METAMORPHIC ROCKS

METAMORPHIC ROCKS META = CHANGE MORPH = FORM Called the “Cinderella Rock” Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE Change occurs because the rock is moved into an environment in which the minerals which make up the rock become unstable and out of equilibrium with the new environmental conditions In most cases, this involves BURIAL which leads to a rise in temperature and pressure

Occurs in rocks due to the effects of METAMORPHISM Occurs in rocks due to the effects of High temperature High pressure

HEAT EFFECTS Temperature increases with depth or contact with magma Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature Changes to a new (high temperature) mineral

PRESSURE EFFECTS Mineral crystals grow larger Pressure increases with depth – weight of overlying rock Mineral crystals grow larger Mineral crystals are more dense Mineral crystals grow perpendicular to pressure Mineral crystals are arranged in parallel layers – PRODUCES FOLIATION

FOLIATION Pressure actually rearranges the minerals into parallel layers. More pressure – minerals grow larger and recrystallize and separate into layers Even more pressure – alternating layers of light and dark minerals called Banding

Random arrangement of minerals Organized arrangement of minerals - banding

METAMORPHIC ROCK MANTRA INTERGROWN CRYSTALS IN AN ORGANIZED PATTERN

Granite Intergrown crystals random pattern Gneiss Intergrown crystals Organized Pattern

2 Types of Metamorphism Regional Metamorphism – Occurs over large areas where there is active mountain building Convergent plate boundaries Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions

MOUNTAIN BUILDING Let’s start with regional metamorphism

FOLIATED METAMORPHIC ROCKS

GRADES OF METAMORPHISM LOW GRADE – LESS HEAT AND PRESSURE – SLATE HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS

FOLIATED METAMORPHIC ROCKS

METAMORPHIC ROCKS WILL OFTEN BE DEFORMED BECAUSE OF INTENSE HEAT AND PRESSURE LOOK AT ROCK SYMBOL FOR GNEISS

DEFORMED GNEISS

A metamorphic rock exposed to too much heat will melt and become ??? MAGMA

CONTACT METAMORPHISM

Contact Metamorphic Metamorphism means "changed form". The Changes occur because of: Heat from magma intruding on the surrounding rock Very little pressure

Near magma chambers (plutons) Rocks in “contact” with the magma are baked New minerals are formed –recrystallization Transition zone of contact metamorphism is usually relatively narrow baking the adjacent rocks

Contact Metamorphism – Baking the adjacent rocks

Symbol for Contact Metamorphism is a line with tick marks When limestone undergoes contact metamorphism what rock will it metamorphose into? Marble!

PARENT ROCK IN THE COMMENTS

LIMESTONE METAMORPHOSES INTO MARBLE

SANDSTONE METAMORPHOSES INTO QUARTZITE