Time-space distribution of silicic plutonism in a gneiss dome of the Iberian Variscan Belt: The Évora Massif (Ossa-Morena Zone, Portugal)

• Published in: Tectonophysics Vol. 747-748; pp. 298 - 317
• Main Authors: Dias da Silva, Ícaro, Pereira, Manuel Francisco, Silva, José Brandão, Gama, Cristina
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 13.11.2018; Elsevier BV
• Subjects: Biotite; Cambrian; Carboniferous; Continental crust; Crustal structure; Crustal thickness; Crystallization; Deformation; Diorite; Domains; Domes; Geochronology; Geochronometry; Geological faults; Geology; Gneiss; Gneiss dome; Granite; Gravitational collapse; Gravitational effects; Gravitational instability; Instability; Lead; Magma; Metamorphism; Metamorphism (geology); Paleozoic; Plate tectonics; Plutonium; Plutons; Quartz; Radiometric dating; Schist; Schists; Strike-slip faults; Synorogenic extension; Tectonics; Thickening; Variscan orogeny; Zircon; Évora Massif; Geochronology; Variscan orogeny; Évora Massif; Synorogenic extension; Gneiss dome; Tectonics
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2018.10.015

In the Iberian Variscan Belt, polyphasic deformation has been recognized as comprising an early phase of crustal thickening, followed by an intermediate phase of crustal extension and doming, and a later phase of shortening. The Évora Massif is a gneiss dome of the westernmost domains of the Ossa-Morena Zone (SW Iberia), which provides a remarkable insight into the late Paleozoic deep crustal structure of the Variscan continental crust of northern Gondwana. In this study, we bring new structural and geochronological U-Pb data for the northern hanging-wall of the Évora Massif. We describe the existence of low-dipping D2 extensional shear zones associated with Buchan-type metamorphism (M2); this enables three tectono-metamorphic units to be distinguished: the Lower Gneiss Unit, the Intermediate Schist Unit, and the Upper Slate Unit. D2-M2 structures experienced subhorizontal shortening (D3) and were transposed by low-plunging folding, thrusting and strike-slip faulting. Zircon grains extracted from Pavia quartz-feldspathic gneiss of the Lower Gneiss Unit yielded a crystallization age of ca. 521 Ma (Cambrian Stage 2–3), which establishes a correlation with tectono-metamorphic units of the footwall and southern hanging-wall of the Évora Massif. U-Pb zircon dating of Divôr foliated quartz-diorite (339 ± 7 Ma), Malarranha weakly foliated biotite-rich granite (322 ± 3 Ma), and undeformed porphyritic granite of the Pavia pluton (314 ± 4 Ma) constrain the timing of emplacement of granitic magmas synchronously with doming. Carboniferous magmatism initiated with doming (ME1 - ca. 343–335 Ma), continued through D2-M2 (ME2 - ca. 328–319 Ma), and lasted until the waning stage of crustal extension (ME3 - ca. 317–313 Ma). The Évora Massif gneiss dome probably formed as result of the combined effect of gravitational collapse of the thickened crust and buoyancy-driven gravitational instability developed in the partially molten continental crust influenced by the transfer of heat from rising mantle-derived (i.e. dioritic-gabbroic) magmas rocks found in the footwall of the Évora Massif. [Display omitted] •Structure of the northern hanging-wall of Évora Gneiss Dome is revealed.•Interplay of Variscan compressional and extensional events in the Ossa Morena Zone•Viséan-Bashkirian HT-LP metamorphism, calc-alkaline magmatism and synorogenic extension•U-Pb SHRIMP geochronology of Lower Paleozoic felsic rocks and regional correlation•Geochronology of granitic rocks constrains tectonic events in the Évora Massif.