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SHRIMP U-Pb ages of detrital zircons from the early proterozoic Contendas-Mirante supracrustal belt, São Francisco Craton, Bahia, Brazil

1994; Elsevier BV; Volume: 7; Issue: 2 Linguagem: Espanhol

10.1016/0895-9811(94)90002-7

1873-0647

Allen P. Nutman, Umberto G. Cordani, Pierre Sabaté,

earthquake and tectonic studies

SHRIMP U-Pb geochronology has been undertaken on detrital zircons in a orthoconglomerate from the metamorphosed Contendas-Mirante supracrustal belt, São Francisco Craton, Bahia, Brazil. The majority of the U-Pb age determinations on the detrital zircons are concordant within uncertainty, and display three principal age groups; 2710-2600 Ma, 2400-2300 Ma and most abundant, 2200-2150 Ma. The conglomerate must have been deposited between ca. 2150 Ma (the youngest detrital zircons) and 2000-1900 Ma, when the Contendas-Mirante supracrustal belt was intruded by peraluminous granites. 3100–3400 Ma gneisses and granitoids crop out as domes within the Contendas-Mirante supracrustal belt, which have been interpreted as reactivated basement to the belt. These gneisses have not contributed a significant amount of detrital material to the conglomerate because the oldest detrital zircons have an age of only ca. 2700 Ma. Instead, the source of the detrital material in the conglomerate might be represented by the Jequié Complex to the east, which consists of late Archaean rocks that were migmatized and intruded by granites in the early Proterozoic. Circones detricos in un conglomerado metamorfico del cinturon supracortical Contendas-Mirante, Sao Francisco Craton, Bahia, Brazil, fueron datados por U-Pb usando SHRIMP. La mayoria de las edades determinadas por U-Pb son acordes y se pueden agrupar en tres grupos; 2710-2600 Ma, 2400-2300 Ma y 2200-2150 Ma, la poblacion mas abundante. La depositacion del conglomerado debio ocurrir entre 2150 Ma (la edad del circon detritico más joven) y el emplazamiento de granitos peraluminicos entre 2000-1900 Ma en el cinturon supracortical. Gneises y granitos en forma de domos con edades de 3100–3400 Ma afloran en el cinturon supracortical Contendas-Mirante y han sido interpretados previamente como reactivaciones del zocalo. Estos gneises no han contribuido significativamente a la materia detritica que forma el conglomerado porque el circon detritico mas joven solo tiene una edad de 2700 Ma. En vez, la provenencia del material detritico el el conglomerado pudo ser representado por el complejo Jequié al este el cual consiste de rocas que fuerón migmatizadas en el Arcaico tardio y intruidas por granitos en el Proterozoico temprano.