Borborema Province Research Articles

Amphibole crystallization as a tool for monitoring complex mixing between basaltic and latitic magmas: The Fazenda Lagoas monzonitic stock, Borborema Province, Brazil

Amphibole is the dominant mafic in the quartz monzonite and microgranular dioritic enclaves of the Fazenda Lagoas stock (623 ± 5 Ma), located in the Macururé Domain, in the central region of the Sergipano Orogenic System. Structures and textures in the rocks studied indicate the presence of several pulses of basaltic magma (diorite enclaves) in the latitic magma (quartz monzonites). The magmatic amphibole crystals correspond to pargasite, edenite, tschermakite and Mg-hornblende. The chemical evolution of amphibole crystals occurs through an increase in Si, Mg, vacancy in the A site, and a decrease in Altotal, K, Na, Fe3+ Ca, Ti (substitutions of edenite, tschermakite, and pargasite). Reduction in temperature, pressure, water solubility in magmas, and increase in oxygen fugacity indicate the evolution of the Fazenda Lagoas plutonic system. Amphibole thermobarometry made it possible to calculate the depth and temperature of the earliest interaction between basaltic and latitic magmas at a depth of 27 km, with latitic magma temperatures between 967 and 940 °C. Subsequently, there were several contributions of basaltic magma until the magma chamber at Fazenda Lagoas was ca. 17 km deep. Fazenda Lagoas stock is one of the shoshonite intrusions of the Macururé Domain, the one that has a record of the deepest hydrated basaltic magma, probably at the base of the ancient continental crust of the Sergipano Orogenic System.

A Review of the Mineral Chemistry and Crystallization Conditions of Ediacaran–Cambrian A-Type Granites in the Central Subprovince of the Borborema Province, Northeastern Brazil

Ediacaran–Cambrian magmatism in the Central Subprovince (Borborema Province, NE Brazil) generated abundant A-type granites. This study reviews published whole-rock and mineral chemistry data from thirteen Ediacaran–Cambrian A-type intrusions and a related dike swarm. It also presents new mineral chemistry and whole-rock data for one of these intrusions, along with zircon trace element data for five of the intrusions. Geochronological data from the literature indicate the formation of these A-type intrusions during a 55 Myr interval (580–525 Ma), succeeding the post-collisional high-K magmatism in the region at c. 590–580 Ma. The studied plutons intruded Paleoproterozoic basement gneisses or Neoproterozoic supracrustal rocks. They are ferroan, metaluminous to peraluminous and mostly alkalic–calcic. The crystallization parameters show pressure estimates mainly from 4 to 7 kbar, corresponding to crustal depths of 12 to 21 km, and temperatures ranging from 1160 to 650 °C in granitoids containing mafic enclaves, and from 990 to 680 °C in those lacking or containing only rare mafic enclaves. The presence of Fe-rich mineral assemblages including ilmenite indicates that the A-type granites crystallized under low ƒO2 conditions. Zircon trace element analyses suggest post-magmatic hydrothermal processes, interpreted to be associated with shear zone reactivation. Whole-rock geochemical characteristics, the chemistry of the Fe-rich mafic mineral assemblages, and zircon trace elements in the studied granitoids share important similarities with A2-type granites worldwide.

Composition and age constraints on a Hadean enriched mantle source revealed by the Paleoarchean São Tomé layered intrusion, NE Brazil

Evidence for Hadean depleted mantle reservoir(s) is well-established by mantle-derived rocks from multiple Archean complexes showing excesses in 142Nd compared to the modern mantle. Yet, the existence of an early enriched mantle source, which should have concomitantly formed during these Hadean silicate differentiation event(s), has only been recently confirmed by well-resolved 142Nd deficits measured in Paleoarchean mafic amphibolites from the São José do Campestre massif of the Borborema Province, NE Brazil. To investigate the nature and extent of this early-formed enriched reservoir, a series of samples from the Seridó belt, NE Brazil, have been investigated for their geochemical and coupled 147,146Sm-143,142Nd isotopic compositions, focusing on the Paleoarchean São Tomé layered intrusion. The São Tomé intrusion is composed of layers of metamorphosed mafic and ultramafic rocks with whole-rock trace element compositions and high olivine crystal Ni contents consistent with an incompatible trace element enriched pyroxenitic mantle source. Most analyzed samples from the Seridó belt yielded negative µ142Nd, as low as ∼ -20 (representing the lowest 142Nd/144Nd ratio ever measured in terrestrial rocks), with an average µ142Nd for the São Tomé intrusion of -9.6 ± 1.4. The São Tomé samples interpreted as the least isotopically disturbed yielded an 147Sm-143Nd isochron age of 3551 ± 368 Ma, consistent with previous zircon U-Pb ages, with an initial ε143Nd = -1.7 ± 1.2. Coupling the long-lived 147Sm-143Nd and the short-lived 146Sm-142Nd systems for the São Tomé rocks suggests a Hadean enriched mantle source formed at ∼4.44 Ga with a 147Sm/144Nd of ∼0.18, which may be complementary to the early depleted mantle recorded by Eoarchean rocks from the North Atlantic Craton, possibly formed during magma ocean crystallization. These results also imply that the record of this Hadean enriched mantle source is not restricted to the São José do Campestre massif but extends to a larger portion of the Borborema Province.

