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Polyphased rare-element magmatism during late orogenic evolution: geochronological constraints from the NW Variscan Iberia

Abstract : U-Pb geochronological data were collected on columbite-tantalite from rare-element pegmatites and granites (Li, Ta, Nb, Be, Sn) from the Iberian Variscan Massif in order to investigate timing of rare-element events during the late evolution of the Variscan belt and the connection with granitoid suites. Our data set emphasises three events: (i) The Argemela rare-element granite, from the Central Iberian Zone (CIZ), emplaced at 326±3 Ma and predates the three main late orogenic granitoid suites, (ii) most of the studied rare-element pegmatites of the LCT family from the Galicia-Trás-Os-Montes Zone (GTOMZ) gave an average age of 310±5 Ma, contemporaneous with an early syn-D3 granodiorite-monzogranite suite and the syn-D3 two-micas granites suite; and (iii) The youngest event is dated at around 301±3 Ma and is marked by emplacements of rare-element pegmatites of the LCT family in both the CIZ and in the South of the GTOMZ. This event postdates the late to post-D3 bt±crd-granodiorite-monzogranite suite emplacements, which are probably not genetically related to rare-element pegmatites. Several pegmatites dated during this study do not display contemporaneous ages with neighbouring supposed "parent" granites. Contemporaneous rare-element pegmatites fields seem to be located along belts as it is observed for granitoids suites. Considering both GTOMZ and CIZ fields, emplacement ages look to decrease toward the South. This is in good agreement with the known propagation of deformation, metamorphism and magmatism between the different geotectonic zones of the Iberian Massif. Lower crustal processes are not at the origin of rare-element granite genesis since in the Iberian Massif, RM magmatism is polyphased with at least three distinct events. Hypothetical sources of RM melts are supposed to be set in a middle to upper crust position, as it has been shown for granitoid magmatism.
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Submitted on : Friday, April 17, 2015 - 11:36:07 AM
Last modification on : Wednesday, September 23, 2020 - 4:37:55 AM

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Jérémie Melleton, Eric Gloaguen, Dirk Frei. Polyphased rare-element magmatism during late orogenic evolution: geochronological constraints from the NW Variscan Iberia. 21 st meeting of the International Mineralogical Association, Sep 2014, Johannesburg, South Africa. pp.288. ⟨insu-01143295⟩

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