Diversity of Rhyacian granitoids in the basement of the Neoproterozoic-Early Cambrian Gurupi Belt, northern Brazil: Geochemistry, U-Pb zircon geochronology, and Nd isotope constraints on the Paleoproterozoic magmatic and crustal evolution

摘要

The Gurupi Belt, in northern Brazil, is a Neoproterozoic-Early Cambrian orogen developed at the south-southwestern margin of the S?o Luís-West African Craton. Several plutonic bodies are exposed as basement units of the Gurupi Belt and represent a variety of granitoid types emplaced at different ages and all show zircon inheritance and chemical and isotopic features that imply participation of reworked Archean to Paleoproterozoic crust in the magma genesis in clear contrast with the juvenile characteristics of the predominant magmatic unit of the neighboring S?o Luís cratonic fragment, the Tromaí Intrusive Suite of 2167-2147Ma. The weakly peraluminous, high-K, calc-alkaline biotite-bearing Cant?o Granodiorite of 2163±4Ma has T_(DM) model ages of 2.21-2.92Ga and e{open}Nd values of +2.7 to -7.1. The 2142±9Ma-old, weakly peraluminous, biotite- and muscovite-bearing Jonasa Granodiorite underwent metamorphism and deformation at 525Ma and shows T_(DM) model ages of 2.14-2.40Ga, with e{open}Nd values of +3.9 to -0.2. Both are, probably, related to a continental arc setting. A relatively large event of strongly peraluminous granitic magmatism took place between 2116 and 2079Ma, and comprises the crust-derived, biotite- and muscovite-bearing granites and leucogranites of probable collisional setting belonging to the Japiim, Tamancuoca, Mo?a and Maria Suprema units. Despite broadly similar, these units show some chemical differences that are interpreted to result from mixtures of variable amounts of sedimentary and igneous sources of Archean to Paleoproterozoic ages. These granites show T_(DM) model ages of 2.19-2.62Ga and the e{open}Nd values range from +3.9 to -0.2, and probably represent collision rocks. Associated in space and time with part of the strongly peraluminous granites, the 2100±21Ma-old, metaluminous to slightly peralkaline granites, quartz-monzonites and quartz-syenites of the Anelis Intrusive Suite have characteristics of potassic to shoshonitic post-collisional rocks. The suite shows T_(DM) model ages of 2.27-2.48Ga and e{open}Nd values of +0.1 to -2.6. The last known event is represented by the post-orogenic, 2085±4Ma-old, weakly peraluminous, high-K, calc-alkaline, biotite-bearing Timbozal Monzogranite, with T_(DM) model ages of 2.27-2.58Ga and e{open}Nd values of +1.1 to -2.8.The strongly peraluminous and different generations of potassic granitoids represent magmatic events with characteristics that may be related to both continental arc subduction and collision processes and indicate that the granitoid bodies represent disrupted fragments of a Rhyacian orogenic belt (continental arc and collision belt) that remains today as basement inliers within the Gurupi Belt in the margin of the S?o Luís-West African Craton. These sequences, together with the juvenile rocks of the S?o Luís cratonic fragment, are part of a protracted Rhyacian orogen that evolved from ～2240. Ma to ～2050. Ma, involving accretionary and collision processes. These sequences also correlate in time and several aspects of evolutionary processes with Eburnean-Birimian terranes of the West-African Craton and Trans-Amazonian belts of the Amazonian Craton.