Pernambuco-Alagoas, Riacho do Pontal, and Sergipano domains of the Borborema Province, Northeastern Brazil: a geological and geochronological synthesis

Abstract In recent years, the number of works seeking to advance the geological and geotectonic knowledge of the Borborema Province has been increasing. However, in the context of the Southern Borborema Province there are few studies aimed at understanding its tectonic evolution in an integrated way. This work presents a review of the lithostratigraphic and geochronological data available for the Pernambuco-Alagoas, Riacho do Pontal and Faixa Sergipana Domains, located in the southern portion of the Borborema Province (Northeast Brazil), in addition to a discussion on the tectonic evolution model. The Southern Borborema Province fully encompasses the state of Alagoas and partially the states of Pernambuco, Sergipe, Bahia and Piauí, and is delimited to the north by the Pernambuco Lineament and to the south by the São Francisco Craton. The methodology involved bibliographical survey, geological cartography, geochronological compilation, creation of detrital zircon histograms for metasedimentary rocks (with unconformity below 10%) and magmatic “barcodes” for ortho-derived rocks and preparation of regional geological profiles. The tectonic evolution of the Southern Borborema Province began with the breakup of the Rodínia Supercontinent (1000 Ma) during the Cariris Velhos Cycle. The processes involved in the interaction of fragments descending from Rodinia are diachronic, in a broad scenario of accretions and collisions that resulted in the merger of Gondwana. The Pernambuco-Alagoas Block is considered a complex tectonic domain, which was affected by the Cariris Velhos (1000 – 950 Ma) and Brasiliana (740 - 570 Ma) orogenies (Caxito & Alkmim 2023), preserving remnants of Archean rocks (Riacho Seco Fragment) and proterozoic. The Riacho do Pontal Domain and the Faixa Sergipana Domain are part of a large folding system formed from the collision of the Pernambuco-Alagoas Domain with the São Francisco Craton, in a tangential deformation, vergent towards the craton, during the Brasiliana Orogeny. From the ages of the syncollisional granites we can infer that the orogenic event that gave rise to the aforementioned folded bands occurred at very close time intervals, presenting a slight diachronism. The article presents an integrated approach to tectonic evolution, however, the need for new studies is quite evident, with an emphasis on isotopic geology, geochronology, geochemistry and geological mapping that can contribute to the understanding of the processes involved in the formation of tectonic domains, their space-time relationships and their implications for the evolution of the Gondwana Continent.

Tectonic Inversion of Intracontinental Basins and the Conundrum of Plate‐Scale Stress Propagation: The Case of the Jatobá Basin, NE Brazil

AbstractWe chose the Jatobá Basin (JB) in the Borborema Province in northeastern Brazil to address two outstanding problems, basin tectonic inversion and stress propagation, because (a) evidence of tectonic inversion is conspicuous in the JB, and (b) the basin sits on intracontinental northeastern Brazil, far from plate boundaries and the most obvious stress sources. We found robust evidence of oblique reverse faulting inside the basin, putting sediments of the JB's depocenter hundreds of meters above the hard granitic host basement. We also found sound evidence of hydrographic flow reversal, that is, earlier basement‐to‐basin runoff, followed by basin‐to‐basement runoff. This change means that formerly the basement stood higher than the basin, and later the basin was uplifted (inverted) to currently stand hundreds of meters higher than the basement, especially where the gravity anomaly map shows the deepest depocenter. Coarse conglomerates, sourced in the uplifted basin and blanketing the adjacent basement for kilometers, are only cut by the current hydrographic network. From these main lines of evidence, we infer recent basin tectonic inversion (Quaternary, i.e., <2.6 Ma?). The WSW‐ENE orientation of the maximum compressive stress needed to invert the basin likely results from Mid‐Atlantic and Andean pushes. We conclude that lithospheric plates can deform in their cores because of stresses propagating from plate boundaries to distant plate interiors, where the lithosphere has been locally weakened and strain has concentrated.

