Continental magmatic arc rotation during the assembly of western Gondwana

Highlights

• U–Pb zircon ages of post-orogenic igneous intrusion defining deformation timing.

• Continental block rotation.

• Post-orogenic brittle deformation rotating a Neoproterozoic continental magmatic arc.

• Field structural analyses and airborne gamma-ray spectrometric data define ductile and brittle deformation evolution.

Abstract

The Ceará Central Domain (CCD) is part of the Borborema Province and is delimited by two major NE-SW-trending strike-slip zones associated with the Transbrasiliano and Senador Pompeu lineaments. These two strike-slip zones formed in Neoproterozoic/Early Cambrian times under ductile conditions and underwent several brittle-ductile and brittle reactivation events from 540 Ma onwards, which affected Precambrian and Phanerozoic rocks, respectively, causing ductile and brittle-ductile and brittle deformation. The Transbrasiliano Lineament is an NNE-SSW-trending, 4000 km-long structure marked by strong magnetic anomalies. It is interpreted to represent a mega-suture active during the Gondwana amalgamation and/or the post-collisional shearing. The Santa Quitéria Continental Magmatic Arc, located between both lineaments, consists of a Neoproterozoic (830-620 Ma) gneissic-migmatitic association affected by collisional metamorphism (640-615 Ma). This arc has been dissected, dislocated, and rotated under brittle-ductile and brittle conditions by a set of secondary strike-slip faults, possibly interconnected with the two major Transbrasiliano and Senador Pompeu lineaments, and most likely have been contemporarily active throughout history. The roughly NNW-SSE-trending Tauá Fault, located southwest of CCD, appears to relate to both fault systems. A closer inspection of gamma-ray spectrometric data suggests a complex network of interconnecting E-W-trending brittle transcurrent faults, some of which show dextral and/or sinistral kinematics, displacing the Santa Quitéria Continental Magmatic Arc and Canindé-Independência units. We suggest a paleo-dextral ductile deformation of the Santa Quitéria Continental Magmatic Arc resulting from the coeval transcurrent activity along Transbrasiliano and Senador Pompeu lineaments. These strike-slip mega-shear zones developed an intricate pattern of the minor (first-, second-, and third stages) interconnecting strike-slip faults, along which the Santa Quitéria Continental Magmatic Arc has been displaced and rotated, under conditions that changed from ductile to brittle-ductile to brittle through time.

Introduction

Large structural lineaments worldwide record several stages of activation and reactivation, accompanied by inverse kinematics and rotational block tectonics within the shear system they belong to, while conditions change from ductile to brittle-ductile, and finally brittle through time (Wölfler et al., 2015). Fault reactivation depends upon their orientation relative to the changing stress field and their ability to accommodate the imposed strains. These, in turn, affect the rotation of blocks along or between fault systems (McKenzie and Jackson, 1983; Nicholson et al., 1994; Holdsworth et al., 2002; Bason et al., 2018).

Two NE-SW continental-scale strike-slip faults associated with the Transbrasiliano and Senador Pompeu Lineaments (TBL and SPL, respectively) delimit the Ceará Central Domain (CCD), which is part of the Borborema structural province in NE Brazil and extends to the African continent (Trompette, 1994; Brito Neves et al., 2000; Fetter et al., 2003; Santos et al., 2008; Araujo et al., 2016). These two shear zones formed in the Neoproterozoic and reactivated several times from 540 Ma onwards. As a result, the Precambrian and Phanerozoic rocks in their vicinity have been affected by ductile and brittle deformation, respectively. Furthermore, from these two lineaments, an interconnecting net of secondary strike-slip faults seem to span, such as the roughly NNW-SSE-trending Tauá Fault and the NW-SE-trending Rio Groaíras faults (Arthaud, 1986; Neves, 1991), which appears to be connected to both fault systems (Fig. 1). The Santa Quitéria Continental Magmatic Arc (SQCMA) is located between the TBL and SPL and consists of a deformed gneissic-migmatitic association of Neoproterozoic age (830-620 Ma) and has been affected by a collisional tectonic event (640-615 Ma) (Fetter et al., 2003; Araujo et al., 2014). This ductile collisional event deformed SQCMA internally and turned its boundaries into transcurrent and thrust faults.

