Unit 1: IntroductionObjectives:1. Understand the link and dependency between civilization and

natural resources2. Understand what resources one may rely on or use on a daily

basis3. Know what geology is and the reasons for studying it as a

science4. Understand how mining and geology is linked to the commodities

market5. Know the differences and roles of a prospector, junior

exploration company, and a senior mining company6. Understand the concept of uniformitarianism and the nebular

hypothesis

Definition of geology : Geology is the study of the Earth and its natural processes

Definition of economic geology : Economic geology is the study of natural resources of the Earth that are considered economic and extractable This includes mineral and ore deposits, oil and gas and any

other extractable material that can be processed “If is cant be grown it must be mined.”

The concept of Uniformitarianism: The idea suggests that “the present is the key to the past”

The Earth’s surface has been continuously modified over ahuge geologic time span

Studying the geological processes that actively shape thecan, allows us to understand how the Earth has evolved through time

The rate of the processes is not the same, but the nature of the processes is thought to be similar

It is assumed that the same physical and chemical laws have operated over the Earth’s history

o Ex: the flow dynamics of a current flowing river aresimilar to how a river flowed millions of years ago

The Earth may change, the laws of physics do notGeologists today believe the Earth today is made up of uncounted and gradual changes that are constantly repeated over very long time spans

This history is punctuated by catastrophic events (volcanic eruptions, Earthquakes, mega storms and meteorites) these events are in context of all the natural systems, relatively sparse and only of temporary significance

The concept of the nebular hypothesis: About 5 billions years ago our solar system was a rotating cloud of hydrogen-rich gas called nebula As the nebula coalesced, most of the hydrogen condensed to

form the sun As the balance of the gas beyond of the sun cooledsolid

minerals condensed from this rotating gas cloud These solid materials were subsequently assembled by

gravity into planets

As the initial “dustball” Earth was forming, colliding particles generated heat due to impact

Some of this heat was trapped in the interior of the slowly compressing Earth

Collisions of particles and larger debrisformed a planet and the presence of naturally occurring radioactive material to provide enough heat to melt the Earth’s interior

As a result of cooling, the Earth is differentiated into; A large iron-rich interior core (inner and outer) A thick, surrounding molten mantle And an outer thin, low density crust (lithosphere) Two types of crus that formed: oceanic and continental

o Oceanic crust is slightly denser than continental- it is lowered and covered with water

o Continental crust is higher above water to form land

Diagram shows the differentiated Earth after it cooledThe cooling of the Earth also resulted in the formation of the atmosphere and oceans

Many minerals and rocks contained gas or water locked in their crystals that were released during the heating/melting of the Earth’s interior

As the surface began to cool, water condensed to form theoceans

Single-celled blue/green algae modified the atmosphere byproducing lots of free oxygen through photosynthesis

o The abundance of free oxygen changed the atmosphere to what it is today

The Commodities Market:Mining is a lucrative business that is supported by key players from areas in government, legal, financial, technical (i.e. engineers), and scientific organizations (i.e. geologists)

To operate a successful mining company: there must be a relationship between individuals in the business community and individuals on the technical side (engineers, geologists, etc.)

One must understand the role and importance of all parties involved

A natural resource such as gold, coal, or diamonds is what economics call “commodity”:

A marketable item that satisfies consumer demandCommodities are not only mining products but also agricultural crops and energy resources

The price of a commodity is controlled by contracts undertaken privately or on the open market (i.e. Toronto Stock Exchange, London Stock Exchange, New York Stock Exchange, etc.)

Contract prices are agreed upon between the buyer and seller and typically depend on the supply of the commodity available and the market demand for the commodity

Ex: potash, titanium, uranium, and coal- product quality and other characteristics of these resources vary from deposit to deposit

Diamonds are an example of these types of contracts Diamonds can be sold individually through private buyers Diamonds can be placed in lots as individual stones or as

a set or group the lots are bid upon by potential buyers

Traders can buy/sell bulk quantities Buying/selling (free trading) can either drive the price

of these commodities up or down The demand for these commodities for industrial purposes

influences the commodity price

Mining commodities are also sold by different measurements Ex: Gold is measured in ounces, iron ore in tonnes and

diamonds in carats

They are divided into 6 main groups: 1. Precious metals (gold and silver)2. Ferrous metals (chromium, tungsten and iron) 3. Base metals or non-ferrous metals (copper, nickel, lead,

zinc)4. Fusionable metals and fuels (coal and uranium)5. Gems and gemstone (diamonds, sapphires, rubies)6. Industrial minerals and rocks (aggregate, quartz,

limestone, grantie)o An industrial mineral is defined as any mineral or

other naturally occurring substance of economic value, excluding ore, mineral fuels and gemstones

Mining Industry Players:Mining: The science, technology and business of mineral discovery and exploitation

On the mining and exploration side of the commodities industry there are three key players: prospectors, juniorexploration companies and senior mining companies

Prospector:

A person engaged in exploring for valuable minerals or in testingsupposed discoveries of the same

A prospector is “engaged in prospecting for valuable mineral depositis, generally working alone or in a small group, and on foot with simple tools or portable detectors”

The role of a prospector: search and discover an area or “showings” where valuable minerals or present the areais called a “prospect” and is considered for further exploration if the quality of the minerals are sufficient

Many of them do not have formal training or a geology education They build their expertise upon years of experience One must know how to look, where to look, and how to

problem solve- they must also love the outdoors Many of them use their own personal finances to stake ground of interest and do preliminary mapping to find the location of the showings Junior Exploration or Mining Company:Also act in many cases as prospectors – the companies are often started by a prospectorPurpose: to search for and find economic mineral depositsThe companies are very small with only a few employees (5-30 people)

Small team=more flexibility and innovative in their direction and decisions can be made faster

When a company is formed a geologist plays a huge role in all operations The companies have no operating revenue from operating mines

They normally raise funds by selling company stocks Without operating revenue the risk is high of finding an

economic deposit- these companies are considered speculative investments on the stock exchange

Major Mining Company:These companies operate one or more mines- what most people thinkof as “mining companies”

Sole business: to extract a natural resource and bring it to the marketMajor companies tend to drill around their own deposits in order to expand the known reserves or they revisit deposits that were already discovered

Majors often opt to purchase or option new properties from junior exploration companies that have made significant or large discoveries

As they are very structured and multi-tiered bureaucracy they have established company guidelines

These companies do not have the flexibility to undertake the high level of risk in exploration and cannot make decisions quickly

Unit 2: Minerals and Gemstones Objectives:1. Understand that minerals are formed from a combination of

elements and what the most common or abundant elements are2. Know the diagnostic properties of minerals and how they can be

used to identify a mineral3. Know the different types of minerals (silicates vs. non-

silicates) and the structural differences between the different groups (amphibole, micas etc.)

