8. Summary
The São Francisco craton is surrounded by several Neoproterozoic orogens and fold belts. Geochronological data of deformation and metamorphism provide constraints for the sequence of collision events that led to the formation of the West Gondwana supercontinent. The assembly was diachronous and occurred in important three-stage Neoproterozoic–Cambrian collision processes (Figure 8).
The Southern Brasília belt (
Figure 2) presents the development of the Tonian Araxá-Canastra-Vazante passive margin and Tonian–Cryogenian intraoceanic magmatic arcs with arc-related sedimentary basins
[20][21][151]. Progressively, the intraoceanic scenario evolves to an arc–continent collision in Cryogenian time. During the late Cryogenian, a retroarc basin (Araxá and Ibiá Groups) occurs, with gravitational sedimentation within a deep submarine fan, which transitions to the gravitational and glacial sedimentation of the Vazante Group (Santo Antônio do Bonito and Rocinha Formations) and Jequitaí Formation to the east, toward the São Francisco paleocontinent
[30][31][37]. Thus, the Southern Brasília Belt shows different basin settings overlapping in time: Tonian passive margin and arc-related basins to Cryogenian–Ediacaran retroarc foreland basin (Ibiá Group) and Ediacaran-Cambrian peripheral foreland basin (Bambuí Group).
Figure 8. Simplified tectonic map of the central–eastern region of Brazil with an indication of the three collisional diachronic events in the formation of the SF Craton: Brasília Belt (collision I: 650–620 Ma), Riacho do Pontal–Sergipano Belt (collision II: 620–570 Ma) and Araçuaí Belt (collision III: 580–520 Ma) (see text). Modified from
[7][152].
The Northern Brasília belt (
Figure 3) is an east- to southeast-verging fold–thrust belt that involves Archean basement, Paleo-Mesoproterozoic rift (Araí Group) and rift-sag basins (Serra da Mesa and Traíras Groups), a Stenian passive margin (Paranoá Group) with the Juscelândia, Indaianópolis and Palmeirópolis volcanosedimentary sequences. During the Ectasian-Stenian, the Paranoá passive margin develops, strongly asymmetrical, associated with an important extensional phase, filled by sandstones, pelites, rhythmites, and carbonates lenses with columnar stromatolites, arranged in transgressive and regressive cycles
[9][53][55]. The Stenian passive margin is related to the deposition of the Paranoá Group sediments and probably the volcano–sedimentary sequences that show ocean floor basalts (MORB)
[9][56].
To the north of the São Francisco craton, the Rio Preto, Riacho do Pontal, and the Sergipano belts are separated from each other by basement highs. The Rio Preto belt shows the Canabravinha Formation was deposited into an asymmetrical rift basin (hemi-graben basin) with gravitational flows and turbiditic sediments (
Figure 4). The belt is interpreted as an intracontinental rift at the termination of the Riacho do Pontal and Sergipano orogens. Neoproterozoic–Cambrian deformation, between 550 and 520 Ma, originated a complex, asymmetrical, and double-verging thrust wedge associated with the northwest curvature of the SFC
[71]. The Riacho do Pontal and Sergipano belts (
Figure 5 and
Figure 6) contain south-verging thrusts involving basement rocks older than 1.8 Ga, Tonian and Cryogenian rift-related units (Brejo Seco, Miaba and Canindé rifts), Cryogenian passive margin assemblages (Casa Nova Group, Monte Orebe ophiolitic rocks, Vaza Barris and Macururé Groups) and Ediacaran continental magmatic arcs
[71][77][78][86][96][97].
The Araçuaí belt (
Figure 7) that fringes the southeastern São Francisco craton contains west-verging thrusts and folds. In the Araçuaí belt, there are Neoproterozoic rocks of the Macaúbas Group, forming the intracontinental Tonian rift and the Cryogenian–Ediacaran passive margin of Serra do Catuni, Chapada Acauã, Nova Aurora, and Ribeirão da Folha formations. Furthermore, there is the Ediacaran continental arc Rio Doce Group and the forearc Salinas basin
[45][119][122][123]. The Macaúbas basin is dominantly a large continental rift with steep N-S and NW-SE normal fault edges. To the southeast, due to differential extension, the basin evolved as a localized passive margin with oceanic crust. The crustal extension was accommodated by E-W transfer faults. Reactivations at the edges of the Macaúbas rift gave rise to thick gravitational sedimentation, with cohesive debris flow (diamictites) and turbidity currents (sandstones and pelites) and glacial influence
[142][143][153], during the early and late Cryogenian. These units of the Macaúbas Group, exposed along the belt, were metamorphosed under greenschist to amphibolite facies conditions and were affected by thrusts, reverse faults, and craton-ward verging folds, developed between 575 and 530 Ma
[121][123]. The Araçuaí orogenic front propagates into the craton interior and interacts with preexistent rift structures, affecting rocks within the Paramirim corridor. To the southern, the Ribeira belt was deformed between 610 and 560 Ma
[7][13][154], with the docking of the Cabo Frio terrane at 535–510 Ma
[155]. The northern Ribeira belt is characterized by a 500 km long network of anastomosing transcurrent shear zones parallel to the belt. A northeast–trending dextral transpressive belt is interpreted as a later oblique convergence between the São Francisco Craton and Congo Craton
[156]. NE-trending, dextral strike-slip shear zones with late collisional leucogranites, pegmatites, and hydrothermal fluids are dated at 535–510 Ma
[154]. The Araçuaí orogen is related to a third collisional event in central-east Brazil, between São Francisco and Congo cratons at 580–530 Ma (
Figure 8).
Paleogeographic maps are presented at the end (
Figure 9), illustrating the diachronic evolution of Neoproterozoic orogens around the São Francisco-Congo (SF-C) paleocontinent. A large Tonian–Cryogenian ocean occurred to the west, with amalgamated intraoceanic magmatic arcs (Brasília belt). To the north (Riacho do Pontal-Sergipano belt) and south (Araçuaí belt), small v-shaped oceans with hyperextended margins occurred, with Ediacaran continental magmatic arcs
[157].
Figure 9. Simplified paleogeographic maps illustrating the diachronic evolution of the orogens around the São Francisco–Congo (SF-C) paleocontinent during the Neoproterozoic.