Metamorphic Environments Contact (or thermal) Hydrothermal Burial Regional Shock (impact) Fault Zone
Contact Metamorphism Contact or thermal metamorphism occurs when an intrusive magma heats the surrounding country (or host) rock and changes the mineralogy and texture
Contact Metamorphism The zone where the rocks are subject to metamorphism is called the metamorphic aureole
Contact Metamorphism The sedimentary rocks are turned into metamorphic rock by contact metamorphism
Contact Metamorphism Even small dykes can form aureole of metamorphic rock a few centimeters thick
Contact Metamorphism The metamorphic aureole is the darker rock that once roofed over the igneous pluton
Hydrothermal Metamorphism Hydrothermal fluids can carry dissolved calcium dioxide, sodium, silica, copper and zinc Ascending hydrothermal fluids can react with overlying rock, creating new minerals (which may have great economic value)
Hydrothermal Metamorphism The most widespread occurrence of hydrothermal metamorphism is along the mid-oceanic ridges As seawater percolates through the newly created crust, it is heated and chemically reacts with the mafic (Fe and Mg rich) basalt
Hydrothermal Metamorphism The ferromagnesian igneous minerals, such as olivine and pyroxene, are changed into metamorphic minerals such as serpentine, chlorite and talc Calcium-rich plagioclase feldspars become more sodiumrich as the sea salt (NaCl) exchanges calcium for sodium
Black Smokers Large amounts of metals, such as iron, cobalt, nickel, silver, gold and copper, are dissolved from the newly formed crust These hot (~350 o C), metal-rich fluids rise along fractures, generating particle-filled clouds called black smokers
Black Smokers Black smokers were first discovered in 1977 around the Galápagos Islands by the small submersible vehicle called Alvin Smokers have now been found in all oceans
Black Smokers Although life is very sparse at these depths, black smokers are the center of entire ecosystems Sunlight is nonexistent, so many organisms must convert the heat, methane, and sulfur compounds provided by black smokers into energy through a process called chemosynthesis
Black Smokers Hydrothermal vents support a large population of chemosynthetic bacteria The bacteria then grow into a thick mat which attracts other organisms such as amphipods and copepods which graze upon the bacteria directly Larger organisms such as snails, shrimp, crabs, tube worms, fish, and octopuses form a food chain of predator and prey
Burial Metamorphism Burial metamorphism occurs when thick accumulations of sedimentary strata on the ocean floor are subducted beneath another plate
Burial Metamorphism This is a low grade metamorphism that typically begins when the subducted sediments reach a depth of 6-10 kilometers (3-6 miles) or when the temperature reaches about 200 o C
Regional Metamorphism Most metamorphic rocks are created during the process of regional metamorphism associated with mountain building During these dynamic events, large segments of the Earth s crust are intensely deformed along convergent plate boundaries
Regional Metamorphism The mountain building applies differential stress literally over a wide regional area Sediments and crustal rock lifted up from the ocean floor are folded and faulted Metamorphism of all grades, from low to high occurs
Regional Metamorphism The Andes Mountains and the Himalaya Mountains (below) are prime examples where regional metamorphism has occurred along thousands of miles of mountain range
Regional Metamorphism The Swiss and Austrian Alps in Europe are other famous examples where extensive regional metamorphism has occurred
Impact Metamorphism Impact metamorphism occurs when an asteroid or comet impacts the Earth s surface These objects can be moving as fast as 100,000 miles per hour (~28 miles per second)
Impact Metamorphism In a fraction of a second, the energy of the rapidly moving object is transferred into heat energy and shock waves as it smashes into the Earth
Impact Metamorphism The impacting asteroid or comet is vaporized The impacted rock is shattered, pulverized and sometimes even melted Minerals in the rock are instantly subjected to both high temperature and high pressure
Impact Metamorphism Rare and unusual metamorphic minerals such as coesite, which are normally never found on the Earth s surface, are nearly instantly formed Staggering quantities of matter are blown into the atmosphere Fortunately for life on Earth, this is a rare event, but these impacts have repeatedly caused mass extinctions
Impact Metamorphism A crater one mile in diameter and 500 feet deep is formed in only 30 seconds A crater ten miles in diameter and a mile deep is formed in 90 seconds The largest known crater on the Earth in located in South Africa and is 180 miles in diameter (Above) Tenoumer Crater in Mauritania
Fault Zone Metamorphism Near the surface, rock behaves like a brittle solid So near the surface, movement along a fault zone fractures and pulverizes the rock, creating what is called fault breccia
Fault Zone Metamorphism In contrast, at depth under higher heat and pressure, rock is ductile and flows like plastic At depth along a fault zone, the mineral structures are deformed by the ductile flow, giving the metamorphic rock a foliated or lineated appearance