From mantle to Iberia: crust-mantle interaction, geodynamic evolution and ore forming systems of alkaline melts in the northernmost Ossa-Morena Zone domains

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Caracterização preliminar da deformação dos ortognaisses alcalinos e hiperalcalinos da Faixa Blastomilonítica (Zona de Ossa-Morena)

Publication . Roseiro, José; Moreira, Noel; Nogueira, Pedro; de Oliveira, Daniel Pipa Soares

SUMMARY: In the Blastomylonitic Belt (northernmost Ossa-Morena Zone), alkaline and peralkaline orthogneisses are found as elongated bodies with WNW-ESE to NW-SE orientation hosted within a strongly deformed Neoproterozoic to Lower Cambrian metasedimentary strata. Despite some similarities between them (ascribed to the very similar nature of their igneous protolith) the deformational features displayed in all of them are different, for example in the mineral segregation and recrystallization (including the development of augens) observed, and in different strike-dip orientation of foliations and lineation plunge. The dissimilarities are presumably due not only from different primary features, but also to the type of ductile shearing and metamorphic conditions they underwent. This way, field data will be complemented with petrographic studies for mineralogical and microdeformation characterization, and crossed to the regional structural information, thus constraining the deformation patterns of the alkaline-peralkaline orthogneisses on the Blastomylonitic Belt.

2023-07Conference object

Open access

Contact metamorphism and dolomitization overprint on Cambrian carbonates from the Ossa‑Morena Zone (SW Iberian Massif): implications to Sr‑chronology of carbonate rocks

Publication . Roseiro, José; Moreira, Noel; Andrade, Laura; Nogueira, Pedro; de Oliveira, Daniel Pipa Soares; Eguiluz, Luis; Mirao, Jose; Moita, Patrícia; Santos, José Francisco; Ribeiro, Sara; Pedro, J.

ABSTRACT: he Cambrian Series 2 Carbonate Formation from the Alter do Chão Elvas-Cumbres Mayores unit (Ossa-Morena Zone, SW Iberian Massif) is composed of regionally metamorphosed marbles and marlstones that underwent chlorite zone metamorphism and preserve the primaeval limestone 87Sr/86Sr ratios (0.7083–0.7088). These are consistent with the established Lower Cambrian seawater curve, and therefore used for age constraints in formations lacking fossil contents. The regional mineralogical and Sr-isotopic features of the carbonate rocks are frequently overprinted by the effects of contact metamorphism induced by magmatic bodies emplaced during rift-related and synorogenic events of the Palaeozoic, as well as by post-metamorphic dolomitization processes. The development of calc-silicate minerals due to contact metamorphism is common in the rocks of the Carbonate Formation and apparently results from the interaction of the protolith with fluids of different origin: (i) internally produced fluids released by conductive heating (observed in external contact aureoles) and (ii) external intrusion-expelled fluids that, besides leading to the appearance of distinctive assemblages, also promote an influx of strontium content (observed in roof pendants). Calc-silicate mineralogy varies substantially throughout the region, likely due to the heterogeneous distribution of silicate minerals of the protolith, progression of intrusion-driven fluids, and the irregular effect of thermal gradients. Results suggest that high-grade contact metamorphism (hornblende facies or higher) and dolomitization processes imposed on the Carbonate Formation significantly influence the isotopic signatures of the carbonates, providing limitations in applying Sr-isotopic chronology.

2024-11Journal article

Open access

High strain peralkaline orthogneisses within orogenic scale shear zones: geological and structural mapping in the Arronches region (Tomar-Badajoz-Córdoba Shear Zone, Ossa-Morena Zone)

Publication . Roseiro, José; Moreira, Noel; Nogueira, Pedro; de Oliveira, Daniel Pipa Soares

ABSTRACT: The lithological units in the Arronches region (included within the Arronches tectonic unit, Tomar-Badajoz-Córdoba Shear Zone, northernmost Ossa-Morena Zone) and in particular the peralkaline orthogneisses therein, have been the target for petrological, geochemical and structural studies in order to constrain its petrogenesis and tectono-metamorphic contextualization within the broader regional geology. Two detailed geological-structural maps of the Arronches region (from the Arronches village and the Fialha area), as well as the structural analysis allow the description of two mylonitic high strain fabrics found in different peralkaline orthogneiss bodies (the dominantly Arronches-type S fabric and the dominantly Fialha-type S-L fabric), which provide better insights about the internal architecture of the Tomar-Badajoz-Córdoba Shear Zone.

2025-04Journal article

Open access

Ordovician–Silurian transition in the Central-Iberian Zone: Just a stratigraphic boundary or a major element in the evolution of the Iberian Variscides?

Publication . Tereso, Vitor; Dias, Rui; Roseiro, José; Romão, José; Coke, Carlos; Fonseca, Rita; Ribeiro, António

ABSTRACT: The Ordovician-Silurian boundary in the Central-Iberian Zone is often considered a normal stratigraphic transition. Nevertheless, in studies carried out in Portugal (e.g. Espinhosela, São Mamede and Buçaco areas) and Spain (e.g. Alcañices Synform) this contact is marked by the development of shear zones subparallel to the lithostratigraphic units. Ongoing structural mapping in Celorico de Basto (Marão region) shows that near Campanhó, the Ordovician (Pardelhas Formation) and the Silurian (Campanhó Formation) units are bounded by a regional shear zone with a normal kinematics (the Covelo do Monte Fault, here presented). Although their origin is debatable, the intraorogenic normal faults are common mechanisms active during Variscan times in the Central-Iberian Zone. In the case of the Ordovician-Silurian boundary, these detachments could be facilitated by shale and organic materials prone to control the development of shear zones.

2025-04Journal article

Open access

Ranked Mappable Criteria for Magmatic Units: Systematization of the Ossa-Morena Zone Rift-Related Alkaline Bodies

Publication . Roseiro, José; Moreira, Noel; de Oliveira, Daniel Pipa Soares; Silva, Marcelo; Eguiluz, Luis; Nogueira, Pedro

ABSTRACT: The Ossa-Morena Zone (SW Iberian Massif) hosts the largest set of Cambro-Ordovician alkaline magmatic plutons related to the Palaeozoic rifting of the northern Gondwana margin so far described. An organized framework for their classification at different scales is proposed through data-driven ranks based on their distinctive petrological features relative to other rift-related magmatic rocks found throughout western Europe. The classification method aims to enhance geological mapping at different scales, regional- and continental-scale correlations, and, as such, facilitate the petrogenetic interpretation of this magmatism. The hierarchical scheme, from highest to lowest rank, is as follows: rank-1 (supersuite) assembles rocks that have distinctive characteristics from other magmatic units emplaced in the same magmatic event; rank-2 (suite) categorizes the units based on their major textural features, indicating if the body is plutonic, sub-volcanic, or a strongly deformed magmatic-derived unit; rank-3 (subsuite) clusters according to their spatial arrangement (magmatic centres) or association to larger structures (e.g., shear zones or alignments); rank-4, the fundamental mapping unit, characterizes the lithotype (alkaline granite, alkaline gabbro, syenite, albitite, etc.) by considering higher ranks (alkalinity and textural aspects); rank-5 characterizes the geometry of individual plutons (with several intrusions) or swarms; rank-6 (smallest mappable unit) corresponds to each intrusion or individual body from a swarm. Although this classification scheme is currently presented solely for the Ossa-Morena Zone, the scheme can be easily extended to incorporate other co-magmatic alkaline bodies, such as those in the NW Iberian allochthonous units or other peri-Gondwanan zones or massifs, in order to facilitate regional correlations of the rift-related magmatism.

2025-02Journal article

Open access