Resumo em Inglês:

Abstract Orthogneisses associated with metavolcanosedimentary successions related to the 1000 - 920 Ma Cariris Velhos event occur mainly in a ca. 700 km-long sigmoidal-shaped belt that crosscuts the Transversal Zone of the Borborema Province and extends to the fold belts located in its southern or external zone (part of the Riacho do Pontal and Sergipano orogens). Despite its importance, the tectonic setting and the role of those rocks in the geological evolution of the Borborema Province are contentious and not yet well understood. New zircon U-Pb SHRIMP data on an augen-gneiss sill of the Afeição Suite intruding mica-schists mapped as part of the Santa Filomena Complex yielded a Concordia Age of 974 ± 11 Ma, indicating that at least part of the metasedimentary rocks in the internal zone of the Riacho do Pontal Orogen are Tonian or older and possibly related to the Cariris Velhos event. Hf-in-zircon isotope data are presented for the first time for Cariris Velhos-related ortho-derived rocks of the Afeição Suite. Analyzed samples yielded εHf(t) in a narrow range between -1.51 and +2.41, with associated TDMHf of 1.6-1.4 Ga, similar to previously obtained Nd isotope data with εNd(t) = -1.0 to +3.1 and TDMNd of 1.5-1.2 Ga. A possible scenario to explain both the geochemical features and the moderately juvenile to slightly evolved, near-chondritic Hf and Nd isotope signatures is a continental arc setting, where fractionated melts produced in the supra-subduction zone mantle wedge carrying a Tonian juvenile signature became contaminated with discrete amounts of Archean-Paleoproterozoic continental crust during ascent, producing Mesoproterozoic model ages which represent the mixture of those two end-members.

Resumo em Inglês:

Abstract A comprehensive tectonic evolution of Proterozoic to Cambrian rocks that integrate the crystalline basement of Rio de Janeiro State, based on the new geological map, is presented. The map combines detailed geological data integrated to a 1:400.000 scale and new geochemical and geochronology data to characterize the distinct terranes amalgamated during three pulses of the Brasiliano orogeny. The Occidental terrane comprises the Tonian to Late Cryogenean passive margin of the São Francisco paleocontinent, including reworked cratonic basement. At the same period, two magmatic arc systems were developed outboard: The Continental Inner arc system represented by the dismembered terranes (Paraíba do Sul, Embú, and Cambuci domain) integrated now in the Central Superterrane: and the Intra-oceanic Outer Arc System, the Oriental Terrane, developed from 860 to 620 Ma. Related active basins were detected in association with the two arc systems that collided at ca. 620 - 595 and 605 - 550 Ma against the São Francisco passive margin. A later collision episode at ca. 535 to 510 Ma brought the Cabo Frio Terrane (Angola tip) and closed the Búzios back-arc basin. Finally, the collapse of the orogenic belt, probably related to slab detachment and asthenosphere upwelling marks transition to Gondwana stabilization.

Resumo em Inglês:

Abstract The Capela, Dores, Aquidabã, Camará, Campo Grande, and Pedra Branca stocks constitute the Macururé Mafic Suite of the Sergipano Orogenic System, Southern Borborema Province. These bodies have elongated and tabular forms, which are concordant with the metasedimentary host rocks foliation. Most primitive terms are hornblendites, gabbros, and diorites, with minor monzonites, granodiorites, and granites. U-Pb SHRIMP zircon ages for Capela (631 ± 3 Ma), Aquidabã (636 ± 4 Ma) and Campo Grande (629 ± 9 Ma) stocks indicate the coeval emplacement of the intrusions. Geochemical data show that these rocks are metaluminous to slightly peraluminous, magnesian and have high-K calc-alkaline to shoshonitic affinities. Rare earth elements (REE) patterns are fractionated and multielement diagrams display depletions at Nb, Ta, and Ti, indicating subduction-related magmatism. Trace elements data suggest that the gabbros and diorites were generated by partial melting of an enriched subcontinental lithospheric mantle in the spinel stability field, which has probably been metasomatized by the interaction with sediments during previous subduction events. Field and petrographic evidence, associated with geochemical and geochronological data support that the magmas of the Macururé Mafic Suite were emplaced in early- to syn-collisional stage during the build-up of a continental arc in the Sergipano Orogenic System, at ca. 630 Ma.

