A long-lived active margin revealed by zircon U–Pb–Hf data from the Rio Apa Terrane (Brazil): New insights into the Paleoproterozoic evolution of the Amazonian Craton

Abstract

We present the first regional in-situ zircon U–Pb–Hf isotopic data from metaigneous and metasedimentary rocks from the Paleo- to Mesoproterozoic Rio Apa Terrane (RAT), a crustal fragment outcropping in the central-western Brazil and north-eastern Paraguay. These new ages and Hf isotopic data delineate three magmatic events, which record the construction of the temporally and isotopically distinct Western and Eastern Terranes of the RAT. The Western Terrane comprises the 2100–1940 Ma Porto Murtinho Complex and the 1900–1840 Ma Amoguijá Belt, which both define a crustal reworking array in εHfT-time space evolving from a precursor source with Hf TDM age of ca. 2700 Ma. The 1800–1720 Ma Caracol Belt constitutes the Eastern Terrane and yields suprachondritic εHfT signatures up to +7.1, indicating significant juvenile input. The metasedimentary Amolar Group and Rio Naitaca Formation in the Western Terrane have maximum depositional ages of 1850–1800 Ma and subchondritic εHfT signatures down to −5.7, similar to the underlying basement of the Amoguijá Belt. In the Eastern Terrane, the Alto Tererê Formation has a maximum depositional age of 1750 Ma and mostly suprachondritic εHfT signatures, similar to magmatic rocks of the underlying Caracol Belt. Together, the new igneous and detrital zircon age and Hf isotopic data record a temporal and spatial transition from 2100 to 1840 Ma crustal reworking in the west to more juvenile magmatism at 1800–1720 Ma in the east. This transition is interpreted to reflect convergent margin magmatism associated with periods of subduction zone advance and retreat in an accretionary orogenic setting. Comparison of the εHfT-time signature of the RAT with the Amazonian Craton suggest penecontemporaneous development, with the Western and Eastern Terranes of the RAT being correlative with the Ventuari-Tapajós and Rio Negro-Juruena Province of the Amazonian Craton, respectively. Our new data also reveal that the εHfT signatures of the RAT are distinct from the Maz terrane, which refutes the MARA Block hypothesis.