Characterization of Structures and Deformation in the Brittle-Ductile Transition, Western Termination of the Chugach Metamorphic Complex, Southern Alaska

Field mapping along the western termination of the Chugach Metamorphic Complex (CMC) revealed a new D2 structure, the Bremner foliation fan. This structure has a high strain, vertically foliated core, with moderate-shallow dipping cleavages to the north and south which rollover into the core. The fan appears to have propagated from below by a shear-zone at depth (O\u27Driscoll, 2006). Description of the Bremner foliation fan revealed that the Bremner shear zone of Pavlis and Sisson (2003) is a D3 structure, and that the Stuart Creek fault is a younger brittle fault with 90km of dextral offset. Electron Back Scatter Diffraction (EBSD) and microstructural observations revealed deformation mechanisms were primarily compositionally controlled, whereas P-T-t conditions played a secondary role. Other factors, deemed to be of lesser influence included increased pressure solution caused by high fluid mobility, a lack of pore space, high levels of free aluminum, and a load-bearing framework of phyllosilicates