Multiple processes of geochemical evolution for the alkaline rocks of Rio Bonito intrusive complex, Rio de Janeiro State, Brazil: 40Ar/39Ar and U-Pb ages and Lu-Hf isotopes on zircon and constraints on crustal signature

Abstract

This article presents geochemical characteristics of the alkaline rocks of Rio Bonito intrusive complex, State of Rio de Janeiro, Brazil, which is constituted mainly by nepheline syenite. The fractional crystallisation of this magma decreases K2O/(Na2O + K2O) and increases (Na + K)/Al. The TiO2, Fe2O3*, MgO, CaO, and P2O5 contents indicate fractionation of titanite, ilmenite, and clinopyroxene or amphibole. The total rare earth elements (REEs) are high, and the REE pattern is linear with negative gradient. The nepheline syenite aplite has low REEs, concave REE pattern, and positive Eu anomaly. The ultrabasic and basic mela-nepheline syenite samples have total REEs and light REEs higher than the felsic alkaline rocks. Therefore, the nepheline syenite magma is not derived directly from the alkaline ultrabasic magma. Laser-spot step‑heating 40Ar/39Ar ages for biotite and amphibole are 65.03 ± 0.70 and 65.03 ± 0.46. U-Pb ages LA-ICP-MS for two samples are 65.49 ± 0.30 and 65.18 ± 0.30. Values of εHf are negative for both samples, indicating an important crustal component in the evolution of Rio Bonito.

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

“…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).…”

Geochemistry and Geochronology (U-Pb and Lu-Hf) of the Soarinho Alkaline Massif (Brazil): Implications on Mantle versus Crustal Signature of Syenitic Magma

“…Therefore, the purpose of this work is to present a geochemical, geochronological (U-Pb), and isotopic (Lu-Hf) study for the Soarinho intrusive complex (Rio de Janeiro, Brazil). We also present U-Pb and Lu-Hf data from Tanguá, comparing them with Rio Bonito's published data [14]. Finally, the Lu-Hf data has the potential to add knowledge about possible sources of evolved alkaline magmas.…”

“…The country rocks of the Soarinho Complex are the syn-collisional granites (Cassorotiba orthogneiss) and paragneiss of the São Fidélis group (Figure 2). The Soarinho complex forms an elongated stock in the NNW-SSE direction, with an area of 33 km 2 and a maximum elevation of 600 m. published data [14]. Finally, the Lu-Hf data has the potential to add knowledge about possible sources of evolved alkaline magmas.…”

“…Therefore, the purpose of this work is to present a geochemical, geochronological (U-Pb), and isotopic (Lu-Hf) study for the Soarinho intrusive complex (Rio de Janeiro, Brazil). We also present U-Pb and Lu-Hf data from Tanguá, comparing them with Rio Bonito's The geochronological data (K-Ar, Rb-Sr, and U-Pb) presented to the SMIP gave rise to intense discussions about the geodynamical model that explained the emplacement of those alkaline rocks in Southeastern Brazil [9][10][11][12][13][14]. The first model is based on the age decrease from west to east (Figure 1) and proposes that this decrease elapses in the passage of the lithosphere over a mantle plume [4,15,16].…”

“…The geochronological data (K-Ar, Rb-Sr, and U-Pb) presented to the SMIP gave rise to intense discussions about the geodynamical model that explained the emplacement of those alkaline rocks in Southeastern Brazil [9][10][11][12][13][14]. The first model is based on the age decrease from west to east (Figure 1) and proposes that this decrease elapses in the passage of the lithosphere over a mantle plume [4,15,16].…”