Ilha dos Búzios, Litoral Norte do Estado de São Paulo: aspectos geológicos e petrográficos

Alves, Francisco Rubens; Gomes, Celso B.

doi:10.5327/s1519-874x2001000100007

Cited by 9 publications

(13 citation statements)

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“…A detailed and complete mineralogical and petrographic description of the Búzios alkaline rocks is given in Alves (1997), with a more concise version published by Alves and Gomes (2001).…”

Section: Geological Aspectsmentioning

confidence: 99%

“…This latter hypothesis usually leads to the mixture of mafic and felsic melts. However, there is no description of field, petrographic or chemical evidences of magma mixing in the area (Alves 1997;Alves & Gomes 2001).…”

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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“…A detailed and complete mineralogical and petrographic description of the Búzios alkaline rocks is given in Alves (1997), with a more concise version published by Alves and Gomes (2001).…”

Section: Geological Aspectsmentioning

confidence: 99%

Section: Petrologymentioning

confidence: 99%

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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“…The felsic rocks are largely predominant and made up mainly by SiO2-oversaturated alkali feldspar syenites and quartz-alkali feldspar syenites (Bellieni et al, 1990;Alves, 1997;Alves and Gomes, 2001;Augusto, 2003;Gomes et al, 2017), SiO2-undersaturated nepheline syenites and nepheline alkali feldspar syenites varieties (Motoki, 1986;Enrich et al, 2009), and related dike rocks composed mainly by trachytes and phonolites. These felsic rocks are spatially and temporally associated with layered mafic-ultramafic alkaline intrusions, as in the São Sebastião and Monte do Trigo islands, composed mainly by a variety of gabbros and minor clinopyroxenites.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…The felsic plutonic rocks made up three roughly subcircular intrusions: the larger Serraria (to the north), the São Sebastião (to the south) and the minor Mirante massifs (to the east) (Figure 3.1B). The first two are made up mostly by SiO2-oversaturated alkali feldspar syenites and quartz alkali feldspar syenites, while in the third, both SiO2-oversaturated andundersaturaded rocks are known (Motoki, 1986;Bellieni et al, 1990;Alves, 1997;Augusto, 2003;Alves and Gomes, 2001;Gomes et al, 2017).…”

Section: Geological Backgroundmentioning

confidence: 99%