This paper presents an architecture for distributed synchronous collaborative visualization and modeling applied to the geosciences. Our goal is to facilitate the creation of heterogeneous collaboration sessions, in which participants may use different versions of a core CAD application, configured with specific functionalities and multimedia user interfaces, through the composition of run-time plugins. We describe the domain requirements, the architectural concepts that facilitate the integration of our collaboration plugins with the core application, and the management of communication channels to allow the definition of role-based control policies adapted to specific types of sessions.