Relationship between the InSAR-measured uplift, the structural framework, and the present-day stress field at Lazufre volcanic area, central Andes

Abstract

The stress regime and structural fabric in tectonically active areas control the shape of magmatic reservoirs and the orientation of dikes. Hence sub-volcanic structures provide potentially good indicators to assess regional geodynamic processes through time. We analyse the spatiotemporal evolution of the Lazufre volcanic area in the central Andes, where a regional-scale elliptical area of surface deformation commenced in 1997. The deformation signal observed by satellite radar interferometry (InSAR) can be explained by a magmatic intrusion located at approximately 10 km depth. We compare this elongated region of deformation with several nearby volcanic structures. We find that a higher concentration of volcanic vents is located within the deforming area compared to the surrounding region. Furthermore, the mean alignment of volcanic structures is NW–SE (N129°), almost perpendicular to the mean elongation of the deformation ellipticity (N28°). Applying the borehole breakout concept, we propose a unifying model that explains magmatic activity both at the short-term (InSAR) and long-term (volcano morphometric parameters): a maximum horizontal compressive stress (SH) oriented NW–SE is found to be constant in time and in space, and is dominant both at the depth of the intrusion and near the surface. Important implications arise, such as the temporal stability of the principal stress directions and the significant role of topographic loading in the stress field analysis.