Dynamics of magma transport
Crustal magma transport is typically described using a complex, non-linear model associated with fluid-driven fracturing, and therefore fundamentally sound modelling forms the basis for interpretation of magmatic intrusions. One of the most basic considerations is that magma-driven sills can be broadly categorized based on the energy dissipation mechanism that is predominant during intrusion growth. In cases where either viscous flow or overcoming fracture toughness strongly dominates fracture behaviour, it is typical to speak of viscosity-dominated or toughness-dominated regimes, each of which defines a class of fracture propagation with significant implications for modelling. This paper presents a straightforward and geometry-independent means for local determination of the expected propagation regime based on an experimentally verified mathematical analysis of the multi-scale, coupled mechanics that govern the near-tip region. The propagation regime is then related directly to the ratio between a characteristic length associated with the near-tip physics compared with the size of the fracture/sill. Sill growth is shown to be expected in or near the viscosity-dominated regime and hence modelling generally must take into account the complexity of the near-tip region rather than relying solely on the tip behaviour implied by linear elastic fracture, although toughness-dominated mafic intrusions can also be anticipated if fracture toughness increases sufficiently rapidly with the intrusion size.
Figures & Tables
Magmas are subject to a series of processes that lead to their differentiation during transfer through, and storage within, the Earth’s crust. The depths and mechanisms of differentiation, the crustal contribution to magma generation through wall-rock assimilation, the rates and timescales of magma generation, transfer and storage, and how these link to the thermal state of the crust are subject to vivid debate and controversy. This volume presents a collection of research articles that provide a balanced overview of the diverse approaches available to elucidate these topics, and includes both theoretical models and case studies. By integrating petrological, geochemical and geophysical approaches, it offers new insights to the subject of magmatic processes operating within the Earth’s crust, and reveals important links between subsurface processes and volcanism.