U-Pb zircon age of Ediacaran Umarizal Granite Suite and emplacement mechanism with high-T hornfels generation in Jucurutu Formation, Borborema Province, NE, Brazil

The Borborema Province, NE Brazil, is marked by several Ediacaran granitic plutons that generated high-temperature metamorphic aureoles in the country rock. However, information about magma emplacement, age of plutonism, and metamorphic conditions are necessary to understand this scenario. To this end, we present field, petrographic, and zircon U-Pb geochronological data for migmatized hornfels and intrusive Umarizal and Tourão-Caraúbas plutons. The field features allowed the construction of a structural evolution model starting with high-temperature sinistral strike-slip shear zones followed by dextral strike-slip movement associated with the magmatic emplacement. Mineral paragenesis of andalusite/sillimanite, garnet, scapolite, and phlogopite in country rocks within the metamorphic aureole indicate temperatures of at least 700-800°C and pressures lower than 4.5 kbar corresponding to the pyroxene hornfels facies. Zircon U-Pb ages of 563.7 ± 6.2 for the Umarizal granite, 589 ± 4.4 Ma for the Tourão-Caraúbas granite, and 580.5 ± 4 Ma for the neosome from contact aureole were obtained. The results show that magma emplacement and HT/LP (high-T/low-P) contact metamorphism were synchronous with a transtensional event. These features suggest a late- to post-tectonic context, following the collapse of the Brasiliano/Pan-African orogenetic chain, that favored Late Ediacaran plutonism and synchronous HT/LP metamorphism.


INTRODUCTION
The Borborema Province (BP) resulted from the collision of two blocks, the Amazonian / São Francisco and the West Africa / São Luís cratons, with tectonic stabilization during the Brasiliano / Pan-African orogenesis (Almeida et al. 1981). This province is limited to the west by the Parnaíba Basin, to the north and east by Meso-Cenozoic sedimentary covers, and to the south by the São Francisco Craton (Fig. 1). This province is made up of a complex mosaic of variably migmatized tectonic blocks amalgamated during the Brasiliano / Pan-African collage. It shows an interconnected network of shear zones, which delimit a voluminous Neoproterozoic intrusive magmatism (Vauchez et al. 1995, Oliveira and Medeiros 2018. Neoproterozoic magmatism has been subdivided according to structural, petrographic, geochemical, and geochronological data. In particular, for the Rio Grande do Norte Domain (RND), Nascimento et al. (2000Nascimento et al. ( , 2008Nascimento et al. ( , 2015 and Angelim et al. (2006) rearranged the various Ediacaran plutons into the following suites: Calc-Alkaline, Shoshonitic represented by São João do Sabugi pluton, High-K Calc-Alkaline Porphyritic represented by Itaporanga pluton, High-K Calc-Alkaline Equigranular represented by Dona Inês pluton, Alkaline represented by Catingueira pluton, and Alkaline Charnockitic represented by Umarizal pluton, the latter being the subject of this study (Fig. 2).
One striking feature of this Ediacaran plutonism is its time correlation with high-temperature (650-850°C) and low to medium pressure (3-5 kbar) contact metamorphism associated with anatexis and thermal aureoles over the adjacent host units (Galindo et al. 1995, Souza et al. 2006, 2017a, 2017b contact of the Umarizal pluton. Integration of these data with those available in the literature allows a better understanding of the structural and kinematics control as well as the pressure and temperature conditions involved in the emplacement of magmas at the end of the Neoproterozoic in this part of the RND. In this regard, the emplacement mechanism and the precise time interval of the high-temperature and low-pressure event observed on supracrustal host rocks are refined.

METHODS AND ANALYTICAL TECHNIQUES
This work was carried out through three distinct steps: • careful review of available bibliographic and cartographic surveys including a compilation of available data from the regional literature and processing of digital images from aerial photographs (1:70,000 scale), and satellite images Landsat-7 / ETM+ and Landsat-8 / OLI; • visit to key outcrops for a detailed description of lithological contacts, crosscutting relationships, and distribution of mineral phases related to the contact aureole; • zircon U-Pb geochronology applied to both plutonic rocks and neosome of migmatized hornfels nearby intrusive contacts.
To conduct the last step, the samples were fragmented with a jaw crusher, followed by 250 mm grinding of these rocks, manual batting techniques, and mineral separation by methylene iodide and Frantz magnetic separator. Zircon grains were selected manually with a binocular loupe, mounted on epoxy resin, and, finally, imaged by cathodoluminescence. All of these procedures were conducted at the Geoscience Institute of Universidade de Campinas (IG / Unicamp). The isotopic data were also obtained at IG / Unicamp on an ICP-MS Element XR (Thermo Scientific) coupled to an Excite193 laser ablation system (Photon Machines) with HelEx ablation cell (25 μm laser beam). Data were reduced with the Iolite software and compared with the reference zircon 91500 (1065.4 ± 0.3 Ma; Wiedenbeck et al. 1995) and with the Peixe zircon (564 ± 4 Ma, Navarro et al. 2017) for data quality control.

