The U–Pb and Lu–Hf zircon record of the Neoproterozoic tectonomagmatic evolution of the Ventania System basement, central-eastern Argentina: The southernmost exposure of the Dom Feliciano Belt?

Abstract

In the Ventania System of central-eastern Argentina, Neoproterozoic igneous rocks of the Sauce Chico Complex (SCC) crop out. They consist of low-grade mylonitized granites and rhyolitic rocks. Metasedimentary rocks are represented by metapelite and metacarbonate xenoliths hosted in Neoproterozoic granites. This work presents lithogeochemical, and coupled LA-MC-ICP-MS U–Pb and Lu–Hf zircon data of Neoproterozoic rocks of the SCC in order to reinforce the already proposed link between these rocks and the Brasiliano/Pan-African Dom Feliciano Belt of southern Brazil and eastern Uruguay. Novel U–Pb results yielded crystallization ages of 623 ± 3 Ma and 608 ± 4 Ma in granite samples, and 545 ± 3 Ma in a tuff sample. Considering these new U–Pb ages and those published in previous works, Neoproterozoic rocks of the SCC can be grouped in Tonian (ca. 784–777 Ma) and Ediacaran (ca. 623–607 Ma) granites, and Ediacaran (ca. 577–544 Ma) volcanic and pyroclastic rocks. Xenocrystic/inherited ages span from the Ediacaran (ca. 555 Ma) to the late Neoarchean (ca. 2535 Ma). Ninety-four spots on zircon grains gave the following U–Pb and Lu–Hf results: ca. 2040–1700 Ma (n = 6, εHf(t) = -14.6/+6.3, TDM = 3.5–2.1 Ga); ca. 1500–850 Ma (n = 9, εHf(t) = -26.3/+4.5, TDM = 3.3–1.9 Ga); ca. 830–700 Ma (n = 26, εHf(t) = -40.5/+10.7, TDM = 4.1–0.9 Ga); and ca. 650–530 Ma (n = 53, εHf(t) = -38.8/+2.9, TDM = 3.9–1.3 Ga). When the Neoproterozoic rocks of the SCC are compared with those of the Punta del Este Terrane of the Dom Feliciano Belt, lithological, geochemical, geochronological, and isotopic similarities are evident. Both regions have Tonian orthoderived rocks (ca. 800–760 Ma) intruded by Ediacaran granites (ca. 630–570 Ma), and late Ediacaran plutonic and volcano-sedimentary rocks (<ca. 580 Ma). Tonian rocks of the Punta Mogotes Formation (Mar del Plata city area, southeasternmost tip of the Tandilia System) might represent the connection between the Punta del Este Terrane and the Ventania System basement. Additionally, the presence of Brasiliano/Pan-African rocks along the southern border of the Río de la Plata Craton effectively eliminates the possibility of the craton extending further south/southwest of the system.