Resumo em Inglês:

Abstract One of the main characteristics of the Borborema Province in northeastern Brazil is the abundance of granitic domains. The Lagoa das Pedras plutonic-volcanic Complex record remnants of early to late Neoproterozoic primitive to highly evolved magmas. U-Pb SHRIMP determinations and whole-rock geochemistry on the granitic to granodioritic Riacho do Icó Stock, which is the largest plutonic body of this complex, were conducted. Zircon dating reveals that this body was intruded in the crust at 607 ± 3 Ma, whereas metamorphic overgrowths are coeval within uncertainty (600 ± 8 Ma). Geochemical characteristics of this stock suggest that it corresponds to Cordilleran-type magmas injected in the lithosphere above a subduction zone. Sr and Y contents in addition to MgO and SiO2 values are compatible with high-silica adakite-like magmas, interpreted as the result of slab melting in deep-seated regions. Based on the integration of this study and literature data, we suggest that the Riacho do Icó intrusion might be a dismembered part of a major continental magmatic arc described in the Central Subprovince of the Borborema Province, marking the onset of the accretionary stage of the Brasiliano orogeny.

Resumo em Inglês:

Abstract The Vieirópolis pegmatite field is characterized by amazonite pegmatites inserted in the Borborema Province. The Serra Branca pegmatite is hosted by the Serra Branca granites, which intruded partially the Serra Negra granites, and stands out by its amazonite mineralization. To comprehend the crystallization conditions and the source of this pegmatite and associated Serra Branca and Serra Negra granites, petrographic, mineral chemistry, geochronological and whole-rock geochemical data were used. The Serra Branca pegmatite is Cs-, Rb-, Pb-, Nb-, and Ta-rich. The Serra Branca granites (563 ± 2 Ma) are metaluminous to weakly peraluminous, crystallized under high fO2 conditions, pressure of 2.68-2.80 kbar and temperatures ranging from 667-670°C, with many zircon grains showing inherited cores of Paleoproterozoic ages. The Serra Negra granites (594 ± 4 Ma) comprises metaluminous granites crystallized under high fO2 conditions, temperatures within 711-751°C, pressure varying from 4.72 to 5.42 kbar. Both granites resulted from distinct partial melting degrees of a source similar to the Caicó Complex orthogneisses. The Serra Branca pegmatite geochemical data suggests that it was originated by extreme fractionation of the Serra Branca granites magma. The Serra Branca amazonite pegmatite is the first pegmatite mineralogically and geochemically characterized as Nb-Y-F (NYF)-type from the gadolinite subtype in the Borborema Province.

Resumo em Inglês:

Abstract Both the Borborema Province of NE Brazil and the geological provinces of NW Africa (the Trans-Saharan Orogen consisted of the Tuareg and Benino-Nigerian shields and the Central African Orogen of Cameroon, Chad, and Central African Republic) are complex geological regions with superposition of distinct deformational, metamorphic and magmatic events and final structural configuration during the Brasiliano/Pan-African Orogeny (ca. 625-510 Ma). These provinces represent the site of major mountain building processes in the Ediacaran/Cambrian transition that culminated in the amalgamation of West Gondwana after the collision of the West African-São Luís, São Francisco-Congo, and Saharan paleocontinents. In the last years, discovery and characterization of key tectonic units such as ophiolites, eclogites, HP/UHP rocks, and both oceanic and continental magmatic arcs are helping to clarify these processes and propose tectonic models for the geological evolution of NE Brazil-NW Africa. Connections of the marginal belts that frame these provinces, bordering the eastern margin of the West African-São Luís Craton (Médio Coreaú-Dahomeyides-Gourma-West Tuareg Shield) and the northern margin of the São Francisco-Congo Craton (Rio Preto-Riacho do Pontal-Sergipano-Yaoundé-Central African) are progressively better constrained, while correlations within the interior, highly reworked and sectioned portions of both the Borborema Province, the Benino-Nigerian Shield, the Central and East Tuareg Shield, Western Cameroon, and Adamawa-Yadé domains are more complicated and demand further investigation. Some of the questions of prime importance in this context are the continuation or not of the 1000-920 Ma Cariris Velhos Belt of NE Brazil into NW Africa, and if the basement-dominated North Borborema/Benino-Nigerian (NOBO-BENI) and Alto Pajeú-Alto Moxotó-Rio Capibaribe-Pernambuco-Alagoas/Adamawa-Yade (APAMCAPAY) domains could represent major decratonized blocks (such as LATEA in the Central Tuareg Shield), perhaps developed due to hyperextension and detachment of a Greater São Francisco-Congo paleocontinent northern margin. In this case, the Goiás-Pharusian and Transnordestino-Central African oceanic realms along with restricted internal oceans such as the hypothetical Piancó-Alto Brígida/Western Cameroon (PAB-WECA) Seaway probably separated these ancient paleocontinental blocks during the Neoproterozoic. The development of subduction zones and the docking of Neoproterozoic juvenile terranes welded the hyperextended Archean/Paleoproterozoic lithospheric fragments together and they became squeezed and reworked in between the major cratonic landmasses during the Brasiliano/Pan-African Orogeny. The quest for the sites of ancient oceans and continents that once composed NE Brazil and NW Africa goes on and tentative scenarios will surely benefit from novel geological, isotopic, and geochronological data put forward in the near future.

