Piancó-Alto Brígida branching system of orogens (PE-PB-CE), Tectonic regionalization and geochronology

Abstract

The Piancó-Alto Brígida branching system of orogens (SPAB) is in the central and center-western part of the Transversal Zone, of Borborema Province, in the states of Paraíba, Pernambuco and Ceará. It is a final tectonic product of an orogenetic development during Cryogenian-Ediacarian periods. The original paleogeographic (and lithostratigraphic) scenery is of difficult reconstitution due to tectonic events (at least three different phases of folding), with lateral variations of the metamorphism’s degree from very low to low grade. These events were followed by an important final phase of escape tectonics (extrusion). Today, the SPAB is geographically branched into different fold belts, bounded by some Paleoproterozoic basement inliers that are expressive both in area and participation in the regional deformation. The main lithological assemblages present in the SPAB belts may be classified as part of typical QPC (quartzite-pelite-carbonate) assemblages, with a striking characteristic of remarkable rhythmicity, as well as the metamorphic gradient very low to low grades up to medium grade (to the belt of the interior of Pernambuco “Supergurpo Salgueiro”). Along the zones near the contacts with the basement (following important fault lines) polymictic breccias and conglomerates, immature sandstones and arkoses (“Formação Olhos d´Água”) are recorded. Even though there are many sources of scientific contributions on this subject in the last 50 years, at different times and purposes, a satisfactory lithostratigraphic classification was not possible. So all the lithostratigraphic terminology (here discussed) should be faced as informal and provisory. Many reconnaissance projects of geochronology have been done along the two last decades. In the last years, a systematic program of geochronological research (Sm-Nd and U-Pb methods) has been developed trying to