In general, I am interested in magma chambers: How do they grow and differentiate? How does material move into, out of, and within them? and Over what timescales do they remain active? I am currently studying the deformation and breakup of mafic/silicic injections into preexisting magma chambers. In one end member situation the intrusion breaks up on entering the magma chamber and produces mafic enclaves, which are common in almost all granites and related extrusive rocks. In an alternative end member case, the intrusion ponds after entering the chamber and spreads over the floor as a gravity current to form continuous layers or sheets. Indeed, one of the most enigmatic features of large silicic plutons is that whereas some are layered, others are not. Using analog experiments in which buoyant particle-fluid mixtures are injected into a shear flow, I identify the conditions in which mafic injections will pond as layers or breakup as enclaves. Scaling theories for the length scale of deformation in my experimental regimes predict that enclave sizes in natural settings will either be comparable to, or much smaller than the injection size. In addition to analogue experiments, I use field measurements of the size distribution of natural enclaves to constrain aspects of the chamber dynamics such as the convective stirring rate as well as the magma rheology. My results have significant implications also for the dynamics of magma mixing. This result leads to predictions for why mafic-silicic layered intrusions might form and also for why some batholiths are relatively homogeneous.

In another related project, I use field observations from the Tuolumne intrusive suite (TIS) of meter-scale ladder dikes to demonstrate that prior to solidification, these features are strongly deformed and broken by shearing motions in a magma chamber. These ladder dikes offer preserved length scales of deformation that can be used to infer fundamental quantities controlling the rheology of silicic magma and chamber flow dynamics at the time that they were formed. Field measurements of the geometry and distribution of ladder dikes in the TIS suggest that the breakup of these delicate features can be linked to the yield strength of the magma during deformation.

If I’m not hiking around in the Sierras or the Cascades looking for enclaves or ladder dikes, I’m either playing my fiddle or banjo with the old time gang here in Vancouver, hanging out in Squamish pretending that I like crack climbing, or squeezing in an “early” morning ski on the North Shore before work.

Below: Kirsten Hodge (Right) and Guillaume Carazzo at a famous eating establishment near Mono Lake