Given the spatial distribution and orientation of SQCMA, we propose its dissection and rotation under brittle conditions and mainly crosscutting, secondary NW-SE-trending transcurrent faults. As not all these faults are described in the literature, additional gamma-ray spectrometric images have been analyzed to find further evidence of previously unknown tectonic lineaments. These possible faults, observed in the gamma-ray spectrometric images, were then located and investigated in the field. We present field evidence and argue that a significant part of the SQCMA dissection and rotation might have occurred along these newly proposed fault lines. To estimate the structural evolution affecting the SQCMA and surrounding areas, this paper presents evidence based on geophysical imagery, field data to attest kinematic stages changing from ductile to brittle conditions, and U–Pb zircon dating by LA-ICP-MS of syn- and post-collisional granitic plutons and dykes affected by brittle, rather than ductile, tectonics.

The Borborema Province (Almeida et al., 1981) belongs to a series of Neoproterozoic structural provinces (fold belts) located in NE Brazil and represents the western part of a major Brasiliano/Pan-African orogenic belt, which can be traced into Central Africa (Caby, 1989; Trompette, 1994) (Fig. 1a). The Neoproterozoic accretionary and collisional processes of the Brasiliano Orogeny are registered in the Palaeoproterozoic gneisses and migmatites of the Borborema Province basement, which surround smaller Archean nuclei. This basement is then overlain by Palaeoproterozoic and Neoproterozoic supracrustal rocks, which were later intruded by Neoproterozoic granitoids and dislocated along a network of shear zones (Ávila et al., 2019). The northern part of the Borborema Province consists of three crustal blocks delimited by major NE-SW to E-W lineaments: a) the Rio Grande do Norte; b) the Médio Coreaú Domain and, c) the Ceará Central Domain blocks (Fig. 1b).

The Ceará Central Domain (CCD) is limited to the northwest by the Transbrasiliano Lineament and Senador Pompeu Lineament to the southeast. It consists of four geotectonic units: the Archean Nucleus, the Paleoproterozoic Basement Gneiss, Supracrustal rocks of Proterozoic (undivided Neoproterozoic) age (Garcia et al., 2014), and the Santa Quitéria continental magmatic arc (Fetter et al., 2003; Arthaud et al., 2008). In addition, a network of secondary faults exists between the Transbrasiliano and the Senador Pompeu lineaments, the best known being the Tauá and the Rio Groaíras faults (Fig. 1c).

The Transbrasiliano Lineament (TBL) (Schobbenhaus et al., 1975) is a NE-SW-trending relic (Brito Neves and Fuck, 2013) of an active mega-suture zone of a subduction zone formed during the Gondwana amalgamation and post-collisional shearing at the end of the Proterozoic and the beginning of the Paleozoic (Brito Neves and Cordani, 1991; Almeida et al., 2000). It stretches out from the boundary of the Rio de la Plata and Pampia Cratons in Paraguay and Argentina until the Brazilian coast in NW Ceará (Rapela et al., 2007; Ramos et al., 2010), and continues further into the African continent, from the coast of Togo until Central Algeria (Trompette, 1994; Cordani et al., 2003; Arthaud et al., 2008; Attoh and Brown, 2008). It stands out as a continental-scale discontinuity in aeromagnetic images and geomagnetic anomaly maps (Fairhead and Maus, 2003), characterized by low s-wave velocities (Feng et al., 2004), Bouguer and isostatic anomalies (Sadowski and Campanha, 2004), remote sensing data, and digital terrain models (Chamani, 2011). According to Costa and Hasui (1988), the first movements along TBL took place around 2050–2220 Ma in Central Brazil, controlled by sinistral kinematics. Brito Neves and Fuck (2014) described extrusion tectonics, accompanied by seismicity and faulting, thus favoring the emplacement of uprising material. Amaral et al. (2017) define a sinistral kinematics under brittle conditions from Upper Ordovician onwards.

