Zircon U–Pb ages of rocks from the Rio Apa Cratonic Terrane (Mato Grosso do Sul, Brazil): New insights for its connection with the Amazonian Craton in pre-Gondwana times

Abstract

This paper presents 14 zircon U–Pb determinations (SHRIMP and LA-MC-ICP-MS) for key geological units from the Rio Apa Cratonic Terrane (RACT), which is considered the southernmost exposed part of the Amazonian Craton in southwestern Brazil. The zircon U–Pb ages and geological data indicate that the RACT was formed by the accretion of magmatic arcs in a continental margin active from 1950 to 1720Ma. The RACT is composed of three major terranes (Western, Eastern and Southeastern Terranes) with distinct evolution histories. The Western Terrane presents orthogneisses and granites formed at ~1950–1940Ma and subduction-related granites and volcanic rocks formed at 1900–1880Ma and 1840–1830Ma. These basement rocks are covered by a greenschist facies metavolcano-sedimentary succession (Rio Naicata Formation) with basal volcanic rocks formed at 1813±18Ma. A gabbronoritic dyke of the Rio Perdido Suite hosted by the Rio Naitaca Formation yields an age of 1589±44Ma. The Eastern and Southeastern Terranes present deformed leucogranites generated within the intervals 1780–1720Ma and 1810–1790Ma, respectively. Both terranes are covered by a metavolcano-sedimentary succession (Alto Tererê Formation) dominated by Barrovian-type amphibolite facies metamorphic assemblages, suggestive of a collisional event. Available 40Ar–39Ar data (hornblende, muscovite and biotite) indicate that the proto-RACT evolved to a collisional orogen between 1310 and 1270Ma and behaved as a cratonic mass after 1270Ma, preceding the assembly of Rodinia. The available data allow us to interpret the RACT as a part of the Ventuari–Tapajós Province of the Amazonian Craton, which was fragmented and dispersed as a microcontinent. It was subsequently reincorporated into the SW Amazonian Craton, along the Sunsás Belt, as an allochthonous terrane. In a global perspective, the tectono-magmatic events of the RACT are consistent with a long-lived accretionary orogen possibly related to an active margin of Columbia.