When was metamorphic rock formed

Learn more: Geologic units containing metamorphic rock. The buildings of our Nation's Capital are constructed with rocks from quarries located throughout the United States and many distant lands. The earliest Government buildings, however, were constructed with stones from nearby sources because it was too difficult and expensive to move heavy materials such as stone any great distance without the aid Ever wondered what the difference between a rock and a mineral was?

This EarthWord should cover it For the first time, geologists have extracted intact rock samples from 2 miles beneath the surface of the San Andreas Fault, the infamous rupture that runs miles along the length of California. Marble is a famous metamorphic rock known for its use in sculpture and architecture.

This particular marble came from the Campbell Quarry in Texas, Maryland. Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one.

Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA. USGS scientist Art Bookstrom looks at puzzling sedimentary structures in metasedimentary rocks of the Apple Creek Formation, near the Jackass prospect, near Iron Creek, in the southeastern part of the Idaho cobalt belt, in east-central Idaho.

Intensely fractured Proterozoic metamorphic basement rock exposed in Poncha Canyon. Systematic structural measurements of fractures in such old rocks indicate a protracted history of brittle deformation in the core of Poncha mountain block that continued into recent rift-related extensional faulting. Outcrop of biotitic meta-sandstone in the lower part of the Gunsight Formation, cut by white quartz veins with alteration envelopes of coarsely crystalline black biotite and minor muscovite.

Skip to main content. Search Search. Apply Filter. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8, feet 2, meters above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized Is glacier ice a type of rock? Glacier ice, like limestone for example , is a type of rock. Glacier ice is actually a mono-mineralic rock a rock made of only one mineral, like limestone which is composed of the mineral calcite.

The mineral ice is the crystalline form of water H 2 O. Most glacier ice forms through the metamorphism of tens of thousands of individual What are sedimentary rocks? Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface.

Sedimentary rocks often have distinctive layering or bedding. The conditions required to form a metamorphic rock are very specific. The existing rock must be exposed to high heat, high pressure, or to a hot, mineral-rich fluid. Usually, all three of these circumstances are met. In order to create metamorphic rock, it is vital that the existing rock remain solid and not melt. If there is too much heat or pressure, the rock will melt and become magma.

This will result in the formation of an igneous rock , not a metamorphic rock. Consider how granite changes form. Granite is an igneous rock that forms when magma cools relatively slowly underground. It is usually composed primarily of the minerals quartz, feldspar, and mica. When granite is subjected to intense heat and pressure, it changes into a metamorphic rock called gneiss.

Slate is another common metamorphic rock that forms from shale. Limestone, a sedimentary rock , will change into the metamorphic rock marble if the right conditions are met. This happens due to geologic uplift and the erosion of the rock and soil above them. At the surface, metamorphic rocks will be exposed to weathering processes and may break down into sediment.

These sediments could then be compressed to form sedimentary rocks, which would start the entire cycle anew. Any rock type can become any other. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Tyson Brown, National Geographic Society. As with igneous processes, metamorphic rocks form at different zones of pressure depth and temperature as shown on the pressure- temperature P-T diagram. The term facies is an objective description of a rock. In metamorphic rocks facies are groups of minerals called mineral assemblages. The names of metamorphic facies on the pressure- temperature diagram reflect minerals and mineral assemblages that are stable at these pressures and temperatures and provide information about the metamorphic processes that have affected the rocks.

This is useful when interpreting the history of a metamorphic rock. In the late s, British geologist George Barrow mapped zones of index minerals in different metamorphic zones of an area that underwent regional metamorphism.

The first of the Barrovian sequence has a mineral group that is commonly found in the metamorphic greenschist facies. Greenschist rocks form under relatively low pressure and temperatures and represent the fringes of regional metamorphism. Many different styles of metamorphic facies are recognized, tied to different geologic and tectonic processes.

Recognizing these facies is the most direct way to interpret the metamorphic history of a rock. A simplified list of major metamorphic facies is given below. Burial metamorphism occurs when rocks are deeply buried, at depths of more than meters 1. Burial metamorphism commonly occurs in sedimentary basins , where rocks are buried deeply by overlying sediments. As an extension of diagenesis , a process that occurs during lithification Chapter 5 , burial metamorphism can cause clay minerals , such as smectite, in shales to change to another clay mineral illite.

