When Earth's tectonic plates interact with one another the rocks that comprise them are deformed, commonly forming great mountain chains. During this deformation, the minerals that make up the rocks can become spatially or crystallographically aligned to form a fabric. The development of rock fabric is a primary factor affecting the strength, or rheological evolution of deforming rocks. Fabric development commonly involves coupling of both physical and chemical processes. For example, crenulation cleavage is the most common type of fabric in multiply deformed rocks, and its formation leads to extreme mineral segregation and rheological anisotropy. It is also commonly associated with the growth of large metamorphic minerals (porphyroblasts), which are used by structural geologists to infer deformation histories and mechanical quantities such as shear strain, shear strain rate and vorticity. Although crenulation cleavage is common throughout the world's mountain chains, and may play an important role in the localization of deformation across a range of scales, the details of its formation, and its possible mechanical significance, remain poorly understood. The investigators and their students are combining field- and laboratory-based studies with computer modeling to address the effects of rock fabric, particularly crenulation cleavage, on the rheological evolution of rocks. The chosen field area is located in the Appalachian mountains of western Maine. The results of this project will be incorporated into web-based educational modules that are intended as resources for earth-science teachers and students at all levels.
