Petrologia do Arquipélago de Martin Vaz e dos Montes Submarinos da Cadeia Vitória-Trindade: Montague, Jaseur, Davis, Dogaressa e Columbia: análise de elementos traços, datação 40Ar/39Ar e de Nd e Sr relacionada à evidência da Pluma de Trindade

• Autor(a) principal: Santos, Anderson Costa dos
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/7023
• topic: Vitoria-Trindade Ridge; Martin Vaz; Seamounts; Ar-Ar Dating; Nephelinites; Cadeia Vitória-Trindade; Martin Vaz; Montes Submarinos; Datação Ar-Ar; Nefelinitos; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

The current work presents the results of chemical mineral analysis, whole rock and isotopic composition of Sr and Nd from five seamounts (Montague, jaseur, Davis, Dogaressa and Columbia) and the Martin Vaz main island, located in the offshore portion of southeastern Brazil. These alkaline intrusions were generated during the Plio-Pleistocene, dated by the 40Ar/39Ar method. They are represented by sodic magmas of nephelinitic composition reveal-ing a magmatic evolution process by fractional crystallization in Martin Vaz Island generating phonolites. The composition of the olivine phenocrysts in the seamounts and Martin Vaz indi-cates a disequilibrium liquid (assuming Fe/Mgol/liq KD ~ 0,30 ±0,03) probably associated with a prior crystallization process from an evolved magma. The green cores pyroxenes from Mar-tin Vaz nephelinite lavas are characterized by a polibaric fractionation. The different chemical compositions in clinopyroxenes corroborate a magma replenishing model. The 87Sr/86Sr (~ 0.703800) and 143Nd/144Nd (~ 0.512800) ratios of seamounts and Martin Vaz do not vary sig-nificantly reiterating a partial melting process from a homogeneous depleted source in com-parison to the Bulk Silicate Earth (BSE). The enrichment pattern in rare-earth elements and isotopic ratios indicates that the metasomatism process is recent and not a long-term source characteristic. Non-modal partial melting models (Fractional Melting and Batch Melting) suggest that the source of the Vitoria-Trindade Ridge magmatism is a mixing between the spinel and the garnet-lherzolite (75-90 Km) generated between 2.0-3,0 GPa which REE en-richment and chemical variability is due to small degree of partial melting (F = 0.02-0.07)