Deformation mechanisms, mineral chemistry and zircon U-Pb geochronological constraints in the south Patos shear zone: implications for the crustal evolution of the Borborema Province, NE Brazil

Carolina Peixoto De Souza,Lauro Cézar Montefalco De Lira Santos,Luis Gustavo Ferreira Viegas

doi:10.1590/2317-4889202120210048

Carolina Peixoto De Souza, Lauro Cézar Montefalco De Lira Santos + Show 1 more

Open Access

https://doi.org/10.1590/2317-4889202120210048

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Abstract

The southern boundary of the Patos Shear Zone (PSZ) is characterized by mylonites resulting from the deformation of Paleoproterozoic basement gneisses, Neoproterozoic metavolcanic and metasedimentary rocks, granitic and granodioritic intrusions. Among the latter, the Santa Terezinha and Catingueira plutons show stretched shapes in agreement with the the shear zone’s regional trend. Recrystallized quartz grains in these plutons accommodate deformation by dislocation creep. The host banded gneisses show similar deformation structures to the plutons. Quartz crystallographic fabrics mainly record the activity of basal and prism slip planes with local contribution of rhomb planes, whilst feldspar clasts show evidence of intracrystalline deformation in the larger porphyroclasts. These characteristics suggest that shearing occurred at lower-amphibolite facies conditions. U-Pb zircon data for the Santa Terezinha pluton yields an age of 625 ± 7 Ma, which, coupled with the pluton elongated shape and microstructure, suggests that its emplacement was pre-kinematic in relation to the Patos shear zone. Post-emplacement elongation of the granite body occurred along the strike-slip trend. Such structural and geochronological constraints highlight the close association between magma emplacement and shear zone deformation during distinct stages of the Brasiliano-Pan-African orogeny in the Borborema Province.

Highlights

Tectonic controls related to the emplacement and exhumation of granitic bodies along strike-slip zones have been largely studied for more than three decades (Hutton 1988, Paterson and Tobisch 1992, Vigneresse 1995, Vauchez et al 1997, Rosenberg 2004)
Based on meso- and microscale structures, bulk rock and mineral chemistry as well as U-Pb geochronology, the following conclusions can be drawn from this study:
CPO fabrics evidenced by the activity of prism slip are developed during shearing at high-temperatures, while the CPOs that record dominance of basal slip are attributed to a subsequent overprint and/ or reactivation event in the Patos shear zone;

Summary

Introduction

Tectonic controls related to the emplacement and exhumation of granitic bodies along strike-slip zones have been largely studied for more than three decades (Hutton 1988, Paterson and Tobisch 1992, Vigneresse 1995, Vauchez et al 1997, Rosenberg 2004). Granitic plutons commonly occur parallel or slightly oblique to the main orientation of shear zones. When this relationship is established, they can be classified as pre-, syn- or post-kinematic (Hutton 1988, Vigneresse 1995, Vauchez et al 1997). The timing of crystallization processes and subsequent shear zone deformation may be assessed by the pluton shape, its internal microstructures and fabrics, as well as its structural relationships with the host rocks (Hutton 1988, Brown and Solar 1999, Archanjo et al 2002, Weinberg et al 2004). The integrated field, petrographic, and geochemical/isotopic investigation of the granitic plutons in distinct chronological scenarios share the common trait of their association with the major shear zones, providing reliable feedbacks between magmatism, deformation, and metamorphism (e.g., Vauchez et al 1995, Santos and Medeiros 1999, Neves et al 2000, Guimarães et al 2004, Neves et al 2006, Archanjo et al 2008, Archanjo et al 2013, Santos and Viegas 2021)

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