MINERALS, METAMORPHISM AND RHEOLOGICAL EVOLUTION

The abundance and distribution of different minerals in polymineralic rocks has a profound effect on mechanical anisotropy, fluid pressure gradients and strain localization throughout large crustal volumes. Growth of large metamorphic minerals like garnet, andalusite and staurolite can lead to marked strengthening, whereas mineralogical segregation associated with crenulation cleavage can lead to marked weakening and impart seismic anisotropy to the crust. The mechanical interactions of weak and strong minerals within a rock establish mechanical connectivity leading to localization of strain and development of shear zones. These same mechanical interactions lead to marked fluid pressure gradients, which aid in transport of fluids that enhance reaction kinetics and help to establish self organization of fabric. In this presentation we provide field-based examples of these phenomena, and use both 2D and 3D numerical experiments to explore implications for strain localization and the coupling of deformation and metamorphism across spatial scales ranging from 1 mm to 1000 km.