Nova Terra 52

formation of the Serie Negra Group, the Montemolín Formation (Eguíluz, 1988; Bandrés, 2001). This metasedimentary formation is intruded by at least five mappable metaigneous intrusive com- plexes. Some mafic-intermediate bodies located mostly to the south preserve equigranular igneous texture. This primary texture is also preserved in poorly strained sections of metagranite- metagranodiorite rocks, while in the parts where these kilometre-scale bodies accumulate more deformation show gneis- sic and even cataclastic texture, mainly in felsic bodies. All litholo- gies included within the upper unit represent an internally coherent tectonic slice with no mechanical contacts between them. However, the strain in this upper unit is heterogeneous and a sin- gle planar fabric that is contiguous regionally and affecting all metasedimentary and metaigneous lithologies seems to be the result of a common tectonometamorphic evolution for the entire unit (Díez Fernández et al., 2021). Finally, the Mérida Massif fea- tures an uppermost unit, referred to as the Carija Unit, which is considered Cambrian in age and is separated from the units below by the Carija detachment (Díez Fernández et al., 2021). 3. Upper Schist-Metagranitoid Unit The tectonostratigraphic characterization of this massif allows a detailed study of the metaigneous complexes included in the Upper Schist-Metagranitoid Unit, the relationship between them and their implication in the evolutionary dynamics of the section of the peri -Gondwanic arc preserved north of the OMC has not been carried out so far. This unit occupies the largest extension in the study area and is located to the south and east of the Merida Massif (Fig. 2). In this unit, the regionally correlated Montemolín Formation (Bandrés, 2001) appears intruded by a number of metaigneous bodies that have been variably strained and elon- gated along the main direction of pre-Variscan (Cadomian) stretch (Sc; Díez Fernández et al., 2021) under low grade metamorphic conditions (greenschist facies). Therefore, the current lens- shaped structure of the metaigneous bodies does not represent a primary one, nor their upper/lower structural position is a qualita- tive reference for a younger/older protolith age, respectively. The primary thickness of the entire unit is unknown, although it is esti- mated to exceed 4000 m (minimum current thickness of the unit after strain). From bottom to top, the lowermost metaigneous com- plex is made up of fine-grained, lens-shaped (metre-scale) bodies of metadolerites, referred as metabasites, (greenschists/amphibo- lites) interlayered with the metasedimentary host series. These metabasites are constituted by horblende and low temperature amphiboles with minor chlorite, (saussuritized) plagioclase, and scarce quartz (Fig. 3a and b). Following upward in the unit the next metaigneous complex appears is an association of slightly deformed metatonalites with minor metagabbros (Don Álvaro Metaigneous Complex, Fig. 2). Don Álvaro metatonalites are consti- tuted by plagioclase (saussuritized in most cases), green and brown hornblende, quartz, biotite with minor chlorite and epidote (Fig. 3c and d). The next metaigneous complex shows extensive deformation appearing as felsic orthogneisses (San Andrés Metaig- neous Complex, Fig. 2). San Andrés felsic gneisses are constituted by quartz, plagioclase, K-feldspar, with minor epidote and scarce chlorite derived from igneous biotite (Fig. 3e and f). Although pho- tolith nature is not clear (compositional heterogeneity could be primary, related to superimposed strain, or both), it cannot be ruled out that this is an ensemble that included various felsic litho- logical ensemble of intermediate-acid affinity. Ascending through the pile, the following set of metaigneous rocks includes meta - granodiorites with minor metatonalites to diorites (Valle Real Metaigneous Complex, Fig. 2). Deformation is generally poor and, in some cases, these rocks preserve the primary igneous texture in green and brown amphibole, plagioclase, quartz, and minor k- feldspar and sphene (Fig. 4a and b). From this point upwards, lay- ers or lenses of metabasite within the metasedimentary sequence are no longer observed. To the top of the unit (Fig. 2), there appears the Valverde Metaigneous Complex composed by metagranites to metagranodiorites, which show an extraordinarily heterogeneous strain, ranging from virtually non-deformed terms to cm-scale ultramylonitic bands (Fig. 4c and d). These felsic rocks of this com- plex are constituted by recrystallized quartz, K-feldspar, plagio- clase, and variable contents of muscovite. 4. Sample selection and methodology 4.1. Sample selection Thirty samples of metaigneous rocks belonging to the Upper Schist-Granitoid Unit were selected for whole-rock geochemical and isotopic (Sr-Nd) analysis. Seven samples belong to metabasites interlayered in the metasedimentary host and were collected in the road that connects Don Álvaro and Mérida towns. The remain- ing twenty-three samples belong to the other four metaigneous complexes. Eight samples were selected within the Don Álvaro Metaigneous Complex, near the town that gives the complex its name. Five samples of the San Andrés Metaigneous Complex were collected mainly near the neighborhood of that name in Mérida city. Five samples were taken from the Valle Real Metaigneous Complex cropping out close to the road that connects Valverde de Mérida and Mérida. The last five metagranite samples belonging to the Valverde Metaigneous Complex were collected to the north in the vicinity of the Valverde and San Pedro de Mérida towns. Sampling was focused on picking the most representative and undisturbed samples, avoiding in any case the sections affected by late fracturing and fluid percolation. The coordinates of the samples are included in Supplementary Table S1. In order to determine the age of crystallization of the granitic protoliths, U-Pb zircon dating has been performed from 1.5 to 2 kg of fresh rock on five representative samples. One sample of metatonalite belongs to Don Álvaro Metaigneous Complex (DAMIC metatonalite); one sample of felsic gneiss belongs to San Andrés Metaigneous Complex (SAMIC felsic gneiss), one sample of a meta- granodiorite collected from the Valle Real Metaigneous Complex (VRMIC metagranodiorite), and two samples belonging to the same metagranitic body of Valverde, one undeformed sample taken in the internal parts of the body (VALMIC metagranite) and one sam- ple taken near the external contact of the igneous body, which appears intensively sheared and affected by penetrative foliation (VALMIC1 metagranite). 4.2. Whole-rock major and trace elements analysis Crushing and powdering of the rock samples were performed at the facilities of the Complutense University of Madrid. Analysis of major and trace elements was carried out at the Activation Labora- tories (ActLabs), Ontario (Canada). Lithium metaborate/tetraborate was used for fusion of the samples, and the elements were deter- mined by ICP-OES (major and some trace) and ICP-MS (most of trace). The detection limits for the analytical procedure range from 0.01% for the majority of the major elements to 0.001% for TiO 2 and MnO. The results of major and trace element analyses are given in Supplementary Table S2. 4.3. U-Pb zircon methodology Crushing and sieving of the rock samples to obtain zircon frac- tions in the size range 36 to 400 l m were performed at the Senck- E. Rojo-Pérez, U. Linnemann, M. Hofmann et al. Gondwana Research 109 (2022) 89–112 The Ediacaran arc section