Serie Negra Group (Bandrés 2001). Its primary immature nat- ure (as inferred from greywackic composition), along with its mafic rocks, suggest it could be equivalent to the lower (and older) member of such group, regionally referred to as Montemolín Formation (Eguíluz 1987). The Figure 5. (a) Orthogneiss from the Lower Gneiss Unit (Magdalena Unit). Main foliation in blue. (b) Biotite-rich gneiss with penetrative foliation (blue line) from the Lower Gneiss Unit (Magdalena Unit). (c) Coarse-grained gabbros and crosscutting doleritic dikes affected by heterogeneous strain in the Mérida Ophiolite. Note progressive and heterogeneous transformation of gabbro into foliated amphibolite along dextral shear zones (blue lines). (d) Banded and cumulate metagabbros from the Mérida Ophiolite. Moderately strained section showing penetrative foliation (blue line). (e) Garnet-bearing amphibolites with penetrative foliation (blue lines) from the Mérida Ophiolite. A sample of banded amphibolites is shown in the lower left corner. (f) Hornblendites from the Mérida Ophiolite (field exposure in the background). 6 R. D. FERNÁNDEZ ET AL. &KDSWHU