Geophysical analysis in a Quaternary compressive environment controlling the emplacement of travertine, eastern piedmont of Argentine Precordillera

摘要

This work carries out the analysis, through a geophysical (gravity) method, of an area in the eastern Piedmont of Eastern Precordillera, Central Andes of Argentina. Geological evidence shows several neotectonic reverse fault scarps affecting Quaternary alluvial deposits located to the East of the Sierra de Villicum. Topographic features observed in the understudy region suggest an important Holocene historical seismic activity, one of them the 15th January 1944 San Juan earthquake (Mw 7.0), the worst natural disaster in Argentina. Several N-S springs and carbonate deposits (travertine) are found aligned along the traces of these active faults, disappearing abruptly to the north and south, possibly due to a tectonic control. Travertine deposits are located along fault traces and have been traditionally considered to be contemporaneous with active faults. The existence of travertine bodies deposited by springs, and their low preservation potential, has for the understudy region a neotectonic significance. The eastern Piedmont of the Sierra de Villicum is characterized by the similar to N-S La Laja west-vergent east-dipping reverse fault and several subparallel faults (e.g., Cantera and Museo faults) that uplift Neogene sedimentary rocks over Quaternary (Late Pleistocene-Holocene) alluvial deposits. Gravity data derived from the global Earth gravity model WGM 1.0 were used in the regional geophysical analysis. The analysis aims to delimit geological structures, which characterized the interest area. Three detailed gravimetric profiles were measured to analyze local anomalies related to the main structures. The gravimetric and geological analysis confirms the existence of north-south faults parallel to La Laja fault related to travertine deposits. On the other hand, a set of southeast-northwest structures that limit and control the travertine bodies both northward and southward are recognized. Employing the gravity method associated with structural analysis, the spatial continuity of these neotectonic structures was defined in those sectors where field evidence is not so clear or blind structures are present. Our study confirms the existence of probable cross strike structures trending NW. We suggest they would represent preexisting crustal fabrics reactivated during the Andean orogeny in the Precordillera province, segmenting this orogen-parallel fold and belt system. One of the main hypotheses is that these fault systems related to basement-involved strike-slip faults perform as control structures in fluid migration during the travertine bodies' emplacement. Thus, our work points to the relevance of travertine location in the analysis of the seismotectonic configuration of a region.