Revistes Catalanes amb Accés Obert (RACO)

Las rocas de textura traquítica de Vilacolum (Girona): correcciones al catálogo de la colección de Grandes Bloques del Museo de Geología de Barcelona

Domingo Gimeno Torrente

Resum


Evidence of outcrops of rocks with trachytic texture at Vilacolum (Girona, NE Spain) are known after Font i Sagué (1907), which classified these rocks as amphibolic andesites. Some years later, San Miguel de la Cámara (1921) reclassified these rocks as trachytes studying from a petrographic point of view a block donated by Font i Sagué. A whole rock geochemical analysis by Burri & Parga Pondal (1935) allowed San Miguel de la Cámara (1936) to confirm his initial amendment. These classification of the Vilacolum rocks as trachytes has been accepted until today (Araña et al., 1983; López Ruiz y Rodríguez Badiola 1985).
This note shows that both Font i Sagué (1907) and San Miguel de la Cámara (1921) achieved good descriptions of the Vilacolum rocks, because in the Baseia-Els Olivets-Vilacolum sector several petrographic types ranging from basaltic trachyandesite to trachyte are found, in correspondance to a differentiation trend by fractional crystallization of an alkalic (potassic) basaltic magma. Hence, the Vilacolum trachytes are not a petrological oddity in the context of the Tertiary and Quaternary Catalonian volcanic province, and can be considered as an analogue to the well known tertiary and quaternary equivalents of the French Central Massif.

Key words: trachyte, trachyandesite, basaltic trachyandesite, kaersutite, pigeonite, whole rock geochemistry, large-block rock's catalogue, Museo de Geología de Barcelona, Vilacolum, Girona, NE Spain.

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