Geochemical behaviour of trace elements during fractional crystallization and crustal assimilation of the felsic alkaline magmas of the state of Rio de Janeiro, Brazil

Motoki, Akihisa; Sichel, Susanna Eleonora; Vargas, Thais; Melo, Dean Pereira de; Motoki, Kenji Freire

doi:10.1590/0001-3765201520130385

Cited by 32 publications

(17 citation statements)

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“…Unfortunately, no isotopic data are available for the Búzios rhyolitic rocks. Crustal assimilation processes are believed to play an important role in the genesis of other alkaline intrusions of Southern Brazil, as suggested by Motoki (1986) and Motoki et al (2015) for the neighboring Vitória Island and the Cabo Frio massif, as well as by Azzone et al (2016) for the mafic-ultramafic complex of Ponte Nova.…”

Section: Petrologymentioning

confidence: 99%

“…Geological information on such alkaline occurrences dates back to the last century -as São Sebastião (Freitas 1947;Hennies & Hasui 1968, 1977Bellieni et al 1990;Garda 1995;Lima & Schorscher 1999), Búzios (Björnberg & Ellert 1955;Alves 1997), Vitória (Motoki & Gomes 1984;Motoki 1986;Motoki et al 1987), and Monte de Trigo (Coutinho & Melcher 1973) -, but more recently these islands, especiallly Monte de Trigo, have become the subject of systematic works dealing mainly with their mineralogy, geochemistry and petrology, like São Sebastião (Augusto & Vlach 2004;Enrich et al 2005), Búzios (Alves & Gomes 2001), Vitória (Motoki et al 2015), and Monte de Trigo (Enrich 2005;Enrich et al 2009Enrich et al , 2016.…”

Section: Introductionmentioning

confidence: 99%

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Geochemistry and petrology of the Búzios Island alkaline massif, SE, Brazil

et al. 2017

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ABSTRACT:The Late Cretaceous Búzios Island alkaline massif intrudes Precambrian charnockites and consists dominantly of syenitic rocks that are cut by a large number of dikes, mostly NE-trending, and representing two distinct suites, a felsic one and a mafic-ultramafic one. Alkali feldspar is the most abundant mineral; other constituents are clinopyroxene, commonly replaced by amphibole/ biotite, and opaques. Accessory minerals include occasionally rare phases bearing Zr, Ti, Nb and Rare Earth Elements (REE). The felsic dikes may also have nepheline (sodalite). The mafic-ultramafic suite, in particular the lamprophyres, shows a primary mineral assemblage with olivine, clinopyroxene and amphibole in addition to a groundmass having glassy material and carbonates (ocelli). The Búzios rocks are chemically evolved, mostly of potassic affinity and mainly belong to the miaskitic series. Variation diagrams for major and trace elements show a bimodal distribution, suggesting an origin from different magmatic pulses. The rocks are interpreted as having been derived by fractional crystallization processes from a basanitic parental magma. The SiO 2 -undersaturated and SiO 2 -oversaturated associations present in the massif are apparently not linked to a single magmatic source, and in the petrogeny residual system two trends are evident: the first one towards the phonolitic minimum and the second one towards the rhyolitic minimum, possibly pointing to amphibole fractionation.KEYWORDS: Igneous petrology; Alkaline rocks; Geochemistry. RESUMO: O maciço alcalino da Ilha dos Búzios, do Cretáceo Superior, é intrusivo em charnockitos precambrianos e consiste predominantemente de rochas sieníticas cortadas por grande número de diques, orientados preferencialmente para NE, representando duas suítes distintas: félsica e máfica-ultramáfica. Feldspato alcalino é o mineral mais abundante; outros constituintes são clinopiroxênio, comumente substituído por anfibólio/biotita, e opacos. Minerais acessórios incluem ocasionalmente fases raras contendo Zr, Ti, Nb e elementos terras raras (ETR). Os diques félsicos podem possuir também nefelina (sodalita). A suíte máfica-ultramáfica, particularmente os lamprófiros, apresenta uma assembleia mineralógica primária com olivina, clinopiroxênio e anfibólio, além de massa fundamental com material vítreo e carbonatos (ocelli

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Section: Petrologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Geochemistry and petrology of the Búzios Island alkaline massif, SE, Brazil

et al. 2017

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“…Mafic alkaline dyke swarms (mostly basanites and alkali basalts, plus rarer camptonites and foidites), together with subordinate felsic differentiates (tephritic phonolites, trachyandesites, trachytes and phonolites) cross-cut some alkaline complexes and the crystalline basement (e.g. Brotzu et al, 1989Brotzu et al, , 2005Sichel et al, 2012;Motoki et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

TheREE-and HFSE-bearing phases in the Itatiaia alkaline complex (Brazil) and geochemical evolution of feldspar-rich felsic melts

et al. 2017

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The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- A nd trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondritenormalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/trachytic/phonolitic complexes of the Serra do Mar and elsewhere

