Fault-volcano interactions with broadly distributed stretching in rifts

Abstract

Areas undergoing pure extension are typically characterized by the formation of faults and fractures orthogonal to themaximumprincipal stress. In these conditions, the presence of a volcano and itsmagmatic systemperturbs the local stress field, leading to changes in faulting magnitude and attitude. This process has been analyzed in many previous modeling works, in which fault-volcano interaction have been reproduced with set ups that create extension over a single discontinuity by use of a standard base-plate. However, many natural rifts display broadly distributed extension between main border faults, with no discrete discontinuities driving deformation. To account for these conditions, in this study we improve the previous works by reproducing and analyzing the interaction of tectonic stresses with volcanic edifices in areas characterized by broadly distributed extension. In particular, we run a set of analogue models, which are extended by stretching a basal elastic sheet. With this improved set up, models are generally consistent with previous ones, but better reproduce the geometry and architecture of faulting in rifts, leading to improved and more rigorously results to compare with real cases. We confirmed that the presence of a volcano and/or an intrusive body locally modifies the fault pattern, concentrating faulting and curving faults. Notably, the rheological contrast between the intrusion and the host rock leads to faults that follow the outline of the body, favoring concentric faults. In contrast radial faults are developed by the volcano load. The combination of intrusion/host rock contrast and volcano loading creates both types of faulting, which are recognized in natural examples. The geometry of the resulting faults is dependent on the coexistence (or not) of intrusion and edifice and on their dimensions. The results indicate that volcanic edifices have a stronger influence on fault attitudewith respect to the presence of intrusions. Experimental results are compared with some natural cases from the East African Rift System. Finally,we suggest that using faulting geometries as a foundation geodetic monitoring and more precise modeling could be used to assess the rift evolution of such extensional magmatic system.