How Do Metamorphic Rocks Change Into Igneous Rocks?

NAVIGATION:  BACK TO MODULE 2 INTRODUCTION

Rocks and the Rock Cycle

ROCKS:

Rocks, rocks, rocks. Weathering is all almost rocks.  Rocks, rocks, rocks.  To empathize weathering, nosotros must showtime learn about rocks.

Rocks are the most common of all materials on earth. They are familiar to everyone. You may recognize rocks in the course of a mount nearly your hometown, the gravel in a driveway, the cliffs lining your favorite line-fishing hole, or the granite or sandstone or limestone your fingers and toes cling to at your favorite climbing surface area.

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

Rocks form in i of two distinct environments: either below the surface of the earth or at its surface. Rocks are composed of minerals. Minerals are naturally occurring, inorganic substances, which take an ordered internal structure giving them a specific advent. Interestingly, ice is a mineral. Some of the more than common rock-forming minerals are quartz, feldspar, pyroxene, hornblende, and olivine. Minerals should not be confused with rocks. For case, granite is a rock. information technology is equanimous of several minerals such as quartz, mica, and feldspar.

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

IMPORTANT!  Don't PANIC considering of the MASSIVE amount of text on this Web page... You lot can learn about stone types and other things in groovy detail below.  But hither's the real important stuff about rocks and stone types that are integral to agreement this module:

• In that location are three rock types - in that location are a lot of sedimentary; some granite; and very little metamorphic rocks on the Colorado Plateau

• The rock cycle happens - how rocks form determines how they will weather

• Rocks weather differentially - without differential weathering, the mural would not be as strikingly diverse!

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 will run into are mudstone and siltstone.  These are soft and easily weathered (lots in the Painted Desert).  Nonetheless another sedimentary rock you will see is limestone.  Limestone is composed of calcium carbonate, which is water soluble (it dissolves in water).  Therefore, the limestone you find in a dry area will remain a rock a lot longer than limestone yous discover in a MOIST area.

Regarding metamorphic rocks, there actually aren't many of these on the Colorado Plateau.. only in the bottom of the Grand Coulee!  So, good thing for you, we are really not going to cover this rock type in this Module.

You will run across a few igneous rocks in this Module...  You see granite (intrusive igneous) and basalt (extrusive igneous).  The granite you lot will see is high upwardly in the La Sal Mountains and the basalt y'all will meet sits as cap rocks on acme of softer, underlying sediments.  A cap rock is a comparatively more resistant rock that protects the rocks beneath it from weathering and eroding.

The fundamental to understanding rock weathering is to realize that rocks weather at dissimilar rates and into unlike forms based on their chemical limerick 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:

Jump to igneous   |  Jump to metamorphic  |  Spring to sedimentary

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THE Rock Cycle: (some content and the diagram below borrowed from NASA)

The rock bicycle best explained as the relationship betwixt earth�s internal and external processes. Weathering (breaking down rock) and erosion (transporting rock fabric) at or nearly the earth'southward surface breaks down rocks into small and smaller pieces. These smaller pieces of rock (such equally sand, silt, or mud) can exist deposited as sediments that, after hardening, or lithifying, become sedimentary rocks. Extreme pressure level from burial, increasing temperature at depth, and a lot of time, can alter any rock type to course a metamorphic stone. If the newly formed metamorphic rock continues to heat, it can somewhen melt and become molten (magma). When the molten stone cools it forms an igneous stone. Metamorphic rocks can form from either sedimentary or igneous rocks. The sedimentary particles from which a sedimentary stone is formed can be derived from a metamorphic, an igneous, or another sedimentary rock. All three rock types can exist melted to form a magma. Thus, the cycle has continued over the ages, constantly forming new rocks, breaking those down in diverse ways, and forming still younger rocks. Rocks at the surface of the globe range in age from over three billion years onetime to a few hundred years old.

Igneous stone 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 stone.

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

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

When it pours out on Earth'south surface, magma is chosen lava. Yes, the same liquid rock thing that you see coming out of volcanoes.  Igneous rock that pours out onto the Earth's surface is chosen igneous extrusive, whereas igneous rock that cools beneath the surface is called igneous intrusive.

On Earth's surface, wind and water can intermission stone into pieces (weathering!). They can also behave rock pieces to some other place (erosion)!. Unremarkably, the rock pieces, called sediments, driblet from the wind or h2o to brand a layer. The layer can be buried nether other layers of sediments. Subsequently a long time the sediments tin can be cemented together to make sedimentary rock. In this way, igneous rock can get sedimentary stone.