4. Know what a rock is and be familiar with the concept of the rock cycle: igneous, metamorphic and sedimentary

Mineral: A naturally occurring inorganic, solid element or compoundwith a definite composition and regular internal structure

Minerals:A substance must meet several criteria to be considered a mineral:

They must be naturally occurring (not man made) They must be inorganic- produced by natural forces (but not

only by living organisms or biological processes) They must be solid- the ice of a glacier is a mineral, but

the liquid water is notMinerals can chemically consist of just one element or of severalelements

Ex: a diamond is a mineral with one single element- pure carbon

When two or more elements are combined they are referred to as a compoundWhen broken down to their most basic form:

Elements are made up of one or more atoms Atoms are composed of a nucleus containing neutrons that

are neutral charge and protons are positive charge Minerals consist of an orderly array of atoms chemically bonded to form particular crystalline structure

Minerals form when atoms bond through ionic, covalent, ormetallic bonding

In covalent bonding minerals, atoms share an electron to achieve electrical neutrality

These bonds are normally stronger than ionic bonds

When metallic bonding happens valence electrons are free to migrate among the atoms

As a result these bonds are weaker and less common Minerals can contain any element that is on the periodic table

Most common elements:Oxygen is the most abundant element on earth followed by silicon,aluminum and iron

These elements are found in most minerralsQuartz (SiO2)is one of the most abundant minerals

Solid Solution:Minerals are solid and on a microscope scale are considered crystallineCrystalline materials are solids in which the atoms are arranged in regular, repeating patternsCrystal structures of minerals form because they are the most stable arrangement of atoms in a solid

Opposite charges attract and like charges repel There must be an equal amount of positive and negative

charges in an element

Characteristics and Properties of a Mineral:Two most fundamental characteristics used to identify a mineral:

1. Unique composition2. Structure

No two minerals are identical in both areas Ex: Diamond and graphite are chemically the same: both

made up of pure carbon- but have different physical properties and internal crystalline structures

Polymorphism: Minerals that have the same chemical composition butdistinctly different crystal structures (diamond vs. graphite)Colour of a mineral is not a way of identifying a mineral

A diagnostic property is a physical property that can be used to identify a specific mineral- measuring the following:Streak: colour of a powdered mineral

Tested by scraping a mineral across the face of a porcelain title and analyzing the colour of powder left

Very useful in identifying metallic ores Not all minerals leave streaks behind- minerals are

harder than a porcelain plate and only scratch it but leave no mark

Hardness: the ability of a mineral to resist scratching Measured using Mohs hardness scale: ten minerals are arranged

in order of hardness from talc (1- the softest) to diamond (10- the hardest)

Crustal form: The shape of well-developed crystals of a mineral Focuses on the internal symmetry of the crystal structure The formation of a mineral is usually interrupted during

its growthCleavage: Property that is controlled by internal crystal structureand represents the tendency of minerals to break preferentially in certain directions

Focuses on the zones of weakness in the bonds of a crystal structure

To test the cleavage plane made by a mineral one will strike the mineral with a hammer and break it

Fracture: Many minerals do not show cleavage and will break randomly

Irregular fracture instead of cleavage One distinctive fracture type is a conchoidal or shell-like

fracture displayed by quartz or volcanic glass

Lustre :a diagnostic property that describes the surface sheen of a mineral- describing lusture using the following terms:

Metallic (bright and shiny like metal) Pearly (soft, iridescent like a pearl) Vitreous (glassy) Earthly (dull)

Specific gravity: of a mineral is related to its density The ratio of the mass of a mineral of an equal volume of

water A mineral having the same density as water has a specific

gravity of 1o The higher the specific gravity, the denser the

mineral

Gemstones:Precious stones or gemstones are not grouped by mineral chemistryor crystal structure

Gemstones are minerals that have bee grouped by colour- comes from a historical practice by identifying stones bycolours (rubies, spphires, emeralds, etc.)

What actually constitute gemstones are minerals that contain chemical impurities

Ex: the mineral corundum is a common gemstone or can be anonprecious mineral- it has many vivid colours (yellow, purple, blue) it is called a sapphire- when corundum is vivid red colour it is called a ruby

If it is not a gem quality, it is called a corundum

Unit 3: Igneous RocksObjectives:1. Know what controls magmas’ composition and the processes that

can modify it2. Understand the Bowen’s reaction series and the sequence of

crystallization3. Know the textures that can occur in igneous rocks based on

magma crystallization sequence, and the rate of cooling4. Understand what and how intrusive and extrusive rocks form,

the different rock textures and compositional classifications5. Know why some volcanoes erupt explosively and why some do not

Magma: is a molten silicate material from which igneous rocks form at very high temperatures

Magmas:Magma is generated when solid rock melt, which breaks down the minerals into its constituent elements

Conversely, rocks form when minerals crystallize from a magma as melt begins to cool

Minerals form very systematic and complex crystalline structure that require long cooling periods

The chemistry of a magma and the initial temperature will dictatewhat minerals form and in what sequence of formation

Lava is magma that is extruded onto the surface Magma is a molten liquid comprised on elements that will

combine to form mineralsPassing from the surface of Earth to its interior, temperatures naturally increase with depthThis geothermal gradient dictates that, on average, the temperatures are high enough to melt rock

This usually occurs in the mantle between 50 and 250 km below Earth’s surface, where temperatures are typically over 1000C

The Effects of Temperature, Pressure, Volatiles and Solids: They all affect the crystallization process of a magma meltIn molten magma, elements can flow in a disordered liquidSince most substances are denser in their solid form than liquid, and increase in pressure tends to favour a compact crystalline structure rather than a disordered liquid state

However, an increase in temperature will break down atom bonds and cause melting

These competing factors are the reason why Earth’s interior is not molten

Magmas naturally contain dissolved volatiles or gas bubbles that can be comprised of carbon dioxide, water, hydrogen sulphide, etc.

The presence of these dissolved volatiles are to lower the melting temperatures of silicate minerals

Although the nature of the volatiles and presence of minerals being melted dictate how much melting temperatures are lowered…

The general principle is that: more volatiles mean a lower melting temperature

o Ex: salt is used to melt ice on roads: the presence of the salt lowers the melting temperature of ice tobelow the freezing point of pure water

The majority of rocks contain a multitude of minerals Therefore the melting temperatures of these rocks are

mostly lower than the temperatures that individual minerals melt in their pure states

Because there are numerous mineral species in rocks and melt at different temperatures, the transition from all solid to all melted or molten material can span several hundred degrees

Various factors affect the melt behaviorMost magmas are not fully melted and are instead a molten “rush” of crystals suspended in a silicate liquid

Crystallization of Magmas:Magmas can be considered a solid solution of two or more mixing end-members (solutions with original “starting” compositions)

They have different compositions/chemistries, so they canform crystals or melt at different temperatures

o Ex: in a magma that contains the composition of olivine ((Fe, Mg)2SiO4) the two end-members will be:1) Fe2SiO4, and 2) Mg2SiO4

o These two end-members (fayalite and forsterite) meltat different temperatures (fayalite: 1205C, forsterite: 1890C)

The melting temperature is determined by the quantity or ratio ofthese end-members (i.e. the more Mg or fosterite end-member, the higher the melting temperature)

Since most magma comes from the upper mantle, and has a similar composition, minerals crystallize in a specific sequence