Resumo em Inglês:

Abstract The appearance of complex megascopic multicellular eukaryotes in the Ediacaran occurred just when the dynamics of a cooling Earth allowed establishment of a new style of global tectonics that continues to the present as “modern-type plate tectonics”. The advent of this style was first registered in 620 Ma-old coesite-bearing Ultra-High Pressure eclogites within the Transbrasiliano-Kandi mega-shear zone along the site of the West Gondwana Orogeny (WGO). These eclogites comprise the oldest evidence of slab-pull deep subduction capable of inducing continental collisions and producing high-relief Himalayan-type mega-mountains. Life, prior to this time, was essentially microscopic. Yet with increasing Neoproterozoic oxygenation and intensified influx of nutrients to Ediacaran oceans, resulting from the erosion of these mountains, complex macroscopic heterotrophic eukaryotes arose and diversified, taking the biosphere to a new evolutionary threshold. The repeated elevation of Himalayan-type mega-mountains ever since then has continued to play a fundamental role in nutrient supply and biosphere evolution. Other authors have alluded to the influence of Gondwana mountain-building upon Ediacaran evolution, however we claim here to have identified when and where it began.

Resumo em Inglês:

Abstract Ferroan granites (585-530 Ma) in the Transversal subprovince of the Borborema Province (BP) comprise two groups: G1) slightly peraluminous to metaluminous, alkali-calcic rocks (Aroeiras Complex and Serra Branca - Coxixola dike swarms (SBCDS)); G2) metaluminous to slightly peraluminous, alkalic to alkali-calcic rocks (Queimadas and Prata intrusions). G1 are transitional from collision to transcurrence (ca. 585 Ma), or transcurrence to transtension (ca. 545 Ma). G2 represents the granitoids intruded during post-collisional crustal thinning (ca. 550 Ma), or coeval with deposition of intracratonic basins (ca. 530 Ma). The large-ion lithophile elements (LILE) and high field strength elements (HFSE) enriched geochemical signature of these granitoids are recognizable in gamma spectrometric maps of regional scale, highest values of K(%), eTh(ppm), and eU(ppm) contrast significantly with country rocks and magnesian granites. This study shows that gamma-ray spectrometric regional maps reflect the geochemical characteristics of the ferroan intrusions. Moreover, in the local maps for each intrusion, it is possible to identify internal heterogeneities in these plutons, which correlate to geological processes, geochemistry, and petrography. Diorites and gabbros show low to medium values of K (1-3%), eTh (5-20 ppm) and eU (0.2-2 ppm), contrasting with the high values of regions with a dominance of ferroan granitoids (K, 3-6%; eTh, 15-60 ppm; eU, 2-4 ppm).

Resumo em Inglês:

Abstract In the southern portion of the Borborema Province, in the Sergipano Orogenic System, three basement inliers have been described: the Domes of Itabaiana and Simão Dias, in Sergipe; and the Girau do Ponciano Dome, in Alagoas. The Itabaiana and Simão Dias Domes occur in the central part of the Vaza Barris Domain, being composed of gneisses and migmatites. The Itabaiana rocks are calc-alkaline with trondhjemitic affinities. The Girau do Ponciano Dome, outcropping in the Macururé Domain, consists mainly of tonalitic, dioritic, monzonitic, granodioritic and high-grade granitic orthogneisses. SHRIMP U-Pb zircon date of a melanosome sample from a trondhjemitic migmatitic gneiss in the central part of Itabaiana Dome provided an age of 2831 ± 6 Ma, indicating that the migmatitic gneisses of this dome are correlated to the Mesoarchean terranes of the São Francisco Craton (Serrinha Block). These rocks represent the oldest geological record in the Sergipe State.

