Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The late Devonian-lower Carboniferous submarine volcanic rocks of the Iberian Pyrite Belt have been studied to determine the origin of magmas, the metamorphic processes involved in their alteration and the overall tectonic setting of the region.;Detailed geochemistry of the dominant volcanic rock types, basalts, andesites and the more voluminous rhyolites shows that the magmas do not result from a simple fractionation process. The mafic magmas provide strong evidence of mantle heterogeneity while the acid magmas are clearly a product of crustal anatexis.;Metamorphic-metasomatic post-crystallization effects, based on geochemical, isotopic and mineral data, indicate a pervasive low-T sea floor hydrothermal event with high water/rock (at least 100 for K-metasomatized acid rocks). Later regional metamorphism occurred with thermal gradients in the range 40-50(DEGREES)C/km. Previous suggestions of subduction zone metamorphic events are disproved. The massive sulphides of the region were formed during the early sea floor cooling process and sea water is shown to be the dominant hydrothermal fluid both from oxygen and sulphur isotopic data.;While no exact analogue of the tectonic setting of the Pyrite Belt is known, the overall igneous-metamorphic situation indicates similarity to typical intra-continental (back-arc?) rifting tectonics.



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