Amazonian Craton

Amazonian Craton
Woudloper · CC BY-SA 3.0 · source
Name	Amazonian Craton
Other names	Guiana Shield; Brazilian Shield
Location	South America
Area	~4,000,000 km²
Age	Archean to Proterozoic
Major units	Guiana Shield; Central Brazil Shield; Roraima Supergroup
Notable minerals	gold; iron; nickel; manganese; bauxite; diamonds

Amazonian Craton The Amazonian Craton is a vast Precambrian continental nucleus underlying much of northern and central South America, incorporating portions of Brazil, Venezuela, Guyana, Suriname, French Guiana, Colombia and Bolivia. As a composite of Archean and Proterozoic terranes, it is central to reconstructions involving Laurentia, Gondwana, Rodinia, West Gondwana and the Pan-African orogeny. Its geology has been investigated by institutions such as the Brazilian Geological Survey, the United States Geological Survey, and research groups at the University of São Paulo and the National University of Colombia.

Geology and Composition

The craton comprises Archean tonalite–trondhjemite–granodiorite terranes, Proterozoic greenstone belts, and extensive sedimentary cover including the Roraima Supergroup and the Belt Supergroup-like successions, with lithologies ranging from gneiss to metavolcanic sequences studied near the Tapajós and Xingu provinces. Key lithostratigraphic units include the Guiana Shield metavolcanic–metasedimentary complexes, the Carajás iron formations, and the Serra do Navio metamorphic rocks, hosting mineral assemblages such as pyrite, chalcopyrite, and magnetite. Metamorphic grades vary from greenschist to amphibolite facies, with localized granulite facies exposures in the Amazonas region.

Tectonic History and Evolution

Tectonic models integrate collisional events along sutures correlated with the Transamazonian orogeny, accretionary processes comparable to the Yavapai–Mazatzal events, and later reworking during the Brasiliano and Pan-African cycles. Paleogeographic restorations connect cratonic blocks with Laurentia and West Africa during Proterozoic supercontinent assemblies such as Rodinia and Gondwana. Plate reconstructions invoke subduction, terrane accretion, and intracontinental rifting that produced basins analogous to the Amazon Rift and led to magmatism comparable to the Sao Francisco Craton magmatic episodes. Strike-slip faulting linked to the Equatorial Atlantic opening played a role during Mesozoic breakup.

Cratonic Boundaries and Subdivisions

Boundaries are defined by major shear zones and suture belts including the Transbrasiliano and Solimões shear systems, the Boca do Acre lineaments, and the western margin adjacent to the Andean orogen. Subdivisions include the Guiana Shield in the north, the Central Brazil Shield with provinces such as Tapajós, Cuiabá, and the Rondonian–San Ignacio Province bordering Bolivia. Adjacent mobile belts include the Amazonian Shield margins and the Maranhão and Pernambuco domains, with basin fills in the Madeira and Trombetas basins marking sedimentary transitions.

Mineral Resources and Economic Geology

The craton hosts major deposits: gold in the Igarapé Bahia and Itapina districts, iron in the Carajás Mineral Province and Quadrilátero Ferrífero, manganese in the Grão Pará region, bauxite on the Pará plateau, and nickel–copper sulfides in the Tapajós and Pitinga areas. Diamondiferous kimberlites and lamproites have been mapped near Mato Grosso and Roraima, with exploration by companies including Vale S.A., AngloGold Ashanti, and Petrobras-linked consortia. Hydrogeological frameworks for the Amazon Basin influence placer deposit distribution and guide artisanal and industrial mining regulation by agencies like the National Mining Agency (Brazil).

Geochronology and Isotopic Studies

Detrital zircon U–Pb ages, Sm–Nd and Lu–Hf isotopic systems from samples across the craton reveal Archean cores aged >3.0 Ga and pervasive Proterozoic overprints between 2.2–1.0 Ga linked to the Transamazonian event. Lead isotopes from sulfide mineralization and Rb–Sr whole-rock data constrain metamorphic pulses synchronous with Brasiliano tectonism. Isotopic mapping comparing crustal signatures with cratons such as West African Craton and Sao Francisco Craton informs provenance studies, while high-precision ID-TIMS work at laboratories linked to GFZ Potsdam and the Royal Ontario Museum refines depositional ages for the Roraima Supergroup.

Geophysical Structure and Seismic Studies

Seismic tomography, gravity and magnetic surveys reveal a thick lithospheric keel with high-velocity mantle roots beneath domains correlated with the Guiana Shield, and thinner lithosphere towards craton margins abutting the Andes and Amazonian rifted provinces. Aeromagnetic lineaments trace Archean crustal blocks and kimberlite trends similar to those mapped by Geoscience Australia in analog contexts. Passive seismic networks operated by the Instituto Nacional de Pesquisas Espaciais and the Lamont–Doherty Earth Observatory provide constraints on crustal thickness variations and on lithospheric anisotropy linked to ancient sutures.

Paleoproterozoic to Neoproterozoic Orogenies

Orogenic cycles from the Paleoproterozoic Transamazonian collision to the Neoproterozoic Brasiliano–Pan-African amalgamation produced collisional belts paralleling events at Sao Luis and Borborema provinces, with granitoid magmatism synchronous with metamorphism. These orogenies generated crustal growth episodes comparable to the Grenville and Pan-African orogenies, forming sutures that are prospective for orogenic gold and greenstone-associated mineralization. Correlative studies with the West Gondwana assembly emphasize the role of these orogenies in stabilizing continental lithosphere and defining modern continental outlines.

Category:Cratons Category:Geology of South America Category:Precambrian geology