Brasiliano belts

Brasiliano belts
Name	Brasiliano belts
Caption	Schematic map of Neoproterozoic orogens in South America
Type	Orogenic belts
Age	Neoproterozoic–Early Paleozoic
Region	South America, West Africa (correlative)

Brasiliano belts are a series of Neoproterozoic to Early Paleozoic orogenic belts across South America associated with continental collision, terrane accretion, and crustal reworking during the assembly of Gondwana. They record polyphase deformation, high-grade metamorphism, and widespread magmatism that overprinted older cratonic nuclei such as the Amazonian Craton, São Francisco Craton, and Río de la Plata Craton. The belts correlate with Pan-African provinces in Africa including the West African Craton margins and play a central role in understanding Gondwana assembly involving margins like the Arequipa-Antofalla Block and the Famatinian Belt.

Etymology and definition

The term derives from early Brazilian geological surveys and international syntheses that contrasted late Neoproterozoic orogenic belts with adjacent cratons such as the São Francisco Craton, Amazon Basin, and Rio de la Plata Craton. Initial definitions appeared in regional syntheses that included provinces like the Brasília Belt, Araçuaí Belt, and Pernambuco-Alagoas Complex, and were formalized in comparative studies alongside Pan-African belts such as the Kibaran Belt and Mozambican Belt. Definitions vary between authors who emphasize tectonothermal age, structural style, or terrane boundary correlations with provinces like the Pampia Terrane and the Cuyania Terrane.

Geological setting and distribution

Brasiliano belts extend across eastern and central South America from the Guiana Shield margins through the Congo Craton-correlative regions toward the southern Rio de la Plata Shield and western Gondwana reconstructions. Major belt segments include the Brasília Belt between the São Francisco Craton and the Amazonian Craton, the Aracuaí orogenic belt along the eastern margin, and the Dom Feliciano Belt adjacent to the Río de la Plata Craton. Correlative Pan-African belts across the Atlantic include the West African Craton margins and the Saharan Metacraton. The belts appear in spatial association with magmatic provinces such as the Brasiliano magmatic arc suites, large granitoid provinces like the Serrinha Massif, and shear zones linked to terrane sutures like the Transbrasiliano Lineament.

Tectonic evolution and orogenic phases

Tectonic models invoke multiple orogenic phases: early rifting and passive margin development tied to breakup of Rodinia; arc accretion and subduction episodes represented by arc complexes similar to the Famatinian arc; major collision and crustal shortening synchronous with Gondwana assembly (Pan-African events), and late transcurrent reactivation during Paleozoic adjustments analogous to the Variscan orogeny in Europe. Key events are dated using radiometric systems applied to rocks from the Seridó Belt, Pernambuco Alagoas Complex, and the Araçuaí–West Congo Orogen, linking magmatism and metamorphism to ages established in the Neoproterozoic chronostratigraphy. Models reference kinematic reconstructions that include terranes such as Pampia, Cuyania, and microcontinents that amalgamated along sutures like the Pelotas Basin margin.

Lithology and metamorphism

Lithological assemblages range from metasedimentary sequences—metapelites, metasandstones, and banded iron formations similar to those in the Serra do Cabral—to metavolcanic successions and extensive plutonic suites including granodiorites and tonalites comparable to the Salitre Suite. High-grade metamorphic rocks such as gneisses, migmatites, and granulites occur in central belt cores exemplified by exposures in the Mantiqueira Complex and the Canastra Complex. Metamorphic conditions record amphibolite to granulite facies transitions with pressure-temperature paths constrained by thermobarometry on minerals from the Itajaí Domain and São Gabriel Block, and by U–Pb zircon ages tied to metamorphic pulses.

Structural features and deformation

Structural architectures comprise large-scale fold-and-thrust belts, regional-scale shear zones including the Transbrasiliano Lineament and the Dom Feliciano Shear Zone, duplex structures, and recumbent folding as observed in the Araçuaí and Mantiqueira segments. Deformation is polyphasic: an early penetrative foliation and isoclinal folds, syn-kinematic granitoid intrusions related to arc magmatism, and late brittle-ductile reactivation producing strike-slip faults linked to basins like the Paraná Basin. Microstructures record dynamic recrystallization, pressure-solution seams, and pervasive schistosity in units correlated with the Itacolomi Group and other stratigraphic markers.

Economic significance and mineralization

Brasiliano belts host diverse mineral deposits: orogenic gold occurrences in orogenic shear zones similar to deposits in the Morro do Pilar district, iron ore in banded iron formations associated with the Quadrilátero Ferrífero, copper and base-metal mineralization in volcanic-hosted systems comparable to the Cerro Verde style, and pegmatite-hosted rare-element concentrations including lithium and tantalum in provinces akin to the Minas Gerais pegmatite fields. Magmatic-hydrothermal systems related to granitoid intrusions have produced tin and tungsten in veins analogous to the Garibaldi occurrences, while sulfide mineralization is locally enriched in the Araçuaí Belt and the Sul-Rio-Grandense Shield.

Research history and controversies

Research began with 19th–20th century mapping by national surveys such as the Serviço Geológico do Brasil and expanded through international collaborations including projects by the United States Geological Survey and universities like the Universidade de São Paulo. Debates persist over correlations between South American belts and African Pan-African systems—controversies involve reconstructions linking the Kalahari Craton, Tanzania Craton, and the São Francisco Craton; the timing of collision versus accretional models for terranes such as Cuyania and Pampia; and the roles of slab break-off versus lithospheric delamination in generating the high-temperature metamorphism recorded in units like the Mantiqueira Complex. Ongoing isotopic studies (U–Pb, Lu–Hf, Sm–Nd) from zircon and whole-rock datasets, and geophysical imaging across structures like the Transbrasiliano Lineament, continue to refine competing models.

Category:Geology of South America