Devonian to Permian post-orogenic denudation of the Brasília Belt of West Gondwana: insights from apatite fission track thermochronology
Introduction
The West Gondwana paleocontinental basement was composed of Archean cratons and Proterozoic lithospheric blocks, welded along Neoproterozoic – early Paleozoic orogenic belts (Fig. 1). After its Paleozoic amalgamation, the basement experienced a transition to a stable platform, where several large intraplate basins or syneclises, surrounded by elevated areas, developed (de Wit et al., 2008). The subsidence of the syneclise depocenters was contemporaneous with Pre-Andean southward-direct subduction of oceanic lithosphere of Panthalassa and associated collision-accretion events, during the entire Paleozoic (Fig. 1) (Du Toit, 1937, 1927; Keidel, 1916). In the late Cretaceous, West Gondwana was affected by progressing fragmentation, and eventually the South American and African continents were separated due to the opening of the South Atlantic Ocean.
The basement cooling of the West Gondwana orogenic belts leading to the post orogenic stability can be understood as the result of interplay between rock-uplift and tectonic forces with erosional processes (e.g. Braun et al., 2006; Braun and Robert, 2005; Pazzaglia and Kelley, 1998; Reiners and Brandon, 2006; Spotila, 2005; Whipple and Meade, 2006). Erosive denudation and sediment production pulses can be periodically renewed by tectonic reactivation, drainage reorganization or climate changes (Fitzgerald et al., 1999; Zhang et al., 2001). Isotopic chronometers, sedimentary record and tectonic evolution of adjacent depocenters are fundamental tools to clearly understand how high-temperature rocks from the crustal roots of orogenic belts are exhumed to the surface (Enkelmann et al., 2014; Fan and Carrapa, 2014; Kasanzu et al., 2016; Tinker et al., 2008; Weber et al., 2004).
Geothermochronometric techniques, such 40Ar/39Ar in potassium bearing minerals, or U/Pb dating on zircon, titanite, and monazite are commonly applied to understand the long-term bedrock tectonic evolution, providing time constraints in the medium to high temperature window (e.g. Babinski et al., 2013; D’Agrella-Filho et al., 2011; Danderfer et al., 2009; Gresse and Scheepers, 1993; Manhica et al., 2001; Nonnotte et al., 2008; Oliveira et al., 2010; Sims et al., 1998; Tohver et al., 2010). However, research that investigated the further evolution of the basement rocks in our study area towards low-temperature conditions are relatively rare comparing to high-medium temperature studies, especially in the northern region.. In ancient settings such as the West Gondwana orogenic belts, the low-temperature thermochronological studies concerning the former post-orogenic exhumation have some additional difficulties (Enkelmann and Garver, 2016). The adversities lie in the fact that data from low-temperature thermochronometers are very sensitive to reheating and ancient orogenic belts are commonly thermally reset over time (Enkelmann and Garver, 2016; Spotila, 2005). Besides, the erosional product information of ancient processes is highly dependent on the preservation of the sedimentary record. The opening of the Atlantic Ocean was responsible for the overprint of previous thermal history information embedded in the West Gondwana bedrock. The Atlantic passive margin of South America and Africa was the subject of a series of thermochronological works that highlight its rift and post-rift thermal evolution (e.g. Cogné et al., 2011; Engelmann de Oliveira et al., 2016; Gallagher et al., 1994; Green et al., 2018; Hueck et al., 2017; Japsen et al., 2012; Jelinek et al., 2014; Krob et al., 2019; Van Ranst et al., 2019; Wildman et al., 2015).
In the hinterland, restricted areas are able to retain their former cooling signals associated with the evolution of the West Gondwana basement and add relevant data for understanding long-term landscape dynamics (Reiners and Brandon, 2006; Spotila, 2005). The Brasília Belt (Fig. 1) is such an example and was spared of major Phanerozoic tectonic events, remaining confined between large cratonic blocks, mainly the São Francisco and Amazonia cratons (Valeriano et al., 2008). This belt is a remnant of the Neoproterozoic orogen formed during the amalgamation cycle that culminated in the ultimate formation of the Gondwana Supercontinent (Pimentel, 2016; Valeriano et al., 2008). After amalgamation, it worked as a paleohigh and source of sediments for its intracratonic sedimentary basins that developed during the Phanerozoic, i.e. mainly the Paraná Basin in this case. This basin preserves seven-kilometer-thick of sedimentary sequences (Milani et al., 2007). The post-orogenic cooling history of the belt is hitherto not constrained by low temperature thermochronometers.