All rock tin be heated. Just where does the rut come from? Within Earth there is heat from pressure (push your hands together very hard and feel the heat). There is heat from friction (rub your easily together and experience the rut). At that place is also estrus from radioactivity (the procedure that gives us nuclear power plants that brand electricity).

So, what does the estrus do to the rock? Information technology bakes the rock.

Remember, all rocks are made up of mineral crystals, or pieces of other rocks made up of crystals.  Baked rock does non cook, but it does alter. It forms crystals. If it has crystals already, it forms larger crystals. Considering this stone changes, it is chosen metamorphic. Remember that a caterpillar changes to get a butterfly. That change is called metamorphosis. Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius.

When Earth's tectonic plates move effectually, they produce estrus. When they collide, they build mountains and metamorphose the stone.

The stone cycle continues. Mountains made of metamorphic rocks can exist cleaved upward and washed away by streams. New sediments from these mountains tin brand new sedimentary rock.

The rock bike never stops.

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Beneath IS A LOT OF INFORMATION -- DON'T WORRY ABOUT CAREFULLY READING THE CONTENT -- It IS A RESOURCE FOR You lot IF Y'all Demand IT!

Igneous Rocks :  Igneous rocks are a type of rock formed from extremely hot (2,200 degrees F) molten masses known as magma. Magma is present everywhere beneath the surface of the earth�s chaff. Generally, magma lies about ninety miles beneath the surface. In certain places, such as Yellowstone National Park, the magma is as close as 40 miles below the surface. On average, every 100 feet you dig down into the earth, the temperature will increase virtually 1.iv degrees F (this is a bit scary - keep this in mind the next time y'all visit a coal mine in Pennsylvania or the next time you descend into a lava tube near Flagstaff!.

Sometimes magma forces its style up to the surface through a vent (such every bit a volcano) and spills onto the surface. This happened near Flagstaff, Arizona at Sunset 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 stone is chosen extrusive igneous stone (information technology is extrusive considering the stone �extruded� out of the basis onto the surface). Extrusive igneous rocks tin can exist distinguished past their small crystal sizes. In all extrusive igneous rock, it is almost impossible to detect crystals without the assistance of a microscope. The faster the stone cools, the smaller the crystals. Some extrusive igneous rocks cool and then apace that they have a glassy texture. Common extrusive igneous rocks are: andesite, basalt, dacite, pumice, rhyolite, and obsidian. The crystals are and so fine in obsidian, that paleo-people and modern surgeons alike utilize/used the rock to manufacture razor-precipitous tools.

However, a much greater volume of this fluid magma never reaches the earth�s surface � it only intrudes into the upper office of the earth�s crust and solidifies. The rocks that form by this process are known as intrusive igneous rocks (information technology is intrusive because the rock did not �extrude� out of the ground onto the surface). Intrusive igneous rocks solidify over a menses of thousands of years. This slow cooling rate allows better development of mineral crystals. Intrusive igneous rocks will have middle visible crystals and volition appear coarse-grained. Igneous intrusive rocks eventually will go exposed at the surface of the world by erosion of the overlying cloth. Common intrusive igneous rocks are: granite, diorite, gabbro, and peridotite.

The La Sal Mountains were formed by widespread igneous activity that began virtually forty million years ago. Caldera explosions erupted thousands of cubic miles of volcanic rocks from several locations. Volcanoes spewed ash and lava. For 20 one thousand thousand years these extrusive volcanic rocks smoothed the landscape, filling depressions with accumulations of ash, flows, and debris literally miles thick. These generally pastel-colored extrusive rocks nevertheless coating much of the high areas of primal and southwestern Utah. Not all of the molten ascent igneous material erupted as volcanic rocks; some material, along with its mineral-begetting fluids, congealed in the earth's crust. Several of these intruded masses having been exposed by erosion or encountered out past exploration drilling became nifty mining districts, such as at Alta, Brighton, Bingham, Park City, and Cedar Metropolis. In the Colorado Plateau, bodies of intrusive rocks domed the overlying sedimentary rocks to form the Abajo and Henry Mountains (likewise as the La Sal Mountains). NOTE:  This paragraph on laccoliths borrowed from here.

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

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

Agents of Matamorphosis

The iii main agents which metamorphose rock are temperature, pressure, and fluids.

1) Temperature

Loftier temperatures tin change rock past changing the structure of the minerals which make up 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; it typically increases at a rate between 20 and 60 �C per kilometer into the Earth. This increase 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 almost the intrusion, simply also metamorphose rock (this is called contact metamorphism).

