1.88 Ga São Gabriel AMCG association in the southernmost Uatumã-Anauá Domain: Petrological implications for post-collisional A-type magmatism in the Amazonian Craton

Abstract

In the southernmost Uatumã-Anauá Domain, central Amazonian craton (Brazil), crop out 1.98Ga basement inliers represented by (meta)leucosyenogranites and amphibolites (Igarapé Canoas Suite), 1.90–1.89Ga high-K calc-alkaline granitoids (Água Branca Suite), a 1.88–1.87Ga alkali-calcic A-type volcano-plutonic system (Iricoumé-Mapuera), Tonian SiO2-satured alkaline granitoids, 1.45–1.25Ga orthoderived metamorphic rocks (Jauaperi Complex) and Orosirian–Upper Triassic mafic intrusions. New data on petrography, multielementar geochemistry, in situ zircon U–Pb ages and Nd and Hf isotopes of alkali-calcic A-type granites (São Gabriel Granite, Mapuera Suite) and related rocks are indicative of a 1.89–1.87Ga volcano-plutonic system integrated to the São Gabriel AMCG association. Its magmatic evolution was controlled by the fractional crystallization combined with magma mixing and cumulation processes. Nd isotope values (εNdt values=−3.71 to +0.51 and Nd TDM model age=2.44 to 2.12Ga) and U–Pb inherited zircon crystals (2115±22Ma; 2206±21Ma; 2377±17Ma, 2385±17Ma) of the São Gabriel system indicate a large participation of Siderian–Rhyacian crust (granite-greenstones and granulites) and small contribution of Rhyacian mantelic magma. εHft values (+5.2 to −5.8) and Hf TDM ages (3.27–2.14Ga) also point to contribution of Paleoarchean–Rhyacian crustal melts and small participation of Siderian–Rhyacian mantle melts. Residual melts from the lower crust have been mixed with basaltic melts generated by partial melting of the subcontinental lithospheric mantle (peridotite) in a post-collisional setting at 1.89–1.87Ga. The mafic melts of such a mixture could have been originated through partial melting of residual ocean plate fragments (eclogites) which ascended onto a residual mantle wedge (hornblende peridotite) and melted it, resulting in modified basaltic magma which, by underplating, led heat to the anatexis of the lower continental crust. This widespread alkali-calcic A-type magmatism was caused by destabilization and magmatic reactivation in the Ventuari-Tapajós and Central Amazonian Provinces, resulting from the Ventuari-Tapajós collision periods. Younger igneous reactivations have been registered at 1.45 to 1.25Ga, ~1.0Ga and ~100Ma, culminating with the production of mafic and felsic alkaline magmas, along of the northern border of the Amazon Basin.