Structural and tectonic evolution of the Argentine Andes at 34º15’S latitude

MESCUA, J. F.; RAMOS, V. A.

Oslo

Congreso; 33rd International Geological Congress; 2008

International Union of Geological Sciences (IUGS)

The Central Andes at the 34º15’S latitude are located within the normal subduction segment developed south of 33ºS. They are in a typical Andean setting, developed to the east of the trench and characterized by Coastal Cordillera (from west to east), a longitudinal valley, an active magmatic arc developed mainly in the Chilean side, a fold and thrust belt along the water divide, and a foreland basin. The cordillera in the Argentine side of the Andes at this latitude can be divided in two main sectors, the Principal and Frontal Cordilleras. The Principal Cordillera (or Main Andes) consists of the Malargüe fold and thrust belt, and is developed from the border with Chile (70ºW) to 69º40’W. This fold and thrust belt shows an internal segmentation involving a western thickskinned sector and an eastern thin-skinned sector. Toward the east (60º40’ to 69º25’ W), the Frontal Cordillera consists of an uplifted basement block. Newly acquired field data have constrained a balanced structural cross section which controls the different alternatives for the structural and tectonic evolution of the Argentine Andes at this latitude. The structural styles vary across the Argentinean Andes controlled by inherited geological features, both structural (faults and lineaments) and sedimentary (lateral facies changes, horizon pinch-outs). The western 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 rifting in Mendoza province during Late Triassic - Early Jurassic times. The outer eastern part of the belt is a thin-skinned with detachment levels within a late Jurassic-Cretaceous sedimentary succession. These Mesozoic deposits pinch out towards the east, with the consequent loss of suitable detachments for the development of the fold and thrust belt. The main pulse of deformation for the Malargüe fold and thrust belt, based on the present information, took place in the Miocene (15 to 7 Ma), but age constrains are scarce. Published ages of pre- and posttectonic volcanic rocks 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 Frontal Cordillera is known to be after the main pulse of deformation in the Malargüe fold and thrust belt and assigned to the Late Miocene.