Metamorphic Rocks

Metamorphism Preexisting rocks change form Rocks that are the result of metamorphism often look very different from the parent rock (rock you start with) Occurs at high temperature and pressure—from a few kilometers down to the upper mantle

Two Types of Metamorphism

Contact Metamorphism Also called low grade metamorphism Occurs when magma intrudes (pushes into) rock Causes only minor changes in rocks Ex: Marble forms when magma intrudes into limestone.

Regional Metamorphism Also called high grade metamorphism Occurs during mountain building events Results in large scale deformation of rocks (big changes) Ex: folded rocks

Agents of Metamorphism Heat—most important agent, comes from magma and increasing depth within Earth, “bake” rocks and minerals change Pressure—stress, like heat increases with depth, rocks flatten and flow, mountain building Hydrothermal solutions—hot water- based solutions dissolve original minerals and deposit new ones

Classification of Metamorphic Rocks Like igneous rocks based on texture and composition Texture Foliated Banded appearance Example: gneiss (pronounced nice) Nonfoliated Do not have banded texture Ex: marble, quartzite