Figure 1:
Simplified geological map of the Sul-Rio-Grandense Shield and Uruguay Shield (cf. Oyhantçabal et al. 2011Oyhantçabal P., Siegesmund S., Wemmer K. 2011. The Río de la Plata Craton: A review of units, boundaries, ages and isotopic signature. International Journal of Earth Sciences, 100(2-3):201-220.), with location of the northernmost exposure of the Acampamento Velho volcanism in the Tupanci region (modified from Philipp et al. 2016: Ductile Shear Zones: 1) Itajai-Perimbó, 2) Major Gercino, 3) Caçapava do Sul, 4) Dorsal de Canguçu, 5) Passo do Marinheiro, 6) Ibaré, 7) Sarandí del Yí, 8) Sierra Ballena, 9) Cerro Amaro, 10) Arroio Grande).
Figure 2:
Simplified geological map of the study area with the location of the samples selected for this study (modified from Menegotto & Medeiros 1976Menegotto E., & Medeiros E.R. 1976. Contribuição ao estudo das rochas ígneas ácidas da região da Serra Tupanci, RS. In: Congresso Brasileiro de Geologia, 29, Ouro Preto. Anais..., Ouro Preto, SBGEO, v. 2, p. 427-432. and Leitzke et al. 2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.).
Figure 3:
Summary of macro and microscopic features of representative effusive rocks at the Tupanci and Picados Hill (cf. Leitzke et al. 2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.): (A) porphyritic rhyolite with glassy matrix; (B) fractured sanidine phenocryst in devitrified matrix; (C) glomeroporphyritic texture with euhedral quartz and k-feldspar phenocrysts; (D) reabsorbed quartz phenocryst with surrounding igneous flow foliation; (E) quartz phenocryst with microbreccia features; (F) spherulites showing evidence for high-temperature devitrification of the matrix.
Figure 4:
Summary of macro and microscopic features of representative pyroclastic rocks at the Picados Hill (cf. Leitzke et al. 2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.): (A) lapilli-size pyroclastic fragments in hand specimen; (B) pumice fragments with distinct orientations in a shard-based matrix; (C) highly-welded ignimbrite with eutaxitic texture of the pumice fragments; (D) stretched pumice fragments with eutaxitic texture and inclusions of quartz crystals under the microscope.
Figure 5:
Classification diagrams for the high and low-Ti groups of silicic rocks from the Acampamento Velho Formation with comparisons between both groups at the Tupanci region and other occurrences of the post-collisional volcanism in southern Brazil. Data taken from Leitzke et al. (2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.), and Sommer et al. (2005aSommer C.A., Lima E.F., Nardi L.V.S., Figueiredo A.M.G., Pierosan R. 2005a. Potassic and low- and high-Ti mildly alkaline volcanism in the Neoproterozoic Ramada Plateau, southernmost Brazil. Journal of South American Earth Sciences, 18(3-4):237-254. ): (A) TAS diagram (Le Bas et al. 1986Le Bas M.J., Le Maitre R.W., Streckeisen A., Zanettin, B. 1986. A chemical classification of volcanic rocks on the total alkali-silica diagram. Journal of Petrology, 27(3):745-750.); (B) SiO2 vs. Zr/TiO2 classification diagram (Winchester and Floyd 1977Winchester J.A., & Floyd P.A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 20:325-343.).
Figure 6:
Cathodoluminescence images of zircons from the (A) Tupanci Hill, with internal zonation due to crystal growth during magma cooling, and (B) Picados Hill, which show features of alteration. White circles show where LA-ICP-MS analysis were performed.
Figure 7:
U-Pb Concordia diagrams displaying obtained data from zircons of the AVF high (A) and low (B) -Ti rhyolites at the Tupanci region, NW of the Sul-Rio-Grandense Shield.
Figure 8:
Multi-element diagram for the low and high-Ti groups of the Acampamento Velho Formation at the Tupanci region, NW of the Sul-Rio-Grandense Shield (cf. Leitzke et al. 2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.) plotted together with literature data: (A) ORG-normalized (Pearce et al. 1984Pearce J.A., Harris N.B.W., Tindle A.G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25(4):956-983.) trace element (+K2O) pattern; (B) chondrite-normalized rare earth elements (REE) pattern (Nakamura 1974Nakamura N. 1974. Determination of REE, Ba, Fe, Mg, Na, and K in carbonaceous and ordinary chondrites. Geochimica et Cosmochimica Acta, 38(5):757-775.).
Figure 9:
Tectonic discrimination diagram for the studied rocks (cf. Leitzke et al. 2015Leitzke F.P., Sommer C.A., Lima E.F., Matté V. 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências, 42(1):5-24.): (A) Rb vs. Y+Nb according to Pearce et al. (1984Pearce J.A., Harris N.B.W., Tindle A.G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25(4):956-983.); (B) Zr vs. 10,000*Ga/Al (Whalen et al. 1987Whalen J.B., Currie K.L., Chappell B.W. 1987. A-type granites: Geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95(4):407-419.).
Figure 10:
Diagram showing εNd vs. T (Ga) for the low and high-Ti rhyolitic rocks from the Acampamento Velho Formation at the Tupanci region, as well as their possible sources (modified from the compilation by Janikian et al. 2012Janikian L., Almeida R.P., Fragoso-Cesar A.R.S., Martins V.T.S., Dantas E.L., Tohver E., McReath I., D’Agrella-Filho M.S. 2012. Ages (U-Pb SHRIMP and LA ICPMS) and stratigraphic evolution of the Neoproterozoic volcano-sedimentary successions from the extensional Camaquã Basin, Southern Brazil. Gondwana Research, 21(2-3):466-482.).
Figure 11:
(A) 208Pb/204Pb vs. 206Pb/204Pb; (B) 207Pb/204Pb vs. 206Pb/204Pb isotopic signatures for the low and high-Ti rhyolitic rocks from the AVF at the Tupanci region plotted together with possible end-member sources evolution with time (cf. Stacey & Kramers 1975Stacey J.S., & Kramers J.D. 1975. Approximation of terrestrial Lead isotope evolution by a 2-stage model. Earth and Planetary Science Letters, 26(2):207-221.).
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