Ruy Paulo Philipp

Paleoproterozoic Magmatic Provenance of Detrital Zircons, Porongos Complex Quartzites, Southern Brazilian Shield

Provenance investigation using detrital zircon U-Pb SHRIMP (sensitive high-resolution ion microprobe) age dating for six quartzite samples (167 spot determinations on 166 grains) indicates that metasedimentary rocks of the Porongos Complex from the southern Brazilian shield were derived almost entirely from Paleoproterozoic sources. Intensive study of igneous and metamorphic rocks in this portion of southwestern Gondwana employing SHRIMP geochronology over the past five years provides important evidence for provenance investigation of zircon grains. Ages of magmatic sources of the zircon detritus in the deformed quartz sandstones show an eight-peak distribution (known equivalent rocks in parenthesis): 2470 Ma (Neto Rodrigues Gneiss), 2350 Ma (Santa Maria Chico Complex Granodiorite), 2200 Ma (Encantadas Complex Tonalite), 2140 Ma (Paso Severino Dacite, Miséria Mylonite), 2100 Ma (Sierra Azul Granite), 2080 Ma (Chacofy Tonalite, Villa Monica Monzogranite), and 2040 and 2020 Ma (Itapema Monzogranite). Ages between 2260 and 2000 Ma correspond to the Trans-Amazonian Cycle, and were already known in the basement of the region, but the 2470 Ma and 2350 Ma ages are a new contribution regarding the tectonic evolution of the southern Brazilian shield. Tectonic scenarios for the Porongos basin fill are restricted to two different environments: (1) cratonic cover, if the fill is near 1500 Ma; or (2) passive margin if the age of fill is near 1000 Ma (this explanation requires additional studies). We have thus elucidated a major problem in the provenance of detrital zircon in the southern Brazilian shield, because we now know that the protolith sediments of the Porongos Complex were deposited under stable tectonic conditions and derived from Paleoproterozoic sources. This occurred after cratonization of the crust and formation of supercontinent Columbia following the end of the Trans-Amazonian Cycle. Nearly all zircon analyses have Th/U ratios higher than 0.2. Thus, only magmatic crystals survived the sedimentary processes. We show that detailed study of detrital zircon is a powerful tool for the understanding of the provenance of sandstones.

Evolução tectônica do Cinturão Dom Feliciano no Sul do Brasil: relações geológicas e geocronologia U-Pb

The Dom Feliciano Belt is an important Neoproterozoic to Cambrian orogenic complex, extending from eastern Uruguay to southern Brazil. It comprises a collage of oceanic domains and continental fragments developed between 900 and 540 Ma between the Rio de La Plata, Congo and Kalahari cratons. The integration of field and structural data with recent isotopic results has introduced new insights on the sources of the magmatism and sedimentary processes. This paper presents a review of the geochronological results combined with stratigraphic, structural and geochemical data. The evolution of the Dom Feliciano Belt involved three orogenic events known as the Passinho (0.89 - 0.86 Ga), Sao Gabriel (0.77 - 0.68 Ga) and Dom Feliciano (0.65 - 0.54 Ga). The first two events involved the closure of the Charrua Ocean generating an intra-oceanic arc (Passinho) and, subsequently, an active continental margin arc (Sao Gabriel). This ocean separated the continental areas represented by the Rio de la Plata Craton and the Nico Perez continental microplate. Closure of the Adamastor ocean resulted in an important collisional event between the Nico Perez Microplate/Rio de La Plata Craton and Kalahari and Congo cratons between 650 and 620 Ma, involving high T/intermediate P metamorphism. At this time of crustal thickening, the partition of the deformation controled the final evolution of the belt with important escape tectonics, responsible for nucleating crustal-scale transcurrent shear zones. These structures were deep and promoted the rise of mafic magmas, which, associated with high regional thermal gradient, lead to an important event of crustal reworking, responsible for the formation of the Pelotas Batholith. The orogenic collapse is represented by late magmatism of Pelotas Batholith and deposition of upper section of the Camaqua Basin.

