Geology, geochemistry, and Pb–Pb zircon geochronology of the Paleoproterozoic magmatism of Vila Riozinho, Tapajós Gold Province, Amazonian craton, Brazil

Abstract

Pb–Pb zircon geochronologic data define two different periods of intense igneous activity in the Vila Riozinho region, Tapajós Gold Province (TGP), south-central Amazonian craton. At ∼2.00–1.97 Ga, the Vila Riozinho volcanic sequence (2000±4 Ma, 1998±3 Ma) and the older São Jorge granite (1981±2 Ma, 1983±8 Ma) were formed. At ∼1.89–1.87 Ga, the younger São Jorge (1891±3 Ma), Jardim do Ouro (1880±3 Ma), and Maloquinha (1880±9 Ma) granites and the Moraes Almeida volcanic sequence (1890±6 Ma, 1881±4 Ma, 1875±4 Ma) were emplaced. Similar age intervals are registered throughout the TGP that is thus a little younger than the Paleoproterozoic terranes of the Maroni-Itacaiúnas Province in the Guiana Shield. Geochemical and geochronologic data demonstrate that the São Jorge pluton is composed of two different granitoids, the older and younger São Jorge granites. These, as well as the Jardim do Ouro granite, are I-type and magnetite series. The São Jorge granites are high-K calc-alkaline and show significant geochemical variation, the Jardim do Ouro granite is more iron-rich and less oxidized. The Vila Riozinho Formation is calc-alkaline to shoshonitic and geochemically similar to the São Jorge granites. The Maloquinha granite and the Moraes Almeida Formation differ from the other studied rocks in petrographic and geochemical characteristics, have aluminous A-type affinities, and were probably derived by low-temperature crustal melting. The volcanic sequences of the studied area, formerly included into the Iriri Group of the Uatumã Supergroup, are divided into the Vila Riozinho and Moraes Almeida sequences. The presence of these two sequences in the same tectonic domain demonstrates the heterogeneity of the Uatumã Supergroup. The TGP registers accretionary processes related to the formation of the Atlantica supercontinent at ∼2.00 Ga. This was followed (at ∼1.88 Ga) by an intracontinental taphrogenic event that lasted throughout the Mesoproterozoic. The tectonic setting of the TGP was thus transitional between a subduction-related magmatic arc and a stable continental block undergoing extension.