Timescales of Magma Transfer and Storage in the Crust

The influx of magma from the mantle into the crust is the principal mechanism by which Earth’s crust grows. Understanding the assembly of igneous rocks, whether those ejected at Earth’s surface or those solidified within the crust, is therefore critical to our ability to delineate crustal evolution. Processes of magmatic differentiation, including crystal–liquid separation, crustal melting, and other thermal and mass exchanges between ascending magmas and pre-existing crust, are intimately linked to the development of compositional heterogeneities and their distribution within the crust. Understanding the kinematics of these differentiation processes, therefore, provides insight into the dynamics of crustal growth. From a volcanological perspective, the crust provides the staging area from which magmas rise to the surface. Understanding the dynamic balance between magma supply and evolution will lead to better understanding of the factors that determine whether magmas will erupt or not and, when they do erupt, whether they will erupt explosively. Many steps may limit the supply of magmas to their sites of crustal emplacement. These steps include melt production and segregation, magma ascent and emplacement into regions of storage, and episodes of outright magma storage. In this chapter, I address the topic of magma storage—and specifically the question of how long magmas may be stored in the crust before erupting or solidifying at depth—by reviewing the manifold ways in which magma storage times have been quantified. This study complements and expands on recent reviews by Hawkesworth et al. (2000) and Condomines et al. (2003). Magma systems.