Geochemical Distribution Patterns of Magmatites from the Archipelago of Fernando de Noronha

Schwab, R.; Bloch, W.

doi:10.1127/zbl_geol_pal_1/1985/1986/1477

Cited by 3 publications

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“…To define the correspondence between the older names and the newer nomenclature, we follow mainly the discussion presented in Ulbrich (1993), Lopes (2002), and Ulbrich et al (2004), and the definitions given in Le Maitre (2002); other discussions and information on the petrography of FN rocks can be found in Gunn and Watkins (1976), Schwab and Bloch (1985), Cornen (1986), Gerlach et al (1987) and Weaver (1990).Data about mineral chemistry of these rocks can be found in a recent paper by Lopes et al (2014).…”

Section: Petrography As a Guideline For Petrogenetic Interpretationsmentioning

confidence: 99%

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Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean

Lopes

Ulbrich

2015

Braz. J. Geol.

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ABSTRACT:The Fernando de Noronha Archipelago presents, on its main island, a centrally-located stratigraphic unit, the Remédios Formation (age around 8 -12 Ma) constituted by basal pyroclastic rocks intruded by dikes, plugs and domes of varied igneous rocks, capped by flows and pyroclastics of mafic to ultramafic rocks of the Quixaba Formation (age around 1 -3 Ma), which is limited from the underlying unit by an extensive irregular erosion surface. A predominant sodic Remédios series (basanites, tephrites, tephriphonolites, essexite, phonolites) can be separated from a moderately potassic Remédios sequence (alkali basalts, trachyandesites, trachytes), both alkaline series showing mostly continuous geochemical trends in variation diagrams for major as well as trace elements, indicating evolution by crystal fractionation (mainly, separation of mafic minerals, including apatites and titanites). There are textural and mineralogical evidences pointing to hybrid origin of some intermediate rocks (e.g., resorbed pyroxene phenocrysts in basaltic trachyandesites, and in some lamprophyres). The primitive Quixaba rocks are mostly melanephelinites and basanites, primitive undersaturated sodic types. Geology (erosion surface), stratigraphy (two distinct units separated by a large time interval), petrography (varied Remédios Formation, more uniform Quixaba unit) and geochemistry indicate that the islands represent the activity of a protracted volcanic episode, fueled by intermittent melting of an enriched mantle, not related to asthenospheric plume activity. KEYWORDS:OIB; South Atlantic Ocean; Mafic to ultramafic volcanic-subvolcanic rocks; Sodic and potassic series. RESUMO: O Arquipélago de Fernando de Noronha mostra na sua ilha principal, na parte central, a Formação Remédios (idade em torno de 8 -12 Ma) constituída por rochas piroclásticas basais invadidas por diques, plugs e domos de variadas rochas ígneas, capeadas por derrames e piroclásticas das rochas máficas a ultramáficas da Formação Quixaba (idade de 1 a 3 Ma), separada da unidade inferior por uma superfície de erosão extensa e irregular. Uma série predominante sódica de Remédios (basanitos, tefritos, tefrifonolitos, essexito, fonolitos) pode ser diferenciada da série moderadamente potássica (álcali basaltos, traquiandesitos, traquitos), pertencente à mesma unidade. Ambas as séries mostram tendências geoquímicas geralmente contínuas em diagramas de variação de elementos maiores e traços, indicando origem por cristalização fracionada (principalmente, separação de minerais máficos, incluindo apatitas e titanitas). São encontradas evidências mineralógicas e texturais apontando

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Section: Petrography As a Guideline For Petrogenetic Interpretationsmentioning

confidence: 99%

“…The archipelago was visited sporadically by geologists who added geochemical and isotopic data (Gunn & Watkins 1976;Stormer & Whitney 1978;Schwab & Bloch 1985;Cornen 1986;Gerlach et al 1987;Weaver 1990). …”

Section: Introductionmentioning

confidence: 99%

Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean

Lopes

Ulbrich

2015

Braz. J. Geol.

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“…Diagramas semelhantes complementados com dados de fonólitos, h'aquiandesitos, etc. levaram Schwab & Bloch (1985) a caracterizar as variações quírnicas das rochas de Fernando de Noronha como sendo o resultado de um processo sirnples de cl'istalização flacionada.…”

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Estudo petrográfico e químico de diques ultramáficos e máficos do arquipélago de Fernando de Noronha, PE

Maríngolo¹

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Paleomagnetism and rock magnetism of Fernando de Noronha, Brazil

Schultz¹,

Calvo‐Rathert

Guerreiro

et al. 1986

Earth and Planetary Science Letters

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Geochemical Distribution Patterns of Magmatites from the Archipelago of Fernando de Noronha

Cited by 3 publications

References 0 publications

Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean

Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean

Estudo petrográfico e químico de diques ultramáficos e máficos do arquipélago de Fernando de Noronha, PE

Paleomagnetism and rock magnetism of Fernando de Noronha, Brazil

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