Petrogênese da suíte alcalina da Ilha Monte de Trigo, SP

Rojas, Gaston Eduardo Enrich; Ruberti, Excelso

doi:10.11606/t.44.2006.tde-04022014-164218

Cited by 1 publication

(4 citation statements)

References 26 publications

(42 reference statements)

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“…1B-1E). However, most results are derived from mineral and/or wholerock K/Ar (Amaral et al 1967, Hennies and Hasui 1977, Motoki 1986, Sonoki and Garda 1988, Alves 1997, Azzone et al 2009 and Rb/Sr methods (Motoki 1986, Montes-Lauar et al 1995, with limited high-precision zircon U/Pb ages (Sato 2006, Sato et al 2008) and 40 Ar/ 39 Ar (Enrich 2005, Enrich et al 2009. The results reveal predominant Upper Cretaceous ages, between ca.…”

Section: Previous Geochronological Datamentioning

confidence: 99%

“…In the northern sector of the Serra do Mar Province, the rocks are predominantly felsic and made up mainly of SiO 2oversaturated alkali feldspar syenites and quartz-alkali feldspar syenites (Bellieni et al 1990, Alves 1997, Alves and Gomes 2001, Augusto 2003, Gomes et al 2017, SiO 2 -undersaturated nepheline syenites and nepheline alkali feldspar syenites (Motoki 1986, Enrich 2005, Enrich et al 2009, and associated trachyte and phonolite dykes. Closely associated plutonic mafic-ultramafic alkaline rocks, represented by gabbros and minor clinopyroxenites, occur as layered intrusions in the São Sebastião and Monte do Trigo islands.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…The average results for the two aliquots from the internal standard GA1550 (MD-2), with proposed ages of 98.50±0.50 Ma (McDougall and Wellman 2011) or 99.44 ± 0.17 ( Jourdan and Renne 2007), yielded plateau ages of 99.66± 0.51 and 99.84 ± 0.50 Ma. For comparison purposes, 40 Ar/ 39 Ar ages previously obtained by Enrich's (2005) were corrected for the new ages proposed for the 40 Ar/ 39 Ar ages by Kuiper et al (2008).…”

Section: General Geology Of the Studied Areamentioning

confidence: 99%

“…These occurrences, along with the mafic-ultramafic Ponte Nova Massif in Minas Gerais and several intrusive units in Rio de Janeiro, were originally considered part of the Serra do Mar Alkaline Province (Almeida 1983, Almeida andCarneiro 1998), and later grouped with the northern sector of this province (Riccomini et al 2005). This alkaline magmatism is bimodal, hosting a variety of SiO 2 -undersaturated and -oversaturated syenite varieties and minor gabbroic rocks, accompanied by a variety of SiO 2 -undersaturated (from ultrabasic lamprophyres, pyroxenites to phonolites) to marginally -saturated (alkali basalts, microgabbros to trachytes) dykes (e.g., Ulbrich and Gomes 1981, Brotzu et al 2005, Enrich et al 2005, Azzone et al 2009.…”

Section: Introductionmentioning

confidence: 99%

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New high-precision 40Ar/39Ar ages for the Serra do Mar alkaline magmatism in the São Sebastião Island, SE Brazil, and implications

2021

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We present new high-resolution 40 Ar/ 39 Ar ages for alkaline layered gabbros and cross-cutting mafic-ultramafic and felsic dykes from the São Sebastião Island, in the northern sector of the Serra do Mar Alkaline Province, São Paulo, Brazil. Duplicate analysis of single kaersutite crystals yielded plateau ages of 88 ± 1 and 87.9 ± 0.8 Ma for a gabbro and 87 ± 1 and 86.0 ± 0.8 Ma for a picrite dyke. Two biotite aliquots from a trachyte yielded ages of 86.0 ± 0.5 and 86.2 ± 0.5 Ma, while an alkali feldspar concentrate yielded ages of 86.0 ± 0.5 Ma. The similar ages obtained for minerals with contrasting closure temperatures suggest that the results are crystallization ages and that the rocks were emplaced at shallow crustal levels. Our results, along with available high-resolution data, point to a relatively narrow time span (ca. 88-85 ± 0.6 Ma) for the entire alkaline magmatism on the island. Other alkaline occurrences both nearby and in the continent's interior reveal similar ages, reinforcing the hypothesis that mantle decompression and upwelling of heterogeneous mantle sources led to crustal extension and fast ascension of a variety of alkaline magma types in this segment of South America.

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