Metamorphic Rocks Definitions Metamorphic Rock Meta Change Grk

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

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

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

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

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

Contact Metamorphism Igneous Intrusions • • Igneous -- size and type of of magma important mafic magma hotter than felsic >>mafic -- heat decreases away from magma forms aa zone of of altered country rocks called >>forms 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 • • aka Cataclastic Metamorphism aka associated with Fault Zones associated -- Places where the Earth's crust ruptured -- Rock pulverized heat and pressure come from movement along the >> heat Fault Mylonite resultant rock is is known as as aa Mylonite • • resultant

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

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

Foliated Texture

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

Foliated MM Rocks slate phyllite schist gneiss MM MM Rocks that could form as as aa shale (sedimentary) parent rock is 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 Non-foliated Rocks. MM Rocks • Marble: - metamorphosed limestone Quartzite: • • Quartzite: -- metamorphosed quartz sandstone quartz

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-Map Metamorphic

Metamorphic Facies distinctive metamorphic mineral assemblages that occur in welldefined 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 • Metamorphism is common along most plate boundaries like this.