Or it can cause quartz sandstone to metamorphose into the quartzite such the Big Cottonwood Formation in the Wasatch Range of Utah. This formation was deposited as ancient near- shore sands in the late Proterozoic see Chapter 7 , deeply buried and metamorphosed to quartzite , folded, and later exposed at the surface in the Wasatch Range today.

Increase of temperature with depth in combination with an increase of confining pressure produces low- grade metamorphic rocks with a mineral assemblages indicative of a zeolite facies. Contact metamorphism occurs in rock exposed to high temperature and low pressure, as might happen when hot magma intrudes into or lava Liquid rock on the surface of the Earth. This combination of high temperature and low pressure produces numerous metamorphic facies.

The lowest pressure conditions produce hornfels facies , while higher pressure creates greenschist, amphibolite, or granulite facies. As with all metamorphic rock , the parent rock texture and chemistry are major factors in determining the final outcome of the metamorphic process, including what index minerals are present. Fine-grained shale and basalt , which happen to be chemically similar, characteristically recrystallize to produce hornfels.

Sandstone silica surrounding an igneous intrusion becomes quartzite via contact metamorphism , and limestone carbonate becomes marble. Contact metamorphism in outcrop. When contact metamorphism occurs deeper in the Earth, metamorphism can be seen as rings of facies around the intrusion, resulting in aureoles.

These differences in metamorphism appear as distinct bands surrounding the intrusion, as can be seen around the Alta Stock in Little Cottonwood Canyon, Utah. The Alta Stock is a granite intrusion surrounded first by rings of the index minerals amphibole tremolite and olivine forsterite , with a ring of talc dolostone located further away.

Regional metamorphism occurs when parent rock is subjected to increased temperature and pressure over a large area, and is often located in mountain ranges created by converging continental crustal plates.

This is the setting for the Barrovian sequence of rock facies , with the lowest grade of metamorphism occurring on the flanks of the mountains and highest grade near the core The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components. An example of an old regional metamorphic environment is visible in the northern Appalachian Mountains while driving east from New York state through Vermont and into New Hampshire. Along this route the degree of metamorphism gradually increases from sedimentary parent rock , to low- grade metamorphic rock , then higher- grade metamorphic rock , and eventually the igneous core The innermost chemical layer of the Earth, made chiefly of iron and nickel.

The rock sequence is sedimentary rock , slate , phyllite , schist , gneiss , migmatite , and granite. In fact, New Hampshire is nicknamed the Granite State. The reverse sequence can be seen heading east, from eastern New Hampshire to the coast. Subduction zone metamorphism is a type of regional metamorphism that occurs when a slab Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism. Because rock is a good insulator, the temperature of the descending oceanic slab Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism.

Glaucophane, which has a distinctive blue color, is an index mineral found in blueschist facies see metamorphic facies diagram. The California Coast Range near San Francisco has blueschist - facies rocks created by subduction -zone metamorphism , which include rocks made of blueschist , greenstone, and red chert.

Greenstone, which is metamorphized basalt , gets its color from the index mineral chlorite. There are a range of metamorphic rocks made along faults. Near the surface, rocks are involved in repeated brittle faulting produce a material called rock flour, which is rock ground up to the particle size of flour used for food.

At lower depths, faulting create cataclastites , chaotically-crushed mixes of rock material with little internal texture. At depths below cataclasites , where strain becomes ductile , mylonites are formed. Mylonites are metamorphic rocks created by dynamic recrystallization through directed shear forces , generally resulting in a reduction of grain size. When larger, stronger crystals like feldspar , quartz , garnet embedded in a metamorphic matrix are sheared into an asymmetrical eye-shaped crystal, an augen is formed.

Shock lamellae in a quartz grain. Shock also known as impact metamorphism is metamorphism resulting from meteor or other bolide impacts, or from a similar high-pressure shock event. Shock metamorphism is the result of very high pressures and higher, but less extreme temperatures delivered relatively rapidly.

Shock metamorphism produces planar deformation features, tektites, shatter cones, and quartz polymorphs. Shock metamorphism produces planar deformation features shock laminae , which are narrow planes of glassy material with distinct orientations found in silicate mineral grains. Shocked quartz has planar deformation features.

Shatter cone. Shatter cones are cone-shaped pieces of rock created by dynamic branching fractures caused by impacts. While not strictly a metamorphic structure, they are common around shock metamorphism. Their diameter can range from microscopic to several meters. Fine-grained rocks with shatter cones show a distinctive horsetail pattern. Shock metamorphism can also produce index minerals , though they are typically only found via microscopic analysis.

