Nova Terra 52

ARTICLE T ectonostratigra p h y of the Mérida Massif reveals a ne w C adomian suture zone e xp osure in Gond w ana ( S W I beria ) Rubén Díez Fernández a , Ricardo Arenas b , Esther Rojo-Pérez b , Sonia Sánchez Martínez b and José Manuel Fuenlabrada c a Instituto Geológico y Minero de España, Tres Cantos, Spain; b Departamento de Mineralogía y Petrología, Universidad Complutense de Madrid, Madrid, Spain; c Unidad de Geocronología (CAI de Ciencias de la Tierra y Arqueometría), Universidad Complutense de Madrid, Madrid, Spain ABSTRACT Neoproterozoic and Palaeozoic rocks of the Mérida Massif (SW Iberia) have been grouped into tectonostratigraphic units. 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 mafic-ultramafic ensemble, referred to as the Mérida Ophiolite (suture zone). 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 previous isotopic data suggest that this suture zone was formed during the Cadomian Orogeny. Superimposed shortening during the late Palaeozoic formed upright to NE-verging folds and thrusts that affected this suture zone and juxtaposed it onto Ordovician strata during the Variscan Orogeny. The Mérida Ophiolite represents a new Cadomian suture zone exposure in the Gondwanan realm of the Iberian Massif, but its root zone is yet to be identified. This ophiolite shares a far-travelled nature with other Cadomian and Variscan suture zone exposures in Iberia, making the latter a piece of lithosphere built through inland transference of allochthonous terranes from peri-Gondwana onto mainland Gondwana during the Neoproterozoic-Cambrian and the Devonian-Carboniferous periods. ARTICLE HISTORY Received 16 July 2020 Accepted 28 November 2020 KEYWORDS Cadomian tectonics; suture zone; Ophiolite; Variscan tectonics; SW Iberian Massif 1 . Introduction Suture zone exposures related to the Cadomian Orogeny affecting the sections of peri-Gondwana pre- served in Europe and North Africa (Neoproterozoic – Cambrian) are scarce in the geological record (El Hadi et al . 2010; Kounov et al . 2012; Arenas et al . 2018), but provide important constraints on the geodynamic and tectonic evolution of peri-Gondwana. However, suture zones of this age are commonly covered by thick sedi- mentary sequences deposited on the margin of Gondwana after suturing, if not reworked or even reac- tivated, and thus blurred, during younger geodynamic cycles such as the Variscan and Alpine. Before extensive, more oriented research can be performed in cases like this, a proper introduction to the main features of a suture zone is essential. In this manuscript we discuss the general setting of a new Cadomian suture zone in the Iberian section of peri-Gondwana, and what are the main elements supporting its existence. Here we present a new geological map, cross- sections, and structural analysis of the Mérida Massif (Iberia) and distinguish its main tectonostratigraphic units and their relationships. Lithological ensembles for each unit have been grouped according to their struc- tural position, crustal affinity and tectonometamorphic evolution. The resulting tectonostratigraphy reveals a previously unrecognized nappe structure (Abalos et al . 1991; Azor et al . 1994; Ribeiro et al . 2010; Díez Fernández and Arenas 2015; Díez Fernández et al . 2019). It also adds another ophiolite and suture zone exposure to the set that features the Iberian Massif, thus strengthening the notion of the Iberian domain of Gondwana as a region built through a series of suturing events. 2 . Geo l ogica l setting The Iberian Massif constitutes the southernmost expo- sure of the Variscan Orogen in Europe (Figure 1), which resulted from the progressive collision of Gondwana, Laurussia, and their respective pericontinental terranes during the Devonian and Carboniferous periods (Ribeiro C ON TACT Rubén Díez Fernández r.diez@igme.es Departamento de Investigación y Prospectiva Geocientífica, Instituto Geológico y Minero de España, Tres Cantos 28760, Spain INTERNATIONAL GEOLOGY REVIEW https://doi.org/10.1080/00206814.2020.1858355 © 2021 Informa UK Limited, trading as Taylor & Francis Group