U-Pb (ID-TIMS) zircon ages on pyroclastic events from Balcarce Formation, Tandilia System, Argentina: unreworked or reworked origin?

Abstract

In eastern Argentina the southernmost outcrops of the Río de la Plata cratonic region are exposed in the Tandilia System in the central part of the Buenos Aires province. The evolution of Tandilia comprises mainly a juvenile igneous-metamorphic Paleoproterozoic (2.2 to 2.1 Ga) basement named Buenos Aires Complex. After a long paleoweathering process the Sierras Bayas Group (c. 185 m thick) is a record of the first Neoproterozoic sedimentary unit (siliciclastic, dolostones, shales, limestones), covered by the Cerro Negro Formation (c.150- 400 m thick, siliciclastics) and assigned to the Upper Neoproterozoic (both were firstly called “La Tinta Group”). The final sedimentary transgression at the Early Paleozoic is the Balcarce Formation (c. 90-450 m thick) (Iñiguez et al., 1989) reflecting an independent marine basin evolution in a passive margin setting.et al., 1989) reflecting an independent marine basin evolution in a passive margin setting.