Alto Pajeu Terrane Research Articles

Precambrian history of the Zona Transversal of the Borborema Province, NE Brazil: Insights from Sm–Nd and U–Pb geochronology

Abstract The Borborema Province has three major subprovinces. The northern subprovince lies north of the Patos shear zone and is comprised of Paleoproterozoic cratonic basement with Archean nuclei, plus overlying Neoproterozoic supracrustal rocks and Brasiliano plutonic rocks. The central subprovince occurs between the Patos and Pernambuco shear zones and is mainly comprised of the Zona Transversal. The southern subprovince occurs between the Pernamabuco shear zone and the Sao Francisco craton and is comprised of a tectonic collage of various blocks, terranes, or domains ranging in age from Archean to Neoproterozoic. This report focuses on the Zona Transversal, especially on Brasiliano rocks for which we have the most new information. Paleoproterozoic gneisses with ages of 2.0–2.2 Ga occur discontinuously throughout the Zona Transversal. The Cariris Velhos suite consists of metavolcanic, metasedimentary, and metaplutonic rocks yielding U–Pb zircon ages of 995–960 Ma. This suite is mainly confined to a 100 km wide belt that extends for more than 700 km within the Alto Pajeu terrane. Sm–Nd model ages in metaigneous rocks cluster about 1.3–1.6 Ga, indicating that older crust was involved in genesis of their magmas. Brasiliano supracrustal rocks dominate the Pianco-Alto Brigida terrane, and they probably also constitute significant parts of the Alto Pajeu and Rio Capibaribe terranes. They are only slightly older than early stages of Brasiliano plutonism, with detrital zircon ages at least as young as 620 Ma; most T DM ages range from 1.2 to 1.6 Ga. Brasiliano plutons range from ca. 640 to 540 Ma, and their T DM ages range from 1.2 to 2.5 Ga. Previous workers have shown significant correlations among U–Pb ages, Sm–Nd model ages, petrology, and geochemistry, and we are able to reinforce and extend these correlations. Stage I plutons formed 640–610 Ma and have T DM ages less than 1.5 Ga. Stage II (610–590 Ma) contains few plutons, but coincides with the peak of compressional deformation, metamorphism, and formation of migmatites. Stage III plutons (590 to ca. 575 Ma) have older T DM ages (ca. 1.8–2.0 Ga), as do Stage IV plutons (575 to ca. 550 Ma; T DM from 1.9 to 2.4 Ga). Stage III plutons formed during the transition from compressional to transcurrent deformation, while Stage IV plutons are mainly post-tectonic. Stage V plutons (550–530 Ma) are commonly undeformed (except along younger shear zones) and have A-type geochemistry. The five stages have distinct geochemical properties, which suggest that the tectonic settings evolved from early, arc-related magma-genesis (Stage I) to within-plate magma-genesis (Stage V), with perhaps some intermediate phases of extensional environments.

Microestruturas e tramas de eixo C de quartzo em milonitos do Sistema de Cisalhamento Campina Grande (PB), Província Borborema

Left-lateral NW-trending and right-lateral NE-trending shear zones form a conjugate structure close to the eastern termination of the Patos Lineament (Borborema Province). C-axis fabrics in quartz-mylonites show single and cross guirdle patterns consistent with kinematic criteria recorded in meso- and regional macroscale. They are related to the activation of mainly basal and rhomboedric ; slip systems in a low to moderate temperature (300 a 600o C). Microstructures in quartz indicate the deformation mechanisms include crystal plastic and recrystallization processes, but ductile-brittle strains in feldspar. The conjugate shear zone system agrees with a bulk NNW-SSE trending shortening direction. It was also responsible for the thrusting of the Paleoproterozoic basement to over younger rocks of the Alto Pajeu terrane. The consistency of the kinematic criteria remains stable even in the latest incremental ductile deformation recorded in ultramylonite bands and in the quartz-c fabrics.

Padrões Isotópicos Sm-Nd no limite entre os terrenos Alto Pajeú e Alto Moxotó, PB

