Composition and processes of the mantle lithosphere in northeastern Brazil and Fernando de Noronha: evidence from mantle xenoliths

Rivalenti, Giorgio; Mazzucchelli, Maurizio; Girardi, Vicente Antônio Vitório; Vannucci, R.; Barbieri, M. Adelaide; Zanetti, Alberto; Goldstein, S. L.

doi:10.1007/s004100050565

Cited by 50 publications

(36 citation statements)

References 44 publications

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“…The major-element composition of mineral phases was determined by electron microprobe according to the methodology reported by Rivalenti et al [27]. Data were checked and corrected using cation mass balance with different O normalization for each phase (amphibole: 23 O p.f.u.…”

Section: Methodsmentioning

confidence: 99%

Occurrence of phlogopite in the Finero Mafic layered complex

Giovanardi¹,

Mazzucchelli²,

Zanetti

et al. 2014

Open Geosciences

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Phlogopite-bearing lithologies are the main constituent of the Phlogopite-Peridotite unit of the Finero sequence and the result of pervasive migration of metasomatizing melts/fluids. Conversely, the presence of phlogopite within the associated Finero Mafic Complex, a mafic-ultramafic pluton intruded into the metamorphic basement of the Adria plate, is mentioned in literature as rare. Recent detailed fieldwork has evidenced the presence of two distinct phlogopite-rich ultramafic lithologies within the Amphibole-Peridotite unit of the Finero Mafic Complex, where phlogopite is always associated with amphibole. Field and petrographic features of these occurrences, as well as major-and trace-element mineral chemistry, are here presented to i) place constraints on the nature of the parent melt from which they have been generated and ii) to address their relationship with the other lithologies of the Finero Complex. We find that these rocks were formed by late melt migrations along shear zones under high-T conditions. The geochemical affinity of these lithologies is different to the tholeiitic-transitional affinity reported in literature for the Finero Mafic Complex. The enrichment in LREE, Th, U and Sr of the associated amphibole possibly suggests that these phlogopite-bearing lithologies are genetically related to the metasomatic events that have affected the Finero mantle massif.

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Section: Methodsmentioning

confidence: 99%

Occurrence of phlogopite in the Finero Mafic layered complex

Giovanardi¹,

Mazzucchelli²,

Zanetti

et al. 2014

Open Geosciences

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“…The basanites of the São José Formation, now assigned agewise to Remédios [6], carry significant amounts of mantle enclaves, thus representing crystallized magmas that were in equilibrium with mantle peridotes [10,11].…”

Section: Discussionmentioning

confidence: 99%

“…The Remédios Formation is mainly pyroclastic, massively invaded by several plugs and dikes of varied alkaline rocks (basanites and related types, phonolites, lamprophyres), while the Quixaba Formation presents melanocratic rocks (basanite and melanephelinite flows). Almeida added a minor third unit, constituted by the basanites of the São Jose Formation, only outcropping on the São José and Cuscuz islands, characterized by the presence of abundant mantle fragments (petrographic data in [1,2,8,9]; for description of mantle xenoliths, see [10,11]). The first K-Ar determinations yielded for the Remédios Formation ages between 12 and 8 Ma (Miocene), while Quixaba rocks were emplaced mostly at ages around 3 to 2 Ma (Pliocene), with the youngest age around 1.4 Ma [4].…”

Section: Geologic and Petrographic Outlinementioning

confidence: 99%

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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“…Geology thus clearly indicates the activity of two volcanic events, separated by a very active erosion interval. To the NW, on the islands of São José and Cuscuz, Almeida (1955) separated a series of basanite flows as a distinct younger unit, that appears as a discordant deposit over Quixaba rocks, which he defined as the São José Formation, also differentiated from other Quixaba rocks by the presence of sometimes abundant peridotitic mantle xenoliths (sizes between mm to decimeters; descriptions in Rivalenti et al 2000;Kogarko et al 2001). Some authors proposed that the São José flows may represent the culmination of the Quixaba volcanism (e.g.…”

Section: Stratigraphic Units and Geologic Occurrencesmentioning

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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Composition and processes of the mantle lithosphere in northeastern Brazil and Fernando de Noronha: evidence from mantle xenoliths

Cited by 50 publications

References 44 publications

Occurrence of phlogopite in the Finero Mafic layered complex

Occurrence of phlogopite in the Finero Mafic layered complex

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

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