O "Sistema Pajeú-Paraíba" e o "Maciço" São José do campestre no leste da Borborema

Abstract

The best areas of exposures of the Pajeu-Paraiba Folding System (SPP) are in the western hinterland of Pernambuco, but the northern part of it - the so-called Alto Pajeu Terrane (TAP) - reaches the coastal zone of Paraiba (east of the 36°00 ' W). This supracrustal terrane is positioned between important regional shear zones that separate it from high grade gneiss domains. To the north, there is the Rio Grande do Norte Terrane (RON)- separated by the Patos Lineament- and to the south there is the expositon of another important fraction of the basement of SPP, the Alto Moxoto Terrane (TAM). Both RON and TAM are considered mega-fragments of a previous Paleoproterozoic supercontinent, while TAP is assumed as a descendant segment of the Meso-Neoproterozoic erogenic belt, probably part of the supercontinent of that time (Rodinia). All these terranes are now juxtaposed and they were deeply reworked by the development of the Brasiliano Cycle, during the amalgamation of the Western Gondwana supercontinent. The TAP is mostly composed of muscovite-biotite gneisses (a), garnet-biotite-schists (b), intruded by augen-gneisses of granitic and syenogranitic composition (c) which are lithological assemblages of Eoneoproterozoic age (Cariris Velhos Cycle). They were diversely reworked and penetrated by granitoids (d) of the Brasiliano Cycle (as well as RGN has been), specially plutonic rocks of the end of Neoproterozoic III. These predominant rock-units (a, b, c) are positioned between major regional dextral shear zones, and their regional features are drawing an wide fan-sinformal structure, due to the Brasiliano reworking. Geochronological determinations -Rb-Sr, Sm-Nd and U-Pb methods- confirm the Paleoproterozoic age of the RGN and its reworking during the Brasiliano, as well as the early Neoproterozoic age (Cariris Velhos Cycle) for the main rock units of TAP. Granitic plutonism and processes of shearing are common events of the Brasiliano Cycle for both, RGN and TAP (as well as for the basement of the TAM, to the south).