The Neoproterozoic basement of the Sauce Chico Inlier (Ventania System): Geochemistry and U-Pb geochronology of igneous rocks with African lineage in central-eastern Argentina

摘要

This study describes the geology, geochemistry, and LA-ICP-MS U-Pb geochronology of igneous rocks that crop out in the Sauce Chico Inlier (SCI) and constitute the Neoproterozoic basement of the Ventania System, Argentina. Magmatism registered in the SCI has developed in two phases. The first phase, of Tonian age, is represented by rift-related talc-alkaline and alkaline granites with ages of 783.8 +/- 3.7 Ma (epsilon Nd-(t) = -7.20) and 776.5 +/- 4.7 Ma (epsilon N-(t) = +1.65), respectively. This phase would be related to the break-up of the Rodinia supercontinent and subsequent opening of the Adamastor Ocean. In the Dom Feliciano Belt of southern Brazil and eastern Uruguay, the Tonian magmatism is represented in the Cerro Olivo Complex of the Punta del Este Terrane and in basement inliers of the Pelotas Batholith. The second phase, of Ediacaran age, started with the intrusion of syn-orogenic tale-alkaline granites (620.8 +/- 5.8 Ma and 620.3 +/- 2.5 Ma; epsilon Nd-(t) = - 9.94/-9.18) and continued with the extrusion of post-orogenic alkaline (577.3 +/- 3.9 Ma; epsilon Nd-(t) = - 6.29) and talc-alkaline (543.6 +/- 4.0 Ma; epsilon Nd-(t) = - 3.38) acid volcanic rocks. This phase would be related to the closure of the Adamastor Ocean, generation of a magmatic arc along the western margin of the Kalahari Craton, and collision between this and the Rio de la Plata Craton. A post-collisional magmatism would have developed due to orogenic collapse (< 580 Ma). With the exception of the Tonian alkaline granite, in the remaining SCI igneous rocks, the juvenile component becomes more important as the crystallization age decreases. The available Nd model ages are between 1.80 and 1.14 Ga and suggest a mixing of older crust with juvenile material. The tectonic evolution of the Ventania System basement is consistent with that observed in the Dom Feliciano Belt and its African counterparts. We present here the first evidence of Tonian magmatism in the Ventania System basement. The results presented here also confirm those obtained previously by other authors. Zircon cores from the SCI igneous rocks have U-Pb inherited ages between ca. 1200 and 900 Ma that could be indicative of a lineage with the Gariep Belt and its Namaqua basement in southwestern Africa.