The quartz polymorphs coesite and stishovite are indicative of impact metamorphism. As discussed in chapter 3, polymorphs are minerals with the same composition but different crystal structures.

Tektites Shock metamorphism can also produce glass. Tektites are gravel-size glass grains ejected during an impact event. They resemble volcanic glass but, unlike volcanic glass, tektites contain no water or phenocrysts , and have a different bulk and isotopic chemistry. Tektites contain partially melted inclusions of shocked mineral grains.

Although all are melt glasses, tektites are also chemically distinct from trinitite, which is produced from thermonuclear detonations , and fulgurites, which are produced by lightning strikes. All geologic glasses not derived from volcanoes can be called with the general term pseudotachylytes , a name which can also be applied to glasses created by faulting.

Barrow noticed and described the metamorphic sequence across a mountain belt showing regional metamorphism , now concluded to represent continental collision. Metamorphic facies are characterized by rock properties or assemblages groups of index minerals. Which metamorphic facies is associated with subduction zones?

By analyzing facies on the Metamorphic PT diagram, blueschist is shown on the left at a low temperature but at a high pressure. The PT diagram indicates that high pressure and low temperature minerals are found at subduction zones.

When magma intrudes pre-existing country rock , the rock will be cooked by the magma. Contact metamorphism occurs when rocks are exposed to high temperatures and low pressures. For example, when a magma intrudes into pre-existing rocks, or a lava Liquid rock on the surface of the Earth. The core The innermost chemical layer of the Earth, made chiefly of iron and nickel. Regional metamorphism occurs when temperatures and pressures are exerted on a rock over a large geographic area.

This is often associated with mountain belts from converging continental tectonic plates. Increasing metamorphic grade can be observed as one travels from the edge of a mountain belt into its high- grade core The innermost chemical layer of the Earth, made chiefly of iron and nickel.

Metamorphism is the process that changes existing rocks called protoliths into new rocks with new minerals and new textures. Increases in temperature and pressure are the main causes of metamorphism , with fluids adding important mobilization of materials. The primary way metamorphic rocks are identified is with texture. Foliated textures come from platy minerals forming planes in a rock, while non-foliated metamorphic rocks have no internal fabric.

Grade describes the amount of metamorphism in a rock, and facies are a set of minerals that can help guide an observer to an interpretation of the metamorphic history of a rock. Different tectonic or geologic environments cause metamorphism , including collisions, subduction , faulting , and even impacts from space.

Use this quiz to check your comprehension of this chapter. By indicating the range of temperature and pressure at which they are stable, index minerals help geologists constrain the conditions of metamorphism.

Marble is the result of metamorphic recrystallization of limestone. How does burial metamorphism occur? Burial metamorphism occurs when sediments are buried in deep depositional basins where heat causes diagenesis to extend beyond compaction and cementation to actual changes in minerals.

What is metamorphism? Metamorphism is the process by which previously existing rocks protoliths are changed in composition and texture by heat, pressure, and active fluids. How does stress differ from strain? Stress is applied force; strain is the resulting change or deformation. If you find a rock with distinct foliation , how was this rock metamorphosed? Directed stress is the likely cause of foliation.

How can you easily distinguish between quartzite and marble using only what you normally carry with you on a hike? The simple test of rubbing them together will do. Quartz is harder than calcite and quartzite will scratch marble. What is the difference between heat and temperature? Heat is thermal energy; temperature is vibrational kinetic energy of atoms caused by heat. Tektites are gravel size grains of glass ejected during an impact event.

What does a phase diagram show? Peter Davis, Pacific Lutheran University KEY CONCEPTS Describe the temperature and pressure conditions of the metamorphic environment Identify and describe the three principal metamorphic agents Describe what recrystallization is and how it affects mineral crystals Explain what foliation is and how it results from directed pressure and recrystallization Explain the relationships among slate , phyllite , schist , and gneiss in terms of metamorphic grade Define index mineral Explain how metamorphic facies relate to plate tectonic processes Describe what a contact aureole is and how contact metamorphism affects surrounding rock Describe the role of hydrothermal metamorphism in forming mineral deposits and ore.

Valuable material in the Earth, typically used for metallic mineral resources. Foliation vs.