Critical analysis between the Ossa-Morena Zone and the Galicia-Trás-os-Montes Zone, Iberian Massif: Geochemical and geochronological comparison and geodynamic implications

Recent studies have suggested the existence of a correlation between the allochthonous units of NW Iberia (Galicia-Trás-os-Montes Zone - GTMZ) with SW Iberia (Ossa-Morena Zone – OMZ) in the European Variscan Belt. Such proposed equivalence is based on lithostratigraphic, tectono-metamorphic, geochronological, and geochemical affinities between these two domains, and implies that both zones had the same Neoproterozoic and early Palaeozoic basins, recording the same magmatic episodes and enduring the same tectono-metamorphic processes related to the Variscan Orogeny. As so, in order to better understand the evolution of these domains during the Ediacaran-Cambrian period, a comprehensive geochemical, isotopic and geochronological analysis of the metasediments that make up the OMZ and the allochthonous units of the GTMZ was carried out. The results show that the metasediments of OMZ and the Lower Allochthonous units of GTMZ present similar geochemical and geochronological features, having been likely deposited near each other, although small, but specific differences between both domains suggest that they do not correspond to the same depocentre. However, no geochemical, isotopic or geochronological correlation can be established with any of these domains and the Upper Allochthonous units of GTMZ. These metasediments display quite exotic features and, as such, were likely deposited in a different narrower basin, located to the W of the basins where OMZ and Lower Allochthonous units of GTMZ were deposited, thus providing precise constraints on the paleogeographic reconstruction of these domains during the Neoproterozoic to Early Ordovician dismembering of Gondwana.