When Sedimentary Rock Is Exposed To Heat And Pressure, What Does It Change Into?

NAVIGATION: Dorsum TO MODULE Ii INTRODUCTION

Rocks and the Rock Cycle

ROCKS:

Rocks, rocks, rocks. Weathering is all about rocks. Rocks, rocks, rocks. To understand weathering, we must outset learn about rocks.

Rocks are the most common of all materials on earth. They are familiar to anybody. You may recognize rocks in the class of a mountain near your hometown, the gravel in a driveway, the cliffs lining your favorite fishing pigsty, or the granite or sandstone or limestone your fingers and toes cling to at your favorite climbing area.

Rocks should exist considered products of their environment - when their environs changes, and so will the ways the stone weathers and erodes, or is otherwise shaped.

Rocks class in one of two distinct environments: either beneath the surface of the earth or at its surface. Rocks are equanimous of minerals. Minerals are naturally occurring, inorganic substances, which have an ordered internal structure giving them a specific appearance. Interestingly, ice is a mineral. Some of the more common rock-forming minerals are quartz, feldspar, pyroxene, hornblende, and olivine. Minerals should not be dislocated with rocks. For example, granite is a rock. it is composed of several minerals such as quartz, mica, and feldspar.

The triad (don't yous love that word, triad?) of rocks that compose the planet are igneous, sedimentary, and metamorphic.

Important! Don't PANIC because of the MASSIVE corporeality of text on this Web page... Y'all can learn about rock types and other things in great detail below. Only here's the real important stuff nigh rocks and rock types that are integral to understanding this module:

There are 3 rock types - there are a lot of sedimentary; some granite; and very niggling metamorphic rocks on the Colorado Plateau
The rock bicycle happens - how rocks class determines how they will weather
Rocks weather differentially - without differential weathering, the landscape would non be every bit strikingly various!

ROCK TYPES:

In this Module, you will encounter a LOT of sandstone . Sandstone is a sedimentary rock that is highly resistant to weathering. Other sedimentary rocks you volition encounter are mudstone and siltstone. These are soft and hands weathered (lots in the Painted Desert). Yet another sedimentary stone you will see is limestone. Limestone is composed of calcium carbonate, which is h2o soluble (it dissolves in water). Therefore, the limestone y'all detect in a dry expanse will remain a rock a lot longer than limestone you find in a MOIST area.

Regarding metamorphic rocks, in that location really aren't many of these on the Colorado Plateau.. only in the bottom of the Grand Coulee! Then, good affair for you, we are really not going to comprehend this stone blazon in this Module.

Y'all will see a few igneous rocks in this Module... You see granite (intrusive igneous) and basalt (extrusive igneous). The granite you will run into is high upward in the La Sal Mountains and the basalt you volition run across sits equally cap rocks on height of softer, underlying sediments. A cap stone is a comparatively more than resistant rock that protects the rocks beneath it from weathering and eroding.

The central to understanding rock weathering is to realize that rocks conditions at different rates and into different forms based on their chemic composition and based on what weathering processes boss the area.

For Style more information on rocks than you are required to know for this Module, visit the following links:

Leap to igneous | Jump to metamorphic | Jump to sedimentary

THE Stone CYCLE: (some content and the diagram below borrowed from NASA)

The rock wheel best explained as the human relationship between earth�due south internal and external processes. Weathering (breaking downward rock) and erosion (transporting stone material) at or near the earth's surface breaks downwards rocks into small and smaller pieces. These smaller pieces of rock (such equally sand, silt, or mud) can be deposited as sediments that, after hardening, or lithifying, go sedimentary rocks. Extreme pressure from burying, increasing temperature at depth, and a lot of time, tin can alter any rock type to class a metamorphic stone. If the newly formed metamorphic rock continues to heat, it can somewhen melt and get molten (magma). When the molten stone cools it forms an igneous stone. Metamorphic rocks can grade from either sedimentary or igneous rocks. The sedimentary particles from which a sedimentary rock is formed can be derived from a metamorphic, an igneous, or some other sedimentary rock. All three rock types tin be melted to form a magma. Thus, the wheel has connected over the ages, constantly forming new rocks, breaking those down in various ways, and forming all the same younger rocks. Rocks at the surface of the world range in historic period from over 3 billion years one-time to a few hundred years old.

Igneous rock tin can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock.