Geologists use the Bowen’s Reaction Series as a guide to orderin which different minerals will crystallize

Minerals that form at higher temperatures are near the top of theseries

Olivine, calcium-rich plagioclase and pyroxene Lower temperature minerals are shown at the bottom

Muscovite, quarts, and potassium feldspar

The Bowen’s Reaction SeriesThe range of temperature of the magma is on the left and the corresponding magma is on the rightThe middle of the chart shows the sequence of mineral formation as a magma coolsOn the right side of the diagram the plagioclase branch is calleda continuous reaction series

This reaction refers to crystals that have already formedbut may be still reacting with the remaining melt

This interaction of crystallized minerals with molten magma can cause solid solution interaction of Ca-rich plagioclase end-members and Na-rich members

As temperatures cool, sodium ions can change places with or substitute for calcium ions

Not all magmas begin at the top of the series or progress throughthe entire seriesThe maximum temperature of the magma prior to cooling dictates the starting point on the reaction seriesConversely, the rate of magma cooling can control at what point the reaction series may stop

Ex: if a very hot magma is cooled rapidly, then olivine and other high temperature minerals will be preserved because there was not enough time for other cooler temperature minerals to form before the magma solidified

On the ferromagnesian side of the diagram the sequence of crystallization is called the discontinuous reaction series

Each mineral is subsequently replaced by another mineral of different composition

This sequence of mineralization also represents a progression of increasingly complex mineral formation

Olivine is the simplest through to biotite being the mostcomplex

The late minerals to form are more hydrous (contain water) This is because water is driven off at a higher

temperature, but is stable at lower temperatures

Magma Composition:Not every magma melt will progress through the sequenceMagma compositions are grouped into 3 types of melts:1. Mafic

o These are rich in magnesium and iron, but poor in silicon

o This magma type crystallizes the higher temperature minerals but does not contain sufficient silica to form crystals in the latter stages (biotite, quartz, etc.)

o These magmas produce rocks that are rich in the minerals at the top of the diagram

2. Intermediateo These are richer in silica, but is poor in iron and

magnesium o These magmas reach the final stages of the reaction

series having eliminated all earlier minerals formed at higher temperature

o These magmas produce rocks that are rich in minerals fromthe lower part of the diagram

3. Felsico These are rich in quartz (silica) and feldspar mineralso Limited compositional range (little iron or magnesium)o Do not produce high temperature minerals (olivine)

Summary: Magma composition is classified based on the quantity of

silica and the relative abundance or iron, magnesium, sodium, and calcium

Chart illustrates the percentage (of volume of) the different minerals and the respective rock composition

Felsic rocks form at lower temperatures and contain more silicon

Conversely, mafic rocks form at high temperatures and arelow in silicon

This chart is used as a guide for determining rock composition based on the percentage of a specific minerals

Textures:Volcanic rocks have distinct textures that give us clues as to how the rock formed

The cooling rate of magmas produce readily observed textures- it determines the size of the individual mineral crystals

Crystal size is controlled by the cooling rate of the magma

A useful chart that shows the relationship between rock composition, extrusive versus intrusive occurrence and the associated textures

Magma that cools rapidly generates finer textures than magmas that cool more slowly

If the magma cools slowly, the crystals have a longer period to grow

Slow cooling rates produce a coarse crystalline rock withbig crystals

Conversely, rapid cooling rates produce crystalline rocks becauseminerals do not have much time to grow their structuresExtremely rapid cooling rates create glassy textures

Ex: Obsidian is volcanic glass: the dark colour is due tothe disordered state of the elements- it cools so rapidlythat minerals do not have time to form

Most obsidian is felsic, some though are mafic obsidian

Magmas can contain volatiles or dissolves gases When a magma cools, the dissolved gas becomes unstable in

the liquid and forms gas bubbles If the magma is cooled rapidly, these gas bubbles become

trapped as the magma hardens around themThis rock is fined grained and also contains pockets of gas bubbles called vesicles

This texture is called vesicular A rock that has vesicular texture is one that contains

abundant holes that were once occupied by volatiles (gas,water, etc.)

Some igneous rocks have a two-stage cooling history The initial stage may involve a slow cooling rate where

large crystals grow The second stage may be a rapid cooling rate that leaves

the rest of the rock, or groundmass, finer-grainedSomething to produce two-stage cooling history:

When a magma is sitting below the earth’s surface and beings to cool slow

It could be erupted from a volcano onto the earths surface- causing the rest of the magma to cool rapidly

The resulting rock that contains the fine grained groundmass surrounding larger grained crystals (phenocrystst) has an overall texture called porphyritic

Igneous rock texture is related to cooling rateGrain sizes can also be impacted by the composition of the melt

Felsic are thick and viscous These lavas as “sticky”, and eruptions tend to be

explosive Felsic melts therefore tends to be finer grained and

lighter in colour- volcanic glasses tend to come from felsic melts

Macif melt, by contrast are very thin and runny (not viscous) These magmas can form crystals quickly since atoms can

move freeSome late-stage residual melts left over after most of the magma has crystallized can contain high concentrations of dissolved volatiles

This texture is called a pegmatite: they tend to contain minerals comprises of unusual elements that do not or could not fit into the regular structures of common silicates

They may contain rare and unusual minerals that can be valuable economically

Classification of Igneous Rocks:Igneous rocks are subdivided into two categories based on depth of crystallization (which is reflected in the textures): Plutonicand Volcanic 1. Plutonic:These rocks are cystallized at depth (below earths surface)The slow cooling rate makes these igneous rocks coarse grained called phaneritic- easy to see with the eye If a plutonic rock is exposed at earths surface- it is assumed that erosion has happened and all the country rock that was abovethe plutonic rock was removed by erosion

Chilled margin is the effect from intruding cooler country rocks- they are found at the edges of plutons

Especially found in plutons that are emplaced at a very shallow depths in the crust, where the county rocks are much cooler

Plutonic rocks are subdivided into four different rock types depending on their compositions, which show proportions of light and dark ferromagnesian minerals

A gabbro is a plutonic igneous rock that consisits entirelyof ferromagnesians and dark, calcic plagioclase feldspar

An ultramafic rock, komatiite is one where feldspar is virtually gone and the whole rock consists of olivine andpyroxene

A diorite is a rock that is more silica rich, with some light coloured sodic plagioclase and potassium feldspar

The most silica-rich of the plutonic rocks is the graniteGranites contain enough silica that appreciable amounts of quartscrystallize, and there are the fewest ferromagnesian minerals

Pictures that show the different igneous textures of plutonic versus volcanic rocks

Fine grained volcanic rocks have a coarse grained plutonic rock that is its compositional equivalent (gabbro and basalt)

The term pluton is used as a general term for any body of igneousrock mass that has crystallized below the earth’s surface

A pluton can be any composition (ultramafic to granitic) and geometric shape

A pluton is classified in two ways: its shape and its relationship to the structures in the surrounding country rock