The origin and fate of organic carbon in graphite–manganese bearing rocks and implications for the Lomagundi–Jatuli Event

Our study helps to unravel the complexity of the Lomagundi–Jatuli event, the largest and longest positive carbon isotope excursion ever recorded on the Earth’s surface, by providing a unique view of Paleoproterozoic graphitic rocks from the Borborema province of Northeastern Brazil. Through detailed mineralogical, textural, chemical and isotopic analyses, we bring a new perspective that provide support to elevated primary productivity and large-scale organic carbon burial during the Lomagundi–Jatuli event. Graphite crystals with distinctive textural features occur in association with silicate and oxidised manganese ores, manganese quartzites, garnetites, and gneisses. The graphites were crystallised at temperatures up to 634 °C, consistent with amphibolite facies metamorphism, according to Raman thermometry. An average total carbon content of 2.1 wt%, with δ13C values ranging from − 15.0 to − 21.5‰, is indicated by whole-rock geochemistry and carbon isotopic composition, respectively. Based on these results, our study proposes that these graphitic rocks may represent remnants of organic matter, possibly derived from bacterial biomass associated with manganese-rich sediments, preserved under reducing environmental conditions in a redox-stratified marine setting. Biological mediation on the origin of silicates is suggested by the close relationship between reduced manganese silicates and graphite. These constraints indicate that Paleoproterozoic graphite-rich rocks represent an important but overlooked reservoir of organic carbon that was partially degassed during the metamorphism of organic-rich sequences. Overall, this research provides new insights for the enigmatic emergence of the Lomagundi–Jatuli event, highlighting the intricate interplay among organic carbon, manganese-rich rocks and Earth's evolutionary processes during this period.

Visible-Near Infrared–Short-Wave Infrared Spectroscopy and Mineral Mapping of Hydrothermal Alteration Zones at the Brejuí W-Mo Skarn Deposit, Seridó Mobile Belt, Borborema Province, Brazil

Abstract The Brejuí W-Mo skarn deposit is the main scheelite deposit of the Seridó tungsten province (Borborema province, NE Brazil). It constitutes the largest Brazilian W ore reserve. The orebodies are hosted in the metasedimentary Jucurutu Formation of the Seridó Group (650–610 Ma), close to the margin of the Neoproterozoic Acari pluton (Brasiliano orogeny). Skarns include prograde and retrograde mineral assemblages. Infrared spectral analysis shows that the skarns mainly reflect retrograde mineral assemblages, formed in three different hydrothermal alteration stages with overprinting. Mineral phases spectrally detected include (1) vesuvianite, actinolite, and phlogopite (alteration stage 1), (2) epidote, prehnite, and illite (alteration stage 2), and (3) laumontite, montmorillonite, chlorite, and gypsum (alteration stage 3; main ore zone). Phlogopite chloritization and actinolite recrystallization were observed in the main W-Mo skarn orebodies. Chloritization is marked by a displacement in the Fe-OH–related absorption wavelength (2,246.5–2,250.5 nm). A spectral index using spectral mixtures of laumontite + montmorillonite + actinolite is proposed here to map mineralized skarn layers (WO3 + Mo ≥ 0.1%) in drill cores. It was used to vector to richer mineralized bodies of the Brejuí deposit successfully and may be applied to similar skarn deposits with the same aim.

Spectral library of gemological minerals from NE Brazil: A reference to aid the reflectance spectra-based discrimination of gem-quality materials

We report a spectral library of gem-quality minerals from NE Brazil and imitation material as a strategic, rapid, nondestructive, and relatively cost-effective tool to be used as a reference to aid in discriminating gemological materials. Our study used spectra data collected by ASD-FieldSpec spectroradiometers (Standard Resolution and High-Resolution Next Generation) for 42 gem-quality mineral samples of beryl, emerald, elbaite tourmaline, euclase, vesuvianite, and apatite crystals from the Borborema Province. In addition, five emerald imitations and nine faceted emeralds from unknown provenances were also used to compose the spectral dataset. The main metals- and molecules-related absorption features were interpreted to show the similarities and differences of the spectral signatures from the minerals and imitation samples. In addition, the principal component analysis (PCA) was applied for data dimensionality reduction of the normalized reflectance spectra (n = 115), and the significance of PCs (99% of variance) was interpreted to highlight the main mineral groups. FreeViz algorithm was employed as an alternative for efficient visualization of PCs’ axes, showing a suitable discrimination of the samples. For example, the clustering of (a) beryl and emerald samples, (b) iron-rich elbaites (blue and green colors), and (c) Cu- and Mn-rich elbaites (Paraíba tourmaline and green varieties) was revealed, summarizing the similarities already expected from the qualitative spectral signature inspections and automating the discrimination of main mineral groups. Beyond introducing a spectral library of gem materials from NE Brazil, the methodology supports studies of gem classification and the authenticity assessment of diverse gem materials. The methodology can also be expanded to other reflectance datasets of gem-quality minerals worldwide.

