Tectonic switches recorded in a Paleoproterozoic accretionary orogen in the Alta Floresta Mineral Province, southern Amazonian Craton

Abstract

The Alta Floresta Mineral Province (AFMP), southern Amazonian Craton, experienced extensive magmatic activity from ca. 2.03 to 1.75 Ga in an uncertain geodynamic setting. New and pre-existing geological, petrographic, geochemical, and zircon geochronological data show that magmatic rocks in the eastern AFMP comprise three magmatic sequences: 2.03–1.93, 1.90–1.85, and 1.83–1.75 Ga. Earlier magmas had garnet-bearing sources, whereas younger ones were derived from shallow, garnet-free sources. We propose a new, four-stage geological framework, comprising five domains, and featuring an accretionary orogen with tectonic switching that alternates between flat subduction and slab-rollback. During flat subduction and crustal thickening in stages A (2.03–1.97 Ga) and C (1.90–1.81 Ga), calc-alkalic to alkali-calcic I-type magmatism was produced, whereas alkali-calcic to alkalic A-type magmatism, and localized I-type granites, were generated during slab-rollback and crustal extension in stages B (1.96–1.94 Ga) and D (1.83–1.75 Ga). The last stage is associated with precious- and base metal porphyry- and epithermal-style systems. We interpret the eastern AFMP as a remaining cratonic block of the eastward Tapajós Domain within the ca. 1.95–1.80 Ga Ventuari-Tapajós Province, and recording 1.85–1.74 Ga magmatism of the Western Amazonia Igneous Belt within the ca. 1.80–1.55 Ga Rio Negro-Juruena Province. Similarities between the AFMP and the Svecofennian orogen (Fennoscandian Shield) suggest that parts of the Columbia supercontinent margins might have operated in similar fashion to Andean-type accretionary orogens.