Document Type

Honors Thesis


Earth Sciences, Physics


Scott Johnson

Committee Members

Peter Koons, Daniel Lux, Samuel Hess, Robert Brinkley

Graduation Year

August 2008

Publication Date

Fall 12-2023


Crystallographic and shape preferred orientation (SPO) fabrics that develop in mylonitic shear zones can preserve the mean kinematic vorticity number (Wm) of bulk flow. Microstructural methods exploiting dynamically recrystallized quartz and porphyroclast SPO fabrics typically yield conflicting values of Wm. The Sandhill Corner Mylonite Zone of the Norumbega Fault System, Maine, USA, serves as a case study for investigating this discrepancy; Wm estimates range from 0.90 to 1.00 employing the former method (Method 1) and from 0.3 to 0.6 employing the latter method (Method 2). Using a numerical model, I show how a low-viscosity layer (LVL) surrounding clasts affects their SPO and makes Method 2 underestimate Wm. I propose a method based on my modeling results for estimating the viscosity contrastη~ between the LVL and rock matrix in natural examples.