Igneous stone forms when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can course crystals when they cool. Igneous stone can form cloak-and-dagger, where the magma cools slowly. Or, igneous stone can form above ground, where the magma cools quickly.

Notice how many time "weathering" and "erosion" (light-green arrows) appear in the above diagram?

When information technology pours out on Earth'south surface, magma is chosen lava. Yes, the same liquid rock affair that y'all meet coming out of volcanoes. Igneous rock that pours out onto the Earth'south surface is called igneous extrusive, whereas igneous rock that cools below the surface is chosen igneous intrusive.

On Earth's surface, wind and water tin can break rock into pieces (weathering!). They can also carry rock pieces to some other place (erosion)!. Normally, the rock pieces, chosen sediments, driblet from the current of air or h2o to make a layer. The layer tin can exist buried under other layers of sediments. After a long fourth dimension the sediments can be cemented together to brand sedimentary stone. In this way, igneous rock can get sedimentary rock.

All rock can be heated. But where does the heat come from? Inside Earth at that place is estrus from force per unit area (push your hands together very hard and experience the heat). In that location is heat from friction (rub your hands together and feel the heat). There is also heat from radioactive disuse (the procedure that gives u.s.a. nuclear power plants that make electricity).

Then, what does the heat do to the rock? It bakes the rock.

Remember, all rocks are made up of mineral crystals, or pieces of other rocks made upwards of crystals. Baked rock does non melt, but it does modify. It forms crystals. If it has crystals already, information technology forms larger crystals. Because this rock changes, it is called metamorphic. Remember that a caterpillar changes to go a butterfly. That alter is called metamorphosis. Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius.

When Earth's tectonic plates movement around, they produce heat. When they collide, they build mountains and metamorphose the stone.

The rock cycle continues. Mountains made of metamorphic rocks can be broken up and washed abroad by streams. New sediments from these mountains can make new sedimentary stone.

The rock cycle never stops.

BELOW IS A LOT OF INFORMATION -- DON'T WORRY Virtually Advisedly READING THE CONTENT -- IT IS A Resource FOR YOU IF You lot NEED It!

Igneous Rocks : Igneous rocks are a type of stone formed from extremely hot (2,200 degrees F) molten masses known every bit magma. Magma is present everywhere below the surface of the earth�south crust. Generally, magma lies nearly xc miles below the surface. In sure places, such equally Yellowstone National Park, the magma is as shut every bit twoscore miles below the surface. On boilerplate, every 100 feet y'all dig down into the world, the temperature will increment nigh ane.4 degrees F (this is a bit scary - keep this in mind the next time you lot visit a coal mine in Pennsylvania or the adjacent time you descend into a lava tube well-nigh Flagstaff!.

Sometimes magma forces its way up to the surface through a vent (such every bit a volcano) and spills onto the surface. This happened about Flagstaff, Arizona at Dusk Crater less than 1,000 years ago. Once magma comes out onto the surface of the earth it is called lava, and it cools rapidly at the surface. The resulting rock is called extrusive igneous rock (it is extrusive because the stone �extruded� out of the ground onto the surface). Extrusive igneous rocks can be distinguished by their small crystal sizes. In all extrusive igneous rock, it is about impossible to discover crystals without the aid of a microscope. The faster the rock cools, the smaller the crystals. Some extrusive igneous rocks cool so speedily that they have a burnished texture. Common extrusive igneous rocks are: andesite, basalt, dacite, pumice, rhyolite, and obsidian. The crystals are then fine in obsidian, that paleo-people and modernistic surgeons akin use/used the rock to manufacture razor-abrupt tools.

However, a much greater book of this fluid magma never reaches the earth�s surface � information technology only intrudes into the upper role of the earth�southward crust and solidifies. The rocks that course by this procedure are known as intrusive igneous rocks (it is intrusive because the rock did not �extrude� out of the ground onto the surface). Intrusive igneous rocks solidify over a menstruum of thousands of years. This ho-hum cooling rate allows ameliorate development of mineral crystals. Intrusive igneous rocks will accept centre visible crystals and will appear coarse-grained. Igneous intrusive rocks somewhen will become exposed at the surface of the world by erosion of the overlying fabric. Common intrusive igneous rocks are: granite, diorite, gabbro, and peridotite.

