Geochemistry and geochronology of mafic rocks from the Vespor suite in the Juruena arc,Roosevelt-Juruena terrain,Brazil: Implications for Proterozoic crustal growth and geodynamic setting of the SW Amazonian craton |
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| Affiliation: | 1. Geological Survey of Brazil (CPRM), SGAN 603, 1° Andar, CEP 70830-100 Brasília, DF, Brazil;2. Geological Survey of Brazil (CPRM), Setor Marista, 148, CEP 74170-110 Goiânia, GO, Brazil;3. Instituto de Geociências, Universidade de Brasília, CEP 70910-900 Brasília, DF, Brazil;1. Department of Oral and Maxillofacial Prosthodontics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan;2. Department of Cellular and Molecular Pharmacology, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan;3. Department of Oral Biology and Engineering, Institute of Biomedical and Health Science, Hiroshima University, Hiroshima, Japan;4. Liaison Center for Innovative Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Japan;5. Department of Advanced Prosthodontics, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan;6. Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan;1. Faculdade de Geociências, Universidade Federal de Mato Grosso, Av. Fernando Corrêa 2367, Coxipó, Cuiabá-MT, 78060-900, Brazil;2. Programa de Pós-Graduação em Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Campus do Vale, Porto Alegre-RS, 91509-970, Brazil;3. CONICET-Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Av. Ángel Gallardo 470, Buenos Aires, C1405DJR, Argentina;1. Centro de Pesquisas Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais (CPMTC-IGC-UFMG), Campus Pampulha, Av. Antônio Carlos 6627, CEP 31270-901, Belo Horizonte, MG, Brazil;2. Laboratório de Geocronologia, Instituto de Geociências, Universidade de Brasília, Campus Universitário, Asa Norte, CEP 70910-900, Brasília, DF, Brazil;3. GEOTOP, Université du Québec à Montréal, P.O. Box 8888, Station Centre Ville, Montreal, Quebec, H3C 3P8, Canada;1. Instituto Nacional de Minas, Av 24 de Julho, 1895, Maputo, Mozambique;2. Instituto de Energia e Ambiente, Av Luciano Gualberto, 1289, CEP, 05508-010, Universidade de São Paulo, Brasil |
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| Abstract: | This study presents new geochemical data on rocks from the Vespor suite, an important mafic unit from the Juruena arc, Roosevelt-Juruena terrain, SW Amazonian craton, northwest Mato Grosso, Brazil, attempting to define their tectonic setting and type of mantle source. The Juruena arc may be part of a magmatic belt (Jamari and Juruena arcs) at the southwestern Amazonian craton during assembly of the Columbia supercontinent. The investigated rocks represent a Paleoproterozoic subduction-related mafic suite of sigmoidal bodies, composed mainly of gabbro, norite, gabbronorite and diorite, that underwent amphibolite facies metamorphism. Here we present also preliminary petrology aspects and zircon U–Pb geochronology. Geochemical character and variation trends of major and trace elements as well as selected trace element ratios suggest that Vespor suite rocks have a tholeiitic lineage of arc affinity controlled by fractional crystallization with a prominent iron enrichment trend. Gabbros, norites and gabbronorites are characterized by enrichment of LILE and weakly to moderately differentiated HFSE patterns, suggesting their deviation from an enriched heterogeneous lithospheric mantle source. Vespor suite rocks are characterized by depletion of Nb–Ta, P and Ti, with flat distribution of HFSE, markedly large variations in most of the LILE, positive anomalies displayed by Ba, K, Th, Sr, Pb and weak negative anomalies of Hf–Zr. These features reflect limited degrees of crustal contamination associated with a subduction-related magma process where the mantle wedge was chemically modified. In addition, the enrichment in LILE and Pb, low values of the ratios (Lan/Smn – 0.83 to 4.58) and (Nbn/Lan – 0.04 to 0.45), but high Th/Yb ratios, gently to moderately sloping REE profiles (La/Ybn = 2.53–7.37), negative anomalies in HFSE (Ta, Zr, Hf, and Ti), and positive anomalies in LILE (Th, Ba, Sr), suggest derivation from a metasomatized lithospheric mantle source above a subduction zone with weak crustal contamination. Both the composition of the mantle source and the degree of partial melting that produced the parental magmas of these rocks, determined by using REE abundance and ratios, indicate that gabbroic/dioritic melts were generated at different degrees of melting of the source: about 5–20% partial melting of a garnet-spinel lherzolite, around 1–10% partial melting of spinel lherzolite source, and approximately 1–5% partial melting of intermediate source composition, and crystallizing between 1.773 and 1.764 Ma. |
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| Keywords: | Mafic rocks Juruena arc SW Amazonian craton Geochemistry Geochronology Paleoproterozoic crustal growth |
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