Resumo em Inglês:

Abstract In the central part or central subprovince of the Borborema Province, in the so-called Transversal Zone, an assemblage of Paleoproterozoic (predominantly Rhyacian) rocks occurs together with sparsely distributed Neoarchean nuclei. These rocks constitute the main basement of the Tonian (Cariris Velhos Cycle) and Ediacaran (Brasiliano Cycle) mobile belts. They are older tectonostratigraphic terranes and par excellence ramifying elements (as “inliers”) of the Neoproterozoic orogenic constructions. This tectonostratigraphic terrane known as Alto Moxotó composes a litho-structural context typical of accretionary orogens, with the presence of granitic, granodioritic, and trondhjemitic orthogneisses (≈ arc-type associations) that stretch out for some hundreds of kilometers (Floresta Suite) and are partially covered by medium-grade pelitic-psammitic sequences (Sertânia Supergroup). This basement outline (Floresta Suite + Sertânia Supergroup) depicts an irregular sigmoidal shape, from the interior of Pernambuco (meridian 39ºW) to the Paraíba coastal area (meridian 34º45'W), along about 450 km, varying from 40 to 80 km in width, resulting in a total area of ca. 28,000 km2. This Rhyacian petrotectonic scenario is conditioned and delimited by extensive (shear + thrust) faults that configure a tectonostratigraphic terrane. Moreover, there are pieces of continuity evidence of this tectonostratigraphic terrane not only in the basement of the adjacent Neoproterozoic mobile belts to the North and South of the TAM in Brazil, but also in Northern Cameroon, in Africa. Within this broader predominantly Rhyacian belt, some small Neoarchean gneissic and migmatitic nuclei were identified. The Rhyacian lithologies reveal evidence (TDM ages) of sources from a Neoarchean paleosubstrate. During the Statherian, the whole Rhyacian context was affected by a series of small-scale magmatic manifestations of varied petrologic composition: syenitic, granitic, granodioritic, and gabbro-anorthositic. In this paper, a synthesis of the bibliographic data is presented, including a series of unpublished (geologic and geochronologic) data that together validate our conviction that we are dealing with an extensive (reworked) fragment (TAM) derived from the basement of a Paleoproterozoic supercontinent (Columbia).

Resumo em Inglês:

Abstract The Glória Norte Stock (GNS) is made up of predominantly porphyritic biotite- amphibole-bearing quartz monzonite, enclosing a large number of microgranular mafic enclaves (MME). The GNS MME are fine-grained rocks with rounded and ellipsoid shapes that show sharp and gradational contacts with the host rocks, suggesting they coexisted with the host monzonite as magmas. The studied amphibole crystals of the two rock types are calcic and correspond to pargasite, edenite, and magnesium-hornblende. Their compositions are influenced by substitutions involving Al3+, Na+, Fe2+, Si4+ and Mg2+ ions, reflecting the decrease in temperature and the increase in oxygen fugacity. They present low Ti and Al contents, and varied Si content (6.2-7.7 apuf). The mg# values range from 0.48-0.84. Pressures for the crystallization of the MME amphiboles vary between 2.6 and 7.8 kbar and the temperatures of solidus and liquidus were estimated between 600-659 and 887-908ºC, respectively. The early MME amphibole crystals with lower Si and Mg content were formed under high pressure (7.8 kbar) and temperature (908 °C). The presence of amphiboles with 862ºC and 5 kbar in MME and GNS reflects that the interaction between these magmas occurred at 18 km of depth.

Resumo em Inglês:

Abstract Mineral chemistry and intensive parameter estimates for the Major Isidoro (626 Ma) and Monteirópolis (627 Ma) magmatic epidote-bearing granitic plutons, emplaced along the Jacaré dos Homens transpressional shear zone (JHSZ), Borborema Province, are focused in this study. These plutons consist of medium-to-coarse grained equigranular to porphyritic tonalite to granite that show abundant dioritic enclaves. These granites contain biotite (Fe# 0.44 to 0.55), Fe-edenite (Major Isidoro), hastingsite (Monteirópolis), titanite, and epidote that often show allanite core as key mafic mineral phases. Pistacite molecular content in epidote is in the interval of 27 to 31 mol%, presenting TiO2 < 0.30%, typical for magmatic epidote. Estimated intensive parameters reveal crystallization at 6.5 ± 1 (Major Isidoro) and 4.7 ± 0.6 kbar (Monteirópolis), temperatures from ~940°C (near-liquidus) to 675 ± 35°C (near-solidus) and oxidizing conditions. Partial corrosion of epidote took place during 15.6 to 32 (Major Isidoro) and 27-49 years (Monteirópolis), corresponding to rather high magma ascension rates of 365 to 750 and 395 to 635 m.years-1, respectively. The JHSZ likely favored upward magma transport at the Sergipano and Pernambuco-Alagoas domains boundary, during the onset of the Brasiliano orogeny (650-620 Ma).

