Deformation and Metamorphism

Jane A Gilotti, University of Iowa

The Earth’s crust is slowly moving. Did you know that the Atlantic Ocean is getting wider at about the rate your fingernails grow, or that India is barging its way slowly northward into the continent of Asia?

The huge forces that move continents stretch and squash parts of the Earth’s crust., generating earthquakes and building mountains. They cause rocks near the surface to be fractured and faulted. At greater depth, the heat and pressure involved can cause folding and/or metamorphism.

Dickson Fjord in Greenland: This huge cliff (over 2,000 metres high!) is made of a metamorphic rock called gneiss.

This was once a series of both igneous and sedimentary rocks, which were deeply buried, folded by huge forces, and completely recrystallised at high temperature and pressure to form this beautifully banded and folded rock.