The La Sal Mountains were formed by widespread igneous activity that began about xl million years ago. Caldera explosions erupted thousands of cubic miles of volcanic rocks from several locations. Volcanoes spewed ash and lava. For xx meg years these extrusive volcanic rocks smoothed the mural, filling depressions with accumulations of ash, flows, and droppings literally miles thick. These by and large pastel-colored extrusive rocks still coating much of the high areas of central and southwestern Utah. Non all of the molten ascension igneous textile erupted as volcanic rocks; some material, forth with its mineral-bearing fluids, congealed in the globe's crust. Several of these intruded masses having been exposed by erosion or encountered out by exploration drilling became nifty mining districts, such as at Alta, Brighton, Bingham, Park City, and Cedar City. In the Colorado Plateau, bodies of intrusive rocks domed the overlying sedimentary rocks to form the Abajo and Henry Mountains (too every bit the La Sal Mountains). Note: This paragraph on laccoliths borrowed from here.

Metamorphic Rocks : morphos is the Greek discussion for ``class'' or ``shape'', and metamorphism means ``change of form''.

Within the Earth, the temperature and pressure are much college than on the surface, and these effects, along with fluids percolating through stone, can change the chemical science, mineralogy, and/or structure of the rocks, without melting them. Rocks which accept undergone these sorts of changes are called metamorphic rocks.

Agents of Matamorphosis

The iii primary agents which metamorphose stone are temperature, force per unit area, and fluids.

1) Temperature

High temperatures can modify rock past changing the construction of the minerals which brand upward the rocks; changing the structure of the minerals changes them into new minerals (remember the definition of a mineral). Two primary sources for loftier temperatures inside the Earth are:

Geotherm
As you dig deeper into the Earth, the temperature increases; information technology typically increases at a rate between xx and 60 �C per kilometer into the World. This increment in temperature with increase in depth is called the geotherm.
Intrusions
Another source of high temperatures inside the Earth is magma intruding cooler rock. These temperature increases are localized nigh the intrusion, but besides metamorphose stone (this is called contact metamorphism).

ii) Pressure level (aka Stress)

Pressure level (or more properly, stress) can also alter rock. There are two master kinds I desire y'all to know about:

Confining Pressure
Force per unit area due to the weight of overlying rock. This kind of pressure is roughly the same in all directions (this is like water pressure when scuba diving), and is the kind which compacts rock during diagenesis. Confining pressure changes stone past compaction and by changing the crystal construction of minerals from relatively open forms to more densely-packed forms. One mineral which does this is olivine, which changes from olivine (isolated silica tetrahedra) to spinel (a much more than tightly-bonded structure) to perovskite (a yet more highly compressed structure).
Directed Force per unit area
Pressure which is ``aimed'', in the sense that it is college in certain directions than in others. Imagine squeezing a brawl of Play-Doh� between your fingers - you direct pressure forth the line betwixt your fingers and thus squish the Play-Doh�. This kind of pressure is usually due to tectonic forces. It changes rocks by changing the structure of minerals and by irresolute the orientation of mineral grains, specially platy minerals like mica or clay.

3) Fluids

Fluids which metamorphose stone are not pore fluids remaining from when sedimentary rocks were deposited. Instead, they come from 2 main sources: hydrothermal fluids from magmatic intrusions and aridity of minerals, similar clay, which contain h2o in their structures (hydrous minerals).

Whatever the source, fluids contain ions dissolved from other rock or from their original source. Every bit fluids percolate through rocks, they tin exchange ions with the existing minerals and thus modify the chemical makeup of those minerals. The other way fluids change minerals is past hydrating minerals which previously did non contain water.

Either way, fluids modify the chemical makeup of minerals, turning them into new minerals, which changes the rocks which were made of the previous minerals. This process of change by fluids is called metasomatism.

Types of Rock Metamorphism

Some kinds of metamorphism:

Burial
Coffin rocks deeply plenty and they will warm up and change. This form of metamorphism is establish anywhere where sediments and rocks are cached deeply, and should strike yous as being pretty similar to diagenesis, which we discussed concluding fourth dimension. The line betwixt diagenesis and burial metamorphism is fuzzy.
Regional
Caused by widespread moderate-to-high temperatures and pressures, as opposed to localized changes along faults or most magmatic intrusions. Yous find this blazon of metamorphism in mountain building regions and nearly subduction zone volcanism.
Contact
Caused by high temperatures near magmatic intrusions. Found in volcanic regions (subduction zones, hot spots) and mountain edifice zones.
Cataclastic
Caused by grinding along fault zones. Found along major faults (similar the San Andreas Fault in California), in mount building zones, and in deformation regions associated with subduction zones.
Hydrothermal
Caused by hot fluids percolating through rocks. Found anywhere where hot fluids can percolate through rocks, notably forth mid-ocean ridges.