The Senador Pompeu Lineament (SPL) is a shear zone formed during the early to middle Proterozoic (Saadi et al., 2003). It trends roughly N40°E, subparallel to TBL, and stretches out into Africa as the Ile Ife Fault (Trompette, 1994). SPL was supposedly reactivated during the Brasiliano Orogeny (650 Ma) and again in the Mesozoic (Saadi et al., 2003). The geochronological data of ca. 0.59 Ga obtained for syn-shear granite intrusions in the Senador Pompeu Shear Zone (Nogueira, 2004) indicate that the movement is younger than the nappe emplacement in Ceará Central Domain (Arthaud et al., 2008). The kinematics was probably right-lateral strike-slip faulting, judging from the analysis of regional morpho-neotectonics and the neotectonic stress field of the northern part of NE Brazil (Saadi et al., 2003).

The roughly NNW-SSE-trending Tauá Fault southwest of CCD appears to be connected to both TBL and SPL fault systems. Kinematic indicators suggest sinistral shearing, with an estimated 30–35 km horizontal displacement (Neves, 1991). According to Neves (1991), the level of exposure of the Tauá Fault gradually reached shallower structural levels as the deformational regime changed from ductile to semi-ductile and then to semi-brittle.

The ca. 100 km-long Rio Groaíras Fault (RGF), located to the east of the Tauá Fault, signals an NW-SE-trending shear zone between TBL and SPL. In addition, cataclasite, ultracataclasite and pseudotachylyte along RGF define sinistral shearing occurring under brittle conditions.

The Santa Quitéria Continental Magmatic Arc (SQCMA) covering approximately 40,000 km² and records several magmatic pulses during which large volumes of magma intruded as veins, layers, sheets, and plutons (Fetter et al., 2003; Arthaud et al., 2008). Araujo et al. (2014) report the initial (primitive) stage of the intraoceanic arc characterized by the “Lagoa Caiçara Unit” at around 830 Ma. The large variety of rocks includes gabbro, tonalite, monzogranite, granodiorite, and granite emplaced in at least two major magmatic cycles. In addition, U–Pb zircon and Sm–Nd whole rock data indicate emplacement of magmas related to the development of this arc from 640 to 611 Ma and 665 to 591 Ma, respectively (Fetter et al., 2003; Castro et al., 2012).

The following stage included syn-collisional deformation and the formation of NW- and SE-dipping thrust fronts (Araujo et al., 2014). This syn-collisional stage led to the formation of an internal boundary-parallel foliation. The metamorphic ages range in the 640-615 Ma interval and suggest coeval regional metamorphism during emplacement (Garcia et al., 2014; Araujo et al., 2014). The second deformational stage is controlled by an oblique collisional setting, in which the NW-SE trending Tauá Fault, Rio Groaíras Fault, Val Paraíso Fault, and Alto Alegre Fault formed. Later post-tectonic granite intrusions, such as the Serra da Barriga, Pajé, and Taperuaba plutons, represent the late magmatic stages, followed by the last magmatic activity represented by aplite and pegmatite dykes.

The airborne gamma-ray spectrometric data were provided by the Geological Survey of Brazil (SGB/CPRM). The acquisition was carried out along N–S flight lines spaced at 500m, with tie lines in the E-W direction spacing of 10 km. Detailed information is given in the CPRM reports (CPRM, 2009). The gamma-ray spectrometric method is used to estimate concentrations of radioelements, i.e., potassium, uranium, and thorium, in rocks and soils at the Earth's surface by measuring the intensity of the gamma-ray radiation that radioactive isotopes of these elements emit during their radioactive decay. Only gamma-ray radiation has sufficient range for airborne geophysical surveying to aid in bedrock and surficial geological mapping. Therefore, gamma-ray imagery allows the depiction of otherwise concealed, hidden, or previously undetected faults.

