Structural characterization of the thrust front of the Malargüe fold-and-thrust-belt (35o- 36o S) and its relationship with intrusion of Miocene igneous bodies

BARRIONUEVO, MATÍAS; MESCUA, JOSÉ; GIAMBIAGI, LAURA; SURIANO, JULIETA; DE LA CAL, HERNÁN; SOTO, JORGE LUIS

Viena

Congreso; EGU General Assembly 2018; 2018

EGU

In the southern part of Mendoza province, Argentina, the Malargüe fold-and-thrust-belt develops as a thick-skinnedbelt during the Andean orogeny. Contraction across this FTB reactivates previous rift structures of the oil-producingTriassic-Cretaceous Neuquén Basin and generates new thrusts which deform only the sedimentary cover. At thislatitude, the main Andean deformation phase started in the early Miocene (∼20 Ma) and advanced to the forelandwith the present-day deformation front near Malargüe city. An expansion of the magmatic arc during the Mioceneis also recorded in the study area.We focused our work in the Agua Botada area, placed on the western flank of the Malargüe anticline near thedeformation front. Using surface information from field surveys and sub-surface data from oil wells and seismicsurveys, we have constructed a series of balanced cross-sections of the Agua Botada area showing the relationshipbetween Mesozoic inverted faults and newly created faults. We have surveyed and mapped in surface and com-plemented with the logs of oil wells, the igneous bodies emplaced in the sedimentary succession of the Neuquénbasin and analyzed the relationship between the intrusion, active structures and the stress field.Mesozoic structures trending NNW to NW were inverted during the Andean contraction probably due to theirorientation, whilst other rift-related structures recognized in seismic data with WNW orientation where not reacti-vated.Based on the relationship between distance and thickness and orientation of the sills and dykes in the area we pro-pose that two volcanic necks, Tronquimalal and Mirano, are the main feeders of the igneous bodies. These feedershave NW to WNW orientations which allow us to infer that the magma flowed using deep rooted structures suchas the WNW rift structures not inverted in the Andean orogeny.We propose a geomechanic model with three main episodes: in the first one (17-10 Ma) the deformation wasfocused to the west of the actual thrust front and the Agua Botada area corresponds to the foredeep zone of theforeland basin.In the second episode (10-7 Ma), the deformation progressed to the east affecting the western part of the studyzone with the activity of thrust faults under a compressive stress field. By this time some sills were emplaced usingthe thrusts as feeders in the western domain, while in the eastern domain a strike-slip/compressional stress regimepromoted the dilatance of WNW rift-related faults that were suitable as magma feeders for the sills and dykes.Finally, in the third episode (7-1 Ma) the deformation moved farther east to the present-day deformation front, reac-tivating the preexisting Malargüe fault as a reverse fault and folding the sedimentary succession into the Malargüeanticline.