Unraveling Precambrian cratonic roots beneath South America: A contribution from surface wave tomography

We examine some aspects of the tectonic evolution of Precambrian cratonic roots beneath South America based on lithospheric distribution of shear-wave velocities. We derive our model by inverting 26,984 fundamental mode Rayleigh wave group velocity dispersion curves, at periods of 9–180 s. We first regionalize our measurements and then invert the result for a 3D S-wave velocity model extending to 200 km depth. Fast velocities beneath the Amazonian and São Francisco cratons, and beneath buried cratonic units in the Parnaíba and Paraná basins, are long wavelength features consistent with previous tomography studies. For the Amazonian craton at 150 km depth, we find an increase of velocities with province age, except for the Maroni-Itacaiúnas province, where we hypothesize that K'Mudku intraplate tectono-thermal events at the middle-late Mesoproterozoic and emplacement of a large igneous province following the breakup of Pangea could have altered at least partially its lithosphere. Our results are consistent with a São Francisco paleocontinent whose borders extend beyond the surface limits of the present São Francisco craton into the neighboring Araçuaí and Brasília belts. Based on slow shear-wave velocities in the upper mantle beneath the Borborema province, consistent with lithospheric thinning, we argue that a possible cratonic root of the São Francisco Paleocontinent beneath this province has likely been eroded away. This analysis is further corroborated by tectonic events that led to the alteration of the Borborema mantle, including hydration in the Paleoproterozoic, rifting in the early-middle Tonian, reworking during Neoproterozoic Brasiliano events, and lithospheric stretching during the breakup of Pangea. Finally, we also image a fast shear-wave velocity structure in the region of the Río de la Plata craton, consistent with magnetotelluric studies.

Passive continental margin subducted to mantle depths: Coesite-bearing metasedimentary rocks from the Neoproterozoic Brasília Orogen, West Gondwana margin

In this contribution, we investigate the ultra-high pressure metamorphism (UHPM), and subsequent pressure–temperature-time (P-T-t) exhumation path recorded by granulites (rutile-kyanite-garnet-Kfeldspar and rutile-titanite-hornblende-garnet gneisses) of a coherent thrust package (Três Pontas-Varginha Nappe) of the southernmost edge of the Brasília Orogen. The Brasília Orogen, along with Northern Borborema Province, Dahomey, and Hoggar Belts, comprise a widespread linear system of orogens developed during the West Gondwana assembly, recording the diachronic closure of the Tonian-Ediacaran long-lived Goiás-Pharusian Ocean. Optical petrography, Raman spectroscopy, mineral chemistry, Ti-in-zircon and Zr-in-rutile thermometry, and U-Pb dating (LA-ICP-MS) of zircon, monazite, and rutile were combined to identify UHP minerals and textures and to track the decompression/exhumation path. Garnet porphyroblasts preserve UHPM chemical domains and are often radially fractured around rounded quartz inclusions. Remnants of microcoesite were detected by Raman spectroscopy within these inclusions, identified by the diagnostic bands at approximately 170 cm−1, 270 cm−1, and 520 cm−1. Coesite remnants were identified across the nappe stack along with 60° angle-oriented rutile needle inclusions in garnet, which suggests exsolution from Ti-bearing UHP garnets. Soccer ball zircon crystals of Ky-bearing granulites, with flat HREE pattern and negative Eu anomaly, yielded a U-Pb age of around 620 Ma. This age is interpreted as the record of the granulite facies metamorphism (750–805 °C and 15 kbar) post-dating the UHPM from the subduction channel. Zircon and monazite record exhumation under high temperatures around 595–590 Ma, and rutile crystals record the final stages of the decompression path from 590 to 585 Ma. Monazite crystallization occurred until 570 Ma. The new data combined with previously reported metamorphic paths, record a time interval of about 25 m.y. for the exhumation of the Tres Pontas-Varginha Nappe under subsolidus conditions. Our findings represent one of the oldest reports of Neoproterozoic coesite-forming UHPM recorded in metasedimentary rocks buried to mantle depths in the subduction of the passive continental margin.

