ectonic control of the Neocomian volcaniclastic sequences and paleogeography in Lago La Plata region (45°S). Inner sector of the lagos La Plata and Fontana fold and thrust belt

Abstract

The area of Lago La Plata in Argentina is an outstanding site to address the relationship between the platform sequences which filled the Lower Cretaceous Río Mayo Basin through the western sector of the basin, and the arc-derived materials in the western sectors. The study of these sequences shows a series of lithostratigraphic units through an extensive mapping in the field and a petrographic study. Based on that, the basinal sequences in the western sector became much more widely extended than previously thought, not only in the basal sections of the Coyhaique Group, but also in the upper terms of this heterogeneous unit. These sequences have had two source areas. A main one from a volcanic arc, and a second source, in terms of importance, from coral reefs. It is worth noting the complete absence of craton-derived materials in these inner sectors of the Patagonian Andes. Moreover, the study of the Neocomian sequences allowed to distinguish a series of angular discontinuities, an older of Middle Cretaceous age and a younger not to well constrained, which are related to the construction of the Patagonian Andes at these latitudes.