Evidencias de deformación frágil durante el emplazamiendo de un Lacolito

Abstract

Laccoliths are dome-shaped igneous intrusions that grow from the inflation of sills, which are emplaced at shallow depths in the upper crust. During the inflation process, stresses are concentrated on the sill tips, producing doming and faulting of the host rocks. This was thought to be the only mechanisms for dissipating stress. New field observations on a well preserved laccolith in southem Mendoza, Argentina, show evidences of brittle deformation during emplacement. This is the case of the Cerro Bayo laccolith, emplaced in an eroded Miocene caldera termed Sierra of Chachauén. This laccolith shows a wide breccia, approximately 200 m width, composed ofigneous rock and fault gauge. The breccia is located inside the laccolith, on the western margin, opposed to the main igneous conduct, which is identified by its clear flow banding. The measurements of the flow ban - ding and the anisotropy ofmagnetic susceptibility (AMS) allow us to model the emplacement ofthe laccolith. Also we tested the robustness ofthe AMS technique for modelling magma flow. Our observations suggest that brittle deformation inside the laccolith is an important mechanism for dissipating stress and has to be taken in account in em - placement models.