Petrologia dos fonólitos do Arquipélago de Fernando de Noronha, PE

Lopes, Ruy Bessa

doi:10.11606/d.44.1997.tde-22012014-162204

Cited by 6 publications

(9 citation statements)

References 13 publications

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“…also [8,9]. Detailed rock descriptions of lamprophyres and phonolites can be found in [13,14]. The Remédios Formation, with its basal unit of pyroclastics, is intruded by several plugs and domes of three petrographic types of phonolites, a sill-like body of essexite and a small plug of alkali basalt (cf.…”

Section: Geologic and Petrographic Outlinementioning

confidence: 99%

“…The Remédios Formation, with its basal unit of pyroclastics, is intruded by several plugs and domes of three petrographic types of phonolites, a sill-like body of essexite and a small plug of alkali basalt (cf. [12,14]) and also by dozens of dikes, with early basanites and related rocks such as tephrites, basaltic trachyandesites, trachyandesites, trachytes, tephriphonolites [1] as well as four different types of lamprophyres ( [1,2,13]). The Remédios Formation presents also fresh plutonic xenoliths, intermingled with finer-grained pyroclastic material, that represent cogenetic products of cumulate crystallization in deeper-seated magma chambers [15].…”

Section: Geologic and Petrographic Outlinementioning

confidence: 99%

“…Detailed information on the mineralogy and petrography of the main FN rock types are summarized in [1]; additional details on phonolites and lamprophyres can be found in earlier work in [14] and [13]. Tables 1 to 9 present selected analytical determinations of the main rock-forming minerals in FN, retrieved from a complete set available in [1], also incorporating information on feldspars and nephelines cited in [14].…”

Section: Mineral Chemistrymentioning

confidence: 99%

“…The typical phenocrysts in phonolites are usually green and homogeneous sodic salites to ferrosalites; also present are pyroxenes with brown (salites) to brownish-rosy cores (titaniferous salites), while the groundmass pyroxenes are ferrosalites to aegirine augites, which appear in the more differentiated group II aphyric phonolites as long prismatic aegirine grains (cf. [2,14]). …”

Section: Clinopyroxenesmentioning

confidence: 99%

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The volcanic-subvolcanic rocks of the fernando de noronha archipelago, southern atlantic ocean: Mineral chemistry

Lopes

Ulbrich²,

Ulbrich³

2014

Open Geosciences

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Fernando de Noronha archipelago presents an older Remédios Formation with subvolcanic intrusions, belonging to two different alkaline series, the sodic (undersaturated: basanites, tephrites, essexites, tephriphonolites, phonolites), and potassic ones (mildly undersaturated to silicic, with alkali basalts, basaltic trachyandesites, trachyandesites, trachytes), and lamprophyres. The upper Quixaba Formation presents nephelinite flows and basanites. A third minor unit, São José, is constituted by basanites carrying mantle xenoliths. Magnesian olivines occur in the Remédios basanites and alkali basalts, and in nephelinites. Melilites are present as groundmass grains in melilite melanephelinites (MEM). Clinopyroxenes (cpx) are mostly salites to titaniferous salites (Remédios sodic series), grading into aegirines in the differentiated aphyric phonolites. Cpx in the lamprophyres show disequilibrium textures. In the Quixaba flows, cpx are salites, enriched in Mg (especially in MEM). Amphiboles, remarkably, are common in tephriphonolites and phonolites and in basaltic trachyandesites, sometimes with disequilibrum zoning textures, and a conspicuous phase in lamprophyres. Dark micas are present as groundmass plates in MEM, OLM and PYM (olivine and pyroxene melanephelinites), with compositional variety (enriched in Ti, Ba, Sr) depending on the composition of the parent rock; BaO can be as high as 16–19%. Feldspars crystallize as calcic plagioclases, sanidines and anorthoclases, depending on the rock types, as phenocrysts and in groundmass, both in Quixaba and Remédios rocks; they are absent in nephelinites. Nephelines are found in Remédios sodic series types and Quixaba rocks. Haüyne and noseane are rarely observed in Remédios rocks.

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Section: Geologic and Petrographic Outlinementioning

confidence: 99%

Section: Geologic and Petrographic Outlinementioning

confidence: 99%

Section: Mineral Chemistrymentioning

confidence: 99%

Section: Clinopyroxenesmentioning

confidence: 99%

See 2 more Smart Citations

The volcanic-subvolcanic rocks of the fernando de noronha archipelago, southern atlantic ocean: Mineral chemistry

Lopes

Ulbrich²,

Ulbrich³

2014

Open Geosciences

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“…More recently, geologists from the University of São Paulo presented contributions on FN (two Master's thesis, one doctorate thesis : Maríngolo 1995;Lopes 1997Lopes , 2002, and several abstracts and publications on the subject (Ulbrich & Ruberti 1992;Ulbrich 1993;Ulbrich et al 1994Ulbrich et al , 2004Maríngolo & Ulbrich 1997;Lopes & Ulbrich 1997Ulbrich & Lopes 2000a, 2000b.A summary paper on the lithogeochemistry and mineral chemistry of the Quixaba Formation was published in a Brazilian journal (Lopes & Ulbrich 2006), and a more recent one on the mineral chemistry of these rocks (Lopes et al 2014). A recent study on FN was presented at Queensland as a Ph.D. thesis, dealing with geochronologic and petrogenetic aspects (Perlingeiro 2012).…”

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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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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Petrology, geochemistry and Sr–Nd isotopes of the Trindade and Martin Vaz volcanic rocks (Southern Atlantic Ocean)

Marques

Ulbrich

Ruberti

et al. 1999

Journal of Volcanology and Geothermal Research

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Petrologia dos fonólitos do Arquipélago de Fernando de Noronha, PE

Cited by 6 publications

References 13 publications

The volcanic-subvolcanic rocks of the fernando de noronha archipelago, southern atlantic ocean: Mineral chemistry

The volcanic-subvolcanic rocks of the fernando de noronha archipelago, southern atlantic ocean: Mineral chemistry

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

Petrology, geochemistry and Sr–Nd isotopes of the Trindade and Martin Vaz volcanic rocks (Southern Atlantic Ocean)

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