The faults were interpreted along with linear gamma-ray spectrometric anomalies and breaks in anomaly patterns visible on the map. Many linear features dislocate geological packages of the same signature, thus showing fault-like characteristics. Most of these features are brittle, but some indicate ductile conditions, as shown in Fig. 2a–b under numbers 1 to 3. Numbers 4 to 7 indicate evidence of brittle dislocations.

The first approach is to identify geological packages of similar signature and distribution. The ones being considered of importance are colored on the map (Fig. 2a). A dislocation or rupture of these geological packages along a gamma-ray linear anomaly suggests the existence of faults and the direction of dislocation and deformation of the material can indicate their kinematics, reactivations, and approximate rheologic behavior.

Some of the geological packages depicted in this study are identical to the ones described and displayed in geological maps – such as the SQCMA and minor granitic intrusions (e.g., Pajé granite), which have been displaced along the already discovered and described Tauá (TF) and Rio Groaíras (RGF) faults. The gamma-ray spectrometric data suggests, at least for RGF, a double reactivation with opposing kinematics (paleo-dextral ductile) and sinistral kinematics under brittle-ductile conditions – see numbers 1 and 4, respectively, in Fig. 2a–b). Other geological packages with similar signature have not yet been described as individual geological units but appear as blocks of the same or similar material only in the gamma-ray images. In the map shown in Fig. 2a, it is possible to note that these geological blocks are clearly crosscut in a roughly E-W direction and displaced laterally along with five linear anomalies. Most of these transcurrent faults have not yet been described in the literature.

The Juá Fault (JF) appears to be sinistral and crosscut and dislocated sinistrally two blocks of SQMA under brittle conditions (Fig. 2a–b, number 7). For the Val Paraíso Fault, dextral movement under ductile and brittle conditions is indicated (numbers 2 and 5), even though relative movement seems sinistral. The central Alto Alegre Fault (AAF) experienced dextral kinematics under ductile conditions (along the E′ part of the fault; number 3), while its W′ branches crosscut and displaced younger granites sinistrally under brittle conditions (number 6). For the Alto Alegre Fault, two dislocation phases have been identified: ductile, paleo-dextral kinematics, followed by sinistral reactivation under brittle conditions.

The deformational history of the SQCMA was triggered by lithospheric convergence that began around 900-800 Ma and is represented by the formation of the intraoceanic Lagoa Caiçara Magmatic Arc (Araujo et al., 2014). The evolution of this convergence allowed the generation of the continental arc and continental collision under high temperature (migmatites and granulites) and ultra-high pressure (Santos et al., 2015) conditions around 650-620 Ma (Fetter et al., 2003; Amaral et al., 2015; Santos et al., 2015). As a result, SQCMA shows an elongated N–S configuration in its central-southern portion, rotation towards NE-SW, and another rotation towards E-W of its northern part (Fig. 2). The metasedimentary rocks bordering SQCMA also confirm this orientation pattern. In the central portion of SQCMA, where the highest temperature conditions prevailed during the crustal anatexis between 620 and 600 Ma, abundant migmatites, diatexites and granitic-granodioritic nuclei occur. Due to the partial melting of these rocks, foliation patterns vary, reflecting the local degree of melting; however, N–S to NE-SW directions and low-angle dips predominate (Fig. 3a-b-c-d). The stretching lineation is weak, plunging gently towards W or NW to NNE.

There is a gradual passage to different migmatites, metatexites, and gneisses towards the edges. Along the edges, massive para-derived sequences crop out, represented by schist, sillimanite gneiss, kyanite-garnet gneiss, quartzite, marble, and calc-silicate rocks. Intercalated in the para-derived sequences, ultra-high pressure metamafic rocks occur.

Structural analysis indicates that ductile shear zones related to thrusting are the most remarkable features in the study area and show a double-verging system with the thrust-shear planes plunging eastward on the western side of the arc and eastward on the western side of it. The thrust-shear zones limit SQCMA and are characterized by low-to medium-angle foliation, usually with down-dip lineation. The thrust fronts move according to the regional structure of the arc (Fig. 2).

