Document Type
Thesis
Abstract
The bulk deformation path in high-strain zones may vary as a function of the tectonic setting in which the rocks are deformed. The purpose of this research was to quantify deformation and vorticity in two well-studied high-strain zones of contrasting tectonic style. We sampled the Pinalefio Mountain high-strain zone (PMHSZ) in southeastern Arizona, a metamorphic core complex formed during Basin & Range extension, and the Brookneal high-strain zone (BHSZ), a Paleozoic transpressional zone in the central Piedmont of Virginia. Previous studies of each zone assumed simple shear deformation. The finite kinematic vorticity number (W,,) of a deformation can be determined if the strain ratio (R,) and the angle (8) between the long axis of the strain ellipse and the high-strain zone boundary are known. We estimated strain using standard Reo techniques on quartz grain shapes. Theta was determined by calculating: 1) the angle between the macroscopic foliation and the published reorientation of the high-strain zone boundary, and/or 2) the angle between the S and C planes (where present) as measured in the field or from thin sections. In the PMHSZ, strain ratios from XZ sections ranged from 2.6 — 8.3 (mean = 4.6), with an average W,, of 0.6. Porphyroclast hyperbolic distribution analysis of ultramylonites yielded a W,, of 0.2. Mylonites from the BHSZ yielded strain ratios of 3.2 — 10.0 (mean = 7.2) and an average W,, of 0.8. Mylonitic rocks in both the extensional PMHSZ and transpressional BHSZ experienced general shear deformation.
Date Awarded
2001
Department
Geology
Advisor 1
Christopher M. Bailey
Recommended Citation
Eyster, Eleanor L., "Vorticity and Strain Analysis of Transpressional and Extensional High-Strain Zones: Examples from the Arizona Basin and Range and Virginia Piedmont" (2001). Geology Senior Theses. William & Mary. Paper 78.
https://scholarworks.wm.edu/geologyseniors/78
