Sub-volcanic breccias: combining ore deposit, volcanology and geophysical perspectives

There is abundant evidence from exploration and mining of porphyry ore deposits that large (>100s of meters) pipes, dikes and irregular bodies of breccia form at kilometers depth, spatially and temporally associated with hydrous arc magmatic systems. This project will bring together the fields of economic geology, volcanology and geophysics, both to physically understand how the barren and mineralized breccias form, as well as to improve our interpretations of volcanic unrest signals recorded today.
The classic paper on "Ore-related breccias in volcanoplutonic arcs" by Sillitoe (1985) compiles information on the size and geometry of breccia bodies, and lithologies, shape, size and vertical displacements of the constituent fragments. The properties of the sub-surface breccia bodies vary considerably (e.g. no vertical displacement of fragments to >1km displacement) and so there must be multiple mechanisms for their formation. The project will concentrate on breccias associated with sub-volcanic magmatic and hydrothermal processes that form by either release of hydrothermal fluids from magmas or from fragmentation and eruption of magmas from reservoirs.
The physical modelling will consider evolving stresses in intrusions and surrounding rocks as volatile-saturated magmas are emplaced and crystallize, exsolving further volatiles, as well as stresses in rocks at depth induced by eruptions and dome/sector collapse (e.g. Montserrat; Druitt et al., 2002). All models, and hypotheses derived from them, will be constrained and tested by evidence from geology.
A second strand of research will assess the expected monitoring signals (seismicity, ground deformation, gas emissions) that would be associated with the formation of breccias like those that have been uncovered by economic geologists. The flip side will be to review unrest signals from modern eruptive and noneruptive crises at volcanoes (e.g. Werner et al., 2011) and consider whether any might be related to processes equivalent to the deep brecciation events in the geological record.