GEOL 11040 Lecture Notes - Lecture 11: Mount St. Helens, Whin Sill, Continental Crust
22 Oct 2018
School
Department
Course
Professor
GEOL 11040 verified notes
11/31View all
Document Summary
Mineral content tells us about tectonic context. Grain size tells us about the cooling rate: Surface area of a sphere = 4 r^2. Very large crystals are more likely to be large intrusion deeper in the crust. The crystalline basement of young continental crust is built from a series of overlapping, cooled plutons. Form the coarsest grained igneous rocks because they cool the most slowly. Shallower intrusions can take a variety of forms. Sills are horizontal intrusions that form where magma squeezes between bedding planes. The dolerite of the whin sill cooled faster than a batholith, so the grains are smaller. They are still easily discernible in this example. Dikes are vertical intrusions that cross-cut bedding at a high angle. If magma does make it to the surface, extrusive rocks can take many forms. Gas content: how much gas is in the liquid, influences pressure of magma - create bubbles in the magma (wow!!!)