GEOLOGICAL CONTEXT
The study region is inserted in the Rio Grande do Norte Domain (RGND), northeastern of BP (Fig. 2). It consists of a Paleoproterozoic gneissic basement (Caicó Complex; Jardim de Sá 1984, over which Neoproterozoic metasedimentary sequences of the Seridó Group were deposited. This group is composed of three formations: Jucurutu (paragneisses with lenses of marble and calc-silicate rocks) at the base; Equador (quartzite and metaconglomerates) in the middle portion; and Seridó (micaschists) on top. These lithologies are intruded by plutonic bodies with distinct petrographic and geochemical characteristics (Silva et al. 2015. In the study area, the contact of the Umarizal pluton with the Jucurutu Formation host rocks is intrusive and marked by an expressive thermal aureole at the hornblende to pyroxene hornfels facies. In this region, Portalegre (PaSZ) and Frutuoso Gomes (FGSZ) shear zones are interpreted as synchronous or late tectonic to the collision of São Francisco and Congo cratons, and probably controlled the emplacement of Ediacaran granitic plutons (Galindo et al. 1995, Vauchez et al. 1995, Archanjo et al. 1998, Trindade et al. 1999. According to Hackspacher and Legrand (1989), mineral associations and metamorphic textures indicate that mylonitization in the PaSZ reached temperatures between 500-350°C and pressures of 5-2 kbar at greenschist facies; with an estimated geothermal gradient of ~20°C/km. However, porphyritic granite emplaced in the PaSZ displays mineral paragenesis compatible with the amphibolite facies, which suggests that the greenschist facies record would be linked to a later retrometamorphic event, unrelated to plutonism (McReath et al. 2002).
The geological mapping conducted in this research (Fig.  3) revealed that the Charnockitic Alkaline Suite (ChAlk) is composed of the main body, the Umarizal pluton, having an area of ~300 km 2 , in addition to nearby smaller satellite occurrences. This pluton crosscuts the Caicó Complex, which is constituted by migmatitic gneisses, and metasedimentary rocks (biotite gneisses, marbles, calc-silicate gneisses) of the Jucurutu Formation and the Tourão-Caraúbas pluton (observed as stocks or dykes; Fig. 3). The best records of the contact metamorphism on country rocks adjacent to the pluton appear in paragneisses and marbles of the Jucurutu Formation (Fig.  4A). This metamorphic aureole is marked by andalusite and garnet porphyroblasts and acicular sillimanite (Figs. 4B and 4C), besides recrystallized granoblastic mosaics of calcite in marbles ( Fig. 4D) with or without phlogopite.
Migmatized hornfels can develop banded (stromatic), schlieren, or nebulitic features. The contact between these rocks and the Umarizal pluton is sharp or irregular, and on the edge of the pluton, there is decreasing grain size along the chilled margin, as it is common in intrusive bodies (Fig.  5A). In country rocks, neosomes vary in compositions from tonalite, biotite-garnet-bearing quartz syenite to granite. In these rocks, fine-grained (< 1 mm; Winter 2013), equigranular, granoblastic, and/or lepidoblastic texture and banded appearance are identified. In tonalitic type (Fig. 5B), its composition includes plagioclase, quartz, hornblende, and biotite. Quartz syenite neosome (Fig. 5C) is composed of quartz, plagioclase, K-feldspar, garnet, biotite, muscovite, titanite, and opaque. Granitic type (Fig. 5D) tends to be slightly porphyritic, and has K-feldspar, quartz, plagioclase, biotite, and minor garnet and opaque. McReath et al. (2002) and Sá et al. (2014) published U-Pb zircon ages for the Umarizal pluton of, respectively, 593 ± 5 Ma and 601 ± 11 Ma. Souza et al. (2017b) reported zircon U-Pb Concordia age for a neosome close to the pluton border of 583 ± 1.8 Ma. The occurrence of microgranitic dykes of the Umarizal granite crosscutting the westward contact of the Tourão-Caraúbas batholith ( Fig.  6), for which an earlier titanite U-Pb age of 580 ± 4 Ma is reported by Trindade et al. (1999), suggests that the different Ediacaran plutonism in the study region is coeval within a short time span of 10-5 m.a.