Provenance of the late Jurassic to Cenomanian sedimentary succession of the Araripe Basin (NE Brazil) and implication for the geodynamic evolution of Western Gondwana

The separation of Gondwana was controlled by preexisting Proterozoic structures and by the development of rift aborted basins, of which the Araripe Basin (NE Brazil) is one of the best examples. Previous studies have focused on the presence and provenance of Aptian–Albian shallow-marine incursions in the Araripe Basin but to date, little attention has been given to its paleodrainage evolution during sedimentation stages. Understanding the paleodrainage evolution is crucial for determining sediment sources and how topographic changes relate to the geodynamic development of the northern part of South America during the fragmentation of Gondwana, and this study investigates the provenance of Mesozoic rift and post-rift sedimentary rocks in the Araripe Basin using a multi-proxy dataset comprising major and trace element concentrations, Sm–Nd isotopic composition, and detrital zircon U–Pb ages. The low Eu/Eu* ratios (0.3–0.9) and high Th/Sc ratios (>0.64) in the most of analyzed samples suggest a felsic and silicic source. The εNd(0) values (−12.3 to −23.7) and TDM ages (1.68 to 2.55 Ga) of analyzed samples suggest overall ancient crustal sources. The presence of oval and elongated zircon grains suggests a major contribution of first-cycle transport sediments. The presence of 2.3–1.8 Ga and 0.63–0.58 Ga U–Pb zircon ages further indicates the dominant contribution of the Borborema Province influenced by the Brasiliano cycle (650–520 Ma). The low contribution of Tonian (∼940 Ma) zircons to the U–Pb zircon age distribution of the rift-beginning stage sample associated with published paleocurrent direction suggests sources located in the northern and northwestern terranes of the Borborema Province. The increase of Tonian (0.9–1.0 Ga) zircon grains during the rift stage suggests a provenance change with a dominant source in the eastern terranes during the rift stage. During the post-rift I stage, the decrease of 1.2–0.72 Ga zircon ages suggests a change in the source areas, with the paleodrainage coming from northern Borborema Province, similar to that of the rift-beginning stage. The samples of the post-rift II stage exhibit dominant contributions of Paleoproterozoic and Neoproterozoic U–Pb ages related to the Albian to Cenomanian uplift of the Borborema plateau during the opening of Equatorial Atlantic Ocean. Together with previous published studies, these findings highlight the significant role played by the post-rift continental uplift to the paleodrainage of the northern part of South America.

Paleoarchean sedimentation and Mesoarchean high-temperature metamorphism in northeastern Brazil: Tracing sources and depositional ages in polymetamorphic rocks

Supracrustal rocks offer a window into tectonic processes of the early Earth, since they are common in the Archean lithosphere. However, these rocks are usually affected by several episodes of metamorphism that can compromise their UPb systematics, leading to equivocal interpretations of depositional ages and sources. In northeast Brazil, supracrustal rocks are frequent within the Archean basement of the São José do Campestre Massif. These metapelitic migmatites show a high-temperature mineral assemblage, with garnet + sillimanite ± spinel and retrograde cordierite, with abundant anatectic melt migration at conditions of upper amphibolite to granulite facies. Zircon UPb dating coupled to trace elements analysis through LA-ICP-MS, as well as zircon internal zoning patterns suggest a maximum depositional age of 3305 ± 16 Ma followed by high-temperature metamorphism in the Mesoarchean, Paleoproterozoic and Neoproterozoic. Mesoarchean high temperature metamorphism occurred between 3084 ± 4 and 3006 ± 6 Ma and generated a wide range of textures that could be grouped in, at least, three stages of zircon growth. The first, during prograde heating, led to dissolution of detrital cores through the process of Ostwald Ripening and reprecipitation in oscillatory zoned rims. The second, probably at peak conditions, occurred above the stability of monazite, as evidenced by high Th/U ratios within zircon grains, rounded shape and sector-zoned cores. The third, during retrograde cooling, is mostly driven by garnet breakdown, and resulted in the crystallization of convoluted rims. Ti-in-zircon temperatures indicate minimum temperatures of 712 ± 21 °C for prograde/retrograde stages and 881 ± 50 °C for peak conditions. The Paleoarchean sedimentation and Mesoarchean metamorphism are coeval with similar events in Kaapvaal and Dharwar Cratons (South Africa and South India, respectively), but show no correlation to any Archean domains in South America to date. Solid-state recrystallization during the Paleoproterozoic (ca. 2.0 Ga) and the Neoproterozoic (ca. 0.6 Ga) correlates with orogenic events in both the Borborema Province and São Francisco Craton, suggesting a common evolution since the Rhyacian.

