Tectonostratigraphy of the Mérida Massif reveals a new suture zone exposure in SW Iberia
Abstract. Dividing a crystalline basement into tectonostratigraphic units, along with the recognition of the nature of their boundaries (primary vs. tectonic), are essential steps to identify major tectonic slices involved in orogeny. The Neoproterozoic and Paleozoic rocks of the Mérida Massif (SW Iberia) have been grouped into five tectonostratigraphic units according to their structural position, continental or oceanic crust affinity, and equivalent tectonometamorphic evolution. Each unit is separated from the rest ones by either crustal-scale thrusts and/or extensional detachments. The lowermost unit (Magdalena Gneisses; lower plate) has continental crust affinity, and rest below a variably strained and metamorphosed mafic-ultramafic ensemble, referred to as the Mérida Ophiolite (suture zone). The Neoproterozoic Montemolín Formation of the Serie Negra Group constitutes a unit with continental crust affinity (Upper Schist-Metagranitoid Unit; upper plate) located on top of the Mérida Ophiolite. A carbonate-rich succession (Carija Unit) occupies the uppermost structural position. Structural and isotopic data suggest that the suture zone depicted by the Mérida Ophiolite and the tectonic piling and main foliation of the Neoproterozoic and Cambrian units were formed during the Cadomian Orogeny. Superimposed shortening during the late Paleozoic formed a train of upright to NE-verging folds and thrusts that affected the Cadomian suture zone and juxtaposed it onto Ordovician strata (fifth tectonostratigraphic unit) during the Variscan Orogeny. Cenozoic contraction during the Alpine Orogeny formed SW-directed thrusts in an intraplate setting. The Mérida Ophiolite represents a new Cadomian suture zone exposure of the Iberian Massif, but its root zone is yet to be identified. This suture zone exposure seems to share a far-travelled nature with other Cadomian and Variscan suture zone exposures in Iberia, making the latter a piece of continental lithosphere built at the expense of allochthonous terranes transferred inland from peri-Gondwana onto mainland Gondwana, both during the Neoproterozoic-Cambrian and the Devonian-Carboniferous.
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