Metamorphic Rocks Metamorphic Rocks Definitions Definitions • • - - "Meta"= Change "Meta"= Change (Grk) (Grk) - - "Morph"= form "Morph"= form (Grk) (Grk) a rock that has been changed a rock that has been changed - - from its original form ( from its original form ( parent parent ) by ) by heat heat , , pressure pressure , and , and fluid activity fluid activity into a new rock ( into a new rock ( daughter ).

Heat Heat Sources Include..... Sources Include..... Magma Magma • • - - temperature of magma temperature of magma - - composition of magma composition of magma • Geothermal gradient Geothermal gradient • - - temperature increases with depth of burial temperature increases with depth of burial - - core of Earth is warmer than outer crust core of Earth is warmer than outer crust

Uniform Pressure vs Directed Pressure Uniform Pressure Lithostatic • • Lithostatic - - "Lithos"= rock, static= unchanged (pressure) "Lithos"= rock, static= unchanged (pressure) - - uniform (aka non-directed) uniform (aka non-directed) - - equal intensity from all directions by rocks equal intensity from all directions by rocks

Directed Pressure one direction of squeezing is much stronger than the others Minerals align themselves to reduce stress.

Types of Metamorphism Types of Metamorphism Contact • Contact • - - caused by igneous activity caused by igneous activity • • Dynamic Dynamic - - aka cataclastic aka cataclastic - - associated with faults & earthquake zones associated with faults & earthquake zones • • Regional Regional - - caused by tremendous pressures caused by tremendous pressures associated with tectonic plate activity associated with tectonic plate activity

Contact Metamorphism Contact Metamorphism Igneous Intrusions • • Igneous Intrusions - - size and type of magma important size and type of magma important > > mafic magma hotter than felsic mafic magma hotter than felsic - - heat decreases away from magma heat decreases away from magma > > forms a zone of altered country rocks called forms a zone of altered country rocks called Aureoles Aureoles Sometimes creates a metamorphic rock called a hornfels -in essence a “cooked” rock

Hornfels- basically any rock that has been “cooked” and metamorphosed by contact with igneous material (magma or lava). Often original rock textures are identifiable

Dynamic Metamorphism Dynamic Metamorphism • • aka Cataclastic Metamorphism aka Cataclastic Metamorphism associated with Fault Zones • • associated with Fault Zones - - Places where the Earth's crust ruptured Places where the Earth's crust ruptured - - Rock pulverized Rock pulverized > > heat and pressure come from movement along the heat and pressure come from movement along the Fault Fault Mylonite Mylonite • • resultant rock is known as a resultant rock is known as a

Regional Metamorphism Regional Metamorphism • • Most common form of metamorphism Most common form of metamorphism • • caused by large scale forces caused by large scale forces - - lithospheric plate collision lithospheric plate collision covers very large areas • • covers very large areas - - metamorphic belts or zones metamorphic belts or zones - - Zones are characterized by Zones are characterized by Index Minerals Index Minerals > > form under specific temperatures and pressures form under specific temperatures and pressures > > metamorphic facies metamorphic facies commonly associated with • • commonly associated with - - shields: stable areas of crystalline rocks Shields and Mountains: areas of crystalline rocks

Metamorphic Textures Metamorphic Textures • • Foliated Foliated - - Folios = page or leaf-like Folios = page or leaf-like - - rock has distinct banding or layering rock has distinct banding or layering > > often not smooth like in sedimentary rocks often not smooth like in sedimentary rocks - - formed under directed pressure formed under directed pressure Non-foliated • • Non-foliated - - no distinct layering character no distinct layering character - - often a massive crystalline texture often a massive crystalline texture - - formed under uniform pressures formed under uniform pressures

Foliated Texture Foliated Texture

Foliated Textures Foliated Textures • Slatey Slatey • • Schistose - - looks like blackboard looks like blackboard - - distinct bands of minerals > > dull surface dull surface - - visible grains visible mineral grains - - smooth, thin layering smooth, thin layering > > garnets, staurolites garnets, staurolites - - breaks into flat slabs breaks into flat slabs - - may have shiny may have shiny > > referred to as slatey cleavage referred to as slatey cleavage appearance - - no mineral grains visible no mineral grains visible > > due to mica minerals due to mica minerals • • Phyllitic Phyllitic • • Gneissic Gneissic - - looks like waxed surface looks like waxed surface - - larger grains larger grains > > has a "sheen" to it has a "sheen" to it - - may look like igneous rock may look like igneous rock - - may have little "waves" on may have little "waves" on - - may have crude banding may have crude banding surface surface > > intensely distorted intensely distorted > > referred to as referred to as crenulations crenulations - - different minerals than different minerals than - - some small grains visible some small grains visible schistose schistose

Foliated MM Rocks Foliated MM Rocks phyllite phyllite slate slate schist gneiss schist gneiss MM Rocks that could form as a shale (sedimentary) parent rock is MM Rocks that could form as a shale (sedimentary) parent rock is exposed to increasing directed pressure and temperature

Migmatite- a very high grade metamorphic rock that has begun to partially melt

Migmatite- note the “blobs” of quartz

Non-foliated textured MM Rocks Non-foliated Rocks • Marble: - metamorphosed limestone • • Quartzite: Quartzite: - - metamorphosed metamorphosed quartz sandstone quartz sandstone

Environment of Formation- EOF look for specific minerals and textures Map out where those minerals are found reconstruct T & P for given minerals Find a modern setting that has similar T & P using Uniformitarianism

Metamorphic Zones Metamorphic Zones

Metamorphic Zones-Map

Metamorphic Facies Metamorphic Facies Hornfels distinctive metamorphic mineral assemblages that occur in well-defined P & T regions and named after the key rocks (and associated lithologies) found Hornfels

Blueschist Can be both a rock, and a facies characterized by specific temperature and pressures The rock commonly has high temp and pressure It commonly has Glaucophane & Lawsonite Usually has smaller Crystals relating to mineralogy

Blueschist Can be both a rock, and a facies characterized by specific temperature and pressures The facies is that constrained by the temp and pressure necessary to metamorphose a basalt parent rock into a blueschist

Greenschist Can be both a rock, and a facies characterized by specific temperature and pressures The rock commonly has low to intermediate temp and pressure It commonly has Chlorite, Actinolite Serpentine, and Epidote. Usually has small Crystals relating to mineralogy

Greenschist Can be both a rock, and a facies characterized by specific temperature and pressures The facies is that constrained by the temp and pressure necessary to metamorphose a basalt parent rock into a schist

Amphibolite Can be both a rock, and a facies characterized by specific temperature and pressures Rock contains predominantly amphiboles Like hornblende and actinolite

Metamorphic Zones Metamorphic Zones • Metamorphism is common along most plate boundaries like this.