The tectonic controls on the Paleoproterozoic volcanism and the associated metallogeny in the South Amazonian craton, Brazil: Sr–Nd–Pb isotope constraints

Abstract

Whole-rock Sr–Nd–Pb isotope data for the Sobreiro and Santa Rosa volcanic sequences and Archean basement rocks near São Félix do Xingu city, northern Brazil, provide constraints for the colossal Proterozoic effusive and explosive well-preserved volcano–plutonic magmatism that covers about 1,500,000 km2 of the Amazonian craton. The basal, 1.88 Ga high-K calc-alkaline andesitic–dacitic Sobreiro Formation shows narrow variations in isotopic ratios [(87Sr/86Sr)i = 0.70352 to 0.70518; (143Nd/144Nd)i = 0.509692 to 0.509972; (206Pb/204Pb)i = 16.0492 to 16.3041; and (207Pb/204Pb)i = 15.6265 to 15.7505] that suggest mixing between the DMM-B and EM-1 and/or EM-2 domains in the melting source. The integration with published data reveals geochemical affinity of the Sobreiro Formation with Andean-type subduction; episodes of subduction angle flattening; and forearc subduction erosion. The latter caused the input of crustal-derived material and oceanic sediments in the trench and mixing with mantle-sourced magmas, a common mechanism active in modern orogenic environments. The upper, fissure-controlled, 1.87 Ga A-type rhyolitic Santa Rosa Formation reveals a high initial ratio [(87Sr/86Sr)i = 0.70949 and a large range of values for (143Nd/144Nd)i = 0.509624 to 0.509909; (206Pb/204Pb)i = 16.7271 to 21.7086; and (207Pb/204Pb)i = 15.8421 to 17.2780], compatible with partial melting of several Archean crustal sources and terrigenous sediments. We supply interpretations relative to tectonism, magma origin and evolution, and formation of arc-related world-class precious and base metals deposits, analogous to the events that occurred in the Andean belt and western North America. It represents new support for more systematic mineral exploration with modern approaches of these poorly studied, but nonetheless promising, Amazonian Proterozoic units.