A pluton that is parallel to any structure in the countryroc is concordant

Concordant plutons can be classified into two shapes: laccoliths (flat bottoms with an arching or doming roof) and lopolithsPlutons that are cylindrical shape are called pipes/necksDykes are igneous rocks that have intruded a pre-existing rock- they cross-cut rock body at any angle Sills are igneous rocks that have intruded pre-existing rocks as well- the intrude parallel to the rockBatholith is a term used for a discordant pluton body that is semi equi-dimensional

They can be big or small but are made up of batches of magma

Igneous: Volcanic: A magma that cools near the surface or rises under pressure and is extruded onto the earths surface is called volcanic

They only form small crystals or no crystals (glass) since they cool so fast

Not easily seen by naked eyeVolcanic rocks are subdivided based on their original magma compositions and texturesColour is often used for identification Most common volcanic rock is basalt

Basalt is the fine-grained compositional equal of gabbro They are both dark coloured (black) and make up the sea

floor, and can be erupted from volcanoes Andesites are similar to diorites in composition

These rocks are lighter in colour (grey or green)Rhyolites are equal to granites in composition

May be pink to grey in colour Difficult to distinguish from andesites

Volcanic rocks that lack a composition are called obsidianThe rocks that are full of vesicles are typically less dense and can float in water called pumice

Textural classifications are based on physical processes that formed them outside of the magma chamber

Ex: a rock that crystallized as a hot fragment after being ejected by a volcano is termed pyroclastic

Extrusive Structures:The shape of a volcano or domes depends on the composition of themagma being erupted

Ex: basaltic magma is less viscous and very dense- mafic lavas are more fluid and accumulate as a broad, domed structure – they tend to be flat and wider

Shield volcanoes are similar to the shape of a shield Most shield volcanoes start on the seafloor and grow up

over time (and multiple eruptions) to form islands and seamounts (Iceland)

The individual lava flows of a shield may be thin (less than a meter) but can cover wide areas (100’s of km’s)

After hundreds of slows over time, a large, flatter volcanic structure can form (The Hawaiian Islands)

Diagram illustrating the structure of A) shield volcano, and B) a composite volcano

Cinder cones are built from lava fragments (bombs, lapilli and mostly scoria)

Generally the products of gas-rich magmas Composed of mostly pyroclastic material and have slopes

of 30-40 degrees Most are elongate from unequal distribution of material

The less mafic and more silicic magmas (andesite and rhyolite) are less dense and more viscous

Upon eruption, the lava oozes out rather than flowsLava tends to build up close to the vent and covers less area- forms a steep-sided volcanic dome

Most deadly volcanoesThese tall volcanoes are called composite or stratavolcanoes

A composite or stratavolcano forms by the eruption of both lava and pyroclastic material from a central ventVolcanoes that erupt andesitic lavas tend to also erupt differentmaterials at different times

They may emit a lava flow at one time, and a pyroclasticsat another

Early lavas flow for grater distances than later lavas contributing to the wide base These volcanoes are the most dangerous because they are explosiveand have steep sides that are vulnerable to lahars and mudslides They are mostly located by the Pacific Ocean in the Ring of Fire

This zone is active and includes the chains of continental volcanoes along the South and North American west coasts (Andes and Cascade Ranges)

Mount St. Helene is located in the Cascade Range and is the most famous recent volcano to erupt in North America

Mount St. Helene is characterized by this sticky, viscous lava that has created a tall peak

Fissure Eruptions:Not all lava extruded onto the earths surface forms volcanoes

Sometimes, such as at mid-ocean ridge spreading centers, there may be a fissure eruption

A fissure eruption is where a long crack forms rather than a single pipe or vent

Fissure eruptions are common in rift environments when the crust is pulled or ripped apart

These eruptions extrude the greatest volume of volcanic material

The picture depicts a low-viscosity lava covering or “flooding” alarge surface area

Showing a fissure eruption in Iceland

These eruptions cause vertical stacking of successive lava flows than can be hundreds of meters in thickness

Because the lavas have low viscosity, their extent can exceed hundreds of square km’s- called flood basalts

Igneous Rocks and Ore Deposits: There are many different types of ore deposits that are associated with igneous rocks

Large igneous plutons are ideal structures to look for metals (nickel, copper, and chromium)

Felsic pegmatite dykes are ideal hosts for rare earth elements (platinum, palladium, tantalum, etc.)Silicate magma composition and the presence of volatiles (sulphurand carbon dioxide) play a key role in determining whether or notore bearing minerals will crystallize and in economic quantities

Unit 4: Weathering and Sedimentary RocksObjectives:1. Understand the weathering processes and how rocks are broken

down into sediments2. Know the sedimentary rock classification siliciclastic and

chemical, how they are classified (i.e. grain size)3. Understand the factors that affect the characteristics of

sedimentary rocks such as climate, distance or mode of transport (i.e. water and wind)

Volcanic processes generate new rock and landmass External processes (weathering and erosion) continually break

down and move material to lower elevationso The result of this weathering and burial is sedimentary rock

Weathering Processes:Weathering is a broad term that encompasses a variety of chemical,physical and biological processes that act to break down rocks inplace at the earths surface

Once the broken down rock products are transported they are put into the category of sediment

Weathering processes are typically categorized as: Mechanical Chemical

Depending on climate rock composition, topography, and climate determines what sediment form, the rate of weathering, and how the sediments are transported

Weathering Processes: Mechanical Mechanical weathering is a process that involves the physical breakdown or disintegration of rocks from large pieces to smallerones without changing their composition

This processes requires the application of physical stress (i.e. water)

In cold temperature, water freezes and expands within rock fractures/cracks When the weather warms the ice thaws to create cracks in the rocks

This freeze-thaw process is termed frost-wedgingFrost-wedging looses rock fragments that tumble down slopes and form large piles called talus slopes at the base of steep outcrops

In arid climates, salt can have a similar physical force and effect on rocks

In extreme climates (desert) the contrast between day andnight temperatures is so great, the rocks bake and expandduring the day (thermal expansion), at night the low nocturnal temperatures (thermal contraction) this cycle of thermal expansion and contraction makes the rocks break apart

Weathering Processes: Chemical Chemical weathering involves the decomposition/breakdown of minerals by chemical reaction with gases (in the air) or dissolution in the water

Water is the most important agent in chemical weatheringSilicate minerals make up most of the earths crust

The weakness of many silicates to chemical weathering canbe determined from the conditions under which they originally formed

General rule: silicates that formed at the highest temperatures tend to be the least stable and therefore the most easily weathered

A rocks tendency to weather chemically is linked to its mineralogical composition

A gabbro that contains mostly high-temperature minerals will weather more than a granite rich in quarts and low-temperature feldspars

The Bowen’s Reaction Series can be used as a general guide to weathering susceptibility

Minerals that form first are the ones that first to be weathered

The major processes of chemical weathering: Dissolution

Oxidation Hydrolysis

Mineral compositions dictate the kind of chemical reactions they undergo and the rate of the reactions

Dissolution:Rocks containing calcite or calcium carbonate are very reactive and susceptible to chemical weathering Minerals decompose by dissolution

