I have a number of long-term research projects located around the globe. While they may seem disparate, each in its own way seeks to understand the evolution of mountain belts and the interactions of plate boundaries in creating those belts. Detailed structural analysis-looking at the small scale evidence of major crustal displacement-is one of the tools I use to investigate mountain belts.
Work in northern British Columbia and Yukon Territory addresses the Late Paleozoic (350 to 250 million years ago) history of the Cordilleran mountain belt-a time when oceanic terranes that would later be accreted to the edge of the continent were developing offshore. What was their character, and their paleogeographic position leading up to collision with North America?
The collision of various micro-plates with the Pacific margin of North America through the Mesozoic and early Cenozoic (150 to 50 million years ago) caused the growth of mountains by shortening and thickening the crust. A series of research projects in northeastern Washington seeks to quantify the amount of shortening involved in mountain building by looking at deformed markers, like trilobites, preserved in the strata.
Together with a team of geology faculty and students from Amherst, Smith, and other liberal arts colleges, I have been seeking to understand the dynamics of the margin of a microplate involved in continental collision 1,790 million years ago. Evidence for this is preserved in highly metamorphosed and severely strained rocks exposed in the heart of the much younger Rocky Mountain ranges of southwest Montana. Did mountain building early in earth's history occur by the same processes we observe in younger mountain ranges? Sheath folds-a unique form of deformed rock layers-developed in these metamorphosed rocks during collision. How did they form and what can their presence tell us about the mechanisms of mountain building? We are analyzing microstructures in one prominent sheath fold to address these questions.