The Pirineus Syntaxis: An Example of the Intersection of Two Brasiliano Fold-Thrust Belts in Central Brazil and Its Implications for the Tectonic Evolution of Western Gondwana

Abstract

The Pirineus Syntaxis (PSX) is a concave to the foreland (toward the craton) curve in the otherwise NS-trending structural grain of the orogenic province bordering the west side of the São Francisco craton. Its geometry reflects the intersection between two non-parallel foldthrust belts of different ages and style, formed during two separate non-coaxial deformation episodes during the Brasiliano Orogenic period of Neoproterozoic (probably around 900-600 Ma). These ages are not well constrained, since very little radiometric dating is available. The two limbs of the syntaxis are here interpreted as the younger and narrower Northern Brasília belt (NBB), and the older and more complete Southern Brasília belt (SBB). Rocks involved in the deformation that formed the PSX include the Paranoá, Canastra and Araxá Groups, generally accepted as passive margin environment and more restricted to the SBB. The Rio do Peixe Group is a volcanic-sedimentary sequence that prevalently occurs in the SBB, while the Intrusive Rock Suite and Related Metasedimentary Rocks predominantly occur in the NBB. The Granite-gneiss complex of the Goiás Massif (GCM) to the west, comprises the metamorphic core of the syntaxis. The collision of the Rio de la Plata (Paranapanema?) craton with the São Francisco craton formed the SBB, that preceded the final collision and accretion of the GCM with the SFC that formed the NBB. A weak collision of GCM with the southern border of the Amazonian craton determined the last deformation phase in the syntaxis. This is the first attempt to subdivide the Brasiliano of central Brazil and thus contributed to a better understanding of the evolution of western Gondwana. The conclusions of this paper were primarily based on field structural analysis.

Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

“…This configuration indicates the underthrusting of the mafic lower crust of the Araguaia Belt, which is probably the lower crust of the Amazon Craton, below the Goiás magmatic arc. The underthrusting of the Amazon craton is recognized as the last convergent event in the evolution of the Tocantins Province, and its tectonic signature can be identified in many surface structures [ Araújo Filho , 2000].…”

“…The Tocantins Province, located in central Brazil, formed during the Neoproterozoic Brasiliano Orogeny when the Amazon, São Francisco/Congo, and Paranapanema cratons converged; the Paranapenema is now under the Paraná Basin [ Marini et al , 1984; Fuck et al , 1994; Pimentel et al , 2000; Araújo Filho , 2000]. The closure and collision of these blocks amalgamated terrains of different ages and geological histories.…”

Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goiás, Central Brazil

“…The Pireneus lineament is the most obvious of these structures, and extends for over 200 km roughly in the EW direction, marking the so-called Pireneus Syntaxis (Araújo Filho 2000). The latter is defined as a concave to foreland curve of the Brasília Belt, interpreted as the result of interference between two structurally different belts: one to the north (northern Brasília Belt) with NNE structural trend and one to the south of the systaxis (southern Brasília Belt), with NNW-trending structures (Araújo Filho 2000). Some of the alkali rich granitoids and quartz syenitic rocks such as the Itapuranga granite and Uruana syenite (known collectively as the Itapuranga Suite, Oliveira 1997) intrude along these E-W lineaments and may be interpreted as syn-or late-tectonic.…”

Petrochronology of high‐pressure granulite facies rocks from Southern Brasília Orogen, SE Brazil: Combining quantitative compositional mapping, single‐element thermometry and geochronology

“…Its development is related to the early assembly of West Gondwana (Dardenne, 2000; Valeriano, Machado, et al, 2004, Valeriano et al, 2008; Valeriano, 2017; Figure 1a). The Southern Brasília Orogen, the portion of the orogen that occurs to the south of the Pirineus Syntaxis (Figure 1b) (Araújo Filho, 2000), is divided, based on rock types and their tectonic setting, into four tectonic domains (Fuck et al, 1994). From east to west and from bottom to structural top, these are (i) the Cratonic Zone and its sedimentary cover; (ii) the External (foreland) Zone that represents the low‐grade metamorphic fold‐and‐thrust belt of the orogen; (iii) the Internal Zone, comprising the tectonically overlying nappes of high‐grade metamorphic rocks; (iv) and the Goiás magmatic arc zone.…”