Transpressional deformation during Ediacaran accretion of the Paranaguá Terrane, southernmost Ribeira Belt, Western Gondwana

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Highlights

  • Geophysics and structural analysis characterize a transpressional collision.

  • Different structural domains are related to the geometry of Luis Alves block.

  • Southern and northern domains present simple and pure-shear deformation respectively.

  • Isotopic data individualizes two deformation stages: D1 (Ediacaran) and D2 (Cambrian).

Abstract

The Paranaguá Terrane is mainly constituted by an Ediacaran arc-related granitic complex, spread in a NE-SW trending elongated stripe, located in the Southern Ribeira Belt, South-Southeastern Brazil. The basement of these granites occurs as a disrupted folded belt composed of metasedimentary and gneissic-migmatitic rocks. The integration of structural and geophysical (gamma spectrometry and magnetometry) data from the Paranaguá Terrane and the adjacent tectonic units, suggests that the deformation in the study area is partially controlled by the geometry of the Luis Alves Cratonic Block, as well as the northern part of Dom Feliciano Belt. The irregular shape of this cratonic unit associated with N-NW tectonic transport direction caused strain partitioning in the area and the development of two structural domains: southern and northern Paranaguá. The southern part is characterized by sinistral transpressional shear zones, while the northern sector is dominated by thrust shear zones that represent a large frontal collision with oblique components. The hierarchy of the structural and microstructural features in the Paranaguá Terrane associated with geochronologic data suggest two deformational phases (D1 and D2) during a transpressive collisional system. The D1 progressive deformational stage is correlated to the main period of granitic crystallization during the Ediacaran and was divided in two moments: i) early D1 (640–610) associated with the regional metamorphism and thrust and folding tectonics with N-NW tectonic transport and; ii) late D1 (610-580 Ma) linked to the strain partitioning and development of the southern (simple-shear dominated) and northern (pure-shear dominated) structural domains with sinistral kinematics, granite emplacement and high-temperature mylonites. The D2 deformation stage (540–500 Ma) is mainly represented by the low-temperature mylonites and deformation under retrograde conditions.

Introduction

The tectonic evolution of the Western Gondwana continent involved a series of collisional orogens that culminated in the amalgamation of several Precambrian terranes from the late Neoproterozoic until the early Paleozoic (Brito Neves et al., 1999; Campos Neto, 2000; Schmitt et al., 2004; Basei et al., 2008; Heilbron et al., 2008; Faleiros et al., 2011; Brito Neves et al., 2014; Konopásek et al., 2016).

The reconstruction of continental margins related to Brasiliano – Pan-African tectonic events depends on how much information we can get from Neoproterozoic granites and metamorphic belts (Trouw et al., 2000; Passchier et al., 2002; Goscombe et al., 2003; Goscombe and Gray, 2007; Heilbron et al., 2008; Siga et al., 2009; Basei et al., 2011). Consequently, the interaction between major tectonic units as cratons, microplates, mobile belts and their respective geometry, plays an important role in the deformational history of these orogenic systems (Tikoff and Teyssier, 1994; Teyssier et al., 1995; Fossen et al., 2018).

In the southwestern part of Gondwana, the coastal Paranaguá Terrane (study area – Fig. 1), an accretionary to collisional system, was juxtaposed onto the Luis Alves craton and Curitiba Terrane to the Ribeira Belt, during the Ediacaran (Fig. 1). This orogenic cycle (Brasiliano – Pan-African) created distinct structural patterns that provided important clues to understand the deformational history of the Paranaguá Terrane, as well as the interaction between different tectonic units.

This study presents the deformational aspects and structural domains of the Paranaguá Terrane and its spatial arrangement, allowing the evaluation of the regional expression and the tectonic significance of the geological features observed in outcrops and in micro- and meso-scale. We propose a new model for the deformation history based on field observations and high resolution aerogeophysical data integrated with previous geologic and geochronologic data. This model highlights that boundaries conditions play an important role in the structural pattern of the Paranaguá Terrane and control strain partitioning.

Section snippets

Geological setting

The study area is located in the southern portion of Ribeira Belt, which is a mobile belt product of the interaction between cratonic blocks (São Francisco, Paranapanema, Luis Alves and Congo) and consumption of the Adamastor Ocean (Silva et al., 2005; Heilbron et al., 2008). The southern Ribeira Belt is formed by Precambrian terranes amalgamated during the Ediacaran and often bounded by thrust or transcurrent shear zones (Basei et al., 1992; Silva et al., 2005; Faleiros et al., 2011). The

Methods

Fieldwork resulted in four transects across the regional structural trend (Fig. 2) and some specific locations in the regions of: A) São Francisco do Sul Island - Garuva – Itapoá (southern Paranaguá Terrane in the Santa Catarina and Paraná State); B) Serra da Prata – Antonina – Paranaguá - Matinhos e Guaratuba (central Paranaguá Terrane in the Paraná State); C) Salto Morato – Guaraqueçaba (northern Paranaguá Terrane in the Paraná State); D) Ariri - Iguape (northern Paranaguá Terrane in the São

Geophysical framework

From the interpretation of the map of the vertical integral of the analytic signal amplitude (VIAS – Fig. 3), which highlights bodies with high magnetic susceptibility and vertical extension, normally associated with regional representative structures (Paine et al., 2001), it was possible to observe that the Paranaguá and Curitiba Terranes present low magnetic domains when compared to the Luis Alves cratonic block.

Using enhancement methods, it is possible to observe the magnetic anomalies in

Structural patterns and strain partitioning in Paranaguá Terrane

The geophysical and structural data clearly individualized two structural domains in the Paranaguá Terrane (see section 4). The southern sector is mainly formed by steep N–S to NNE-SSW striking foliations with a predominance of strike-slip to oblique stretching lineations (Fig. 2, Fig. 6), frequently associated with the development of structures with sinistral kinematics (Fig. 7) and strike-slip to transpressional shear zones. The northern sector, contrastingly, present moderate to low angle

Final remarks

  • An integrated analysis of aerogeophysical maps and structural data, together with geochronological data, indicates that the Paranaguá Terrane was a product of a transpressional orogeny resulting from a complex interaction of the Luis Alves Cratonic block with adjacent terranes in the Ediacaran.

  • The convergence in the NNW direction generated a partitioning of the deformation due to an increase of collision obliquity further north and created portions dominated by simple-shear (southern sector)

Acknowledgments

The authors are thankful to the funds from the PETROBRAS/LAMIR/FUNPAR Microbial Project (n° 23075.120789/2016–11); The Fieldwork collaboration from the geologists Gustavo Machado Marangon, Msc. Eduardo Menozzo da Rosa, Msc. Larissa Santos and Msc. Guilherme Fedalto; The geophysicist Francesco Antonelli and the geologists Msc. Jessica Weihermann and Msc. Luizemara Szameitat in the geophysics processing; The team from the Laboratório de Análise de Minerais e Rochas (LAMIR-UFPR); The support from

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