Encontrados 14 documentos, a visualizar página 1 de 2
The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the
Pereira, M. Francisco; Linnemann, Ulf; Hofmann, Mandy; Chichorro, Martim; Sola, Rita; Medina, Jorge; Silva, Jose B.U–Pb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovician (Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of the southwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passive margin transition. The LA-ICP-MS U–Pb data set (375 detrital zircons with 90–110% concordant ages) is dominated by N...
Tracing the Cadomian magmatism with detrital/inherited zircon ages by in-situ U...
Pereira, M. Francisco; Chichorro, Martim; Solá, A.M. Rita; Silva, Jose B.; Sánchez-Garcia, Teresa; Bellido, FelixU–Pb SHRIMP geochronology on zircon extracted from a granite, a sandstone and a quartzite of the SW Iberian Massif (Ossa-Morena Zone), was used in order to investigate the contribution of Late Neoproterozoic (Cadomian) tectonothermal history to the crustal growth of northern Gondwana. The analysed Cambrian rocks were sampled along the southern margin of the Coimbra–Cordoba shear zone (Barquete granite and Crato...
The role of bedding in the formation of fault–fold structures,
Pereira, M. Francisco; Silva, Jose B.; Ribeiro, CarlosFold-fault structures within a major transpressional shear zone of the SW Iberian Massif were investigated by combining geological mapping, cross-section analysis and microtectonic studies. A significant example of contractional deformation is displayed in the Portalegre-Esperanc¸a Shear Zone (PESZ) where a heterogeneous Ordovician stratigraphic sequence, showing a strong competence contrast between quartzites,...
Rift-related volcanism predating the birth of the Rheic Ocean
Sanchez-Garcia, Teresa; Bellido, Felix; Pereira, M. Francisco; Chichorro, Martim; Quesada, Cecilio; Pin, Christian; Silva, Jose B.Two very different periods of magma emplacement in the crust of the Ossa-Morena zone (early and main events) in SW Iberia have been previously interpreted to record a Cambrian/Early Ordovician rifting event that is thought to have culminated in the opening of the Rheic Ocean during the Early Ordovician. New stratigraphic, petrographic, geochemical and Sm–Nd isotope data from Cambrian volcanic rocks included in ...
Exhumation of high-pressure rocks in northern Gondwana during the Early
Pereira, M. Francisco; Apraiz, Arturo; Chichorro, Martim; Silva, Jose B.; Armstrong, R.A.The Coimbra–Córdoba shear zone (CCSZ) represents a major intra-continental shear zone of the European Variscan orogen. The shear criteria found in metamorphic rocks of the CCSZ are consistent with sinistral transcurrent movements. Isoclinal and open folds with axes parallel to the stretching lineation are responsible for dip variations in the mylonitic foliation, but are related to the same kinematics. In selec...
Comment on ‘‘Geodynamic evolution of the SW Europe
Pereira, M. Francisco; Silva, Jose B.; Chichorro, MartimRibeiro et al. [2007] have presented a geodynamic view of the SW Iberia Variscides based on data from Portugal. Their treatment of already published data is commendable, and the knowledge gained will surely encourage the discussion of the SWEurope Variscides. However, in our opinion, Ribeiro et al.’s modeling and interpretation of the Ediacaran–Lower Ordovician ( 560–470 Ma) geodynamic evolution are of limited ...
Zircon U–Pb geochronology of paragneisses and biotite
Pereira, M. Francisco; Chichorro, Martim; Williams, Ian S.; Silva, Jose B.Sensitive high-resolution ion microprobe U–Th–Pb age determinations on detrital and inherited zircon from the E ´ vora Massif (SW Iberian Massif, Portugal) provide direct evidence for the provenance of the Ossa–Morena Ediacaran basins (Se´rie Negra) and a palaeogeographical link with the West African craton. Three samples of the Se´rie Negra paragneisses contain large components of Cryogenian and Ediacaran (c. ...
Tectonothermal analysis of high-temperature mylonitization in the
Pereira, M. Francisco; Apraiz, Arturo; Silva, Jose B.; Chichorro, MartimMylonites in pelitic and quartzofeldsphatic gneisses from the Ouguela tectonic unit (Coimbra–Córdoba shear zone, SW Iberian Massif) have been studied as an example of high-temperature ductile deformation associated with transcurrent tectonics. Detailed microstructural and P–T analysis indicates that ductile deformation evolved from a metamorphic peak at approximately 650–750 °C and 7.5–9.5 kbar (quartzofeldspha...
Cambrian ensialic rift-related magmatism in the Ossa-Morena Zone
Chichorro, Martim; Pereira, M. Francisco; Diaz-Azpiroz, M.; Williams, Ian S.; Fernandez, C.; Pin, Ch.; Silva, Jose B.The Late Ediacaran (c. 560–550 Ma) Série Negra sediments of the Évora–Aracena metamorphic belt, Ossa-Morena Zone, SW Iberian Massif, preserve a record of the erosion of an Avalonian–Cadomian magmatic arc and subsequent related turbiditic sedimentation. Detrital zircon from the Série Negra is characterized by predominantly Ediacaran and Cryogenian ages, with few Paleoproterozoic and Archean cores, and a marked l...
Crustal growth and deformational processes in the northern
Pereira, M. Francisco; Silva, Jose B.; Chichorro, Martim; Moita, Patricia; Santos, J. Francisco; Apraiz, Arturo; Ribeiro, CristinaThe aim of this article is to present a compilation of available information on the Évora Massif based on structural mapping, whole-rock geochemistry, recognition of metamorphic mineral assemblages, and geothermobarometry. In our view, transcurrent movements responsible for strong orogen-parallel stretching were dominant and had a major role in the geodynamic evolution of this part of Ossa-Morena zone (southwes...
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