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

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 epsilon(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 epsilon(Nd), evolved crustal magmatism could be used as a proxy in studies of the genesis of these and possibly other Phanerozoic massive sulphide deposits.