ENERGY BUDGET OF OROGENESIS AND IMPLICATIONS OF A LAZY EARTH (Invited Presentation)

We teach our introductory students that crustal deformation is a result of the Earth shedding its heat. If energy is what drives plate tectonics, it makes sense to use an energetic formulation to describe the processes that build and shape mountains. Deformational processes convert energy from one form to another at a wide range of time and length scales. For example, fault slip converts stored strain energy to frictional heat, breakdown energy and seismic shaking. The first order energy budget of the processes that build and shape mountains can be described by an equation with terms that each parameterize a wealth of processes. Tectonic work of convergence, magmatic flux and gravitational potential energy drive deformation and sediment transport. Meanwhile, energy can be consumed by deformation within the rock, released during slip events as frictional heat and seismic shaking, released as heat and kinetic energy of volcanic eruptions and released by the kinetic energy of sediment transport. The most enigmatic of these terms may be deformational work. While some portion of the internal work is stored elastically between and released during earthquakes or volcanic eruptions, the rest is converted by fabric development processes, such as pressure solution, into chemical energy. Unlike Coulomb failure or viscous flow laws, the energy framework applies to all levels of the crust. The tradeoffs between dominant processes are governed by work optimization; the lazy Earth seeks to deform in the most efficient way possible. The energy budget also provides a framework to explore interactions between mountain shaping processes that bridge disciplinary silos. For example, we can investigate how slip along a reverse fault provides energy of material uplift that becomes available to drive sediment transport. By considering the energy budget inputs and outputs, we can also assess the energy available for damaging hazards, such as earthquakes, eruptions and landslides. While some components to the orogenic energy budget, such as the rate of convergence, are well constrained from direct observations, other components, such as the stress state, need to be inferred from models. Consequently, to develop the energy budget of orogenesis we need to integrate insights from a wide range of field, laboratory and modeling studies.