Geological and geophysical interpretation of the Espírito Santo Basin and the Abrolhos region: petrography, radiometric dating and seismic visualization of volcanic rocks

Abstract

Geologic and geophysical interpretation of structural, magmatic and sedimentological features outcropping in the Abrolhos Archipelago (offshore of the Espirito Santo – Mucuri basins along the eastern Brazilian margin), and petrographic and geochronologic studies of igneous rocks, characterized a sequence of volcanic (basalts, diabase, breccia, etc.) and sedimentary rocks (fine grained to coarse grained sandstones and conglomerates in channels, sandstones with concordant stratification and locally discordant with the volcanic rocks, siltites, silty shales, etc.) which were uplifted after their original deposition between the Late Cretaceous and the Paleogene. The  geochronological dating, based on the Ar-Ar method, suggests an interval of magmatism between 40 and 60 Ma.  The field works suggest that siliciclastic rocks outcropping in the islands constitute a unique example of Paleogene Tertiary turbidite sedimentation in the Brazilian continental margin.  Thick layers of massive sandstones with an external lobate geometry, overlying silty rhythmites, particularly in the eastern portion of the Santar Bárbara Island, are probable deposits of dense flows (hyperpycnal) deposited in mid platform to upper bathyal environments. The tectonic and seismic-stratigraphic interpretation suggests that these rocks were uplifted in a compressional event, probably associated  with salt tectonics, affecting the sedimentary layers and creating angular unconformities that reach up to the Neogene.