Melanite-bearing nepheline syenite fragments and 40Ar/39Ar age of phlogopite megacrysts in conduit breccia from the Poços de Caldas Alkaline Massif (MG/SP), and implications

Vlach, Sílvio Roberto Farias; Ulbrich, H.; Ulbrich, Mabel N. C.; Vasconcelos, Paulo M.

doi:10.1590/2317-4889201820170095

Cited by 11 publications

(6 citation statements)

References 38 publications

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“…The syenites (nepheline-and alkali-feldspar) would represent the older pulse, and the trachytes and phonolites would represent the more recent pulse. The same pattern (plutonic rocks + volcanic rocks) is also observed in other alkaline bodies of the PCCFA, such as Poços de Caldas, Passa Quatro, Itatiaia, Tinguá, Mendanha, Tanguá, Rio Bonito, and Ilha de Cabo Frio (Amaral et al 1967;Araujo 1995;Brotzu et al 1992;Brotzu et al 1997;Brotzu et al 2007;Chiessi 2004;Enrich et al 2005;Geraldes et al 2013;Guarino et al 2019;Montes-Lauar 1988;Mota et al 2012;Motoki et al 2012;Motoki et al 2013;Sichel et al 2008;Sígolo et al 1992;Silva 2019;Silva et al 2020;Vlach et al 2018).…”

Section: Discussionsupporting

confidence: 60%

Geochemical and isotopic constraints on the petrogenesis of the Cretaceous alkaline Morro Redondo intrusive complex, Rio de Janeiro, Brazil: implications for alkaline magma genesis

Mota,

Silva,

Jourdan

et al. 2024

JGSB

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The Morro Redondo Complex is composed of plutonic and volcanic alkaline rocks. This igneous complex is part of the Poços de Caldas -Cabo Frio Magmatic Alignment (PCCFA). This study aims to contribute to the understanding of the petrogenesis of the rocks in the Morro Redondo complex and, thereby, contribute to the debate on the genesis of the PCCFA. In this work, we conducted analyses of whole-rock geochemistry, 40 Ar/ 39 Ar thermochronology, U-Pb geochronology on zircon grains, and Rb-Sr, Sm-Nd, and Lu-Hf isotopic analyses. Four distinct lithotypes are present: nepheline syenites, alkali feldspar syenites, trachytes, and phonolites. The rocks of the Morro Redondo complex are miaskitic, have intermediate values of SiO2, and show significant crustal assimilation, mainly observed in the relationship between the SSI and (Na+K)/Al indices, together with the Hf isotopic signature. A hornblende crystal obtained from a sample of nepheline syenite provided a plateau age of 74.35 ± 0.50 Ma. The initial ratios of 87 Sr/ 86 Sr range from 0.70565 to 0.71042, and the initial ratios of 143 Nd/ 144 Nd range from 0.51234 to 0.5124. Hf data suggest a hybrid origin for the Morro Redondo complex, with sources from both crustal and mantle origins. The data obtained indicate that at least three magmatic pulses contributed to the formation of the Morro Redondo complex, with the participation of both crustal and mantle sources, generating magmas of miaskitic affinity.Geochemical and isotopic constraints on the petrogenesis of the Cretaceous alkaline Morro Redondo intrusive complex, Rio de Janeiro, Brazil: implications for alkaline magma genesis with the igneous complexes are alkaline composition dikes related to the ENE-EW fault system (Brotzu et al. 2005). The ages of the Poços de Caldas -Cabo Frio Alignment bodies vary decreasingly from east to west between 84 and 39 Ma, although not linearly (Santos and Hackspacher 2021). It is worth mentioning that most alkaline bodies of the PCCFA tend to intrude Neoproterozoic sin-, late-or post-collisional granites and syenites from the Brasília and Ribeira belts (Valeriano et al. 2011;Tupinambá et al. 2012;Rosa and Ruberti 2018). Materials and methods GeochemistrySamples selected for geochemical analysis were analyzed at the ACTLABS laboratory in Canada. The analytical techniques included atomic emission spectrometry (ICP-AES) for oxides. X-ray fluorescence in fused pellets for trace elements, S, Cl, Rb, Sr, Ba, and Zr, atomic absorption spectrometry for determining Mn, Mg, Na, K, Cu, Mo, Sn, and Pb elements. Optical spectrometry for trace elements Nb, Y, Ni, and V, and rare earth elements (REE) were analyzed by mass spectrometry (ICP-MS). Rb-Sr and Sm-Nd isotopesSamples for Sr and Nd isotopes were analyzed at the Given that the debate on the genesis of the PCCFA remains open, we will present information on the Morro Redondo Complex in this work. This alkaline body belongs to the magmatic alignment. In this contribution, we constrain the formation processes (petrogenesis) and sources of alkalin...

