Timing of granitic magmatism in the northern Borborema Province, Brazil: aU-Pb study of granitoids from the Alto Pajeu Terrain

The Alto Pajeu Terrain (APT) is a SW-NE trending fold belt in the Neoproter ozoic Borborema Province (NE Brazil), formed by metasedimentary sequences i nterlayered with metavolcanosedimentary units, both intruded by granitic ro cks of different compositions and ages. The tectonic evolution of the APT i nvolves Mesoproterozoic and Neoproterozoic transtensional and contractional tectonic events. In this study, we present U-Pb zircon ages of five granit oids selected according to a generally accepted relative chronology: (a) th e Tuparetama granite and Tuparetama migmatitic granite with low angle gneis sic foliation represent syn-tangential rocks presumably related to a Transa mazonian event; (b) the Amparo granite with high angle gneissic foliation r elated to the Brazilian/Pan-African event; and (c) the Tabira and Jabitaca post-strike-slip granites. The results obtained do not confirm the generall y accepted chronology of events. Granites previously classified in differen t groups (Tuparetama, Amparo, and Jabitaca) belong to the same orogenic cyc le (Brazilian). Large batholiths, previously suspected to have been emplace d after the strike-slip deformation, represent older crustal remnants withi n them. In each case they consist of particular rock types - an alkaline hi gh-temperature granite (Tabira) and a 'granulite' (Tuparetama migmatitic gr anite). These older ages imply that pre-Brazilian crust-forming events such as the Transamazonian Orogeny (Tuparetama migmatitic granite estimated at ca. 2050 Ma) and Cariris Velhos event (Tabira granite at ca. 972 Ma) occurr ed in the APT, and their records survived the intense recycling which chara cterizes the Brazilian/Pan-African orogeny. (C) 2000 Elsevier Science Ltd. All rights reserved.