2) Pressure (aka Stress)

Pressure (or more properly, stress) can likewise modify rock. There are ii main kinds I want you to know almost:

• Circumscribed Pressure
  Pressure 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 rock by compaction and by changing the crystal structure 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 tightly-bonded structure) to perovskite (a still more highly compressed structure).
• Directed Pressure
  Pressure which is ``aimed'', in the sense that information technology is higher in sure directions than in others. Imagine squeezing a ball of Play-Doh� between your fingers - y'all direct pressure along the line between your fingers and thus squish the Play-Doh�.  This kind of pressure is usually due to tectonic forces. Information technology changes rocks by changing the structure of minerals and past irresolute the orientation of mineral grains, specially platy minerals like mica or clay.

3) Fluids

Fluids which metamorphose rock are non pore fluids remaining from when sedimentary rocks were deposited. Instead, they come from ii main sources: hydrothermal fluids from magmatic intrusions and dehydration of minerals, like dirt, which contain water in their structures (hydrous minerals).

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

Either way, fluids change 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 past fluids is chosen metasomatism.

Types of Rock Metamorphism

Some kinds of metamorphism:

• Burial
  Bury rocks deeply enough and they will warm upwardly and modify. This form of metamorphism is found anywhere where sediments and rocks are buried securely, and should strike you every bit existence pretty similar to diagenesis, which we discussed last time. The line between diagenesis and burying metamorphism is fuzzy.
• Regional
  Acquired by widespread moderate-to-loftier temperatures and pressures, as opposed to localized changes forth faults or near magmatic intrusions. You discover this blazon of metamorphism in mountain edifice regions and nearly subduction zone volcanism.
• Contact
  Caused by high temperatures virtually magmatic intrusions. Found in volcanic regions (subduction zones, hot spots) and mountain building zones.
• Cataclastic
  Caused by grinding forth fault zones. Constitute along major faults (similar the San Andreas Fault in California), in mountain building zones, and in deformation regions associated with subduction zones.
• Hydrothermal
  Acquired past hot fluids percolating through rocks. Constitute anywhere where hot fluids can percolate through rocks, notably along mid-ocean ridges.

Metamorphic Rocks and Stone Textures

Three major texture and rock types for metamorphic rocks that yous need to know:

• Foliated Rocks
  Characterized by parallel planes formed through directed pressure and preferred growth orientations of sure platy minerals. 2 common kinds are schist and gneiss, which have been used in a not bad many really bad geological puns.
• Not-foliated Rocks
  Don't have those planes, usually because they are made of mineral grains which are cubic or spherical, and therefore take no preferred orientation. Two mutual examples are marble and amphibolites.
• Deformational
  Caused past cataclastic metamorphism. The nigh common rock of this kind is called a mylonite; there is a big mylonite belt in the mountains south of Palm Springs, CA.

Metamorphic Course

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

More specific distinctions can exist made through lab experiments in which various kinds of rocks are squeezed and heated up and the changes observed. Through this kind of piece of work, geologists take constitute a set of index minerals, which are common minerals which form under particular combinations of pressure and temperature. Armed with noesis from these experiments, field geologists can get out and make maps of mineral location to make up one's mind how metamorphism is distributed over large regions of rocks.

Metamorphic Facies

Two central points virtually metamorphism are:

• If y'all start with 2 unlike rocks (say a basalt and a sandstone) and heat them up and squeeze them identically, so that they take gone through the same pressure level/temperature conditions, you volition get new minerals. Those minerals will be different for the different rocks, fifty-fifty under identical pressure level/temperature conditions.
• If you outset with 2 identical rocks (say ii chunks of the same sandstone) and heat them and squeeze them differently, and then that they take gone through different sets of pressure level/temperature atmospheric condition, you will get new minerals. Those minerals will be different for the aforementioned rocks nether different pressure/temperature weather condition.

Keep that in mind: you go different minerals from unlike rocks nether the aforementioned weather condition and you lot get different minerals from the aforementioned rocks under different conditions.

Geologists have formalized these statements into a system of classifications for rocks by force per unit area and temperature conditions, then that a given combination of pressure level and temperature will requite a specific course of rocks. These classifications are chosen metamorphic facies.

The nearly important thing near metamorphic facies is that if you know the kind of metamorphic stone you lot have, you tin piece of work backward to observe out the pressure/temperature conditions under which it formed. This is vital data for figuring out past tectonic conditions in the region, since certain facies class in certain plate tectonic environments.

For instance, blueschists class nether depression temperatures and moderate-to-high pressures, which indicates that the cloth which metamorphosed was shoved downward into the Earth so rapidly it didn't have much time to warm upwards. What kind of plate tectonic environment displays these features? Subduction zones!