Umarizal granite
The Umarizal pluton encompasses three petrographic facies named Umarizal, Lagoa, and Ação. The Umarizal facies corresponds to quartz monzonites and quartz syenite with fayalite and/or orthopyroxene and minor hedenbergite, Fe-edenite, and biotite. The accessory phases are allanite, magnetite, ilmenite, zircon, and apatite. The Ação facies is restricted to the northeastern portion of the main body, and consists of monzogranites with quartz + hornblende symplectites, Fe-edenite and biotite, and accessory allanite, apatite, zircon, ilmenite, and titanite. Rapakivi varieties may occur occasionally (Galindo 1993, Galindo et al. 1995. The Lagoa Facies crops out as satellite bodies intrusive into the Tourão granite and has granite composition and mineralogy like those of the Ação Facies. It shows fayalite-rich olivine with skeletal habit and partial resorption texture, besides forming double corona with grunerite and hornblende (Fig. 7A). Hornblende and vermicular quartz symplectites delineating a corona around diopside-hedenbergite ( Fig. 7B), as well as myrmekite, pertithe, and mesoperthite textures are also found.
Gabbro-norite is associated with the Umarizal pluton and form decimetric enclaves and small stocks with up to 0.2-0.5 km 2 of outcropping area. They have mafic mineralogy  composed of orthopyroxene, clinopyroxene, and biotite, with diopside-hedenbergite and titanite as accessory phases. Hornblende and vermicular quartz symplectites also occur as corona in enstatite-rich pyroxenes, like those found in the Umarizal Granite.

