Transcript Document
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 Sources Include..... Include..... Magma •• Magma -- temperature temperature of of magma magma -- composition composition of of magma magma Geothermal gradient gradient •• Geothermal -- temperature temperature increases increases with with depth depth of of burial burial -- core core of of Earth Earth is is warmer warmer than than outer outer crust crust Uniform Pressure vs Directed Pressure Uniform Pressure Lithostatic •• Lithostatic -- "Lithos"= "Lithos"= rock, rock, static= static= unchanged unchanged (pressure) (pressure) -- uniform uniform (aka (aka non-directed) non-directed) -- equal equal intensity intensity from from all all directions directions by by rocks 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 caused by by igneous igneous activity activity Dynamic •• Dynamic -- aka aka cataclastic cataclastic -- associated associated with with faults faults & & earthquake earthquake zones zones Regional •• Regional -- caused caused by by tremendous tremendous pressures pressures associated with with tectonic tectonic plate plate activity activity associated Contact Metamorphism Igneous Intrusions Intrusions •• Igneous -- size size and and type type of of magma magma important important mafic magma magma hotter hotter than than felsic felsic >>mafic -- heat heat decreases decreases away away from from magma magma forms aa zone zone of of altered altered country country rocks rocks called called >>forms 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 •• •• aka Cataclastic Cataclastic Metamorphism Metamorphism aka associated with with Fault Fault Zones Zones associated -- Places Places where where the the Earth's Earth's crust crust ruptured ruptured -- Rock Rock pulverized pulverized heat and and pressure pressure come come from from movement movement along along the the >> heat Fault Fault Mylonite resultant rock rock is is known known as as aa Mylonite •• resultant Regional Metamorphism Most common common form form of of metamorphism metamorphism •• Most caused by by large large scale scale forces forces •• caused -- lithospheric lithospheric plate plate collision collision covers very very large large areas areas •• covers -- metamorphic metamorphic belts belts or or zones zones -- Zones Zones are are characterized characterized by by Index Minerals Minerals Index form under under specific specific temperatures temperatures and and pressures pressures >>form metamorphic facies facies >>metamorphic commonly associated associated with with •• commonly -- shields: areas areas of crystalline rocks rocks Shields andstable Mountains: of crystalline Metamorphic Textures Foliated •• Foliated -- Folios Folios == page page or or leaf-like leaf-like -- rock rock has has distinct distinct banding banding or or layering layering often not not smooth smooth like like in in sedimentary sedimentary rocks rocks >>often -- formed formed under under directed directed pressure pressure Non-foliated •• Non-foliated -- no no distinct distinct layering layering character character -- often often aa massive massive crystalline crystalline texture texture -- formed formed under under uniform uniform pressures pressures Foliated Texture Foliated Textures Slatey •• Slatey -- looks looks like like blackboard blackboard dull surface surface >>dull -- smooth, smooth, thin thin layering layering -- breaks breaks into into flat flat slabs slabs referred to to as as slatey slatey cleavage cleavage >>referred -- no no mineral mineral grains grains visible visible Phyllitic •• Phyllitic -- looks looks like like waxed waxed surface surface has aa "sheen" "sheen" to to itit >>has -- may may have have little little "waves" "waves" on on surface surface referred to to as as >>referred crenulations crenulations -- some some small small grains grains visible visible Schistose •• Schistose -- distinct bands of minerals -- visible visible grains mineral grains garnets, staurolites staurolites >>garnets, -- may may have have shiny shiny appearance due to to mica mica minerals minerals >>due Gneissic •• Gneissic -- larger larger grains grains -- may may look look like like igneous igneous rock rock -- may may have have crude crude banding banding intensely distorted distorted >>intensely -- different different minerals minerals than than schistose schistose Foliated MM Rocks slate phyllite QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. schist gneiss MM MM Rocks Rocks that that could could form form as as aa shale shale (sedimentary) (sedimentary) parent parent rock 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Non-foliated textured Non-foliated RocksMM Rocks • Marble: - metamorphosed limestone Quartzite: •• Quartzite: -- metamorphosed metamorphosed quartz sandstone 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 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 Metamorphic Zones • Metamorphism is common along most plate boundaries like this.