ESS 101 Lecture 4: Continental Boundaries
27 Feb 2017
School
Department
Course
Professor
Document Summary
Andesite is a volcanic rock formed at subduction zones. Large crystals form when cooling rate is slow fine matrix when cooling rate is fast. Fine grain crystals show that lava crystalized at the surface of the earth. Two crystal sizes shows that the magma starts to crystalize below ground and then continue . Two stages of cooling: slowly underground and then explosive eruption. Partial melt tends to crystalize 10-15km underground. As the continental lithosphere arrives at the subduction zone, it is difficult to subduct because of its low density. The collision causes the up-warping and deformation of the ocean floor and ocean lithosphere. Sometimes segments of the upper mantle can be squeezed to the surface along where the suture zone (where the two continents are stitched together. Example: formation of appalachian mountains resulted from the collision of the african and european plates with north american plate prior to 300 million years ago.