Sm-Nd isotopic studies were carried out to recognize and define two different groups of geologictectonic terranes of the eastern most part of the Transversal Zone (central sub-province) of the Borborema Province, northeast of the South American Platform. The first recognized group (I), formed by granitic orthogneisses and supracrustal rocks is the Alto Pajeu Terrane - APT - that exhibits an isotopic signature with T DM values between 2.28 and 1.37 Ga, high negative values for eNd(0) ( ; 0.12 that indicates a possible isotopic fractioning. The second group (II) is composed mostly by orthogneisses (a minor supracrustal belt -Sertânia complex), the Alto Moxoto Terrane -AMT - exhibits an isotopic signature with higher T DM values, between 3.0 and 2.0 Ga, very negative values for eNd , between -20 and -35, and 147Sm/144Nd lower than those of the group I, i.e. between 0.12 and 0.08. The eNd(t) values calculated for the assumed ages of both groups are respectively: group I eNd (950)= -14 up to +1.28; group II - eNd (2000) = -11.28 up to +1.73. Additionally, these distinct isotopic patterns worked out as a complementary tool for the geological mapping, as well as, they have gradually been reiterated by means of the study of the Brasiliano granitic plutonism (Ediacaran in age) that occurs piercing both, APT and AMT. Data obtained by other geochronological methods (U-PB and Rb-Sr) for this granites and for the pre-Brasiliano terranes themselves were in good agreement with these above discriminated patterns.

Petrogenesis of A-type Granitoids from the Alto Moxoto and Alto Pajeu Terranes of the Borborema Province, ne Brazil: Constraints from Geochemistry and Isotopic Composition

A-type granitoids (∼512 Ma) either intruded into Paleoproterozoic gneiss of the Alto Moxoto Terrane (Prata Complex and Serra da Engabelada Pluton) or into Early Neoproterozoic metavolcanic metasedimentary sequence of the Alto Pajeu Terrane (Serrote Santo Antonio Pluton), constitute a small proportion of Brasiliano (= Pan-African) granitoids in the Central Tectonic Domain of the Borborema Province, northeastern Brazil. The Prata Complex consists of syenogranites, monzogranites, mafic enclaves of diorites and norites. The felsic and mafic members are not genetically related through fractionation. Mingling and mixing were extensive processes within the Prata Complex. The granites evolution appears to have involved fractionation of alkali feldspar, biotite, apatite and sphene without significant wall-rock assimilation. The Serra da Engabelada and Serrote Santo Antonio plutons consist of biotite syenogranites, with rare mafic enclaves. The studied granitoids are dominantly metaluminous, characterized by Fe-rich biotite and Fe-hornblende. High total alkalis, Y, Nb and REE and low CaO, MgO and Sr abundances and high FeO/(FeO+MgO) ratios characterize these granitoids. Chondrite-normalized REE patterns show enriched LREE, moderate to strong negative Eu anomalies and more or less flat heavy REE. The studied granitoids and diabase from dykes and enclaves show negative eNd (512Ma) values (-14 to -10), high incompatible elements such as LILE, HFSE and REE, suggesting important contribution of Paleoproterozoic crust. The origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust. Such isotopic signature of the diabase from the dykes also reflects a Paleoproterozoic enriched lithospheric mantle in the area. The intrusion of the studied granitoids contemporary with sub-volcanic bimodal magmatism and deposition of many Cambrian "pull-apart" basins in the north and central tectonic Domain of the Borborema Province, suggest intrusion during post-tectonic relaxation of the Brasiliano orogeny following the assembly of West Gondwana.

A Zona Tectônica Teixeira Terra Nova - ZTTTN - fundamentos da geologia regional e isotópica

A sigmoidal-shape linear tectonic occurs from Teixeira (Paraiba, to the north-northeast)- to Terra Nova (Pernambuco, to the south-southwest) as a line diagonal to theTransversal Zone, which is the central tectonic portion of the Borborema Province, thus dividing this province into two different litho-structural and tectonic domains. To the north and northwest occur the Early Neoproterozoic Riacho Gravata (RG) and the Neoproterozoic Pianco-Alto Brigida (PAB) terranes, both of them characterized by supracrustal rocks with low-grade of regional metamorphism. To the south-southwest occur the Alto Pajeu terrane (TAP, Early Neoproterozoic, orthognaisses and mesozonal supracrustal rocks) and the domain of its basement, the Alto Moxoto terrane (TAM, Paleoproterozoic in age), with high grade metamorphic rocks. This proposedtectonic zone is mostly composed by orthogneisses (from TAP and its Paleoproterozoic basement) pierced by an almost continuous series of intrusive granitic and syenitic rocks (plutons and stocks) of the Ediacaran period (ages between 630 and 570 Ma). During the evolutionary history of this linear portion of the plateau of the Borborema province there are some (direct and indirect) records of polycyclic geologic events of the Paleoproterozoic, Early Neoproterozoic, Ediacaran, Cambrian and Cenozoic era (a sedimentary veneer, evolution of a supergenic crust and regional uplift) with interesting implications for the regional geology, geography and social-economic development. In this paper the emphasis will be given to the isotopic data (Rb-Sr, Sm-Nd, mostly) along this special and the domains that it separates, as well its role on the regional tectonic framework. For this purpose, we take into consideration an expressive amount of available geological and isotopic data, obtained along the last decade (most of them not published) from different sources. Additionally, some first interpretative hypotheses will be postulated, where this tectonic (ZTTTN) would be formed as by-product of three parallel Neoproterozoic subduction zones.