Petrology of dioritic, tonalitic and trondhjemitic gneisses from Encantadas Complex, Santana da Boa Vista, southernmost Brazil: paleoproterozoic continental-arc magmatism

The Encantadas Complex is a unit composed of dioritic, tonalitic and trondhjemitic gneisses with minor hornblendite. This complex is intruded by granites of Neoproterozoic age. Major and trace element data indicate metaluminous to slightly peraluminous composition related to the medium-K calc-alkaline series. Compositional parameters are consistent with a common evolution from less differentiated magmas, probably through fractional crystallization. The orthogneisses show LaN/YbN ratios from 10 to 50, K2O/Na2O varying from 1.1 to 3.0, Y contents from 3 to 39 ppm, Yb from 0.3 to 3.7, and Lu with contents in the range 0.06 and 0.54 ppm. Such geochemical features are similar to those of Archaean tonalitic rocks and are usually described in rocks formed by partial melting of mafic rocks under high-pressure conditions leaving an eclogitic residue. The presence of diorites and hornblendites, associated to tonalitic and trondhjemitic gneisses suggests, on the other hand, that tonalitic magmas could be formed by hornblende-controlled fractionation of hydrous basaltic magmas. Tonalitic gneisses show U-PbSHRIMP zircon age of 2, 263 ± 6 Ma for igneous crystallization and 2, 045 ± 10 Ma for the metamorphism. The geochemical parameters, tectonic and geochronological features of Encantadas Complex are consistent with magmas derived from mantle metasomatized by subduction-related fluids in a continental-arc.

Reavaliação e novos dados Geocronológicos (Ar/Ar, Rb/Sr e Sm/Nd) do Batólito Pelotas no Rio Grande do Sul: implicações Petrogenéticas e Idade de Reativação das Zonas de Cisalhamento

O Batolito Pelotas e constituido por suites graniticas com idades U/Pb (em zircao, Evaporacao e SHRIMP) e Pb/Pb (em zircao, por evaporacao) situadas no intervalo de 575 a 633 Ma, com um padrao de idade mais antigo entre 625 e 635 Ma (Suite Pinheiro Machado) e outro mais novo entre 575 e 600 Ma (Suites Viamao, Encruzilhada do Sul e Dom Feliciano). As razoes isotopicas Sr87/Sr86 situadas entre 0,7060 a 0,7016, juntamente com valores de µNd fortemente negativos (em geral, entre -5 a -10) e idades modelos T DM (entre 1600 e 2200 Ma), indicam a predominância de processos de reciclagem de materiais de uma crosta provavelmente Paleoproterozoica (Ciclo Transamazonico). Por outro lado, a presenca de magmatismo basico e feicoes de misturas de magmas nas Suites Pinheiro Machado, Viamao, Encruzilhada e Dom Feliciano associados com magmatismo alcalino (Sienito Piquiri), com idade Pb/Pb (em zircao, por evaporacao) entre 610 e 615 Ma, sugerem tambem contribuicao mantelica na constituicao do batolito. As idades Ar/Ar aqui obtidas a partir de rochas miloniticas de zonas de cisalhamento (de baixo e alto ângulo) que afetam o batolito sugerem a existencia de um importante evento tectonico ocorrido entre 540 e 530 Ma. Este evento teria sido responsavel pela reativacao em regime transpressivo de zonas de cisalhamento mais antigas, relacionadas com a colocacao das suites graniticas do batolito, e geracao de estruturas-em-flor positiva em varios dominios do mesmo. Esta tectonica parece se articular no espaco e no tempo com a tectonica extensional relacionada com a instalacao da Bacia do Camaqua.

Age constraints of the glaciation in the Paraná Basin: evidence from new U–Pb dates

The absence of absolute dating in glacial deposits of the Paraná Basin prevents better understanding of the complete history of the Late Palaeozoic Ice Age in Western Gondwana and the climatic change that took place in the late Carboniferous. In this study, new U–Pb radiometric ages date the topmost glacial deposits of the Itararé Group at 307.7 ± 3.1 Ma (Kasimovian−Moscovian) and the base of post-glacial deposits of the Rio Bonito Formation at 298.8 ± 1.9 Ma (Ghzelian−Asselian). Correlation of glacial and post-glacial deposits of the Paraná Basin with other southwestern Gondwana basins shows that the end of the Late Palaeozoic Ice Age is asynchronous. Supplementary material: Laser ablation inductively coupled plasma mass spectrometry U–Pb zircon data and methods for the ash sample of the Itararé Group and the tonstein sample of the Rio Bonito Formation are available at https://doi.org/10.6084/m9.figshare.c.3278273.