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“…The total alkalis versus silica diagram ( Figure 42; see List of Figures), higher Nb/Y ratios ( Figure 43), and steeper slopes of Wells Gray sideromelane on chondrite-normalized rare earth element (REE) diagrams (Figures 48 and 49) confirm that, for samples analyzed in this study, those from Wells Gray are more alkaline than those from Helgafell. Sideromelane analyses from the two Helgafell outcrops appear to have distinguishable characteristics with those low in the stratigraphic section showing subtly higher Nb/Y ratios ( Figure 43) consistent with higher percentages of melting (Condie, 2003;Floyd & Winchester, 1975;Greenough & MacKenzie, 2015;Greenough & Ya'acoby, 2013) as well as subtly lower Zr/TiO 2 ( Figure 43) indicative of slightly less differentiation (Hastie et al, 2007;Motoki et al, 2015;Murphy, 2007). The eruption that produced the unit may have been precipitated by the arrival of a new batch of magma to the magma chamber.…”

Section: Sideromelane Compositionsmentioning

confidence: 94%

A Comparative Study of Glaciovolcanic Palagonitization of Tholeiitic and Alkaline Sideromelane at Helgafell, Iceland and Wells Gray-Clearwater Volcanic Field, Bc Canada

Massey¹,

Greenough²,

Edwards³

2017

Geological Society of America Abstracts With Programs

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Pleistocene glaciovolcanic eruptions occurred frequently beneath continental-scale ice sheets producing vitric, fragmental volcanic deposits in Helgafell, Iceland (tholeiitic basalt) and Wells Gray, BC, Canada (alkali olivine basalt). They are highly susceptible to hydrothermal alteration that transforms sideromelane (basaltic volcanic glass) into palagonite (early amorphous material) and secondary minerals (i.e. zeolites, clays and sulfides). Compositional controls, mass transfer and geochemical-textural relationships are investigated by optical microscopy and analyses of major (12) and trace (32) elements in glass-palagonite pairs by Electron Microprobe Analysis (EMPA), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and geochemical modelling. Helgafell's thinner (6-10 µm vs. 10-20 µm) palagonite rims demarcate highly vesicular (30.2% vs. 4.9%) sideromelane that has more secondary minerals (1.4% vs. 0.5%) than Wells Gray's microlite-rich (12.3% vs. 0.1%) sideromelane. The thicknesses of palagonite rims are similar whether the sideromelane is unaltered or completely altered. Multi-dimensional scaling confirms that sideromelane composition, reflecting igneous processes, strongly controls the chemistry of palagonite. A comparison of element behavior in the palagonite from both localities reveals a tendency for water-soluble cations (Cl, K, Na, Rb, Cu, Mn, P) to correlate with water concentrations. Plots of element ratios (Nb/Y vs La/Nd; Sc/Ta vs Zr/Th) calculated from "immobile" elements show that palagonite from Wells Gray and Helgafell are distinct, and have ratios that are similar to sideromelane that produced the palagonite. Thus some palagonite compositions reflect primary magma compositions based on immobile elements. Gresens' mass transfer calculations confirm minimal movement of these elements during palagonitization. However, the same calculations reveal a pattern of Cu, Cl, Ni, Rb and U addition and Na, Ca, Mg, P, V and Mn removal that is similar at both localities. Microprobe traverses identified eight prominent trends across the glass-palagonite interface and palagonite rim, which do not appear to be controlled by sideromelane composition. Several element concentrations decrease in palagonite, including Si (by ~3-10%), Al, Ca and Na, while Ti, Fe and Mg concentrations increase. Locally, the palagonite has an inner Ti-rich zone. The gradual increase in Mg across the palagonite rim may be indicative of changes in solubility and pH. Preface The sites chosen in Iceland and British Columbia to sample and analyze for this thesis were at the suggestion of co-supervisor, Dr. Benjamin Edwards. Sample collection, cutting and preparation was completed by the author. Stephen Wood at the University of Western Ontario cut the thin sections. Standards used during the SEM-EDS and EMPA-WDS analyses were provided by both the Smithsonian and Micro-Analysis Consultants Ltd.

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Geochemical behaviour of trace elements during fractional crystallization and crustal assimilation of the felsic alkaline magmas of the state of Rio de Janeiro, Brazil

Cited by 32 publications

References 34 publications

Geochemistry and petrology of the Búzios Island alkaline massif, SE, Brazil

Geochemistry and petrology of the Búzios Island alkaline massif, SE, Brazil

TheREE-and HFSE-bearing phases in the Itatiaia alkaline complex (Brazil) and geochemical evolution of feldspar-rich felsic melts

A Comparative Study of Glaciovolcanic Palagonitization of Tholeiitic and Alkaline Sideromelane at Helgafell, Iceland and Wells Gray-Clearwater Volcanic Field, Bc Canada

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