Browsing by Author "Remus, Marcus Vinicius Dorneles"

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    Complexos máfico-ultramáficos do escudo Sul-rio-grandense : revisão com ênfase na geoquímica dos elementos da série 3D de transição.
    (1992) Hartmann, Leo Afraneo; Wildner, Wilson; Remus, Marcus Vinicius Dorneles; Suita, Marcos Tadeu de Freitas
    Os complexos máfico-ultramáficos do Rio Grande do Sul foram reavaliados, com ênfase nos dados disponíveis para elementos químicos da série 3d de transição. Os complexos apresentam geralmente três componentes, quais sejam, ultramáfico (principalmente peridotitos, serpentinitos e xistos magnesianos), máfico e metassomático. Este último componente está bem desenvolvido na maioria dos complexos e foi identificado mas não estudado em detalhe. A suíte gabróica está presente em diversas áreas, tal como Pedras Pretas, e mostra uma química da série 3d de transição desde menos evoluída até mais evoluída, podendo ser classificada da mesma forma que em outras séries do mundo. Os serpentinitos são semelhantes entre si, independente da área avaliada, normalmente mostrando características residuais exceto em Pedras Pretas, onde a química do protólito gabróico foi mantida. Os peridotitos do Cerro da Mantiqueira são harzburgitos e a sua química da série 3d não pode ser distinguida de serpentinitos. Na região do Arroio Cambaizinho, os xistos magnesianos contendo várias proporções de tremolita + clorita + magnetita + ilmenita foram testados em camadas com um a cinco metros de espessura e que apresentam continuidade lateral de afloramento de centenas de metros. Eles mostram química uniforme na mesma banda e parecem corresponder a lavas magnesianas, de afinidade possivelmente komatiítica, metamorfizada na fácies anfibolito. As lavas foram derivadas de um manto enriquecido em elementos LILE ou contaminadas por material crustal.
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    Estudos químicos, físicos e isotópicos em zircões.
    (1996) Hartmann, Leo Afraneo; Vasconcellos, Marcos Antonio Zen; Leite, J. D.; Takehara, Lucy; Remus, Marcus Vinicius Dorneles; Suita, Marcos Tadeu de Freitas; McNaughton, Neal Jesse
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    Integrated ophiolite and arc evolution, southern Brasiliano Orogen.
    (2020) Alves, Tiara Cerva; Hartmann, Leo Afraneo; Remus, Marcus Vinicius Dorneles; Lana, Cristiano de Carvalho
    Integrated study of Tonian ophiolite mélanges and intra-oceanic arc of the São Gabriel juvenile terrane exposes a key geotectonic unit in the evolutionary history of Gondwana during Brasiliano Orogeny. LA-ICP-MS U-Pb geochronology in rutile and zircon were combined with Lu-Hf and rare earth elements in zircon. We report the first rutile dating of ultramafic rock in the Brazilian Shield of 787.6 ± 2.6 Ma for the Cambaizinho ophiolite magnesian schist. Dating of rutile corresponds to the metamorphic age of the mantle section of the ophiolite. São Gabriel arc infrastructure is represented by the Cambaí Complex, including the Vila Nova Suite metatonalite with zircon U-Pb age of 724.6 ± 3.2 Ma and late Sanga do Jobim Suite monzogranite intrusions with two main pulses at 698.9 ± 4.2 Ma and 673.9 ± 6.8 Ma. Zircon εHf(t) values are positive for both rocks and range between +10.1 and +7.4 in metatonalite and +9.2 to +2.5 in monzogranite. Detrital zircon from metasedimentary rocks support superstructure arc investigation. Ages range from 817 to 650 Ma, with strong concentration between 750 and 730 Ma. Positive εHf(t) values and Rare Earth Elements (REE) signature point to main source of metasedimentary rocks in the arc, with ophiolitic contribution. Therefore, geotectonic processes in the Brasiliano Orogeny include the construction of São Gabriel terrane with Tonian oceanic crust evolving to intra-oceanic subduction until 650 Ma to final development along the margin of continental crust. Overthrusting of the São Gabriel terrane onto the Rio de La Plata Craton occurred at 650–620 Ma. Our data correlate with Tonian intra-oceanic arcs from Brasilia belt (Goiás arc ca. 862–630 Ma) and Ribeira belt (Serra da Prata arc – 856–838 Ma; Rio Negro arc – 790–620 Ma). Oceanic crust generation combined with subduction to form Tonian arcs along the Brasiliano Orogen were most significant for construction of West Gondwana.
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    Oceanic crust and mantle evidence for the evolution of tonian-cryogenian ophiolites, southern Brasiliano Orogen.
    (2020) Werle, Mariana; Hartmann, Leo Afraneo; Queiroga, Gláucia Nascimento; Lana, Cristiano de Carvalho; Silva, Juliana Pertille da; Michelin, Cassiana Roberta Lizzoni; Remus, Marcus Vinicius Dorneles; Roberts, Malcolm; Castro, Marco Paulo de; Leandro, Carolina Gonçalves; Savian, Jairo Francisco
    Unravelling the complexity of tonian-cryogenian (950–680 Ma) evolution of ophiolites requires the search for rare mineral systems and their quantification with varied techniques. Ophiolites in the Brasiliano Orogen are widely distributed over 2,000 km along the eastern half of South America. We selected two ophiolites from different geotectonic settings of the Sul-Riograndense Shield, southern Brasiliano Orogen, to delimit the evolution of the oceanic phase of the orogen. The southern portion of the Bossoroca ophiolite is inserted in the Sao ˜ Gabriel juvenile terrane and contains rare metasomatic tourmaline in chloritite close to serpentinite and metamorphosed Cr-spinel. The southern Bossoroca ophiolite was intruded by Cerro da Cria and Ramada Granites and the U-Pb-Hf isotopic study of zircon from these rocks constrains the crustal evolution of the Sao ˜ Gabriel juvenile terrane. Capan´e ophiolite has similar age (793–715 Ma) as the Bossoroca ophiolite and was inserted in the Porongos fold-thrust belt with preserved Cr-spinel of mantellic composition. Integrated use of Cr-spinel mineral chemistry, B isotopes in tourmaline in the Bossoroca ophiolite and zircon U-Pb-Hf isotopes of granites associated with the southern Bossoroca ophiolite revealed several steps in the evolution of the ophiolites in the Dom Feliciano Belt. Capan´e Cr-spinel cores have mantle-derived compositions (Mg# 0.66 – 0.69; Cr# 0.51 – 0.53), tourmaline from the Bossoroca ophiolite is dravite and has δ11B = 0 to + 3, and granites crystallization ages are 578 ± 3.2 and 612 ± 12 Ma (εHfzrn = − 10 to − 25). Zircon from other dravite occurrences of the Bossoroca ophiolite were previously dated at 920 Ma. We unraveled the main steps in the evolution of ophiolites from the southern Brasiliano Orogen, with emphasis on the Bossoroca and Capan´e ophiolites, during their trajectory from mid-ocean ridge (920 Ma), formation of dravite in oceanic crust, preservation of mantellic cores in Cr-spinel, and intrusion of craton-generated granites at 612–578 Ma.