Metamorphic Rocks and Rock Textures

3 major texture and rock types for metamorphic rocks that you need to know:

Foliated Rocks
Characterized by parallel planes formed through directed pressure and preferred growth orientations of sure platy minerals. Two common kinds are schist and gneiss, which accept been used in a great many really bad geological puns.
Non-foliated Rocks
Don't have those planes, normally because they are made of mineral grains which are cubic or spherical, and therefore have no preferred orientation. Ii common examples are marble and amphibolites.
Deformational
Caused past cataclastic metamorphism. The most common rock of this kind is called a mylonite; in that location is a big mylonite belt in the mountains s of Palm Springs, CA.

Metamorphic Grade

Geologists who study metamorphic rocks have come up up with the concept of metamorphic grade to describe how 'metamorphosed' a rock is. It runs from depression class, where the rocks are inappreciably changed from their original course due to low pressures and temperatures, to high form, where the rocks are heavily altered due to high pressures and/or temperatures.

More specific distinctions can be made through lab experiments in which various kinds of rocks are squeezed and heated up and the changes observed. Through this kind of work, geologists take found a gear up of index minerals, which are common minerals which form nether particular combinations of pressure and temperature. Armed with knowledge from these experiments, field geologists tin can go out and make maps of mineral location to determine how metamorphism is distributed over large regions of rocks.

Metamorphic Facies

Two cardinal points about metamorphism are:

If you starting time with two different rocks (say a basalt and a sandstone) and heat them upwards and clasp them identically, and so that they have gone through the same pressure/temperature weather, you will get new minerals. Those minerals volition be different for the dissimilar rocks, even under identical force per unit area/temperature conditions.
If yous start with ii identical rocks (say two chunks of the same sandstone) and heat them and squeeze them differently, so that they have gone through different sets of pressure/temperature conditions, you will get new minerals. Those minerals will exist unlike for the same rocks under different pressure/temperature conditions.

Proceed that in listen: you get different minerals from different rocks nether the aforementioned conditions and y'all get different minerals from the same rocks under dissimilar conditions.

Geologists accept formalized these statements into a arrangement of classifications for rocks past pressure and temperature weather, so that a given combination of pressure and temperature volition requite a specific class of rocks. These classifications are chosen metamorphic facies.

The most important matter about metamorphic facies is that if you know the kind of metamorphic rock you have, you lot can work astern to observe out the pressure/temperature conditions under which information technology formed. This is vital information for figuring out past tectonic atmospheric condition in the region, since certain facies form in certain plate tectonic environments.

For example, blueschists form under low temperatures and moderate-to-high pressures, which indicates that the fabric which metamorphosed was shoved down into the Earth so quickly it didn't have much time to warm up. What kind of plate tectonic environment displays these features? Subduction zones!

Sedimentary Rocks:

Once material is weathered from rocks, it is transported away and subsequently deposited somewhere else, and eventually is turned into new rocks. Such rocks are called sedimentary rocks, and they're the subject of this lecture.

What are sediments?
What is a sedimentary stone?

Sediments are loose particles of former rocks. They can either be bits of rock (ranging from mineral grains all the mode to boulders) or material which was dissolved and then later precipitated from h2o to form solid crystals.

Subsequently these sediments are deposited, they may be buried and undergo a set up of physical and chemical changes which turn them into solid rock. Rocks formed from sediments are chosen sedimentary rocks.

Types of Sedimentary Rocks

There are three chief types of sedimentary rocks I desire yous to know about:

Clastic
Made from solid particles which were weathered from previous rocks.
Chemical/Biochemical
Made from sediments which precipitate from water (usually seawater) through chemical or biochemical processes

Sedimentary Cycle

All sedimentary rocks go through a cycle similar to this one:

Weathering from previous rocks
Erosion of weathering products
Send of particles from weathering region to someplace else
Deposition of sediments
Burial of sediments
Diagenesis

We will illustrate these processes with clastic rocks, then discuss chemical and biochemical rocks.