They dissolve in waterAlthough minerals are insoluble in pure water, in nature a small amount of acid can dramatically increase the corrosive effects ofwater

Natural acids are produced by a number of processes including carbon dioxide mixing with atmospheric water, decaying organic debris and release of volcanic gases

Rain water mixed with carbon dioxide in soils also increases acidity this decomposes most rocks easily and produces soluble products that can be carried away bywater

The pH scale showing the measurements of acidity (left) to alkalinity (right)

pH 7 is considered neutral

When calcite or halite are chemically weathered they dissolve The chemical formula for the breakdown of halite is:

NaCI(s)Na^+(aq) +CI^-(aq)In water, one molecule of the mineral halite breaks down into onepositively charged sodium ion and one negatively charged chlorineion

These ions are soluble in water (aq)

Oxidation:Oxidation is another form of chemical weatheringIron is an ion that is most susceptible to oxidationThis process is where oxygen combined with iron to form iron oxide

Electrons are lost from one element during the reaction- here iron loses electrons to oxygen

This process is faster in water climates than more arid climates

The basic formula for iron oxidation is: 4Fe(s)+3O(20(g)2Fe(2)o(3)(s) (s) represents a solid and (g) represents a gas The reaction in words: 4 iron atoms and 2 oxygen gas

molecules react to create 2 iron oxide molecules Oxidation also reacts with ferromagnesium (Fe and Mg bearings) minerals such as olivine, pyroxene and amphibole

Ferromagnesian silicates leave behind insoluble iron oxides (hematite) and iron hydroxides (goethite) and sometimes clays

It is important for breaking down sulphide minerals (pyrite, arensopyrite, etc.)

Breakdown of these sulphide minerals produces sulphide acid

Oxidized sulphide minerals release sulphuric acid and insoluble iron compounds into ground water

This occurs naturally but mining exposes large amounts ofsulphides at one time, speeding up the process (mine-acidcan be generated)

Hydrolysis:Hydrolysis involves the addition of H+ to crystal lattices

This creates an unstable arrangement of atoms in the mineral, causing it to breakdown

In nature, water contains carbonic acid Carbonic acid ionizes the water to form hydrogen atoms

and bicarbonate atomsThe mineralogical composition of the rocks determine their susceptibility to chemical weathering

Ex: feldspars containing potassium weather into clay minerals

Hydrogen atoms “attack” the potassium (K^+) in a feldsparstructure by replacing it

The removal of potassium makes the structure unstable andmore easy to break down

The chemical formula of hydrolysis of feldspar is: 2KAISi(3)O(8)+2H(^+)+9H(2)0H(4)A1(2)Si(2)O(9)+4H(4)SiO(4)+2K(^+) orthoclase+ acid + waterkaolinite + silicic acid + potassium

Soil:Soil covers most of the land surfaces and is one of the most indispensable resources o earthOnce oil has been created, plats can colonize the surface and support more complex organisms such as animals and humans Earths surface is covered by regolith:

A layer of rock comprised of mineral and rock fragmentsThe source of mineral matter is known as parent material and can influence a soil by affecting the rate of weathering/soil formation and chemical makeup

This impacts soil fertility and soil formationOver time, weathering processes diminish the effects of the parent material

General rule: soil becomes thicker over time

The most influential factor on soil is climate (temperature and precipitation)

Higher temperatures and precipitation can lead to thickersoil layers and chemical alteration of the parent material

They also influence the degree of leaching of various materials and nutrients, and control the type of plant and animal life present

Sediment to Sedimentary Rocks:Based on the principle of uniformitarianism, it is believed that:

The processes and environments throughout the evolution of earth have ultimately not changed

Geologists that study ancient sedimentary rocks look at modern environments as an analogue (processes have likelynot changed over 5 billion years)

Diagensis is a term that includes the set of processes that changeunconsolidated sediment into sedimentary rock

It is a term that encompasses all the chemical, physical and biological changes that solidify sediment after deposition (due to burial) before it is buried enough to undergo true metamorphism

Continuous sediment results in earlier deposited sediments being continually buried deeper over time

The weight of the overlying sediments puts pressure on those buried below (lithification)

The temperature of 200C is the boundary between diagenisis and metamorphism, marking the point at which clay minerals re-crystallize to micas (higher temperature structures)Cementation occurs with compaction and involves a chemical change where material is added between the grains to make them stick together

Diagenesis and lithification turn unconsolidated sediment into hard sedimentary rock

Previous unconsolidated sediment (sand on a beach), sticks together to form sedimentary rock (sandstone)

Sedimentary Rocks:Sediments accumulate on earth’s surface they comprise a thin and discontinuous layer in the upper portion of the crustThe composition and textures tell us about the origin the sediment was deposited

Sedimentary rocks indicate past environments and clues tothe mechanisms used for their deposition

Similar to igneous rocks, sedimentary rocks can be classified Classification is based on mineralogical composition and

particle size and the ways they are formedSedimentary rocks are divided into two main groups:

Detrital Chemical

Detrital rocks also called silicilastic are further subdivided based on mineral composition

Siliciclastic Sedimentary Rocks:Siliciclastic sediments are comprised of small fragments of pre-existing weathered rocks or mineralsClays and quartz are the most abundant weathering byproduct of silicate minerals (i.e. feldspars)They are named based on the fragment size they contain, with no implication as to the composition of these fragments

The grain size indicated how far the material traveled from its original unweathered host rock

In general: the larger the grains means the shorter the distance travelled and the lesser the degree of weathering

A particle size classification chart All sandstone in the world will have grain sizes between

1/16th and 2mmRocks that contain large fragments (pebble to cobble size) of pre-existing rocks can be called a conglomerate or breccia

Conglomerates consist of rounded pebbles and cobbles that range in size from a pea to big boulders

If the fragments are angular and not rounded it is calleda breccia

Large particles require water velocities to carry it awayRocks that have smaller fragments (sand grains) are called sandstones

Sandstones can form in a variety of environments such as streams, coastlines and desserts

These rocks are hard to see with the naked eye and are called: Mudrocks: comprised of fine, mud-sized sediment They can be divided into siltstones, mudstones, and shales

Because of their elongated form, clay minerals tend to accumulatein layers

Mudrocks with aligned particles that develop “sheet” layers are called shales

Shales are often weak since they are not well cemented

Chemical Sedimentary Rocks:Chemical sediments precipitate from a solution

The precipitated material solidates to form a chemical sedimentary rock

Grain sized is not used as a classification propertyPrecipitation can occur by organic or inorganic processes

Inorganic processes involve chemical activity or evaporation

Organic activity involves the precipitation or depositionof chemical sediments via a biochemical origin

Biological or organic sediments are not a distinct class of sedimentary rocks, but are considered a chemical sediment subclass

Evaporates, limestones, and banded iron formations are examples of chemical sedimentary rocks

Each rock forms in a unique sedimentary environment

Sedimentary Rocks: Structures and Features:These rocks and structures record the environment and related processes of deposition

In some cases, direction of transport can be determined as well as the area of source can be identified these features can be categorized into bedding related structures, surface features and evidence of biogenic activity

