The Sierra de Aguirre Formation, Uruguay: Post-collisional Ediacaran volcanism in the southernmost Dom Feliciano Belt

Abstract

The Sierra de Aguirre Fm. in southern Uruguay constitutes one of several post-collisional basins of the Dom Feliciano Belt, preserving an important volcanic record associated with this protracted stage of the orogenic system. This study combines new stratigraphic, structural, geochronological and isotopic geochemical results, together with a reassessment of the available geochemical data, to present new insights in the evolution and sources of the basin, as well as a contextualization of it within the post-collisional development of the belt. The opening of the basin was related to a major discontinuity within the belt, with geometrical features suggesting an inverted half-graben structure. Stratigraphic and petrographic studies indicate that the Sierra de Aguirre Fm. preserves the original unconformity with its basement, and represent distal volcanic deposits. U–Pb SHRIMP-IIe zircon ages establish an interval of ca. 10 m.y. for the filling of the basin, between 581.7 ± 5.1 Ma and 571 ± 8 Ma. After the end of deposition, the basin underwent folding associated with the development of axial plane cleavage under lower greenschist facies conditions. This event is interpreted to represent regional transpression recorded also in nearby shear zones between 570 and 560 Ma, as constrained by new K–Ar ages in muscovite and white mica fine fractions. Geochemical and isotopic signature indicate dominant crustal sources for the volcanism, compatible with the basement of the eastern domain of the Dom Feliciano Belt, supporting a trend also observed in the coeval plutonic magmatism.