Julia Ann “Jan” Tullis was an American structural geologist and emerita Professor at Brown University.

[3] Tullis' research involved experimental investigations of the deformation mechanisms, microstructures and rheology of crustal rocks using constant strain-rate Griggs-type solid medium apparatus including adaptations for molten salt assemblies.

[4] Her two major goals were to enable more accurate inferences concerning the thermomechanical history of naturally deformed rocks based on their preserved microstructures and crystallographic preferred orientations, and to provide mechanical data and flow laws to enable more accurate modeling of crustal deformation under various conditions.

[5] Experiments were conducted on monophase and polyphase aggregates, both natural and synthetic, over a wide range of pressure and temperature conditions equivalent to those from the shallow to the deep crust, and involving varying controlled water contents.

[6] These experiments investigated the role of phase distribution and contiguity in the progressive deformation of polyphase aggregates, and documented a number of processes resulting in strain weakening and localization, such as in mylonite zones.