Country rocks
Paragneisses, marbles, and calc-silicate gneisses from the Jucurutu Formation appear in the SW portion of the area or as mega xenoliths within the Umarizal pluton. Marbles and calc-silicates crop out as discontinuous NE-SW oriented lenses of kilometer-sized and extend to E-W when approaching the Patos Shear Zone. Microscopically, they show granoblastic, fine-to medium-grained equigranular texture, and vary from calcitic, pure marbles to impure types (Figs. 8A and 8B). There are continuous millimeter-to centimeter-thick bands defined by alternations of carbonate-rich (predominantly calcite) and actinolite-tremolite-rich layers, in addition to minor diopside-hedenbergite, phlogopite, and meionite-rich scapolite (Figs. 8C and 8D). Plagioclase, quartz, microcline, titanite, and epidote occur as accessories phases. Morais Neto (1987) and Archanjo et al. (1998) report occasional occurrences of forsterite-rich olivine and wollastonite.
Paragneisses occur in the S-SE portion and as mega xenoliths within the Umarizal pluton, both commonly partially migmatized. They show migmatitic features extending up to 1-2 km from the contact with the intrusion. The mineralogical composition of paragneiss is marked by quartz, plagioclase, biotite, garnet, and sillimanite (Figs. 8E and 8F), besides andalusite, chlorite, muscovite, epidote, titanite, and hornblende as accessories.
U-Pb results for 54 spot analyses from the SS4 sample (Tourão-Caraúbas Granite) are shown in the Supplementary  Table A1. Zircon grains show oscillatory or complex zoning, elongated prismatic habits and bipyramidal grain shape (
U-Pb results of 48 spot analyses from the SS21 sample (Umarizal granite) are shown in Supplementary Table A2. Zircon grains have an average length (L) of 244 ± 56 μm, width (W) of 76 ± 18 μm, and L/W ratios = 3.3 ± 1.0 and Th / U of 0.58 ± 0.11 (Th = 99 ± 199 ppm, U = 194 ± 474 ppm). They are generally euhedral, elongated prismatic crystals, homogeneous, usually zoned due to overgrowth slightly younger rims, suggestive of continuous crystallization of two generations of zircon, with some grains exhibiting older internal portions (Fig. 10A). This    is reflected in the high error in calculated ages. Spots analyses < 10% discordant (Fig. 10B) provide a 206 Pb/ 238 U weighted average age of 565 ± 22 Ma (MSWD = 2.3). However, using a probability diagram for 206 Pb/ 238 U age distribution for the spots with < 5% disagreement (Fig. 11A), two distinct groups are observed, within the error range, and with very good statistical parameters. Four spots from a younger group, characterized by oscillatory zonation, corresponding to the grain edge (Fig. 11B), resulted in a 206 Pb/ 238 U weighted average of 563.7 ± 6.2 Ma (MSWD = 0.21). The oldest group, observed in homogeneous zircons or core portions, which may have patchy-type zoning (Fig. 11B), encompassing 32 spots, produced a 206 Pb/ 238 U weighted average of 587.2 ± 2.3 Ma (MSWD = 0.98). A third group, aged > 600 Ma, is considered here as an inheritance. The youngest age (563.7 ± 6.2 Ma) may represent the age of the Umarizal granite, the other dates are interpreted here as inherited ages. An alternative interpretation would be to interpret zircons with 587.2 ± 2.3 Ma as antecrystals (Davidson et al. 2007) possibly related to a mixture of the Umarizal and Tourão-Caraúbas felsic magmas.
Dating a neosome of migmatized hornfels at the border of Umarizal Granite Sample SS59B was collected from the SW contact of the Umarizal pluton. It represents a neosome resulted from the partial melting of biotite-garnet-bearing paragneiss of the Jucurutu Formation. This neosome occurs as injections truncating the paragneiss paleosome and has occasional porphyritic texture marked by microcline phenocrysts (Fig. 5D). Data for 46 spots analyses are shown in the Supplementary Table A3. Zircon grains are prismatic (Fig. 12A), usually bipyramidal, elongated, with mean length (L) and width (W) of, respectively, 261 ± 67 μm and 67 ± 16 μm, and L/W ratio of 4.0 ± 11. They show oscillatory zoning and form a homogeneous population with Th/U ratios of 1.36 ± 0.43 (Th = 215 ± 155 ppm, U = 157 ± 94 ppm), being interpreted as new zircon generated in the fusion process of thermal metamorphism. Spots with <5% discordance provided a Concordia age of 583.8 ± 1.8 Ma (MSWD = 4.0) and a 206 Pb/ 238 U pooled mean age of 580.5 ± 4.0 Ma (Fig. 12B). The latter is interpreted as the age of the thermal event.

TECTONO-METAMORPHIC CHARACTERIZATION
The structural framework of the region is characterized by three tectono-metamorphic events. The oldest events, called D 1 and D 2 , are interpreted to have happened prior to the Umarizal and Tourão-Caraúbas plutonism. The younger event (D 3 ) includes an extensional stage that favored the opening of space for the emplacement of the magmas that originated the Umarizal and Tourão-Caraúbas granites and was taken as concomitant with the contact metamorphism of the country rocks (event Mc). The D 3 event ended with space closure and reactivation of ductile shear zones. Finally, a brittle deformation (D 4 ) is registered by faults, breccias, and cataclasites, corresponding to the reactivation of ancient structures during the Phanerozoic.