Gamma-ray spectrometry, magnetic and gravity signatures of Archean nuclei of the Borborema Province, Northeastern Brazil

Gamma-ray spectrometry, magnetic and gravity signatures of Archean nuclei of the Borborema Province, Northeastern Brazil

The Early Paleozoic sedimentary record in northeastern Brazil: Unravelling the sedimentary provenance and evolution of fluvial systems after the Western Gondwana assembly

The sedimentary units of the geographically isolated basins of NE Brazil are historically interpreted as coeval and part of the same depositional system that was ultimately responsible to the deposition of the first sedimentary sequence of the intracratonic Parnaíba Basin. We present the first integrated detrital zircon U-Pb age dataset from the Early Paleozoic basins of NE Brazil, providing new insights into the depositional evolution and erosional history after Western Gondwana assembly. The lowermost sedimentary units (Ipu, Cariri, and Tacaratu formations) of eleven NE Brazil sedimentary basins (Parnaíba, Araripe, Tucano-Jatobá, Lavras da Mangabeira, Fátima, São José do Belmonte, and Mirandiba) were analyzed by a multi-proxy approach aiming to propose new insights on the paleogeographic reconstruction and stratigraphic correlations. Sedimentary provenance data, together with paleocurrents measurements consistently towards NNW-NW, suggests that the primary source for all the Early Paleozoic sedimentary units of NE Brazil were elevated orogenic areas related to the Brasiliano Orogeny to the south of Borborema Province (e.g., Riacho do Ponta, Rio Preto, and Sergipano belts). Based on detrital zircon U-Pb ages, we position the beginning of sedimentation of these basins in the Ordovician. The U-Pb age spectra for all analyzed sedimentary successions are remarkably similar. The analysis of KDE plots, CA-DA gap curves, and (dis)similarity tests, reinforced the correlation and contemporaneity of all the Ordovician sedimentary successions of NE Brazil. The conceived paleogeography model points to deposition of all the analyzed successions in a ramp, slightly tilted towards NW, where continental-scale fluvial system drained Neoproterozoic orogenic areas (i.e., Brasiliano Orogeny) dispersing huge volumes of sediments towards Borborema Province interior.

Post-collisional magmatism and local lithospheric thinning in the Neoproterozoic Alto Pajeú Domain, northeastern Brazil: Geochemical and isotopic evidence

The 595–560 Ma post-collisional magmatism in the Alto Pajeú Domain, Borborema Province, northeastern Brazil, is characterized by the intrusion of voluminous high-K calc-alkaline, shoshonitic and ultrapotassic magmas. The nature of the source rocks and the geodynamic context associated with the generation and emplacement of this post-collisional magmatism is still enigmatic. In this study, we report new UPb ages, elemental geochemistry, mineral chemistry and SrNd isotope data for rocks from the Pajeú batholith. LA-ICP-MS zircon UPb dating revealed that this batholith was formed by at least two distinct magma pulses. The oldest pulse (ca. 592 Ma) consists mainly of porphyritic quartz monzonites to monzogranites with abundant mafic microgranular enclaves (MMEs), while the younger pulse (ca. 568 Ma) is composed of equigranular biotite granites. The porphyritic monzogranites are magnesian, have intermediate to acidic compositions (SiO2 = 62.2–67.6 wt%) and high Mg# (44–55) values. In contrast, biotite granites are ferroan, have high SiO2 (69.3–73.1 wt%) and low Mg# (16–36) values. Both rock types are characterized by enrichment in LREE and LILE and depletion in HREE and HFSE, but with more fractionated REE patterns for biotite granites ([La/Yb]N = 67.4–101.5) than for porphyritic rocks ([La/Yb]N = 35.8–54.8). The SrNd isotopic values for the different rock types are roughly similar. However, biotite granites show slightly higher initial 87Sr/86Sr (0.71265–0.71412) ratios and more negative εNd (t) (−18.45 to −18.67) values than porphyritic monzogranites (initial 87Sr/86Sr ratios from 0.71077 to 0.71155 and εNd (t) from −16.04 to −16.96). These geochemical and isotopic signatures, together with mineral chemistry data, suggest different sources for the two rock types. The biotite granites are of purely crustal origin, derived by partial melting of a Paleoproterozoic amphibolitic lower continental crust, while a mixture of melts derived from the Paleoproterozoic continental crust and magmas derived from an enriched lithospheric mantle could explain the origin of porphyritic monzogranites. Based on the spatial and temporal distribution of magmatic rocks from the Alto Pajeú Domain, we suggest that a local lithospheric thinning model could explain the evolution of post-collisional magmatism in this region of the Borborema Province.

