CAMPO DE ESFORÇOS PLIO-PLEISTOCÊNICO NA ILHA DA TRINDADE (OCEANO ATLÂNTICO SUL, BRASIL) E SUA RELAÇÃO COM ATECTÔNICA REGIONAL

Abstract

PLIO-PLEISTOCENIC STRESS F1ELD IN THE TRINDADE ISLAND (SOUTHERN ATLANTIC OCEAN, BRAZIL) AND ITS RELATIOSHIP WITH THE REGIONAL TECTONICS The volcanic island of Trindade, of alkaline nature, is the emerged portion of a large volcanic building whose base is submerged about 5000 m depth. The analysis of the pattern of orientation of the Pliocene-Pleistocene dike swarm of the northeast portion of the island, as well as of the lengthening of phonolithic plugs, has allowed the determination of an NW direction of SHmax (in the case corresponding to σ1) during the emplacement of the intrusive bodies, compatible with an ENE-WSW to E-W right-lateral binary. The direction determined for σ1 in the island is parallel to the larger axis of the volcanic building, suggesting the same tectonic control during its formation. On the other hand, the Vitória-Trindade Chain shows differentiated segments with NW-SE, NE-SW and E-W directions, probably corresponding to changes in the direction of σ1 during the Tertiary in this oceanic portion of the South American Plate. These changes are partly compatible with the variations verified in the adjoining continental portion of Southeastern Brazil. Differences in the depth of the basement to the north and to the south of the Vitória-Trindade Chain corroborate its behavior as a fracture zone, that would have acted as conduit for the magmatism associated with the Trindade Plume. The incompatibility verified between the expected direction of SHmax during the Pliocene and Pleistocene in the Trindade Island and the direction of the studied dikes implies in a non-rigid behavior of this segment of the South American Plate