The principal structural features that characterize the Neoproterozoic compressive deformation are preserved as penetrative gneissic layering defined by flattened, stretched, and aligned plagioclase, amphibole, mica, and quartz and a mineral lineation evidenced by aligned biotite, feldspar, muscovite, sillimanite, and quartz. The gneissic banding comprises parallel layers of mafic and quartz-feldspathic composition and interlayered mafic-ultramafic bodies. High-strain zones are characterized by gradational evolution of augen-gneiss into schist and then ultramylonite quartzite. Associated elongated mafic-ultramafic bodies (mafic granulite and retrograde-eclogite) and garnet-bearing leucogranite strongly suggest that the principal deformation is responsible for crustal accretion and exhumation of these rocks in the western domain. This evidence is highlighted by preserved down-dip, medium-plunging (30°) stretching lineation in the metabasic rocks that attest to the considerable exhumation rate of these rocks.

Towards the SQCMA eastern margin, the transition to the Lagoa Caiçara Unit metatexites and gneisses occur in diffuse patterns. In this sector, the regional foliation shows a direction that conforms with the contour of the arc, dipping moderately (15°-45°) towards NW and N. Along the SQCMA western and eastern edges, massive para-derived sequences represented by schist, sillimanite gneiss, kyanite-garnet gneiss, quartzite, marble, and calc-silicate rocks crop out frequently intercalated with ultra-high pressure metamafic rocks. Fold axes have a SE orientation and resulting from E-W and NW-SE shortening that developed isoclinal recumbent to open folds. Kinematic indicators such as asymmetric feldspar, S–C structures, mica fish, and microfolds indicate the sense of shear with different orientations in the peripheral areas (Fig. 3).

Although the principal structure present in this domain is a NE-SW- to N–S- and E-W-trending thrust fault system that displays a consistent down-dip to oblique stretching lineation, an important set of strike-slip shear zones also occur in the area. The evolution of the compressional regime causes both the formation of NW-SE transcurrent zones and the progression of thrust zones to transcurrent zones. This evolution occurs clearly in the SQMA eastern and western portions, where vertical foliation and sub-horizontal stretching lineation result from lateral escape tectonics (Fig. 3e-f-g-h).

The thrust fronts of the SQCMA western portion progressively evolve to transcurrent systems, evidenced by the verticalization of the main foliation and progressive clockwise rotation of the E-W down-dip stretching lineation from the interior of the arc towards NE-SW, probably under the influence of the Transbrasiliano westward lineament (Fig. 2). Several decameter-sized transcurrent lineaments have been identified in the field, as suggested in the regional interpretation of the gamma-ray spectrometric images. The transition from thrust to transcurrent tectonics is indicated in the outcrop by stress accumulation and the development of vertical planes, sometimes associated with high-temperature deformation with associated migmatization (Fig. 3e) that truncates the low-angle foliation. At a more advanced deformation stage, low-angle tectonics is completely obliterated by transcurrent tectonics (Fig. 3f-g-h). The ductile faults are both sinistral and dextral, mainly striking NNW-SSE to NE-SW. The NW-SE strike-slip faults are represented by the Rio Groaíras, the Val Paraíso, the Alto Alegre, and the Juá faults.

In contrast to other localities in the Borborema Province, strike-slip faults are less abundant in the Ceará Central domain. NW-SE-striking transcurrent zones show that they were active at relatively high temperatures within the sillimanite zone. However, the most important transcurrent fault in the study area is the Rio Groaíras Fault, which boundary the Itataia and Santa Quitéria tectonic blocks. Mylonite to ultramylonite gneissic rocks has been found along the fault zone developed under amphibolite-greenschist metamorphic conditions (Fig. 4a–b). Kinematic indicators show that orthogneiss ductile conditions evolved from initially high-temperature dextral shearing and associated superposed incremental deformation to sinistral movements under greenschist conditions. The NW-SE-trending Rio Groaíras Fault, which displaces the Pajé granite under brittle conditions, reveals a closer look at overall sinistral kinematics under simple shear, forming drag folds in a brittle-ductile environment (Fig. 4c). The dissected quartz veins in the Pajé granite indicate dextral movement (Fig. 4d). Furthermore, granitic gneiss was affected by two different fracture systems: NNW-SSE-trending epidote-filled fractures sinistrally displaced by NNE-SSW-trending minor faults and simple ENE-WSW-oriented fractures (Fig. 4e) and forming fault breccia (Fig. 4f).