Clastic Rocks: Send

There are a number of dissimilar ``transportation agents'', or ways in which sediments are moved from 1 place to another; practically all of them move things downhill or downstream. Here'southward a brief list of some:

Rivers
Glaciers
Air current
Bounding main Waves/Tides/Currents

All these modes tin can send clastic particles of various sizes, and the size each can transport depends on the force with which it flows. For example, a river can transport clastic particles of all sizes when it is flowing apace, loftier in the mountains or during a flash flood. As the current slows, the river drops big particles first, then the next size, then the adjacent, and so on. When the current is very gentle, just the smallest particles are carried. This miracle is chosen sorting.

Another phenomenon resulting from send of clastic particles is called rounding. Basically, as particles are moved downstream, they bounce around and chips are taken off, particularly around the corners. In this way, the abrupt edges are worn away and a smoother, rounder particle is left. The farther a particle travels, the rounder and smoother it will be.

Clastic Rocks: Degradation

Rivers (and all other modes) ship clastic cloth downstream and and then drop it someplace; this procedure is chosen deposition or sedimentation. Places where this occurs are called sedimentary environments.

Clastic Rocks: Burial/Diagenesis

Equally sediments are deposited, they build layers of fabric. These layers are buried past later sediments, which are buried by later sediments, and and so on and so on.

As more and more sediments are deposited, the sediments most the bottom become heated upward and squeezed more and more. The sediments brainstorm to undergo diagenesis, which is an umbrella term for physical and chemical changes which turn sediment into sedimentary rocks.

Physically, the main change is compacting sediments and squeezing out fluid in the pores between sediment grains; imagine squeezing water out of a sponge. One of the major chemic changes is that new minerals tin form between the clastic grains and cement the grains together; calcite is a common cement. On the other manus, some of the more than soluble clastic grains may dissolve over fourth dimension or be replaced by other materials.

Nomenclature of Clastic Rocks

There are two major kinds of clastic sedimentary rocks to hash out: sandstones and fine-grained rocks.

When sand lithifies, it turns into a sandstone. Sandstones can be classified past a number of unlike criteria, only the most common are grain size and shape and mineralogy. There are iii major kinds of fine-grained clastic sedimentary rocks:

Siltstone
Made of lithified silt.
Shale
Fabricated of silt and clay, and tend to break on thin planes. Some kinds of shale comprise lots of oily stuff and may be important sources of oil in the future. Purely as a sidelight, y'all can light these rocks on fire with a blowtorch (of course, it's really the oily stuff burning, not the rock, but it'due south still impressive to run across a rock ``burning''.)
Mudstone
Made of lithified mud, normally blocky and olfactory property musty when you breathe on them.

Chemical/Biochemical Rocks: A Brief Overview

Having dealt with clastic rocks, we now expect at chemical and biochemical rocks. The raw materials to make these rocks are chemical solutions of water containing various ions dissolved from pre-existing rocks. These ions are dissolved in the water and catamenia with information technology downstream into lakes and the bounding main. Once the material arrives in the ocean, it can be precipitated out of the water through either biochemical or inorganic chemic ways.

Chemical and biochemical materials, one time precipitated as solids, go through diagenesis just as clastic rocks do, though chemical changes are more important for these rocks than are concrete changes. I common chemic change is changing aragonite, which is fine-grained calcium carbonate, to less fine-grained calcite.

Chemical and biochemical rocks can be classified by chemistry, and here are three major kinds:

Carbonates
Rocks which are made from lithified carbonate materials. They are formed mostly in ocean waters, and mostly are biochemical. In fact, many of the carbonate rocks plant are really formed from the shells of marine critters similar foraminifera, gastropods (snails), and such. Coral reefs are also made from carbonate materials. The most important carbonate rock is limestone.
Evaporites
Starting time with a shallow brackish lagoon in an arid region and evaporate water from it; evaporite minerals will precipitate and lithify on the floor of the lagoon. Common rocks formed are carbonates, stone salt, and gypsum. These materials are also formed in saline inland lakes, such every bit the Nifty Common salt Lake in Utah and Mono Lake in California.
Cherts
Cherts are formed in the deep, deep ocean in some places. They are made from lithifying silica-rich gunk called ``siliceous ooze''. This siliceous ooze is actually made from the shells of expressionless diatoms!