O SISTEMA TAFROGÊNICO TERCIÁRIO DO SALIENTE ORIENTE NORDESTINO NA PARAÍBA: UM LEGADO PROTEROZÓICO

This paper presents data on the E-W to ENE-WNW-trending graben and horst system in the easternmost part of Paraiba State, Brazil. The installation of this Tertiary tectonic unit was performed following previous structural trends of the Precambrian basement, comprising as a typical case of brittle-ductile structures reactivation. The graben and horst system are positioned in the easternmost part of the Borborema Province, whose main evolutionary phase occurred from the Late Neoproterozoic to the Cambrian, superposing lithostructural units of the Neoproterozoic Alto Moxoto terrane (to the south), composed of orthogneisses and peraluminous supracrustal rocks, and of the Eo-Neoproterozoic Alto Pajeu Terrane (to the north), comprising volcano-sedimentary supracrustal rocks metamorphosed under amphibolite facies. During the closing events of the Brasiliano Cycle, these terranes were penetrated by Cambrian fissural basic intrusives that crop out along the WNW-ESE direction (most of them). This basic dyke swarm is reported here for the first time. During the Tertiary, the most important period for the regional geomorphological evolution, the main structural Brasiliano trends were reactivated as extensional faults, leading to the formation of the taphrogenic system discussed here. At that time, some new faults of extensional character were also formed. As similar occurrences have been described elsewhere (e. g. Rio Grande do Norte State), these facts bring new elements for the discussion of the regional geology of Borborema Province, especially in terms of geomorphological evolution (certainly, a new aspect to be considered) and groundwater resources (heavily demanded in such semi-arid area). Additionally, the occurrence of such brittle Tertiary tectonism in the (next) interior of the continent necessarily opens again the problem of the structural behavior of the Cretaceous coastal basins, in order to investigate the formation of structural traps for hydrocarbon during this period.

Origin and Intensive Parameters in the Crystallization of Ultrapotassic Syenites: The Serra Do Man Pluton, Northeastern Brazil

The late Neoproterozoic ultrapotassic Serra do Man pluton intruded supracrustal schists and igneous rocks of the Alto Pajeu tectonostratigraphic terrane, in the Borborema province of northeastern Brazil. This quartz-alkali feldspar syenite is composed of microcline, albite, normally zoned aegirine-augite, winchite (formed after pyroxene), titanite and apatite, with the major-element geochemistry in consonance with early fractionation of pyroxene-titanite-apatite assemblage. Chondrite-normalized REE-patterns are LREE-enriched (La/Lu ∼ 20) with discrete negative Eu anomaly, and primitive mantle-normalized elemental concentration diagrams display enhanced negative Nb, P and Ti anomalies that are also observed in patterns of similar rocks in NE Brazil. Whole-rock d 18O values are rather high (avg. +8.7% SMOW) and in the +7.8 to +8.6% SMOW range when clinopyroxene-corrected. A five-point whole-rock Rb-Sr isochron yields an age of 580±28 Ma with high Sr o (0.7108), which together with eNd (0.58 Ga) value of -17 and t chur of 2.3 Ga allow hypothesizing a Paleoproterozoic enriched-mantle source for the syenites in the ultrapotassic province of the Alto Pajeu terrane. The aegirine-augite, titanite, and quartz assemblage attests to a high oxygen fugacity prevailing during magmatic crystallization. The almost complete absence of primary hydrated phases assures that the magma was rather anhydrous, and its viscosity, at the liquidus temperature, was relatively high. Density is slightly higher than expected for syenitic magmas (2.8 g/cm 3), being explained by a relatively high iron content of the magma. Geothermobarometry suggests shallow emplacement and temperatures of 700-750°C and 850-900°C, respectively, for the solidus and liquidus of the magma.

