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Petrology and geochronology of the Porriño late-Variscan pluton from NW Iberia : a model for post-tectonic plutons in collisional settings
González Menéndez, Leopoldo (Instituto Geológico y Minero de España)
Gallastegui Suárez, Gloria María (Instituto Geológico y Minero de España)
Cuesta Fernández, Andrés (Universidad de Oviedo. Departamento de Geología)
Montero, P. (Universidad de Granada. Departamento de Mineralogía y Petrología)
Rubio Ordoñez, Álvaro (Universidad de Oviedo. Departamento de Geología)
Molina Palma, José Francisco (Universidad de Granada. Departamento de Mineralogía y Petrología)
Bea Barredo, Fernando (Universidad de Granada. Departamento de Mineralogía y Petrología)

Data: 2017
Resum: The Variscan orogen of NW Iberia contains abundant syn- and post-tectonic granitoids. The post-tectonic granitoids are metaluminous to slightly peraluminous, I-type granites, monzogranites ± granodiorites ± tonalites. The Porriño pluton studied here is a epresentative example. It consists of two units: i) a pink-red, peraluminous, biotite graniteand ii) a gray, metaluminous to peraluminous, biotite (± amphibole ± titanite) monzogranite, including maficintermediate enclaves. SHRIMP U-Pb dating yielded 290-295Ma ages for all the units. The mineralogy and geochemistry show that the pink-red granite has features of I- and A-type granites, whereas the gray monzogranite and enclaves are I-types. Sr isotopes show scattered values for the pink-red granite (87Sr/86Sr295Ma ≈ 0. 702-0. 710) and uniform values for the gray monzogranite and enclaves (87Sr/86Sr295Ma ≈ 0. 705-0. 706). Geochemical results indicate a peritectic entrainment of clinopyroxene + orthopyroxene ± Ca-plagioclase ± ilmenite ± garnet, and minor accessory phases (± zircon ± titanite ± apatite) into a melt similar to the leucocratic gray monzogranite. A mafic-intermediate source is proposed for the gray monzogranite and its enclaves. Restitic protoliths generated granitic melts with A-type features such as the pink-red granite. The I-type nature of many post-tectonic granitoids could be explained by the previous extraction of S-type syn-tectonic granites that left restites and less fertile rocks. Late orogenic new melting affected the previously unmelted and more mafic lithologies of the lower-middle crust, and gave rise to I-type granitoids. Repeated melting events affecting such lithologies and previous restites could have generated granitic melts with A-type features.
Drets: Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l'obra original i es reconegui l'autoria. Creative Commons
Llengua: Anglès
Document: Article ; recerca ; Versió publicada
Matèria: Post-orogenic magmatism ; Variscan orogeny ; Post-tectonic granites ; Monzogranites ; Enclaves
Publicat a: Geologica acta, Vol. 15 Núm. 4 (December 2017) , p. 283-304, ISSN 1696-5728

Adreça alternativa: https://raco.cat/index.php/GeologicaActa/article/view/330794
DOI: 10.1344/GeologicaActa2017.15.4.3


29 p, 3.0 MB

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