The Val Paraíso Fault develops a N-NE medium-angle foliation with an associated low-angle stretching lineation towards SE and E in a lateral ramp context, apparently adjusting to the shear sense of the fault, suggesting dextral kinematics under ductile conditions (Fig. 4c). In addition, this fault appears to have been reactivated under brittle conditions with dextral kinematics (Fig. 4k-l), forming decimeter-scale dextral faults. Significant accumulations of rounded centimeter-to decameter-sized quartz blocks exist in between outcrops of gneissic or pelitic material.

The Alto Alegre Fault creates a lateral ramp whose NW-SE-trending, low-to medium-angle foliation plane develops directional stretching lineation (Fig. 4d). Mylonites developed along this fault and kinematic sensors show that dextral movement took place. The S side of the presumed fault shows a foliation of 025/30 and 010/35 orientation. These values correspond to a roughly parallel s-plane orientation of a possible E-W-trending fault.

The progressive change from ductile to brittle conditions is not evident in the area under study, even though drag folds with hinge thickening have been found along the Rio Groaíras Fault, indicating a brittle-ductile regime. The dissected quartz veins show intralayer dextral movements, even though the overall sense shear appeared to be sinistral (Fig. 4 e-f). The brittle behavior is well recorded as reactivations along the previously described ductile transcurrent faults. The brittle and cataclastic faults appear to be mostly sinistral with an overall E-W to NW-SE trend. Their trend and kinematic behavior align with the kinematics and trends from the major shear zones identified in the gamma-ray spectrometric images. For all inspected shear zones, movements under brittle conditions have been recognized. The Juá Fault appears to have formed entirely under brittle conditions, but not necessarily later than RGF, AAF, and VPF, only closer to the surface, hence under lower-temperature conditions.

In the surmised fault area close to the Alto Alegre village, several decimeter-sized blocks to meter-sized quartz blocks are scattered in the field, probably remnants of a cataclastic fault. The NE-SW-trending (meter-scale) felsic veins could represent large-scale tensional fractures within a large (almost kilometer-sized) E-W-trending sinistral transcurrent shear zone. Furthermore, along with the westward continuation of the Alto Alegre Fault, monzogabbro dykes were emplaced subparallel to the brittle orientation of the host rock.

To the NW, close to the village Juá, a sinistral cataclastic fault occurs with the fault surface dipping 010/80 and crosscutting a granite with interbedded amphibolitic layers (268/16; 284/15). Kinematic indicators clearly show a sinistral shearing. A probable continuation of this fault has been found westwards (Fig. 3), with fault surface dipping 045/55 and showing sinistral kinematics, and eastwards in a granite cave with a cataclastic fault dipping 020/85.

The U–Pb zircon ages for the igneous plutons and dykes were obtained by LA-ICP-MS at the Isotope Geology Laboratory of Institute of Geosciences (University of Campinas) using a Photon Machines Excite 193, equipped with a two-volume HelEx ablation cell, coupled with an ICP-MS Thermo Fisher Element XR, following the analytical procedures in Navarro et al. (2015). The laser operating conditions were 10-Hz frequency, 40-s ablation time, and fluence compatible with a spot size of 25 μm in diameter. Zircon 91500 was used as primary reference material (Wiedenbeck et al., 1995), and the Peixe zircon (Navarro et al., 2017) as quality control reference material. Data were reduced using Iolite v2.5 (Paton et al., 2011), which involves subtraction of gas blank followed by downhole fractionation correction compared with the behavior of reference zircon 91500.