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studied region were subdivided into three distinct sectors (Fig.  14), described as follows: • the PaSZ to the north and northwest; • the FGSZ to the west and southwest; • the south of the pluton.
These structural sectors are shown in Figure 14 with the respective projections of structures D 2 and D 3 . The strike of S 2 for most structures agrees with the NE trend of the FGSZ region, with smooth dip, while the PaSZ region has two main structure groups, one with NE-SW direction and strong dip and another with SE strike and dip varying from weak to strong. The southern region of Umarizal also has two main groups, one with ENE-WSW direction and another with E-W direction, with dip changing from weak to strong.
The S 3 structures in the FGSZ region dip mainly to NNW. No such structures were found in the PaSZ region. The third event (D 3 ) is interpreted as being progressive in two stages. The first stage, here called D 3A , is related to a regional distention system, with displacement components to ESE in the SW portion and to NNE in the NW part, which allowed the alkaline charnockite suite to be accommodated synchronously or in the late stage of D 3A . This event is accompanied by high-temperature metamorphism with an injection of nearly concordant neosomes within the gneissic banding and is here linked to the movement of the PaSZ and FGSZ, which delimit the Umarizal pluton. The PaSZ, north of the pluton, has a NE-SW direction and lengthens from the Rio do Peixe Basin (~ 120 km SW of Umarizal) to the Cretaceous Potiguar Basin (~ 25 km NW of Umarizal; Fig. 2).
The D 3A event is responsible for the formation of a subvertical foliation and a subhorizontal stretching lineation in the PaSZ. This area is marked by low-angle extensional shear bands with an indication of transport toward SE (Fig. 15A). The FGSZ, to the west, has an NW-SE direction, curving in the region of Martins to Frutuoso Gomes; it presents a smooth to moderate dip toward NE and predominance of sinistral S/C structures filled with granite neosome (Fig. 15B). The arrangement of these structures suggests that the block east of the FGSZ and south of the PaSZ moved eastward during the D 3A stage. This movement would have generated synformal and antiformal folds with NW-SE directed axial plane S 3 and low angle S/C structures, which opened space for the accommodation of the Umarizal granite, triggering the contact metamorphism process (M C ). This metamorphic event resulted in recrystallization of previous phases and the appearance of the following hornblende to pyroxene hornfels facies paragenesis near pluton contact (< 2 km): • meionite-rich scapolite + calcite + garnet in calc-silicate rocks; • diopside + phlogopite + calcite in marbles; • sillimanite/andalusite + garnet in biotite-gneisses and migmatites derived.
Following Morais Neto (1987) and Archanjo et al. (1998), forsterite and wollastonite in marbles and calc-silicates, and orthopyroxene in leucosomes of the Caicó Complex orthogneisses were also ascribed to the M C event. Kase and Metz (1980) report the equilibrium of forsterite for a temperature range of 530-750°C (reaction R1 below). According to Spear (1995), the growth of orthopyroxene can be linked to the reaction R2 with stability curves between 700 and 800°C and pressure of 0.5 to 16 kbar. On the other hand, the presence of sillimanite / andalusite in partially migmatized biotite-gneisses or pluton mega xenoliths may be related, according to Spear (1995), with partial fusion reactions R3 and R4, under temperature conditions above the temperature of the hydrated granite solidus and pressures < 4 kbar. 1 diopside + 3 dolomite = 2 forsterite + 4 calcite + 2 CO 2 (R1) biotite + plagioclase + quartz = orthopyroxene + K-feldspar + melt (R2) muscovite + plagioclase + quartz = K-feldspar + Al 2 SiO 5 + melt (R3) biotite + Al 2 SiO 5 + plagioclase + quartz = garnet + k-feldspar + melt (R4) The second stage, here called D 3B , is related to a contractional system that overlapped the previous one. It is evidenced by clockwise strike-slip reactivation of the PaSZ and thrusting in the FGSZ. Macrofolds developed in this stage are commonly symmetrical with normal and open style. Lineations related to D 3B show a smooth dip to NE (Fig. 14). This event is also marked by asymmetric porphyroclasts with pressure shadow, recrystallization tail, and S/C shear bands (Fig. 15C). The M 3 metamorphism, related to D 3B , has a retrometamorphic

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Figure 16 outlines an integrated model of evolution considering the structures described above.

Metamorphic P-T conditions associated with the plutonism
Zircon U-Pb dating and petrographic data from migmatized hornfels, metapelites, and granites having contact aureoles in various places of the Borborema Province, in addition to the synchronous (re)activation of a ductile shear zone in a context of high-temperature / low-pressure (HT / LP) conditions, are reported in the literature. These results point out to an important and expressive peak of regional high-grade metamorphic episodes during the Ediacaran (Souza et al. 2006, Archanjo et al. 2013. In paragneisses, mineral associations of the hornblende to pyroxene hornfels occur, locally with garnet (almandine), scapolite, sillimanite / andalusite, and rare hypersthene. Several places show incipient to extensive migmatization of paragneisses, which imply that the partial melting curve for

