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Elemental and isotopic (Sr-Nd-O) geochemistry and U Pb zircon geochronology of late-stage, post-collisional, shallow-level magmatism in the Dom Feliciano Belt northern sector

2023; Elsevier BV; Volume: 442-443; Linguagem: Inglês

10.1016/j.lithos.2023.107057

1872-6143

Lucas Vargas Moraes, Luana Moreira Florisbal, Valdecir de Assis Janasi, Maria de Fátima Bitencourt, Lucelene Martins, Larry M. Heaman, Barry Shaulis, Richard A. Stern,

earthquake and tectonic studies

The Dom Feliciano Belt Ediacaran post-collisional magmatism is widespread in southern Brazil and Uruguay and is represented by the Florianópolis Batholith in its northern sector. The Zimbros Suite (Area 1) comprises the Zimbros Granite, emplaced within the Major Gercino Shear Zone (MGSZ) at the waning stages of its activity, and the Morro dos Macacos Granite, emplaced nearby but outside the high-strain zones. Conversely, the Cambirela Plutono-volcanic Suite (Area 2) occurs far from the MGSZ deformation sites and encompasses the Ilha, Vila da Penha, and Serra do Tabuleiro granites and the Cambirela Silicic Volcanic Sequence (rhyolites + ignimbrites). The plutonic units from both areas are coeval (ca. 590 Ma) and characterised by high-SiO2 (74–79 wt%, except for the Zimbros Granite 0.84) A2-type granites that compose two distinct shallow-level plutono-volcanic systems installed in a post-collisional setting at the final stages of the Dom Feliciano Belt. The units emplaced far from the MGSZ (Area 2) are derived mostly from crustal sources with minor mantle contribution. They were likely produced by dehydration melting of quartz-feldspathic (+hornblende) subalkaline rocks of low water contents and reduced character. Field relations, the metaluminous to slightly peraluminous A-type character, the weakly negative ƐNdt, high Fe#, Ce/Nb and Y/Nb ratios and the low to intermediate δ18O values (+3.4 to +7.3 ‰) are compatible with such conditions. In contrast, the dataset for the Zimbros Suite (Area 1), coupled with the previous interpretations that attest to the mantle origin of this unit, points to rocks derived from fractional crystallisation of tholeiitic melts with large crustal assimilation of rocks with similar composition to the source rocks of Area 2 (i.e. subalkaline, hornblende-bearing quartz-feldspathic rocks), hybridized at shallow-level conditions and accompanied by recurrent mantle contribution favoured by the MGSZ. The Cambirela Plutono-volcanic Suite volcanic units share all the characteristics presented for the granitic rocks and are composed of earlier, crystal-poor rhyolites (586 ± 5.0 Ma) and later ignimbrites with sharp faciological variation (580 ± 4.8 Ma) indicating different maturity stages of long-lived magma chambers. The variable U-Th contents and the bimodal δ18O signatures (+3.4 ± 0.2‰ and + 6.9 ± 0.2‰) of the volcanic units further indicate open-system magmatic processes and the co-eruption of melts from distinct magma chambers of the Cambirela plutono-volcanic system.