Reconstructing Paleoproterozoic volcanic environments: Eruptive styles and evidence of phreatomagmatism in the Amazonian Craton's Colíder Group

Abstract

Paleoproterozoic rocks are essential for understanding Earth's tectonic evolution, particularly in regions where juvenile crust and ore deposits formed. The Amazonian Craton features well-preserved Paleoproterozoic volcanic records, including age ranges linked to the Orocaima, Uatumã, and Colíder Silicic Large Igneous Provinces (SLIPs). Stratigraphic frameworks are supported by the description and interpretation of lithofacies. In the present work, we identify different eruptive styles (effusive and explosive) of the Colíder Group in the Alta Floresta Mineral Province. We have also described, for the first time in Alta Floresta Mineral Province, deposits associated with a phreatomagmatic eruption. The ancient volcanic successions comprises massive hypohyaline rhyolite lavas representing effusive dynamisms, with crystallization ages (U-Pb in zircon) around 1800 Ma, while lapilli tuff and tuffs represent explosive deposits with massive and stratified structures. The pyroclastic rocks compose an ignimbrite deposit. Four types of ash aggregates (ash pellets, coated ash pellets, accretionary lapilli, cored accretionary lapilli) suggest an origin associated with phreatomagmatic deposits. Additionally, epiclastic deposits are characterized by the reworking of primary volcanic rocks and basement rocks. These different eruptive styles allow us to reconstruct a paleoenvironment where water and magma interact during volcanic eruptions. This setting is typical in ancient and recent volcanic calderas, intra-caldera basins, or calderas where there is direct contact with seawater or riverine waters. Our discovery provides new data for the reconstruction of this Paleoproterozoic volcanic terrane and will be valuable for interpreting the geological evolution of this craton in the future.