Tonian to early Cryogenian synorogenic basin of the São Gabriel Terrane, Dom Feliciano Belt, southernmost Brazil

ABSTRACT A provenance and stratigraphic study of the Neoproterozoic Pontas do Salso Complex (PSC), western portion of the Dom Feliciano Belt (DFB), was conducted with U–Pb zircon geochronological analysis of the metasediments and the host rocks. The U–Pb isotopic data from detrital zircon of the metasediments indicate the source from the latest Middle Tonian to Late Cryogenian (between 897 and 684 Ma) and maximum depositional age of 685 ± 18 Ma in an arc-related basin setting adjacent in the Sao Gabriel Arc. The metasediments of the PSC form an elongated body in the N35°E direction and occur in the central portion of the São Gabriel Terrane (SGT), which is constituted by ophiolitic complexes and arc-related rocks, generated probably during the final consolidation of Rodinia supercontinent, although this question is still open. Low- to medium-K calc-alkaline, metaluminous affinity, and trace-element geochemistry suggest that the chemical composition of the protoliths was generated from metasomatized mantle sources in subduction zones. The PSC is composed of meta-arkoses, with subordinate metaconglomerates and metapelites. The meta-arkoses are disposed in plane-parallel layers, which also internally feature small-scale cross-bedding structures. The matrix has a blastopsammitic, poorly selected, fine to coarse texture, and hexagonal quartz and plagioclase porphyroclasts with superimposed thermal metamorphism. The polymict metaconglomerates are matrix-supported, with 15–55% of clasts of metavolcanic rocks, metasediments, undeformed granites, and quartz veins. The metapelites comprise mainly muscovite phyllites with syn-tectonic garnet and chloritoid porphyroblasts. The PSC represents a sedimentary succession deposited on an arc-related basin formed during the collapse and uplift of the SGT.

The Dom Feliciano Belt in Southern Brazil and Uruguay

The Dom Feliciano Belt is an orogenic association that extends from southern Brazil to Uruguay parallel to the Atlantic coastline for over 1100 km. It was assembled in the Neoproterozoic, during the Brasiliano orogenic cycle, and is the result of interaction between the Rio de la Plata, Congo and Kalahari cratons, together with several microplates, juxtaposed along major shear zones. Along its extension, the Dom Feliciano Belt is exposed in three sectors: in the Brazilian states of Santa Catarina and Rio Grande do Sul, and in Uruguay. The blocks that acted as direct forelands to the belt in South America are smaller fragments to the main cratons: Luis Alves and Nico Perez. Three main lithotectonic domains are recognized in the belt, from east to west: a granitic batholith, a metasedimentary sequence and an association of foreland basins. Basement inliers are common, and evidence intense reworking and magmatism during the Neoproterozoic. Cryogenian to Ediacaran granitogenesis is widespread and voluminous, and usually displays an evolutionary tendency from medium- to high-K calc-alkaline, finishing with alkaline magmatism. The early evolution of the Dom Feliciano Belt is recorded in the Sao Gabriel Terrane, in which convergent tectonics is associated with intense juvenile magmatism, ophiolite complexes and accretion between 870 and 680 Ma. This is followed by two more deformational phases, identified in all three sectors. A convergent phase is associated with the deformation of the metavolcano-sedimentary complexes, shear zone nucleation and granitic magmatism associated with high-grade collisional metamorphism. This stage is constrained between c. 650–620 Ma in Santa Catarina and Rio Grande do Sul, and between c. 630–600 Ma in Uruguay. The last stage marks a transition to strike-slip deformation, with common shear zone reactivation associated with refolding in the metamorphic associations and widespread post-collisional granitic and volcanic magmatism. This phase is predominant from 610 to 550 Ma. The opening of the foreland basins was initiated during this period, probably associated with transtension along the main structures. Late-stage deformation and magmatism is common until 550–540 Ma. Abundant geochronological data have been added to the Dom Feliciano Belt in the last decades, leading to more precise time constraints for most of the geologic processes in the orogen. Details of its tectonic model, however, are still matters of debate, in terms of both the setting of its main units and its position into the assembly of southwestern Gondwana.

Petrology and isotope geology of mafic to ultramafic metavolcanic rocks of the Brusque Metamorphic Complex, southern Brazil