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hydrated granite system has been reached and, thus, indicate temperatures of at least 620-700°C and maximum pressures of 4.0 kbar (Yardley 1989, Winter 2013. In pure marbles, there is a progressive increase in grain size, whilst in impure marble and calc-silicate rocks, the formation of meionite-rich scapolite is prominent, implying temperatures above 800°C (Newton and Goldsmith 1976, Moecher and Essene 1990, Almeida and Jenkins 2017. Such mineral associations may reflect that the peak of temperature crossed the pyroxene hornfels facies and the anatexis isograd (Yardley 1989, Winter 2013. The occurrence of andalusite and the absence of kyanite and synchronous tectonic fabric, combined with the presence of hornfels along with the pluton intrusion, suggest pressures below 4.5 kbar (Holdaway 1971, Pattison 2001, Pattison et al. 2002, Winter 2013). This means a shallow depth for magma emplacement, at the middle to upper continental crust. The presence of fayalite only in the central portion of the Umarizal pluton could reflect slightly warmer conditions in this region (> 750°C) during magma cooling or some barrier keeping it from hydration (Bucher andFrost 2006, Frost andFrost 2008).
Temperature conditions for the formation of the textures and minerals described above are consistent with an HT / LP metamorphic environment associated with anhydrous intrusions (Winter 2013). The effect of the thermal metamorphism occurs to about 1-2 km from the pluton contact. Additionally, the occurrence of both angular paleosome and rounded and/ or deformed fragments from the host rocks along the pluton contact may imply complex processes of emplacement and could involve superposition of emplacement mechanisms (Barton et al. 1991, Brown and Solar, 1998.

The thermal event and its continental extension
Integration of our new U-Pb zircon geochronological data with previously published results suggest interpreting the geological context of the studied region as follows: • chronocorrelation of Ediacaran magmatic pulses of the Umarizal region in the time range of 580-560 Ma; • the Umarizal suite has an age of 564 Ma, with its other zircons aged 580-600 Ma, inherited from the Tourão-Caraúbas, and the 587 Ma zircons being antecrystals from this pluton. Table 1 summarizes the modal, geochemical, and mineral chemistry between the Tourão-Caraúbas and Umarizal granitoids, based on Galindo (1993), Campos et al. (2016), and our data reported here. The Umarizal magmatism shows rare-earth patterns very similar to those of the Tourão-Caraúbas granitoid, although they are distinct in geochemical and petrographic Figure 16. Suggested tectonic evolution. The process begins with an anti-clockwise extensional movement of the PaSZ coupled with a normal extensional movement of the FGSZ, allowing the emplacement of Umarizal magma and provoking contact metamorphism (Mc) of the host Jucurutu Formation rocks (the D3A event). In the next stage (D 3B ), tectonic inversion occurs, when the PaSZ acquires clockwise kinematics and the FGSZ functioned as thrust fault.

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grounds (Galindo 1993). In addition, this author presents data showing whole-rock geochemical similarity between these two granitoids, especially when comparing parameters such as oxygen fugacity, SiO 2 concentration, #Fe, and mineral-chemical types.
The geochronological results reported herein, and the aforementioned interpretations are both coherent with the intrusion of the Umarizal body into the Tourão-Caraúbas granitoid, as observed through dykes and interdigitated or sinuous contacts (Fig. 6B). These kinds of features suggest that the Tourão-Caraúbas magma was still hot enough to allow the capture of crystals or magma mixture. Although the second hypothesis is incompatible with the age of the analyzed neosome, such a possibility cannot be ruled out considering the regional context.
In a broader aspect, the reported time range (600-580 Ma) encompasses other Ediacaran granitoids intrusive into the Seridó Group and commonly associated with HT/LP metamorphism (Fig. 17), such as the Acari Granite (Itaporanga type; 577 ± 5 Ma - Archanjo et al. 2013;585 ± 6 Ma -Souza et al. 2019), the Totoró Gabbro-Norite and granite (Shoshonite and Itaporanga types, with the respective ages of 595 ± 3 and 591 ± 4 Ma; Archanjo et al. 2013), and the Catingueira pluton along the Patos Shear Zone (Alkaline type; 573 ± 14 Ma; Souza et al. 2017a). These ages match a mineral + whole rock Sm-Nd isochron for peraluminous neosomes (575 ± 2 Ma - Souza et al. 2006;590 ± 3 Ma -Souza et al. 2019), and ages for the Japi Alkaline Granite (599 ± 3 Ma; Souza et al. 2016) and Gameleiras -and Serrinha plutons (573 ± 7 -576 ± 3 Ma; Galindo et al. 2005) to the east of the Picuí -João Câmara Lineament. The presence of all those bodies over an expressive surface area strongly suggests a prominent regional thermal anomaly in this part of the Borborema Province in the late Ediacaran period (600-559 Ma). Lima et al. (1989) proposed temperatures of intrusion in the range 580-700°C and pressures of 4-6 kbar for the region to the east of the Umarizal Granite based on thermobarometric data in pyroxene-hornfels from the contact of Seridó Formation micaschist with the Totoró Gabbro-Norite. Such results are consistent with the emplacement of Ediacaran plutons slightly preceding a regional HT / LP transpressional event around 575 Ma in northeast Brazil and west Africa (Archanjo et al. 2013).
When considering the geological provinces in West Africa as continuous with those of the Borborema province during the Brazilian orogen, it is worth mentioning that a large number of African Ediacaran plutons produced metamorphic aureoles on hosting supracrustal rocks, with geologic, petrographic, metamorphic, and geochronological characteristics akin to those reported here for the Umarizal region. Oyawoye (1962) and Ferré et al. (1997) described gradual contacts between fayalite-quartz monzonite and biotite-hornblende granite at Bauchi and Rahaman (Nigeria) with zircon U-Pb ages of 638-580 Ma for orthopyroxene-bearing granites (Tubosun et al. 1984, Dada et al. 1989) and migmatization of 581 ± 10 Ma (Ferré et al. 1996). Dada et al. (1995) distinguished two charnockite granitoid groups: • calc-alkaline granodioritic association at Toro; • sub-alkaline monzonitic association at Bauchi, Saminaka and Dindima regions.
Considering the whole context described above, the peak of heat flow during the Ediacaran could have triggered a relevant thermal and tectono-metamorphic input for the thermo-tectonic evolution of both the Borborema Province and the geological blocks of NW Africa. Granitic systems on this scale would significantly change the rheological and mineralogical parameters leading to a prominent modification of the continental geothermal gradients (Paterson and Fowler 1993a, Ingram and Hutton 1994, Brown and Solar 1999.

