Metamorphic Rocks

What is a metamorphic rock? Rocks in which minerals, texture and/or structures have been changed by heat and/or pressure

Conditions for metamorphism Temperature Pressure Chemically active fluids

What is the relationship between temperature & Metamorphic Rock? 1. Below 200°C – rocks are stable for millions of years °C – still below melting point (solid) but some atoms are able to move around and rearrange 3. Above 600°C – minerals begin to melt (form igneous rocks)

How does pressure make a metamorphic rock? About 1 mile to 25 miles deep – vertical pressure from overlying rocks

How does pressure make a metamorphic rock? Along continental margins – due to mountain building forces (horizontal pressure)

How are chemically active fluids used to make metamorphic rocks? Water in pore spaces aids in atomic movement

What results from metamorphism? Same amount of mass squeezed into a smaller volume, density increases Spaces between rocks (cracks, etc.) are squeezed shut, porosity decreases

What results from metamorphism? Existing crystals become aligned perpendicular to pressure

What results from metamorphism? New minerals are formed because atoms have different “comfortable position” under new temperature and pressure conditions

Metamorphic Textures Foliation: non- continuous “layering” due to mineral alignment perpendicular to pressure

What are the metamorphic textures? 1. Slatey cleavage – tendency of fine- grained rock to split along foliation planes (not necessarily coincident with stratification)

What are the metamorphic textures? 2. Schistosity – visible parallel crystals of mica, chlorite, or talc

What are the metamorphic textures? 3. Gneissic layering – alternating light and dark minerals

What are the metamorphic textures? Non-foliated: single mineral rocks have crystals that grow equally in all directions Examples: QuartziteMarble

What are the foliated metamorphic rocks? 1. Slate – metamorphosed shale or an extrusive igneous rock Dull looking - Platy

What are the foliated metamorphic rocks? 2. Phyllite – shiny surface on foliation planes, micro-crystals began to develop Sheen

What are the foliated metamorphic rocks? 3. Schist – visible parallel crystals of mica Looks sparkly

What are the foliated metamorphic rocks? 4. Gneiss – alternating bands of light and dark crystals

What are the foliated metamorphic rocks? Granite Shale  Slate  Phyllite  Schist  Gneiss Smooth Platy SheenSparkly Layers (Dull)

What are the Non-foliated Metamorphic Rocks? sandstone Quartzite – metamorphosed sandstone Very hard 

What are the Non-foliated Metamorphic Rocks? Marble – metamorphosed limestone Fizzes with acid 

What are the Non-foliated Metamorphic Rocks? Metaconglomerate/metabreccia – rock breaks through instead of around clasts Examples: MetaconglomerateMetabreccia

What are the types of metamorphism? Regional metamorphism  Contact Metamorphism 

Regional Metamorphism Pressure from force colliding crustal plates Temperature raised by compression, friction, and movement inward toward interior Associated with linear mountain chains

Contact Metamorphism Results from physical contact with something a. magma or lava (high temperature, low pressure) b. meteorites (low temperature, high pressure)

Contact Metamorphism Small scale Pressure due to gravity, any foliation which forms is usually horizontal

Where rocks form determines what kind of rock will be produced.

Rock Cycle