Sedimentary rocks are deposited in various layers called beds or strata, and are represented by a different rock type

Ex: you may have a mudstone that is overlain by a sandstone- on top of the sandstone there may be an ancient limestone coral reef

Each stratum is unique (mudstone, sandstone, and limestone)

When geologists look at all the stacked stratum as a sequence it is called stratigraphy

They will look at grain size, texture and other features of each stratum to determine the different conditions that each layer was deposited

They will then look at how these conditions changed from layer to layer and how it evolved overtime

Sedimentary bedding is not always horizontally stacked (like cakelayers)

Water and wind moving over topography can move in one direction sloping surfaces

Cross-bedding (stacking of slanted bedding in a sedimentary layer) in a sandstone of a dessert dune

The orientation of the inclined beds indicates direction of flow and the change in direction flow creates a changein orientation of the cross-beds

Cross-beds are mostly found in river deltas, sand dunes, and stream deposits

Ripple marks affect a sedimentary bedding plane (top surface) at a certain point in time when sediment was being deposited

Ex: rhythmic motions of waves moving back and fourth overa shoreline (i.e. beach) produce wave ripples that are symmetrical

Ripples can also form in a setting where the wind or water continually flow in one direction and are called asymmetrical ripples

Most common in river channels or sand dunes

Note: the shadows are deeper on one side of the ripples indicating the asymmetry

Mud cracks or desiccation cracks Features that occur on fine-grained sediments or

typically clays To form, the water-laid sediments must be exposed to air When they dry out, water is lost and the volume of the

sediment shrinks, then it forms polygonal mud cracks on the surface that is exposed to the sun

Form in environments such as tidal flats or lake bottoms of seasonal playa lakes

Biogenic features:Some evidence of organisms can be found in the form of fossils

Fossils are either the physical remains of ancient life (i.e. a shell) or the evidence hat life existed in the form of bioturbation (tracks or burrows)

Fossils play a key role in correlating rocks of similar age around the worldIn many cases, soft tissue is preserved in the form of imprints called trace fossils

this photo shows plant imprints that have left an impression and perhaps some residual organic matter- the actual plant material is gone though

Footprints can also be preservedPreservation of some fossils require the replacement of the original material by other minerals

This addition of minerals to the original is called petrification or premineralization

Unit 5: Sedimentary Environments:Objectives:1. Be familiar with the different sedimentary environments and the type

of sedimentary rock that can form in each setting2. Know the three different stream types, gradients, velocities and

environments they form in3. Know the different parts of the shoreline and the effects of waves

and tides4. Know how deserts occur and the role of seasonal water and wind

transportation

Sedimentary Environments:Sedimentary environmental conditions are recorded in a series of sedimentary rock layersSedimentary facies is a unit that is comprised of a set of characteristics that reflect the conditions of a particular individualenvironment Different sedimentary environment include: streams, coastlines, oceans, and desserts

Streams:Water will only flow when there is a slope or gradient

The slope or gradient of the river will determine the rate of flow and the shape of the river

Discharge is the amount of water flowing down a stream and is expressed as the volume of water flowing past a point per unit of time (i.e. cubic meters per second)

Stream discharge increases during periods of flood even thoughthe gradient remains the same

Factors such as rainfall and snowmelt can affect stream discharge

When discharge increases, the depth and/or the width of the river must increase to accommodate the larger volume of water

A river can transport sediment downstream in three ways:1. Dissolved load

Dissolved material contributed via inflows of ground water2. Suspended load

Comprised of visible sediment particles that are carried downstream in the river current (clay and silt particles)

They are small enough to be picked up by slight force (lower velocities) and are in suspension in the channel flow

3. Bed load When river velocities are high, large particles (boulders and

cobbles) can be rolled along the stream bed They are too large to be carried in suspension They can be moved by rolling, sliding, or saltation (leaping,

skipping) across the stream bed Bed load is mostly moved during times of flood

The type of materials that a river carries in suspension are controlled by flow velocity and settling velocity

When the velocity drops and there is no energy to keep the load suspended (settling velocity), the sediment goes to the bottom ofthe stream

Types of streams:Three basic types of streams:1. Braided rivers

They are steep gradient rivers that flow down the slopes of mountains

Fast water especially during spring thaw can carry very large particles that deposit as intrachannel bars when there is an obstruction in the river path

These rivers have higher sediment to water volume ratio The fast flowing water is very erosive so they tend to incise

V-shaped valleys between mountain ridges When the rivers dry up, boulders, gravel, and large sand

grains are left as sedimentary deposit Braided rivers through the Yukon to Alaska and the Alaskan

mountains deposited gold nuggets in intrachannel gravel deposits in Alaskan rivers placer gold deposits let to the famous Alaskan Gold Rush in the 1890’s

2. Meandering streams These rivers are lower gradient rivers that typically occupy

broad floodplains They are formed by lateral erosion of its banks or cutback from

higher velocities on the outside of the meander bend and deposition of sediment on the inside of the meander bend or point bar where the velocity is lowest

The constant erosion of the outside cut bank and deposition ofthe inside point bar makes the river migrate sideways in the direction of the cut bank

When the two meander rocks meet, a new channel segment is formed called a cutoff

The water flows through this new channel, not around the mender loop

The leftover water is called an oxbow lake and becomes filled upwith sandstone

3. Anastomosing river This is the lowest gradient river These rivers are made up of multiple separate stream paths They have leeves on both sides of their banks and do not migrate

across a floodplain Sediments eventually clog the stream path overtime and then a

new stream path is found

Shorelines:Shorelines are dynamic environments that are affected by winds that…

Generate surface currents Density differences that create deep-ocean circulation The Moon and Sun that produce tides

The transition from land to water is always changingThe dominant proves that modifies shorelines is wind-generated waves

They can travel very far until they encounter a barrier (i.e. shoreline)

Waves mark the transfer of energy through a medium (water)In open water, this wave energy moves forward, but the water does notEach water particle moves in a circular motion during the passage of awave

The orbital diameter of the water particle at the surface = the wave height

The energy transferred from the winder to water hits the surface and below the surface a certain depth

Below ½ a wave length, the water motion disappears(wave base)

Wave particle motion is greatest near the surface of water anddecreases with water depth

The larger the wave, the larger the wave particle motion (larger wavelength) and the deeper depth where the motion affects the water (larger wavelength=larger ½ wavelength)

When the wavelength and velocity decreases, the height of the wave increases

Height increases to the critical point where the steep wave front collapses

The resulting turbulent water made by the breaking waves is called the surf

When waves are larger, and the wave base deeper, wave base comes into contact with the seafloor further away from the shore (in deeper water)During a storm, the waves have the greatest impact on the shoreline

Tides are controlled mostly by the gravitational attraction between Earth and the Moon

The earths rotation creates tidal bulges in the oceans by competing gravity and inertial forces

Waters are “pulled” by this gravitation attraction between the Moon and Earth

The waters bulge toward the moonThe position of the moon changes throughout the day

The bulge (attraction to the moon) remains in the same place relative to the moon as the earth rotates