Mechanism of magma emplacement
During the emplacement of syntectonic magmas, features such as foliation, lineation, metamorphic layering, and the shear Table 1. Comparative geochemistry of the Umarizal and Tourão-Caraúbas granitoids. Data compiled from Galindo (1993), Campos et al. (2016), and this work.

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band can develop over the country rocks, as well as composite S/C magmatic fabric, as underlined by Blumenfeld and Bouchez (1988), Benn and Allard (1989), Paterson et al. (1989), and Schulmann et al. (1996). The absence of these features demonstrates that no expressive ductile deformational episode (here named D 3 ) has acted synchronously during emplacement of the Umarizal pluton. Therefore, it is concluded that the ductile fabrics observed on the Jucurutu Formation host rocks were formed shortly before the magma emplacement. According to Galindo (1993), the granitic magma that formed the Umarizal pluton was originated by partial melting of the lower granulitic crust and rose through ductile shear zones (the deformation episode D 3A ). Afterward, Archanjo et al. (1998) suggested a contemporaneity of the pluton with plastic deformation of the country rocks under metamorphic conditions equivalent to the upper amphibolite facies and syntectonically to the reactivation of the FGSZ. Through magnetic susceptibility anisotropy data, Archanjo et al. (1998) suggested a diapiric emplacement for the Umarizal magma, controlled by the shear zone. On the other hand, McReath et al. (2002) suggested a lacolithic geometry having a feeding system underneath the Jucurutu Formation rocks.
Considering the geobarometric conditions operating during magma rising, McReath et al. (2002) advocated that the beginning of crystallization of the magma, which produced the Umarizal pluton, occurred at 7-8 kbar, formed the association fayalite + quartz or orthopyroxene. They also reported the crystallization of amphibole at slightly lower pressures (4.7-5.7 kbar), by using the Al-in hornblende geobarometer. These pressure estimates are within those determined by Campos et al. (2016), in the range 4.8-6.0 kbar for the Tourão-Caraúbas granite that occurs in the same region. Therefore, these pressure ranges do not satisfy the barometric conditions for mineral associations present in the contact aureole of the Umarizal pluton. Based on the presence of andalusite / sillimanite in the contact aureole, the pressure in the region should not exceed ~4.5 kbar for magma emplacement, with the higher pressures possibly corresponding to earlier mineral crystallization phases (Holdaway 1971, Winter 2013. Archanjo et al. (1998) explained the transport and emplacement model for the Umarizal pluton during extensional movements along the FGSZ that allowed migration of magma through a flat structure in the lower crust. Following these authors, the extending shape to the east in the northern portion of the Umarizal body occurs by dextral kinematics control in the PaSZ. However, as considered in this work, the dextral component in the PaSZ would have occurred at a later stage to the extensional movement. Furthermore, in the hypothesis of dextral and extensional kinematics occurring simultaneously in PaSZ and FGSZ, sinistral component would affect the magmatic fabric and the shape of the pluton, which was not observed.  Dantas (1996).
The first stage corresponds to the production of magma by partial melting and its separation from the source region.
Step (2) refers to any models allowing magma to rise through the crust. The third step corresponds to the mechanisms that contribute to the emplacement and accommodation of magma at shallower depths. The mineralogical associations generated during the contact metamorphism of the host rocks allow us to assume a transition region between the middle and upper crusts for the Umarizal pluton emplacement, a situation akin to the one described by Paterson and Fowler (1993b) and Weinberg (1996).
