For the past half decade we have been using axisymmetric numerical models to study the mechanics of magma reservoir inflation in an effort to understand the factors that control tensile rupture of the…

For the past half decade we have been using axisymmetric numerical models to study the mechanics of magma reservoir inflation in an effort to understand the factors that control tensile rupture of the wall and the nature of the intrusions that result. These studies have been driven by recognition that a flaw exists in the standard treatment used by most researchers assessing this process quantitatively during the last century; in essence, standard treatments fail to correctly account for the three-dimensional nature of the host rock stress tensor. Detailed elucidation of this argument for a homogeneous, semi-infinite halfspace has shown that incorrect elimination of two lithostatic stress tensor components has key implications for several volcanological processes, including interpretation of the conditions that lead to tensile rupture of the reservoir wall (grosfils, j. Volc. Geotherm. RES., 2007). Subsequent efforts have demonstrated the importance of retaining the full three-dimensional stress tensor when the host rock includes mechanical layering (long and grosfils, j. Volc. Geotherm. RES., 2009) and when edifice loading is present (hurwitz ET AL., j. Volc. Geotherm. RES., 2009; galgana ET AL., j. Geophys. RES., 2011). Lessons derived from the collaborative research efforts cited above, integrated with a review of pertinent literature published in recent decades, indicate that existing models for the mechanics of ring fault initiation and caldera formation also incorporate the same critical flaw. IT is important to resolve this problem and reassess the mechanics of ring fault initiation because (1) caldera formation is a fundamental volcanological process that continues to shape the terrestrial planets, (2) the mechanics of caldera formation are incompletely and incorrectly understood, (3) understanding the mechanical conditions under which ring faults and calderas form will advance our understanding of subsurface magma plumbing systems in ways that complement petrology-derived inferences, and (4) the geological records preserved on earth, venus and mars clearly illustrate the considerable extent and magnitude of the devastation that can accompany caldera formation and associated eruption events. There is obvious scientific and societal motivation to improve our understanding of the processes that precipitate, and are associated with, caldera formation. Since calderas often develop in tectonically complex environments, this proposal builds on our previous efforts by outlining a plan to develop fully three-dimensional models that can be used to gain insight into ring fault initiation and caldera formation in such settings. Specifically, targeting calderas on earth, venus and mars for comparative study, we will (1) examine the process of ring fault initiation and caldera formation in a halfspace subjected to a regional differential stress; (2) examine the process of caldera formation in a strong/thick lithosphere when a relatively small edifice is present; and, (3) examine the process of caldera formation within weak/thin lithosphere subjected to flexural displacement caused, for instance, by edifice loading or underplating.