In a day there are two high tides and two low tides Spring tide is when the tides are at their highest because of the

alignment of the Sun and Moon

Neap tide is when the tides are at their lowest because of the slanting angle of the Moon to Earth and Sun

As a tide rises and falls there is a horizontal flow of water called tidal currents

The water advances toward the coastal zone and is called flood currents

When the tide falls, water flows away from the shore back to the sea This seaward flow is called ebb currents

When there is no directional flow the current is called slack water

Sediment accumulation on a coastline is complex and represents a dynamic environmentA coasts profile can be divided into three main components to help separate and define the different sedimentary in the environments 1. The base or bottom of the coastal profile is the offshore zone

It is permanently submerged and below the base of fair-weathered waves

Storm waves may touch the surface of this zone2. Fair-weather wave base is the depth at which fair-weathered waves (not

storm) touch bottom and where breakers start to form 3. Shoreface zone is the area closer to land

It lays between the fair-weathered and the low-tide mark It is subject to continuous wave action This zone is characterized by the constant transport of

sediment due to waves, tides, and longshore currents

A beach marks the shore face limit and permanent vegetated land The foreshore zone of a beach is always affected by the repeated

swash and backswash of breaking waves and low-tide to high-tides

The backshore zone of a beach is above normal to high-tide level and is “behind” the foreshore

Unique situations can form different coastal features including spits,baymouth bar, barrier islands and lagoons

Lagoons can form between the islands and shore and represent quiet water which allow for deposition of shale deposits

Lagoons and swamps are important environments for the formation of coal deposits

A lagoon is a body of water that exists behind a barrier island- it mostly experiences tide action- only experiences wave action during storm periods

Oceans:Two important ocean environments that are important in relation to economic deposits1. The abyssal plain:

It is the large expense of ocean floor deeper than storm wave base

Water velocity is extremely low Mud particles deposit In extreme storm conditions and avalanches down the slope, is

sand deposited on this plain 2. Coral reefs:

the most common type of biological chemical sediment

Organisms in a coral reef build their structures out of calcium carbonate that solidify to limestone

Buried shells are called fossils When fragments of life forms the rock is called a fossilferous

limestone Coral reefs and calcite-shelled organisms can only live in

warm, clean, and shallow (need sunlight), marine environments Similar to sandy shorelines, ancient coral reefs can be

important reservoirs for oil and gas deposits

Deserts:30% of earths surface is comprised of dry regions

In arid climate, water is sparse and chemical weather is drastically reduced

Debris and rock fragments are more mechanically weatheredTwo basic climate types:1. Desert (arid):

A region that receives less than 25 cm of rain per year2. Steppe (semi-arid):

A region that receives between 25-50 cm of rain fall per yearLocated in subtropics around the globeThe formation of these arid regions are affected by: latitude, mountains, and overall climate can control air pressure, wind and rainfall patterns

Latitude:The sun directs most of its energy near the equator to warm the earthssurface

The cool air cannot hold as much water as warmer air which creates vapour water to condense and fall as rain (why there are tropical rainforests near the equator)

Since the air is warm, but try it can cause water from the land surface to evaporate into the atmosphere

The worlds dry regions/deserts are located at about 30 north and 30 south latitudes

Mountains: Rain-Shadow Deserts:Without mountain-building, wetter climates would prevail in many areasthat are now aridMountains are obstructions to air current and affect the air flow and moisture distribution of air pressure systems Moisture condenses and rainfall occurs on the windward side of the mountain range

Now, the air is drier and cooler and flows down the leeside ofthe mountain and sinks to the surface

It absorbs water from the earth and becomes warmer The dry zone on the leeside of the range is called a rain-shadow

desert

Wet warm air rises to pass over a mountain range- as the air rises, it cools and loses its moisture by raining on the windward slopes

After this moisture is lost, the dry cool air pass over the mountains and drops on the leeward side

Polar, Coastal and Interior Deserts:In the polar regions of the earth, cold air is constantly descending and the dry air associated with stable high-pressure cells prevents rain cloud formationThe conditions dominate the north Artic

Annual rainfall: between 10-20 cm (some areas low as 5cm)Some regions are warmer (South America)

The air becomes heated and absorbs moisture from the land, creating a coastal desert

The Gobi desert is an example of an interior desert It is a region, that latitude should receive lots of rainfall

It is set behind the Himalaya Mountains, this region is a desert

It does not occur, or on the immediate leeside of the mountainrange

Seasonal Water:In deserts, streams are dry for most of the time

There are some short periods when they do flow after rain, called ephemeral streams

Playa lakes are temporary lakes fed by the seasonal streamsStream water normally contains dissolved salts within their dissolved bed load

When large quantities of salt are deposited in a playa lake, and water is evaporated evaporate deposits will form

Water becomes supersaturated with salt The decrease in lake water results in a specific sequence of

salt minerals Ex: when nine tenths of a lakes water is evaporated, halite

will precipitate- next gypsum willThe last salts to crystallize are potassium and magnesium (slyvite, aka potash)

Death Valley in the US is an example where economic evaporite deposits were deposited

Wind:Wind is not always confined to channels and spreads out over a large area laterally and vertically

Majority of bed load carried by wind is sand that moves by saltation (skipping and bouncing)

The process of coarse grains (sand) being moved is called surface creepFiner grained material (finer than sand) can be carried by the windThe removal of only lighter material can result in only coarse material (cobbles, pebbles) called desert pavement – a feature of the Outback of Australia

Saltation of sand grains by wind also act as abrasives on rock surfaces

This “sand blasts” the rocks making the surfaces smooth- this forms rock sculptures in deserts

Sand dunes are the most common feature in desert environments Wind speeds slows down Dunes commonly grow to 30-100 meters, giant dunes can be up to

500 metersSeveral different types of sand dunes that can form

The type of dune forms depending on wind direction, wind velocity, amount of vegetation present, and the availability of sand

Unit 6: Metamorphism and Metamorphic RocksObjectives:1. Know what metamorphism is and how it can change the parent rock2. Understand what metamorphic grade is and what the index minerals are

for the different grades3. Understand the different types of metamorphism and what processes

are involved4. Know the different metamorphic facies, the associated index minerals

or textures and the relative temperature and pressure ranges

Metamorphism:Metamorphism: the change that takes place within a body of rock as a result of it being subjected to conditions that are different from those in which it is formedMetamorphic Rocks

Form by the recrystallization or reformation of minerals within an existing rock

Sedimentary or igneous recrystallize when higher pressures and/or temperatures surpass the original cooling temperature of one or more minerals

These pressures and temperatures are not enough to melt the rock into magma, but they do cause some minerals to recrystallize by promoting exchange of their elements

Ex: clay minerals in a sedimentary rock will recrystallize to mica minerals at higher temperatures

Metamorphism is used to describe what happens to rocks when they become buried beneath other rocks, and are subjected to higher temperatures and pressures than those at surfacethe main factors that influence the mineralogical makeup of a metamorphic rock are