The Brusque Metamorphic Complex (BMC) is one of the main units of the Tijucas Terrain within the Dom Feliciano Belt, located in the state of Santa Catarina in southern Brazil. In the Itapema region, the BMC is composed chiefly of metasediments, including subordinate metabasalts, meta-ultramafic rocks, and clinoamphibole schists. The metavolcanic rocks form 4 m-thick lenses interlayered with metapelites and calc-silicate schists. Based on the observed textures and the associated structural, bulk-rock geochemical, and mineral chemical data, these metamafites and ultramafites were ancient lava flows of tholeiitic basalts and ultramafic cumulates. The mineral parageneses of the metabasalts are albite + actinolite + chlorite + epidote + titanite + magnetite and oligoclase + hornblende + epidote + titanite + magnetite, indicating progressive transformations produced under greenschist to amphibolite facies conditions. Volcanogenic metasediments show the same geochemical patterns as the metabasalts, whereas the metamorphosed ultramafic rocks consist of cumulates generated by crystal fractionation and flow segregation. The studied rocks show similar rare-earth element (REE) patterns, characterized by clearly higher normalized contents of light REEs compared with heavy REEs, without Eu anomalies in the metabasalts and positive Eu anomalies in meta-ultramafic rocks and volcanogenic metasediments. In accordance with the trace element contents that indicate a within-plate nature, the corresponding mafic melts apparently formed in the mantle by partial fusion and were subsequently enriched with crustal components during ascent into the sialic crust. The analysed 143Nd/144Nd and 87Sr/86Sr ratios lie between 0.5123 and 0.5126 and 0.7067 and 0.7086, respectively, and are thus typical of tholeiitic basalts of the continental plateau type. Initial ϵNd(936) values and derived model ages (T DM) between 1028 and 1762 million years support a mantle source or sources, with extraction and emplacement in the Neoproterozoic. Field relations and geochemical data (including isotopic data) indicate the generation of the studied mafic and ultramafic rocks in a continental rift. In the regional geologic context, the formation of the BMC volcanic and metasedimentary units marks a period of fragmentation of the Palaeoproterozoic continental crust. This extensional event is preserved regionally in gneisses from the Santa Catarina Granulitic Complex and the Camboriú Complex.

The Nico Pérez Terrane of Uruguay and Southeastern Brazil

The Nico Perez Terrane of Uruguay and southeastern Brazil is characterized by an important component of Archean crustal growth and extensive post-Archean crustal reworking recorded in Paleoproterozoic zircon magmatic crystallization ages in widely distributed granitic orthogneisses. Supracrustal blocks of an older Neoarchean to Siderian sedimentary cover including BIFs, quartzites and marbles are preserved only as minor relics. Additionally, an intraplate Mesoproterozoic record includes anorthosite complexes, metagabbros, amphibolites, felsic volcanic rocks and sediments assumed to correspond to a stable platform cover. Rocks with similar isotopic features occur also as basement inliers and roof pendants in the batholiths of the Dom Feliciano Belt. Two different subterranes are recognized in the Nico Perez Terrane, separated by the north-northeast-trending Cacapava–Sierra de Sosa Shear Zone. The granulite-facies Valentines Rivera and Santa Maria Chico granulitic complexes crop out in the western side of the shear zone and were less reworked during the Neoproterozoic, while the Pavas Block of Uruguay and several basement inliers in the Tijucas Terrane and Pelotas Batholith of Brazil were strongly reworked. Cooling ages, extensive shear zones and granite intrusions document this reworking that was probably facilitated by a thin lithosphere. The Nico Perez Terrane represents a fragment of the Congo Craton separated during the Neoproterozoic.

Análise petrográfica e proveniência dos metassedimentos do Complexo Pontas do Salso, Terreno São Gabriel, Cinturão Dom Feliciano, RS

The Pontas do Salso Complex occurs in the south part of the Sao Gabriel Terrane, western portion of the Dom Feliciano belt, center-west of the Rio Grande of South. To evaluate the stratigraphic relationships and characterize the units of the complex was carried out a detailed geological and structural mapping, with collection of samples for petrographic analysis, assessment of relations between metamorphism and deformation and modal count of the constituent minerals to define the provenance of the metasediments. The Pontas do Salso Complex consists of meta-arkoses with subordinate occurrence of metaconglomerates and metapelites. The meta-arkoses presents fine to coarse blastopsamitic texture with porphyroclasts of hexagonal quartz and plagioclase. The polimitic metaconglomerates are matrix supported and show between 15 and 55 % of the clasts. The pelitic rocks are mainly composed of muscovite phyllites. The analyzed samples were classified as arkoses and lithic arkoses and the majority of the arenites fell on the field of Dissecated Arc. The orogenic metamorphism developed clorite, biotite/cloritoid and garnet zones, defining Upper greenschist to amphibolite facies conditions. The metasediments were still subjected to thermal metamorphism, however, the sedimentary structures and the volcanogenic and granitic sources are preserved. The presence of clasts of tonalites and granodiorites related to Lagoa da Meia Lua Suite suggests that the deposition of the metasediments is posterior to the emplacement of the units of this suite, whose U-Pb SHRIMP zircon ages are between 690 to 680 Ma.