This paper presents results of low temperature thermochronometry, in particular Apatite Fission Track (AFT) analysis, performed on seven basement samples from the Brasília Belt, and will be linked to the sedimentary basin evolution of the adjacent Paraná Basin. With the new apatite fission track data, it is attempted to further give insights into the outstanding research questions on the Phanerozoic evolution of the region and the effects of the opening of the South Atlantic Ocean on the Neoproterozoic orogenic lithosphere of the continental interior of South America.
Section snippets
Brasília Belt
The Brasília Belt comprises an Archean to Paleoproterozoic basement which, together with Proterozoic metasedimentary rocks, a Paleoproterozoic juvenile magmatic arc (Goiás arc), and Neoproterozoic granitic intrusions, is folded and thrusted toward the São Francisco Craton (Fig. 1B) (Pimentel et al., 2000). This tectonic unit is the result of the Neoproterozoic orogeny during an early phase of the Gondwana Supercontinent amalgamation that consumed the large Goiás-Pharusian ocean crust over a
Analytical procedures
Seven samples for Apatite Fission Track (AFT) analysis were acquired from the Precambrian crystalline rocks from the Brasília Belt at the northeastern border of Paraná Basin (Fig. 1). Details of sample lithology and geographical locations are provided in Table 1. The samples were crushed and sieved to retain the sand fraction. Apatite grains were separated by conventional panning, magnetic separation, heavy-liquid and hand-picking protocols. They were mounted in Struers CaldoFix-2 epoxy resin
Results
The results of seven apatite fission track (AFT) analyses are shown in Table 2 and geographically displayed in Fig. 3. All samples pass the chi2 test of homogeneity. The AFT central ages range from Devonian, 386 ± 31 Ma (sample 8) to Triassic 243 ± 13 Ma (sample C15). Samples C15 and C17 contained less than 20 analyzable apatite grains, therefore they are not used for in depth discussion, although they corroborate the results of the other samples. Despite few data, the age-elevation plot (Fig. 4
Devonian to Permian Brasília Belt exhumation and Paraná Basin subsidence
The thermochronological analyses of samples from the Brasília Belt not surprisingly, show cooling ages (central AFT ages) younger than the Neoproterozoic formation of the belt (900-600 Ma) (Pimentel, 2016), but clearly older than the West Gondwana break-up in the early Cretaceous (Mizusaki et al., 1998). The AFT central age versus MTL plot and thermal history models from samples 8, 9, C14, C16 and N13, indicate fairly rapid cooling of the Brasília Belt basement below temperatures of ∼120-40 °C
Conclusions
Our new AFT data in addition with the thermal history modeling of the Neoproterozoic basement of the Brasília Belt allow us to draw the following conclusions:
- •
Relatively fast post orogenic cooling occurred during the Devonian to Permian (∼400-350 Ma) in the Brasília Belt. The exhumation of the southern portion of the belt was associated with the effect of tectonic extension during the breakup of cratonic lithosphere that generated the subsidence of the Paraná Basin. The Brasília Belt, that
CRediT authorship contribution statement
Ana Carolina Fonseca: Conceptualization, Investigation, Validation, Formal analysis, Writing - original draft. Gabriella Vago Piffer: Conceptualization, Investigation, Writing - original draft. Simon Nachtergaele: Methodology, Validation, Writing - original draft. Gerben Van Ranst: Methodology, Formal analysis, Writing - original draft. Johan De Grave: Methodology, Validation, Resources, Writing - original draft, Supervision, Project administration. Tiago Amâncio Novo: Conceptualization,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (Project 306520/2018-4). The first and second authors thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES (the research fund of Brazilian Ministry of Education) for the master’s scholarships. SN’s contribution was supported by Research Foundation – Flanders (FWO) through PhD fellowship. We are grateful to Dr. Bart Van Houdt for performing the irradiations at the SCK in Mol
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2023, Journal of South American Earth SciencesComments on “Devonian to Permian post-orogenic denudation of the Brasília Belt of West Gondwana: Insights from apatite fission track thermochronology” by Fonseca et al. (2020)
2022, Journal of GeodynamicsCitation Excerpt :Here, it is essential to note that the SW-direction paleocurrents of the Furnas Formation, cited by Fonseca et al. (2020), were measured on tidal facies (Assine, 1999 and verbal communication), and can only be used with great discretion for provenance reconstructions. Fonseca et al. (2020) stated that “The previous paleocurrent data of the three supersequences (Rio Ivaí, Paraná and Gondwana I) of the Paraná Basin (Alessandretti et al., 2016; Assine, 1999; Assine et al., 1998; Gesicki et al., 2002; Lobato and Borghi, 2005; Mottin et al., 2018; Scherer and Lavina, 2006) points to the Brasília Belt as a possible source area.” Here, our comments will be explicitly focused on the sedimentary dispersion pattern of the Gondwana I Supersequence (Milani et al., 2007), excluding the already discussed Furnas Formation and Itararé Group.