Resumo em Inglês:

Abstract Records of large crustal masses in the northwest of Borborema Province (BP) spread over more than 300 km are found as numerous granitic bodies amid a high-grade metamorphic gneissic-migmatitic terrain. The Tamboril-Santa Quitéria Complex (TSQC) is a Neoproterozoic example of these records; it is located in the north of the Ceará Central Domain (CECD) and its origin is related to a continental magmatic arc at different evolutionary stages of the arc. The Uruburetama Granite (UG), object of this study, fits into this context and constitutes one of the most representative batholiths occupying an area of 1,500 km2. Dozens of other similar plutons have been recorded in cartographic works that show similarities which suggests the grouping of these bodies in the Uruburetama Granitic Suite (UGS), previously included in the TSQC. The UG consists of a variety of plutonic rocks associated with mafic-dioritic dikes and its metamorphic products. Six petrographic facies were identified among the plutonic rocks: biotite-hornblende monzogranites and syenogranitic varieties, biotite-hornblende granodiorites, in addition to quartz syenite, leucomonzogranites, and diorites rocks. These rocks are affected by deformation, with greater intensity at the edges of the batholith, where thrust shear zones with transcurrent components were installed, generating tectonic fabrics (mylonitic foliations, stretch lineation, almond feldspar porphyroclasts, and ribbon quartz). Despite the superimposed deformational effects, magmatic relict textures are partially preserved, mainly toward the central portion of the pluton. The UG and the associated plutons are hosted by migmatized orthogneisses, paragneisses with garnet, sillimanite or kyanite, marbles, calcium-silicate gneisses, micaschists, sillimanite quartzites, and amphibolite lenses. The contact relations are diffuse with gradation for migmatites, and in rare cases, intrusive contacts with gneiss mega-xenolites are registered. The geochronological data obtained by Pb-evaporation zircon in two samples of the UG show average ages of 655 ± 2 and 656 ± 1 Ma. U-Pb zircon data for the same samples showed slightly younger age values of 559 ± 10 and 634 ± 10 Ma, respectively. The ages obtained are considered as representative of the magmatic phases of UG crystallization in the context of the evolution of the Santa Quitéria Magmatic Arc (SQMA), with the main magmatic phase of the UG in the Cryogenian. However, the age of 559 Ma would represent a younger magmatic event in the evolution of the arch. Overall, these ages correspond to the “Pre-Collisional I” or “Early-Sin-Orogenic” phase of a large collisional belt in the west of BP, and the younger ages must represent events related to the continuity of the orogen convergence of the Latest-Pre-collisional I (634 Ma) and Post-Collisional I (559 Ma) phases. Sm-Nd whole-rock isotopes data showed εNd(t) values predominantly negative (-25.6 and −0.9), and Nd-TDM model ages of 2.90 and 1.2 Ga. The results of the Lu–Hf isotopes analysis for the Bt-Hbl monzogranite sample showed negative εHf values (-26.75 to −35.48) and Hf-TDMC model ages of 3.12 to 3.65 Ga while the results for Bt-Hbl granodiorite showed εHf values of −2.07 to +1.08 and Hf-TDMC model ages of 1.46 to 1.66 Ga. These data point to the existence of two distinct and older crustal sources in the generation of these granitoids, one in the Mesoarchean, and the other in the Mesoproterozoic. The Archean ages correspond to the basement in the south of the CECD (Tróia Massif and Granjeiro Complex); on the other hand, the Mesoproterozoic ages are up for discussion, since terrains with this type of age do not occur adjacent to the BP. On the other hand, it can be interpreted as a mixture of sources, one of them probably juvenile, neoproterozoic, with contamination of the Archean crust. Thus, the UG is considered one of the most important records of the beginning of the evolution of the Santa Quitéria Magmatic Arc associated with a wide collisional belt in the “West Gondwana Orogen” in the west of Borborema Province.