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Sedimentary Rocks:

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

What are sediments?
What is a sedimentary rock?

Sediments are loose particles of quondam rocks. They can either be bits of stone (ranging from mineral grains all the fashion to boulders) or material which was dissolved and so later precipitated from water to form solid crystals.

After these sediments are deposited, they may exist buried and undergo a set of concrete and chemic changes which plough them into solid rock. Rocks formed from sediments are chosen sedimentary rocks.

Types of Sedimentary Rocks

There are 3 principal types of sedimentary rocks I want yous to know about:

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

Sedimentary Cycle

All sedimentary rocks go through a cycle like to this i:

1. Weathering from previous rocks
2. Erosion of weathering products
3. Transport of particles from weathering region to someplace else
4. Deposition of sediments
5. Burial of sediments
6. Diagenesis

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

Clastic Rocks: Transport

At that place are a number of unlike ``transportation agents'', or ways in which sediments are moved from one place to another; practically all of them motility things downhill or downstream. Here'due south a cursory list of some:

• Rivers
• Glaciers
• Wind
• Ocean Waves/Tides/Currents

All these modes can transport clastic particles of various sizes, and the size each tin transport depends on the force with which information technology flows. For case, a river can ship clastic particles of all sizes when information technology is flowing rapidly, high in the mountains or during a wink alluvion. Equally the current slows, the river drops big particles first, and so the next size, then the side by side, and and so on. When the electric current is very gentle, only the smallest particles are carried. This phenomenon is called sorting.

Some other phenomenon resulting from ship of clastic particles is called rounding. Basically, equally particles are moved downstream, they bounciness around and chips are taken off, especially around the corners. In this way, the abrupt edges are worn abroad and a smoother, rounder particle is left. The farther a particle travels, the rounder and smoother it volition be.

Clastic Rocks: Deposition

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

Clastic Rocks: Burial/Diagenesis

As sediments are deposited, they build layers of cloth. These layers are cached by later sediments, which are cached by afterward sediments, and so on so on.

As more and more than sediments are deposited, the sediments near the bottom get heated up and squeezed more and more. The sediments begin to undergo diagenesis, which is an umbrella term for physical and chemical changes which plough sediment into sedimentary rocks.

Physically, the principal modify is compacting sediments and squeezing out fluid in the pores between sediment grains; imagine squeezing water out of a sponge. One of the major chemical changes is that new minerals can form between the clastic grains and cement the grains together; calcite is a common cement. On the other hand, some of the more soluble clastic grains may deliquesce over time or be replaced by other materials.

Classification of Clastic Rocks

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

When sand lithifies, information technology turns into a sandstone. Sandstones can be classified by a number of different criteria, just the nigh common are grain size and shape and mineralogy. There are three major kinds of fine-grained clastic sedimentary rocks:

• Siltstone
  Made of lithified silt.
• Shale
  Made of silt and clay, and tend to suspension on thin planes. Some kinds of shale comprise lots of oily stuff and may exist important sources of oil in the futurity. Purely every bit a sidelight, you can light these rocks on burn with a blowtorch (of form, it'due south really the oily stuff burning, not the stone, simply information technology'due south even so impressive to see a rock ``burning''.)
• Mudstone
  Fabricated of lithified mud, ordinarily blocky and smell musty when you breathe on them.

Chemic/Biochemical Rocks: A Brief Overview

Having dealt with clastic rocks, we now wait at chemic 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 h2o and flow with it downstream into lakes and the ocean. Once the textile arrives in the sea, it tin be precipitated out of the h2o through either biochemical or inorganic chemical ways.

Chemical and biochemical materials, once precipitated as solids, go through diagenesis simply as clastic rocks do, though chemical changes are more important for these rocks than are physical changes. One common chemical modify is irresolute 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 fabricated from lithified carbonate materials. They are formed mostly in ocean waters, and more often than not are biochemical. In fact, many of the carbonate rocks found are really formed from the shells of marine critters like foraminifera, gastropods (snails), and such. Coral reefs are also made from carbonate materials. The most important carbonate rock is limestone.
• Evaporites
  Start with a shallow stagnant 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, rock salt, and gypsum.  These materials are also formed in saline inland lakes, such every bit the Great Salt Lake in Utah and Mono Lake in California.
• Cherts
  Cherts are formed in the deep, deep bounding main in some places. They are made from lithifying silica-rich gunk called ``siliceous ooze''. This siliceous ooze is actually fabricated from the shells of expressionless diatoms!

Source: https://www2.paradisevalley.edu/~douglass/v_trips/wxing/introduction_files/rocktypes.html

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