O SISTEMA TAFROGÊNICO TERCIÁRIO DO SALIENTE ORIENTE NORDESTINO NA PARAÍBA: UM LEGADO PROTEROZÓICO

Abstract

This paper presents data on the E-W to ENE-WNW-trending graben and horst system in the easternmost part of Paraiba State, Brazil. The installation of this Tertiary tectonic unit was performed following previous structural trends of the Precambrian basement, comprising as a typical case of brittle-ductile structures reactivation. The graben and horst system are positioned in the easternmost part of the Borborema Province, whose main evolutionary phase occurred from the Late Neoproterozoic to the Cambrian, superposing lithostructural units of the Neoproterozoic Alto Moxoto terrane (to the south), composed of orthogneisses and peraluminous supracrustal rocks, and of the Eo-Neoproterozoic Alto Pajeu Terrane (to the north), comprising volcano-sedimentary supracrustal rocks metamorphosed under amphibolite facies. During the closing events of the Brasiliano Cycle, these terranes were penetrated by Cambrian fissural basic intrusives that crop out along the WNW-ESE direction (most of them). This basic dyke swarm is reported here for the first time. During the Tertiary, the most important period for the regional geomorphological evolution, the main structural Brasiliano trends were reactivated as extensional faults, leading to the formation of the taphrogenic system discussed here. At that time, some new faults of extensional character were also formed. As similar occurrences have been described elsewhere (e. g. Rio Grande do Norte State), these facts bring new elements for the discussion of the regional geology of Borborema Province, especially in terms of geomorphological evolution (certainly, a new aspect to be considered) and groundwater resources (heavily demanded in such semi-arid area). Additionally, the occurrence of such brittle Tertiary tectonism in the (next) interior of the continent necessarily opens again the problem of the structural behavior of the Cretaceous coastal basins, in order to investigate the formation of structural traps for hydrocarbon during this period.