Source of the synkinematic magmatism in the Dorsal de Canguçu Transcurrent Shear Zone, Dom Feliciano Belt, southern Brazil

Abstract

The synkinematic magmatism of the Dorsal de Canguçu Transcurrent Shear Zone within the Dom Feliciano Belt began around 618 Ma with the emplacement of metaluminous calc-alkaline granitoids known as the Quitéria Granite. Thereafter, larger volumes of peraluminous granitoids from the Cordilheira Suite were emplaced, encompassing the Arroio Francisquinho Granite at 615 Ma and the Cordilheira Granite at 607 Ma. This magmatism spans about 20 km in width and 200 km in length along the shear zone's outcrop and is situated at an estimated depth of 10 km. The isotopic data for the Quitéria Granite (87Sr/86Sri = 0.725275 to 0.732669; εNdt = −5.4 to −6.7; Nd-TDM model age ca. 1.6 Ga; 206Pb/204Pb = 18.6052 to 19.2942) can be used to evaluate sources. Thus, this granite appears to be a depleted mantle end-member mixed with metasedimentary rocks of the Porongos Complex, with approximately 10 % assimilation. In the Cordilheira Suite, the Arroio Francisquinho Granite displays, respectively, 87Sr/86Sri = 0.735406 to 0.817517; εNdt = −5.6 to - 7.7; Nd-TDM model ages = 2.1 to 3.3 Ga; 206Pb/204Pb = 18.31 to 22.42. The Cordilheira Granite isotopes shows 87Sr/86Sri = 0.748207 to 0.784353; εNdt = −7.0 to −10.2, Nd-TDM model ages = 1.8 Ga to 2.7 Ga; 206Pb/204Pb = 18.53 to 21.56. The Cordilheira Suite granites have distinct sources, with a suggested derivation from the Várzea do Capivarita Complex and Porongos Complex metasedimentary rocks, respectively, both by batch melting of ca. 10 % of the crust. Besides, different melting processes are suggested for their formation, involving fluid-fluxed and dehydration melting, respectively. The petrogenetic-tectonic model suggests that the Dorsal de Canguçu Transcurrent Shear Zone favored the emplacement of the Quitéria Granite due to mantle-crust derived magmas entering the shear zone. In the sequence new magmas were generated by crustal melting, corresponding to the Arroio Francisquinho Granite and Cordilheira Granite.