Structural and tectonic evolution of the Argentinean Andes at latitude 34°15´S

MESCUA, GIAMBIAGI, RAMOS

Oslo, Noruega

Congreso; 33° International Geological Congress; 2008

The Argentinean-Chilean Andes at latitude 34º15’S are part of the Central Andes, located within the normal subduction zone developed south of 33ºS. They are a typical subduction related orogen, limited to the west by the Chilean Trench and characterized (from west to east) by a longitudinal valley east of the Coastal Ranges, an active magmatic arc developed in Chilean territory and on the intenational border, a fold and thrust belt and a foreland basin. The foreland ranges in the Argentinean side of the Andes at this latitude can be divided in two main sectors. The Cordillera Principal (Main Andes) consists of the Malargüe fold and thrust belt, and is developed from the border with Chile (70ºW) to 69º40’W. The Malargüe fold and thrust belt shows an internal segmentation involving a western thick-skinned sector and an eastern thin-skinned sector. Toward the east (60º40’ to 69º25’ W) the Cordillera Frontal (Frontal Andes) is found. This range consists of an uplifted basement block. Newly acquired field data have permitted the construction of a balanced structural cross section and the analysis of the possible models of structural and tectonic evolution of the Argentinean Andes at this latitude. The structural styles vary across the Argentinean Andes reflecting control by inherited geological features, both structural (faults and lineaments) and sedimentary (lateral facies changes, horizon pinch-outs).  The inner Malargüe fold and thrust belt records the influence of pre-existing extensional structures. These structures are related to the development of the northern extension of the Neuquen basin in Mendoza province during Late Triassic - Early Jurassic times. The outer Malargüe fold and thrust belt is a thin-skinned belt with detachment levels within a late Jurassic-Cretaceous sedimentary succession. These Mesozoic deposits pinch out towards the east, with the consequent disappearance of suitable detachments for the development of the fold and thrust belt. ((The Cordillera Frontal is composed mostly of volcanic and plutonic rocks of Permian-Triassic age. Paleozoic sediments, low grade metamophics and granites are also found in the range. These Paleozoic to Triassic rocks were the basement for the Neuquen Basin.)) se podría sacar The main pulse of deformation for the Malargüe fold and thrust belt took place in the Miocene (15 to 7 Ma), but age constrains are scarce. Published ages of pre- and post-tectonic volcanics south of the study area suggest that structures in the thick- and thin-skinned sector were active simultaneously. This is coherent with field observations in the study area. At least one out-of-sequence deformational event is recognized in the whole belt. Uplift of Cordillera Frontal is known to be posterior to the main pulse of deformation in the Malargüe fold and thrust belt. It is therefore assigned to the late Miocene.