Defining the chronology of deformational events is not trivial. Using igneous bodies affected by these events or emplaced in large structures or undeformed igneous rocks helps define the relative timing of the deformation event. The Ceará Central Domain encloses several granites and igneous bodies with a wide range of ages. Some of them are closely connected to ductile events, especially with the ductile and brittle strike-slip shear zones. Thus, we collected samples from five igneous bodies (located in Fig. 1) that present robust field control relative to the deformational events, such as: i) calc-alkaline granitic augen-gneiss related to the Santa Quitéria Continental Magmatic Arc (sample VC-52); ii) granite and diorite elongated along the NW-SE Tauá Shear Zone (respectively samples TJRK-39 and TJRK-40B); iii) ductile undeformed rhyolite Tauá dyke emplaced in the Archean-Paleoproterozoic Cruzeta Complex (sample TJRK-42), and iv) post-tectonic Pajé granite (samples TJRK-43 and TJRK-45) and monzogabbro dike along the E-W Alto Alegre Fault (Fig. 5a-b-c-d-e-f).

For all six samples, the cathodoluminescence (CL) images of the selected zircon grains for U–Pb dating show that lengths vary from 70 to 250 μm, width-to-length ratios from about 1:1 to 1:8, and external morphology from subhedral to euhedral (Fig. 5g). Some zircon grains are broken but define an incipient prismatic habit with bipyramidal termination. The internal texture is essentially oscillatory zoning. No overgrowth is visible around the zircon grains. Combined with high Th/U ratios (0.21–1.76; Table 1), these features indicate that the ages obtained for the analyzed grains represent primary crystallization. The continental arc-related magmatic bodies underwent intense deformation and metamorphism ranging from incipient greenschist facies to partial melting, generating diatexites. The Santa Quitéria calc-alkaline granite (Fig. 5a) shows a mylonite texture with foliation parallel to the regional trend and usually down-dip stretching lineation. U–Pb zircon data defined a Concordia age of 640 ± 3 Ma (Fig. 6a), interpreted as the crystallization age of the Santa Quitéria granite.

The Tauá granite (sample TJRK-39) shows moderate ductile deformation with a low-dip foliation (Fig. 5b) and is elongated along the NNW-SSE-trending sinistral Tauá shear zone. Twenty zircon grains defined a Concordia age of 583 ± 3 Ma (MSWD = 0.83) (Fig. 6b). A diorite facies (TJRK-40B) related to the Tauá magmatism shows incipient ductile deformation (Fig. 5c), probably because it occurs farther from the shear zone. Twenty-four zircon grains were analyzed, and twelve grains yielded ±3% concordance and defined a Concordia age of 594 ± 3 Ma (MSWD = 1) (Fig. 6c). Further NE of the Tauá shear zone, two NW-SE-trending dyke swarms of subvolcanic nature occur. Thirty-seven zircon grains were analyzed, and thirty-four grains conformed to the concordance criterion (100 ± 5%), pointing to a Concordia age of 583 ± 3 Ma (MSWD = 1.4) (Fig. 6d). The monzogabbro dyke (TJJV-130) along the E-W Alto Alegre Fault shows a concordance zircon age of 541 ± 4 Ma (Fig. 6e). Zircons from two post-tectonic Pajé granite rock types were analyzed: the light gray coarse-grained facies (sample TJRK-43 – Fig. 5e), and the fine-grained facies (sample TJRK-45 – Fig. 5f), containing subvolcanic xenoliths. The Pajé granite is crosscut and sinistrally dislocated by the Rio Groaíras Fault reactivation. Twenty-two zircon grains from sample TJRK-45B yielded mean crystallization ages of 536 ± 3 Ma (Concordia age, MSWD = 1.4) (Fig. 6f). Zircon grains from sample TJRK-43 indicate two different populations in the Concordia diagram. Five zircon grains from the older population define a Concordia age of 533 ± 4 Ma (MSWD = 0.83) (Fig. 6g). Five zircons from the younger population show a Concordia age of 506 ± 6 Ma (MSWD = 0.56) (Fig. 6g), which corresponds to the crystallization age, while the older population is interpreted as inherited zircons from the older granite facies.