Following the proposal of Paterson et al. (1991), the thermal aureole around the Umarizal body can encompass four main mechanisms: • stopping; • assimilation and / or anatexis of the country rocks; • magma accommodation within spaces generated by an extensional tectonic; • diking.
Among the features corroborating these processes, we outline the following: • the shape of igneous bodies that is usually rounded and unoriented when far from shear zones, but parallelized and more elongated when approaching these structures; • the presence of hectometric or kilometric xenoliths and magmatic breccias (stopping) close to the contact of the igneous body with the host rocks; • following Frost and Frost (2011), the stages of crustal assimilation during magmatic evolution associated to mafic magmas are quite characteristic during the ascension of opx-bearing granitic alkaline magmas; • the occurrence of migmatitic features inside the metamorphic aureoles contouring the pluton; • the absence of compressional ductile structures concomitant to the intrusive body in the country rocks; • the occurrence of normal / extensional oblique structures in the FGSZ; • the sinistral strike-slip structures preceding the dextral kinematics in the PaSZ. Figure 18 illustrates the model proposed for the study area by considering the above arguments. The emplacement system that best fits the geological and structural characteristics of the Umarizal pluton is the one involving laccoliths  / lopoliths and sills / dykes as proposed by Rubin (1993). According to the model, both transport and magma emplacements are controlled by space opened during extensional tectonics (Castro 1987, Hutton et al. 1990, Rubin 1993. Firstly, basaltic magmas, represented by gabbros and norites, originated in the upper mantle and granitic magmas derived from the melting of Paleoproterozoic infracrust (Nd T DM model age of 2.16 Ga, ε Nd (t) of -16.4; Sá et al. 2014) are positioned in magmatic chambers at middle crustal depth. Succeeding the thermal effect provoked by emplacement and cooling of magmas, tectonic reversal occurs, leading to a westward movement of the eastern block and the consequent behavior of the PaSZ and FGSZ with dextral strike-slip and thrusting kinematics, respectively. An alternative emplacement model involves lowering the floor of the magma chamber, with the magmatic intrusion taking advantage of the shear zones and basement/ supracrustal contact, and then migrating northwards. In this case, it is possible to infer that the Umarizal granite is a thin body and its country rocks are exposed in the southwestern portion because of anti-formal folding and subsequent erosion of the granite upper portion.

CONCLUSIONS
The data presented allow us to suggest the following conclusions: • PaSZ and FGSZ were initially evolved, respectively, as sinistral transcurrence and extensional normal, reversing in a second moment to dextral transcurrence and thrusting; • This initial episode led to the opening of spaces that served as magma conduits (mainly by diking) and the formation of laccolith / lopolith magma chamber; • U-Pb zircon dating of neosome from migmatized hornfels and from the Tourão and Caraúbas granites provided the ages of 580 ± 4 Ma, 589 ± 4 Ma, and 563 ± 6 Ma, respectively; • The emplacement of the Umarizal pluton at upper crustal level (4-5 kbar) and high temperatures (~ 800°C) generated contact aureole of up to 2 km width, with stabilization of metamorphic parageneses involving andalusite, sillimanite, scapolite, garnet, and forsterite within metasedimentary host rocks and xenoliths; • It is suggested that the emplacement of the Umarizal and Tourão-Caraúbas granites and the subsequent thermal effect have taken place within a time of ~26 Ma (589-563 Ma); • Since plutonic bodies emplaced at high temperatures in a low-pressure environment also occur in eastern Africa and share similar geological, structural, geochemical, and geochronological characteristics with the Borborema Province, it is conceivable to correlate the charnockitic magmatism to a more widespread episode of thermal input in both regions in the Late Ediacaran.