O terreno Alto Moxotó no leste da paraíba ("Maciço Caldas Brandão")

The Alto Moxoto Terrane (TAM), at the east of Paraiba State is mostly composed of sheared orthogneisses, porphyritic granodioritic gneisses and it bears an imbricated sheet of Al-rich (garnet-biotite-sillimanite) gneisses, deeply affected by migmatization phenomena. This litho-structural assemblage is drawing a regional asymetric antiformal structure, with its axial zone running parallel to the BR-230 highway (E-W trending). It is limited in both, north (Alto Pajeu terrane) and south (Rio Capibaribe terrane) sides by important shear zones, which are feather faults connected with the development of the Pernambuco lineament, to the southwest. The adopted designation of is based upon its singular geological features, in terms of lithological and structural characteristics, Paleoproterozoic in age and sharp limits with the different confining terranes. TAM is here considered as a mega-fragment of the Atlântica Supercontinent, that was built up by the Paleoproterozoic Collage (Transamazonian) and that was preserved in the framework of West Gondwana (Brasiliano/Pan African Collage) as a terrane. This terrane shows conspicuous continuity to the far interior of the province, to the southwestern part of Pernambuco State, and so doing, it demontrates that the former designation of Caldas Brandao Massif must be ruled out, as obsolete for many reasons. Geochronological determinations using Rb-Sr, Sm-Nd and U-Pb methods confirm the Paleoproterozoic age of this terrane, with the presence of some Archean protoliths as well as the various degrees of structural reworking and isotopic reseting promoted by the Brasiliano Cycle. This cycle was responsible for some intrusive granites, for most of the general geological features, like usual informal limits and even the present shape of the TAM, a typical reworked basement inlier.

O "Sistema Pajeú-Paraíba" e o "Maciço" São José do campestre no leste da Borborema

The best areas of exposures of the Pajeu-Paraiba Folding System (SPP) are in the western hinterland of Pernambuco, but the northern part of it - the so-called Alto Pajeu Terrane (TAP) - reaches the coastal zone of Paraiba (east of the 36°00 ' W). This supracrustal terrane is positioned between important regional shear zones that separate it from high grade gneiss domains. To the north, there is the Rio Grande do Norte Terrane (RON)- separated by the Patos Lineament- and to the south there is the expositon of another important fraction of the basement of SPP, the Alto Moxoto Terrane (TAM). Both RON and TAM are considered mega-fragments of a previous Paleoproterozoic supercontinent, while TAP is assumed as a descendant segment of the Meso-Neoproterozoic erogenic belt, probably part of the supercontinent of that time (Rodinia). All these terranes are now juxtaposed and they were deeply reworked by the development of the Brasiliano Cycle, during the amalgamation of the Western Gondwana supercontinent. The TAP is mostly composed of muscovite-biotite gneisses (a), garnet-biotite-schists (b), intruded by augen-gneisses of granitic and syenogranitic composition (c) which are lithological assemblages of Eoneoproterozoic age (Cariris Velhos Cycle). They were diversely reworked and penetrated by granitoids (d) of the Brasiliano Cycle (as well as RGN has been), specially plutonic rocks of the end of Neoproterozoic III. These predominant rock-units (a, b, c) are positioned between major regional dextral shear zones, and their regional features are drawing an wide fan-sinformal structure, due to the Brasiliano reworking. Geochronological determinations -Rb-Sr, Sm-Nd and U-Pb methods- confirm the Paleoproterozoic age of the RGN and its reworking during the Brasiliano, as well as the early Neoproterozoic age (Cariris Velhos Cycle) for the main rock units of TAP. Granitic plutonism and processes of shearing are common events of the Brasiliano Cycle for both, RGN and TAP (as well as for the basement of the TAM, to the south).

Geochemical Characterization of Granites of Distinctly Different Ages in the Alto Pajeu Terrane, Borborema Province, Northeast Brazil

This work presents geochemical data for granitic plutons that intruded the Alto Pajeu terrane, Borborema Province, northeastern Brazil, during several distinct tectonic cycles. The Alto Pajeu terrane is represented in the study area by metasedimentary (São Caetano Formation) and metavolcanosedimentary (Irajai Formation) sequences overlying a gneissic-migmatitic basement. Several granitic plutons of different ages, mineralogical proportions, and chemical compositions have invaded the supracrustal and basement rocks. Two deformational events, one tangential (older) and the other transcurrent (younger), were identified. The metamorphic grade determined for the metasedimentary rocks varies from amphibolite to high amphibolite facies, with temperatures ranging from 600 to 680°C and pressures from 6.0 to 7.5 kbar. Three magmatic events with distinct ages were identified for the tectonic evolution of the Alto Pajeu terrane in the study area. The older magmatic event is related to the Transamazonico orogenic cycle (∼ 2.0 Ga), the intermediary magmatic event to the Cariris Velhos cycle (∼0.97 Ga), and the younger magmatic event to the Brasiliano orogenic cycle (∼0.55 Ga). The Cariris Velhos- and Brasiliano-age granites are geochemically classified as peraluminous, subalkalic granites of the calc-alkalic series, whereas the Transamazônico-age granite is metaluminous and alkaline. Geochemical data presented and discussed here suggest that the magmatism related to the three tectonic events had distinctly different sources and petrogenetic evolutions.