Devonian to Permian post-orogenic denudation of the Brasília Belt of West Gondwana: insights from apatite fission track thermochronology

Abstract

The Brasília Belt in southern Brazil is a Neoproterozoic orogenic belt that represents the northern border of the Paraná Basin, a long-lived early Paleozoic intracratonic basin. The belt is surrounded by cratonic domains and were modestly affected and reactivated by the opening of the South Atlantic Ocean during the Cretaceous. Here we present new apatite fission track data from crystalline rocks of the Brasília Belt. The apatite fission track central ages range from 386 to 243 Ma and the mean track lengths range between 13.4 and 14.5 μm. Thermal history modeling reveals Devonian to Permian cooling, which we interpret as the main final exhumation of the Brasília Belt, implying that indeed the influence of posterior Mesozoic and Cenozoic geodynamic history on the belt was limited. The Paraná Basin and surrounding elevated terranes therefore provide a time window to study the tectonic history of Gondwana and the effect of far-field intraplate stresses on the interior of West Gondwana. Rapid basement exhumation of the Brasília Belt is coeval with extension and tectonic subsidence in the Paraná Basin as a result of continent-scale tectonic forces occurring over entire West Gondwana.

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.