Abstract

Recent research on the palynostratigraphy and the magmatism (physical volcanology and geochemistry) of the Portuguese part of the Iberian Pyrite Belt (IPB) has provided new results which allow a better understanding of the regional geology. The study was concentrated on the Albernoa, Serra Branca and Mina de São Domingos antiforms and comparisons are made with the Pomarão Anticline and the Neves Corvo mine region.

Palynological data suggest that in the studied antiforms the felsic and mafic volcanism appears to be of late Famennian age and dolerites may be younger, of post Strunian age. In the Pomarão and Neves Corvo structures the felsic volcanism and mafic lavas and intrusions range from the late Famennian to the Viséan. The new palynostratigraphic ages obtained confirm that the antiforms are true tectonic windows, as described in previous structural interpretations.

Reconstructions of the volcanic facies architecture show that the volcanic sequences are dominated by submarine lavas (domes and cryptodomes) and deposits from high-concentration voluminous gravity flow containing abundant pyroclasts. These deposits may have been sourced from explosive eruptions from submarine vents. In the case of the Neves Corvo mine region the volcanic episodes are well constrained by palynological ages.

The lithogeochemistry of mafic rocks from Albernoa and Serra Branca supports an extensional setting for the IPB, with apparent arc signatures being caused by crustal assimilation. The felsic rocks from both areas, but especially from Albernoa, provide a problematic geotectonic classification partially because of their anomalously low high-field-strength element contents, possibly caused by relatively low temperatures of crustal fusion. These relatively low temperatures are confirmed by zircon and monazite saturation models which, in addition, appear to help discriminate VMS-favorable from barren felsic rocks.