Paleoproterozoic, Mesoproterozoic, and Paleozoic sedimentary successions of the Southwestern Amazonian craton: geochemistry, provenance, and post-sedimentary events

The Amazonian Craton is home to many Statherian to Calymmian taphrogenesis events that evolved over Large Igneous Provinces. The NW-SE faults on the Western Amazonian Igneous Belt (1.82-1.74Ga) and their reactivations, which facilitated the deposition of the Beneficente Group (1.76-1.60Ga), Prainha Formation (1.46Ga), and Alto Tapajos Group (Silurian-Devonian), are associated with these events in the southwest Amazonian Craton. Mineralogical composition, whole-rocks geochemistry, and Nd-Sr-Pb isotopic data show that the three sedimentary successions originated in the provinces of Rondonia-Juruena and Tapajos Parima, particularly during two rift stages. Beneficente Group deposition is associated with Paleoproterozoic Rift 1, while the Prainha Formation represents the post-rift 1, and Alto Tapajos Group deposition is associated with Paleozoic Rift 2. In addition, the Prainha Formation also received sediment supply from the Sunsas Province. These three sedimentary successions have an intrinsic relationship with the reworking of the local basement and their own reworking that occurred from the Paleoproterozoic to the Paleozoic. Autochthonous reworking, particularly in the Colider and Beneficente groups, is demonstrated by Ti-magnetite grains, volcanic and arenite fragments in the Prainha Formation sublitharenite, and by angular microcline grains, high Au content, a Pb whole-rock isochron yielding the 1.796 +/- 0.096Ga age, and by epsilon(Sr(0)) vs 1/Rb relationship in Alto Tapajos Group. epsilon(Nd(t)) and flat REE patterns and some positive Eu anomalies in the Prainha Formation and Alto Tapajos Group record the influence of the mafic rocks of the Mata-Mata suite. A Pb-Pb whole-rock isochron allowed hydrothermal activity recognition at 1.32Ga in the Vila do Carmo Formation. This event was ratified by positive Eu/Eu* (1.3-1.43), Ce/Ce* (1.24-2.84), and Gd/Gd*(similar to 1.5) anomalies. Finally, Nd model ages, geochemistry, and Sr isotopes allow for correlating the local basement and the overlaying sedimentary successions along the Columbia and Gondwana boundaries. [GRAPHICS] .