Late Ediacaran post–collisional granite in Babouri–Figuil (Northwest Cameroon): Implication for crustal–mantle contributions in an extensional setting

The Babouri–Figuil Magmatic Complex (BFMC, adjacent to the central-south Chad domain) is located on the southern flank of the Saharan Metacraton. It is amongst the least geologically studied regions in Cameroon; only a few key research papers on geochronology and isotopes have been completed. The emplacement of granitic bodies is poorly constrained between the early and late–Neoproterozoic with inherited zircons of older Paleoproterozoic–Neoproterozoic ages. In this study, undeformed biotite granite massifs (Lombel and Badesi) were studied, and their geochronologic, geochemical and mineral chemical data, including Nd–Sr–Hf isotopes, are presented. The massifs are enriched in pink K-feldspar (orthoclase and microcline; 60–65 wt%) and plagioclase (8–10 wt%) anastomosing to intergranular quartz (18–20 wt%) and biotite (3–5 wt%) crystals. The Lombel massif yielded a Concordia age of 566 ± 2.5 Ma (MSWD = 1.6, zircon U–Pb), slightly older than the Concordia age of 556 ± 2.7 Ma (MSWD = 2.1, zircon U–Pb) obtained for the Badesi massif. These are interpreted as emplacement ages, which post–date arc magmatism by ∼ 45 Ma. The geochemistry of the massifs showed sub- to mid–alkaline, high–K alkali–calcic, and weakly peraluminous compositional characteristics. The calculated biotite temperatures ranged from 613 to 647 °C, pressures from 100 to 300 MPa, and H2O from 3.0 to 3.5 wt%. Whole–rock composition geothermobarometry revealed low pressure of 100–500 MPa, depths of 3.5–18 km and low oxygen fugacity (ΔQFM = −0.6), indicating reducing crystallization conditions. The estimated radiogenic isotopic values are similar for both massifs, falling in the range from initial εHf(t) = +2.6 to +8.4 and initial εNd(t) = +1.3 to +2.1, with a corresponding average initial Sr of 0.70212–0.70458. These radiogenic isotope values suggest a mantle–derived origin for this granite or the melting of a juvenile mafic crustal protolith, as confirmed by the two–stage model age obtained (TDM2 = ∼ 1.2 Ga). Given that biotite is interstitial in alkali feldspar and plagioclase in both massifs, this suggests that biotite chemistry records conditions of magma evolution. Overall, these results confirm that the studied massifs are post–collisional products emplaced at shallow crustal levels under evolved magmatic conditions. They are coeval with a few post–magmatic intrusions in the central–south Chad and emplaced after the Sao–Francisco Congo Craton collided with the Saharan Metacraton. The ages obtained enabled a possible correlation with several Neoproterozoic post–collisional granites in Cameroon, south-central Chad, Central African Republic and Borborema Province of Brazil. The ages also revealed that continental assembly coupled with regional late–magmatism occurred during the Proterozoic.

Geochemical and isotopic evidence for early neoproterozoic (ca. 1000 Ma) subduction-related magmatism in the central Borborema Province, Brazil

Early Neoproterozoic (1000-920 Ma) rocks related to the Cariris Velhos event in the central Borborema Province have been linked to either continental rifting or accretionary-collisional orogenesis. The Serra do Jatobá Suite is located in the southwestern part of the Alto Pajeú Terrane along with coeval metasedimentary sequences and Ediacaran granites. This suite is composed of alkali-calcic, meta-to peraluminous granodiorites to monzogranites that share similarities with both ferroan- and magnesian granite series. Chondrite normalized REE (Rare Earth Elements) patterns are moderately fractionated with pronounced negative Eu anomalies. Incompatible element spidergrams show a negative Nb–Ta anomaly, similar to those observed in Cordilleran-type granites. U–Pb zircon data constrain the crystallization ages at around 1000 Ma, whereas calculated εNd(t) values range between −1.74 and −0.94. Obtained TDM model ages range from 1.76 to 1.54 Ga, which corresponds with source ages for the Cariris Velhos magmatic rocks. Our findings suggest that subduction took place in the early Neoproterozoic in the Borborema Province, pointing to an accretionary nature for the Cariris Velhos event.

