Magmatic Evolution and Tectonic Setting of the Iberian Pyrite Belt Volcanism

rocks has been carried out to determine the primary magmatic aYnity tectonics; Iberian Pyrite Belt and tectonic setting of the Iberian Pyrite Belt volcanism. Most of the basaltic rocks are continental tholeiites, but a few samples show an alkaline aYnity. The origin of the basaltic rocks and their diversity of compositions are explained by a single mixing model between E- and N-MORB (mid-ocean ridge basalt) and as- INTRODUCTION similation of crustal material. Calc-alkaline intermediate and silicic Volcanic-hosted massive sulphide deposits are mainly rocks include basaltic andesites, andesites, dacites and rhyolites. associated world-wide with calc-alkaline submarine volVolumetrically, dacites and rhyolites are the most abundant. Inter- canism. Petrological and geochemical data, together with mediate and silicic rocks are not related by fractional crystallization, stratigraphic and structural studies, have been of major nor is there a relationship between the basaltic and calc-alkaline importance in constraining geological models of the volrocks by the same process. We suggest that in the Iberian Pyrite canism associated with massive sulphide deposits. InBelt silicic calc-alkaline magmas were generated on a large scale tegrated studies in areas such as the Kuroko province in by the invasion of continental crust by mafic magmas generated in Japan (Ohmoto, 1983), the Mount Read Volcanics in the underlying upper mantle. The diversity of compositions shown Tasmania (Crawford et al., 1992), and the Mount Windsor by dacites and rhyolites can mainly be explained either by diVerences Volcanics in northwestern Australia (Stolz, 1995), have in the composition of the source rocks or by diVerent degrees of revealed that this volcanism may be developed during partial melting of upper-crust rocks. Andesites, however, formed by diVerent stages of the subduction process, always being mixing between basaltic magmas and upper-crust material. The new located on the overriding plate. geochemical data agree with previously published tectonostratigraphic This paper documents the petrology and geochemistry data which suggest that the Iberian Pyrite Belt volcanism formed of the volcanism of the Iberian Pyrite Belt, an Early on the South Portuguese plate owing to strike-slip tectonics. This Carboniferous metallogenic province that extends from Portugal to Spain in southwest Iberia and constitutes local extensional tectonic setting was related to transtension as a

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