Metamorphic Rocks: • Meta = change Morph = form • Metamorphic rocks form from changes to preexisting rock caused by heat and pressure • Metamorphism can occur locally over a small area, or over a large area covering many kilometers Two Types of Metamorphism • Regional Metamorphism - heat and pressure are significant over a wide area (many kilometers) • Contact Metamorphism - occurs over a small area when pre-existing rocks come into contact with hot liquid magma from an igneous intrusion Metamorphic Rocks • Classified on the basis of type of metamorphism (Regional or Contact) and texture: – Foliated (occurs w/regional metamorphism) – Non-foliated (usually occurs w/ contact metamorphism) Regional Metamorphism • Changes to rock over a large area • Layers of rock deep in the Earth’s crust experience the following: – High temperatures (depth and friction) – High pressures (weight and crustal movement) – Exposure to hot liquids, water, and gases • Results: – Mineral grains are compressed – minerals “migrate” through rock and begin to separate – minerals are aligned within rock in response to pressures to produce foliation Regional Metamorphism • Foliation - the alignment of minerals within a rock caused by heat and pressure This sample is clearly foliated see the mineral alignment??? Draw the foliation that results from regional metamorphism BEFORE AFTER Metamorphic Grade (degree of metamorphism) Sedimentary Rock Low-Grade Metamorphic Rock MediumGrade Metamorphic Rock MediumGrade Metamorphic Rock HIGH-Grade Metamorphic Rock SHALE SLATE PHYLLITE SCHIST GNEISS Clay minerals, stratified, soft, and fragile, dull in appearance Harder, microscopic mica minerals begin to form, less air space; dull shine Micas still Visible mica grains; microscopic, but foliation obvious; begin to reflect other minerals may more light; “silky” be seen sheen in appearance Clearly “banded” appearance as minerals separate into alternating bands This nice piece of schist has large, visible garnet crystals in it This sample of schist shows mica minerals that have grown large enough to reflect light Contact Metamorphism • Occurs over as small area around magma (igneous bodies) – country rock (pre-existing, in-place) is baked by the hot temperatures associated with magma – hot liquids and gases mix with country rock • Results: – minerals migrate and fuse together – no foliation or alignment since pressure is not significant Contact metamorphism has occurred around this igneous intrusion Draw layers of rock getting metamorphosed by coming into contact with magma Metamorphism – Parent Rock Definition • Parent Rock - the pre-existing rock from which a metamorphic rock forms Metamorphism Sedimentary Material Sedimentary Rock Metamorphic Rock Pebbles, gravel, sand Conglomerate Quartzite, Gneiss Sand Grains (usually quartz) Sandstone Quartzite Clay (usually kaolin), Silt Shale, Mudstone Slate, Phyllite, Hornfels, Schist Lime (shells, fragments, grains) Limestone Marble Metamorphic Rock Quiz • Metamorphic Rocks form from changes to other rocks in response to pressure and heat • TRUE Metamorphic Rock Quiz • Metamorphic rocks are classified by their mineral composition primarily • FALSE Metamorphic rocks are classified on the basis of texture and type of metamorphism Metamorphic Rock Quiz • Foliation in metamorphic rocks is the alignment of minerals in response to high temperatures along with great pressure • TRUE! Metamorphic Rock Quiz • Only contact metamorphic rocks experience foliation • FALSE Regional metamorphic rocks become foliated due to high pressure in addition to high temperatures Metamorphic Rock Quiz • Shale is a low-grade metamorphic rock • FALSE Shale is a sedimentary rock Metamorphic Rock Quiz • Middle to high grade metamorphic rocks appear shiny because as mica minerals crystallize they begin to reflect light • TRUE! Metamorphic Rock Quiz • Extremely high grade metamorphic rocks experience more alignment of minerals into distinct bands • TRUE Metamorphic Rock Quiz • Rocks that come into contact with an igneous intrusion will only change into igneous rocks • FALSE The high heat near an igneous intrusion will “burn” the surrounding rock and change it into metamorphic rock Metamorphic Rock Quiz • The pre-existing rock that was changed into a metamorphic rock is called the “Grandma” rock • FALSE The original rock is called the parent rock Metamorphic Rock Quiz • The sedimentary rock limestone can become changed by metamorphism into a metamorphic rock called marble • TRUE [...]... • TRUE Metamorphic Rock Quiz • Metamorphic rocks are classified by their mineral composition primarily • FALSE Metamorphic rocks are classified on the basis of texture and type of metamorphism Metamorphic Rock Quiz • Foliation in metamorphic rocks is the alignment of minerals in response to high temperatures along with great pressure • TRUE! Metamorphic Rock Quiz • Only contact metamorphic rocks. .. Regional metamorphic rocks become foliated due to high pressure in addition to high temperatures Metamorphic Rock Quiz • Shale is a low-grade metamorphic rock • FALSE Shale is a sedimentary rock Metamorphic Rock Quiz • Middle to high grade metamorphic rocks appear shiny because as mica minerals crystallize they begin to reflect light • TRUE! Metamorphic Rock Quiz • Extremely high grade metamorphic rocks. .. which a metamorphic rock forms Metamorphism Sedimentary Material Sedimentary Rock Metamorphic Rock Pebbles, gravel, sand Conglomerate Quartzite, Gneiss Sand Grains (usually quartz) Sandstone Quartzite Clay (usually kaolin), Silt Shale, Mudstone Slate, Phyllite, Hornfels, Schist Lime (shells, fragments, grains) Limestone Marble Metamorphic Rock Quiz • Metamorphic Rocks form from changes to other rocks. .. alignment of minerals into distinct bands • TRUE Metamorphic Rock Quiz • Rocks that come into contact with an igneous intrusion will only change into igneous rocks • FALSE The high heat near an igneous intrusion will “burn” the surrounding rock and change it into metamorphic rock Metamorphic Rock Quiz • The pre-existing rock that was changed into a metamorphic rock is called the “Grandma” rock •... Quiz • The pre-existing rock that was changed into a metamorphic rock is called the “Grandma” rock • FALSE The original rock is called the parent rock Metamorphic Rock Quiz • The sedimentary rock limestone can become changed by metamorphism into a metamorphic rock called marble • TRUE