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Section: Discussionsupporting

confidence: 60%

Geochemical and isotopic constraints on the petrogenesis of the Cretaceous alkaline Morro Redondo intrusive complex, Rio de Janeiro, Brazil: implications for alkaline magma genesis

Mota,

Silva,

Jourdan

et al. 2024

JGSB

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“…Abundant geochronological data obtained by different methods are available for the massif and apparently confirm their long magmatic history (K/Ar age between 64 and 83 Ma, with a median value of 77 Ma, Ulbrich et al 2005). These authors also reported Rb/Sr measurements giving an isochron age of 78.6 ± 6.6 Ma, and more recent work by Vlach et al (2018) yielded an Ar/Ar plateau age of 87 (ca.) Ma for phlogopite crystallization in conduit breccia.…”

Section: Introductionmentioning

confidence: 78%

A review of mineral assemblages of agpaitic rocks from the Poços de Caldas alkaline massif, southeastern Brazil

Gomes,

Azzi,

Atencio

2023

Braz. J. Geol.

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This study revises the early-magmatic, late-magmatic, and hydrothermal mineral assemblages occurring in rocks of agpaitic affinity, mainly represented by nepheline syenites and phonolites, from the Poços de Caldas alkaline massif. Mostly composed of different types of silicates, these rocks include rare minerals of of distinct groups, such as sulfides, oxides, carbonates, phosphates, sulfates, niobates, and notably halides, with villiaumite (NaF) as an important phase indicative of extreme alkali enrichment. Hydrothermal alteration products of nepheline and alkali feldspar typically consist of feldspathoids and zeolites. The rare minerals are of varied origin, from magmatic crystallization to hydrothermal and weathering processes. In general, they tend to occur interstitially or form euhedral crystals, especially when filling cavities or growing out from their walls. Petrological conditions involving the formation of the agpaitic rocks and their mineral assemblages are discussed.

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“…At about 510°C, fine magnetite grains have a relaxation time of about 10 3 Myr (Butler 1992), ensuring that the Cretaceous rocks can preserve the trustworthiness of the acquired magnetization. Therefore, the 89-76 Myr age interval (Vlach et al 2018) based on various methods must be restricted to an 83-76 Myr interval to represent the magnetization polarity better. Ulbrich et al (2002) argued that the best estimation for this massif is about 79 Myr.…”

Section: Discussionmentioning

confidence: 99%

“…Among those, the Poços de Caldas paleomagnetic pole is the more reliable, based on extensive sampling. All studied sites are of reverse magnetization, placing the magmatism outside the CNS, although ages obtained by various methods are in the range of 89-76 Myr (Vlach et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The Late Cretaceous alkaline magmatism in the SE Brazilian coast: new paleomagnetic data and age constraints

Ernesto

Raposo²

2023

Braz. J. Geol.

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Alkaline dikes from the Santos-Rio de Janeiro coast, SE Brazil, mainly from São Sebastião and Búzios islands, yielded a Late Cretaceous paleomagnetic pole (SR) located at 319.7°E 81.2°S (N = 44, A 95 = 3.0°, k = 44). This pole includes some sites of alkaline stocks from São Sebastião Island of the same age and supersedes the previous pole for this island. To match the available radiometric ages and the prevailing normal polarity remanence of the rocks with the geomagnetic polarity time scale, the SR pole is placed at 84 Myr. Another group of alkaline rocks, dikes located mainly in Rio de Janeiro, was assigned an age of less than 70 Myr. The ages of the Poços de Caldas, Itatiaia, and Passa Quatro paleomagnetic poles are also discussed based on available radiometric data. Assuming a rigid plate, the SR pole indicates the southward movement of about 7° with virtually no rotation between 100 and 84 Myr. From approximately 84 to 70 Myr, a clockwise rotation of 8° is postulated, with slight variation in latitude.

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Melanite-bearing nepheline syenite fragments and 40Ar/39Ar age of phlogopite megacrysts in conduit breccia from the Poços de Caldas Alkaline Massif (MG/SP), and implications

Abstract: The Poços de Caldas Alkaline Massif, located in southeast Brazil

Cited by 11 publications

References 38 publications

Geochemical and isotopic constraints on the petrogenesis of the Cretaceous alkaline Morro Redondo intrusive complex, Rio de Janeiro, Brazil: implications for alkaline magma genesis

Geochemical and isotopic constraints on the petrogenesis of the Cretaceous alkaline Morro Redondo intrusive complex, Rio de Janeiro, Brazil: implications for alkaline magma genesis

A review of mineral assemblages of agpaitic rocks from the Poços de Caldas alkaline massif, southeastern Brazil

The Late Cretaceous alkaline magmatism in the SE Brazilian coast: new paleomagnetic data and age constraints

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