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|Title: ||Time-space distribution of silicic plutonism in a gneiss dome of the Iberian Variscan Belt: The Évora Massif (Ossa-Morena Zone, Portugal)|
|Authors: ||Dias da Silva, Í.|
|Keywords: ||Gneiss dome|
|Issue Date: ||2018|
|Citation: ||Dias da Silva, I., Pereira, M.F., Silva, J.B., Gama, C. (2018). Time-space distribution of silicic plutonism in a gneiss dome of the Iberian
Variscan Belt: The Évora Massif (Ossa-Morena Zone, Portugal). Tectonophysics 747-748: 298-317|
|Abstract: ||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 sub-
horizontal 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 synchro-
nously 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.|
|Appears in Collections:||GEO - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica|
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