Spectroscopic study of rose quartz from the Taboa pegmatite (Borborema Province, Brazil) irradiated with high gamma doses

Spectroscopic study of rose quartz from the Taboa pegmatite (Borborema Province, Brazil) irradiated with high gamma doses

Constraints on the source and petrogenesis of early Ediacaran shoshonitic mafic magmatism and high-K calc-alkaline granitoids in the Sergipano Orogenic System, Borborema Province, Brazil

The early Ediacaran Capela pluton (ca. 630 Ma) is intruded into the metasedimentary succession of the Sergipano Orogenic System along the oriental segment of the Macururé Domain, southeastern Borborema Province, NE Brazil. This body is an uncommon example of mantle-derived shoshonitic mafic rocks associated with high-K calc-alkaline granitoids emplaced in a pre- to early-collisional context. Here, we aim to unravel the petrogenesis of this plutonic association to determine the role of crustal contribution to magmatism and its geodynamical significance during the early stages of the Brasiliano/Pan-African Orogeny. The Capela pluton comprises cumulate hornblendites, gabbronorites, gabbros, diorites, granodiorites, quartz monzonites, and granites. Shoshonitic mafic rocks and high-K calc-alkaline granitoids show significant enrichments in LILE and LREE compared to HREE and HFSE. Ultramafic and mafic rocks display a conspicuous crustal signature, yielding subchondritic εNd(t) and zircon εHf(t) values, along with variable radiogenic Sr–Pb isotopic compositions. The dominant factors controlling the geochemical features of the mafic magmas were the enriched signature of the lithospheric mantle source and the degree of partial melting. Mantle source metasomatism is thought to have occurred by incorporating subducted sediments into the mantle wedge before the onset of the Brasiliano Orogeny. Geochemical modeling demonstrated that low partial melting degrees (5–10%) of phlogopite-bearing lithospheric mantle in the spinel stability field metasomatized by 5–10% subducted sediments may account for the main characteristics of the mafic rocks. Introducing sedimentary material into the mantle caused a decrease in Sm/Nd and Lu/Hf ratios while increasing the Rb/Sr, U/Pb, and Th/Pb ratios, which led to the time-integrated evolved isotopic signature observed in the mafic rocks. The coeval granitoids are metaluminous to slightly peraluminous and display Nd–Pb isotopic compositions similar to those of mafic–ultramafic rocks. The petrological and isotopic features of the granitoids are consistent with derivation from an ancient mafic lower crustal source. We argue that the ascent and emplacement of hydrous mantle-derived magmas as successive sills into the lower crust produced a deep hot zone beneath the Sergipano Orogenic System during the onset of the Brasiliano/Pan-African Orogeny. Aqueous fluids released from such potassic mafic magmas favored the partial melting of surrounding rocks, producing contemporary felsic magmatism.

Quaternary sedimentation over the Precambrian basement of Borborema Province (NE, Brazil): Tectonic and climatic controls

This study characterizes the existence of Quaternary sediments in the Transversal Zone of the Borborema Province (Northeastern Brazil). The sediments comprise paleosoils, unconsolidated sands and gravel deposits, which overlie Precambrian basement rocks. The new data on these deposits includes sedimentological and stratigraphic aspects, and age definition through quartz optically stimulated luminescence (OSL) method. The outcrops were subdivided in two broad groups (named RL and Rca) referring to nearby towns where the samples were collected. OSL ages from the RL group provided ages between ca. 160.15 ± 38.26ka to 4.30 ± 2.18ka, whereas the sediments in the Rca group present OSL ages from 67.45 ± 18.24ka to 7.67 ± 2.74ka. The geochronological results reveal that these sediments were deposited during a time period from the Pleistocene to the Holocene. Deposits are chronocorrelated to Post-Barreiras (ca. 74-2ka in age), apart from the Barreiras Formation (ca. 25 to 17Ma in age), by an expressive hiatus in the Northeast Brazil. Our investigation suggest that the sediments, in the study area, are a reworking of crystalline basement and differs genetically from Post-Barreiras in the coastal zone, which are reworked from the Barreiras Formation. The combination of intense humid chemical weathering during the Pleistocene-Holocene influenced the quaternary deposition in the study area. In addition, the regional brittle tectonic reactivation of shear zones also during the Paleogene influenced the space of accommodation that allowed the deposition of these sediments.