Microstructural and Lattice-Preferred Orientation Analyses of Ductile Shear Zones: Maggia Nappe, Switzerland
Author
Barnhart, William Douglas
Subject
Washington and Lee University -- Honors in Geology
Shear zones (Geology) -- Switzerland -- Maggia
Geology, Structural -- Switzerland -- Maggia
Metadata
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Microstructures of 24 samples and quartz lattice-preferred orientations (LPO) of 13 samples from the crystalline Maggia Nappe, Switzerland were measured in order to assess the deformation history, mechanisms, and conditions of ductile shear zones related to nappe formation. Microstructures suggest dislocation accommodated dynamic recrystallization as evidenced by grain size reduction and grain boundary area reduction (GBAR). However, weak LPOs suggest diffusion processes that destroyed previously developed LPOs. Large grain size ( ~ 100-300in) suggests a major component of diffusion creep-accommodated grain-boundary sliding (GBS) followed by grain size growth. Undulatory extinction in grains implies grain growth was not entirely post deformational. Assuming stain rates of 10-13 s-1, the deformation history of the Maggia Nappe at PIT conditions of 450�-650� C and 3-10 kbar is constrained as 1) development of a lineated magmatic fabric, 2) development of ductile shear zones and strong LPO through dislocation creep, 3) onset of diffusion creep-accommodated GBS after sufficient grain size reduction, 4) destruction of LPOs, and 5) syn- and post- deformational grain growth.