Tectonic evolution of the Malargüe Fold-Thrust Belt at 34.5°S

PALMIERI, GUILLERMO; BRISSON, SOFIA; PONTET, DAMIÁN; FENNELL, LUCAS; MARTOS, FEDERICO; FOLGUERA, ANDRÉS

Conferencia; AAPG International Conference & Exhibition; 2019

Un order to provide additional constraints about the tectonic evolution of the Malargüe fold-thrust belt at 34.5º S, we carried out a stratigraphic and structural characterization of the Atuel depocenter (northern Neuquén Basin) and the foreland basin at this latitude.In the Atuel depocenter, a sedimentary profile of the Lower Jurassic Puesto Araya Formation revealed a thick deltaic succession composed mainly of low-grade metamorphic sandstones that towards the top turns more volcaniclastic with tuff and andesitic volcanic lava intercalations, that reflects the proximity of the volcanic arc. The sedimentological and structural analysis of this region allowed to recognize syn-extensional deposition of the Lower Jurassic Puesto Araya Formation. Also, extensional structures were recognized in the Río Damas and Lo Valdes Formation, indicating that mechanical subsidence was likely active until Early Cretaceous time.A series of sedimentary profiles were performed in the foreland basin at these latitudes. The succession begins with a series of amalgamated channels and floodplain deposits corresponding to the Upper Cretaceous Diamante Formation. Paleocurrent and provenance data indicate a gradual change in source area towards the top of the sequence, reflecting a rearrangement, in the drainage pattern, due to a regional compressional stage. Moreover, the presence of progressive unconformities and important thickness changes associated with growing structures support its characterization as the first syn-orogenic unit in the Andes at these latitudes. Additionally, this study aims to understand the transition between the Late Cretaceous and the Miocene contractional phases through a thorough characterization of Paleogene deposits. Therefore, another sedimentary profile across the Malargüe Group revealed the presence of the mostly fine-grained Loncoche, Roca, Pircala, and Coihueco Formations, whose sedimentary environments suggests a post-Cretaceous tectonic quiescence and a subsequent Miocene deformation event detected through the presence of growth strata in the Agua de la Piedra Formation.Analyzing the depositional mechanisms of the different sedimentary units is essential to understand the tectonic evolution of the Andes at 34.5ºS. In addition, an accurate temporal constraint of the different deformation events is of paramount importance for the exploration and development of hydrocarbons in one of the most important basins in Argentina.