Geochemistry and U–Pb dating of felsic volcanic rocks in the Riotinto–Nerva unit, Iberian Pyrite Belt, Spain: crustal thinning, progressive crustal melting and massive sulphide genesis

Abstract

We present new geochemical, Sm–Nd and U–Pb data on the felsic volcanic rocks containing the world-class volcanic-hosted massive sulphide deposits in the Riotinto–Nerva unit, Iberian Pyrite Belt, Spain. Three new U–Pb ages from older plagioclase–quartz-phyric dacites and plagioclase-phyric rhyolites to youngest plagioclase–quartz-phyric rhyolites indicate a time span for felsic volcanism ranging from 351.5 ± 0.4 to 345.7 ± 0.6 Ma. The youngest felsic rocks exhibit lower ε Nd , as well as contrasting Ti, Sr, Zr, Hf and Eu/Eu* values. We interpret that in the Riotinto–Nerva unit crustal melting successively affected shallower, more evolved horizons in the crust. Progressive crustal melting is consistent with current interpretations of the Iberian Pyrite Belt in terms of a late Devonian–Early Carboniferous transtensional setting, coupled with underplating by basic magma. We suggest that low ε Nd , evolved crustal magmatism could be used as a proxy in studies of the genesis of these and possibly other Phanerozoic massive sulphide deposits. Supplementary material: Details of the analytical methods and whole-rock data for basalts are available at http://www.geolsoc.org.uk/SUP18452 .

A seismic geotraverse across the Iberian Variscides: Orogenic shortening, collisional magmatism, and orocline development

“…The magmatism of southwest Iberia (magmatic zone IV in Figure ) is a different case compared to the one in Central Iberia. It is characterized by bimodal magmatism (largely mafic) of earliest Carboniferous age, and mafic magmas are here the key to interpret coeval crustal melting [e.g., Schermerhörn , ; Valenzuela et al ., ]. The tectonic context of this magmatism and the associated sedimentary basins is an intraorogenic extensional event of arguable origin [ Simancas et al ., ].…”

“…[]; Valenzuela et al . []), is bimodal (basalts, gabbros, rhyolites, and granites; Schermerhörn []) and associated with normal faulting and basin formation, thus being interpreted as a transient rifting stage not found elsewhere in the Iberian Massif. Interestingly, a great volume of mafic rocks may have been imaged in the middle crust [ Simancas et al ., ; Carbonell et al ., ; Schmelzbach et al ., ; Palomeras et al ., ; Brown et al ., ].…”

Introduction and Geological Setting of the Iberian Pyrite Belt

“…The geochemical similarities between the volcanic rocks of the VSC and the TTG plutonic rocks of the SNB (Schütz et al 1987;Thiéblemont et al 1998; Díez-Montes and Bellido-Mulas 2008; Díez-Montes et al 2011), as well as the available U-Pb geochronology data (Barrie et al 2002;Dunning et al 2002;Valenzuela et al 2011) suggest that the Volcano-Sedimentary Complex was approximately coeval and cogenetic with the TTG plutonic rocks of the Sierra Norte Batholith.…”

“…U-Pb dating of zircons has been carried out in several places in the IPB (Nesbitt et al 1999;Barrie et al 2002;Dunning et al 2002;Rosa et al 2009;Valenzuela et al 2011). The age determinations were predominantly made of felsic rocks (rhyolites and rhyodacites).…”

“…The volcanic rocks are only approximately 25 % of the stratigraphic record of the VSC, the remaining 75 % are mainly mudstone. Studies of the volcanic facies architecture of the VSC in several areas of the IPB interpreted the felsic volcanic centres as constructed by a combination of effusive and explosive volcanic units and high-level intrusions (e.g., Martí Molist et al 1994;Soriano and Martí 1999;Boulter 1993Boulter , 1996Donaire et al 2002;Rosa et al 2008;Valenzuela et al 2011). Recently, a regional study of the volcanic and sedimentary facies architecture in SW Iberia pointed out that the felsic volcanic centres correspond to "lavacryptodome-pumice cone volcanoes" (Junta de Andalucía 1999; Rosa et al 2010a).…”