A. The bulk composition of the rockB. The pressure and temperature conditions at the time of

crystallization C. The composition of the fluid phase in the rock during

metamorphism Metamorphic rocks all originate from a parent rock

The type and degree of change in the transformation of the original parent rock to the new rock depends on the type of intensity of the individual or combined metamorphic processes

The chemical composition of a metamorphic rock largely reflects that of its parent rock

The texture and specific mineral make up, depends on the particular physical processes involved during metamorphic transformation

This means, although the minerals of the rock may change, the overall chemical composition of the rock does not (it will still have the same quantity of elements, they will just be rearranged)

The minerals in the parent rock are stable only with a specific range of temperatures and pressures – the rock will become affected by fluids, pressure, and temperature

Temperature is one of the most important factors in metamorphism Heat drives chemical reactions for mineral recrystallization,

and influences the reactivity and mobility of chemically active fluids

Within the crust of the earth, both temperature and pressure increase with depth

The rate of temperature increase is generally between 20-30C for each km of burial- this is known as geothermal gradient

The geothermal gradient differs from place to place in Earth It can be very high in areas with volcanic activity , or where

there is a magma chamber close to surface

At low temperatures (150-200C), some minerals can be converted to alteration products (clay or chlorite)

At higher temperatures, other mineral reactions will take place, creating transformations to minerals (muscovite, biotite, epidote, garnet, staurolite, etc.)Metamorphic reactions commonly result in a recrystallization and/or a coarsening of mineral crystals in a rock

Ex: a mica-schist will have large crystals of mica, even though its precursor was a shale in which the clay minerals were fine-grained

This rock has large garnet porphyroblast crystals that are testament to higher temperatures that have caused the mineralsto change, and new minerals to form (rock has been recrystallized)

This rock shows foliation that happens when the rock is subjected to pressure and temperatures

The minerals are realigned but have not recrystallizedPressure is another important factor in metamorphism, and is responsiblefor changing the physical characteristics of a rock

It can influence the temperature at which specific minerals are stable

Important: when discussing the deformation of rocks, the term stress is used instead of pressureThe presence of fluid/water in a rock is critical to the process of metamorphism

Most of the water is derived from the minerals own structure, however other volaties (carbon fioxide) also play important roles

Ex: clays have water in their mineral structure- some of that water is released when the clay is converted into a new mineral

Fluids are important in crystallization of new mineral grains in areas of low stress

Water can also migrate during metamorphism, and in these caseschange the overall composition of the rock

Metamorphic rocks are described in terms of their metamorphic grade This term refers to the intensity of metamorphism (degree of

pressure and temperature) An increase in metamorphic grade is indicated by the

sequential appearance of minerals that are stable at progressively higher temperatures

These index minerals have been determined by laboratory studies, and are used to define metamorphic grade

Ex: chlorite begins to form at 200C and a rock that contains chlorite is considered low grade

Sillimanite forms in environments where temperatures exceed 600C which are high grade

Types of Metamorphism:Metamorphic conditions are classified into three categories: burial, regional, and contact metamorphism1. Burial metamorphism

Very mild, with slight increases in temperature and pressure A step beyond diagenesis

Related to burial of sediments in a basin where the geothermalheat produces very low grade metamorphic reactions, forming such minerals as zeolites (hydration of silicates) and chlorites

The depth usually is about 8km below the surface and temperatures up to 200C

When a body of rock becomes buried, it is also subjected to pressure The confining pressure is a uniform pressure acted on a body of

rock in equal amounts from all directions Under low pressures and temperatures the rocks get denser, but

not deformed

Regional Metamorphism:With long compression, the rocks will become more plastically deformed, resulting in foldingMetamorphism related to tectonic collisions and mountain building is knows as regional metamorphism

It affects very large areas of up to thousands of square kmThe grade metamorphism is likely to be most extreme beneath the central part of a mountain belt

The crust is the thickest and rocks buried to the greatest depth

The effects of regional metamorphism are only revealed when a mountainbelt is eroded, exposing the rocks which were buried deep within mountain beltsIn most areas, concentric zones of increasing metamorphic grade have been outlined by examining the metamorphic index minerals in the metamorphosed rock

Granite are present at the cores of some fold belts, indicating that temperatures there were not hot enough to meltthe pre-existing rock fully

Regional metamorphism is more intense than burial metamorphism Metamorphic rocks are products of the high temperatures and

pressures resulting from deep burial and tectonic forces It is a type of “burial” metamorphism, but at much greater

depths

Diagram illustrates how the geothermal gradient changes with depth, and how it changes in a different tectonic setting

Crustal thickness has a huge impact on the geothermal gradientRegional metamorphism is commonly a consequence of mountain building, where large volumes are uplifted other rock formations As the height of the mountains is increased, the depth to which the underlying rock is buried is increased

Burial depth is about 20 km (under the Himalayan Mountains) will result in temperatures of 400-800C and very high pressure, due to both the weight of the overlying rock, and from he tectonic forces

Direct pressure occurs Stress directions are stronger than others that are a result

of the weight of the overlying rock and stress related to tectonic activity

Texture changes with increasing temperature and pressure

Horizontal compressional stress causes rock bodies to shorten horizontally and thicken vertically

During mountain building, colliding plates generate compressive forces These stresses normally result in the body of rock being

squeezed in one direction, and stretched out in anotherThe original texture of the rock is changed as the body of rock is deformed by being stretched/squeezed

The new minerals that are formed tend to be elongated along the direction of the least stress

Ex: if the greatest stress is from east and west, minerals will grow preferentially in the north-south direction

The resulting alignment of minerals is known as foliation With low pressures, minerals will either rotate to align with

or grow in the “least stress” directionRock can also be forced down beneath the growing mountains For regional metamorphism, index minerals are used to classify the metamorphic grade

At shallow burial levels and low temperatures rocks are classified as zeolite facies that include dominantly textural changes, but few mineralogical changes

With increased depth (200-500C) rock are classified as greenschist facies as minerlogical changes happen with recrystallization of low temperatures (T) minerals such as ones that contain water (i.e. clays recrystallize to chlorite)

Chlorite is green and abundant chlorite in a rocks gives it a strong green colour

With increasing temperature and pressure (P), larger volumes of water are squeezed or driven out of the rockAt temperatures between 500-700C and pressures of 3-7 kilobars, the rocks are classified as amphibolite facies as minerals recrystallize to their higher temperature stable forms

The new formed mineral is amphibole With even higher temperatures of 700C+ and pressures 7 kilobars+, evenmore water is lost and mineral recrystallize to high temperature stable minerals called granulite faciesIn unique situations where rocks are only shallowly buried but experience high pressures (not temperatures), these rocks have abundant water in their mineral structures and produce a unique blue metamorphic mineral called glaucophane

Called blueschist faciesMetamorphic facies classification can be thought of as a progressing through a modified Bowen’s Reaction series in reverse

Heating up and compressing rock causes higher temperature and pressure minerals to stabilize

Above granulite facies rock will remelt to form mamga – when the magma is brought to shallower levels again, the Bowen’s Reaction series will restart as the magma cools

Zeolites occur at very low pressures and temperatures, whereasgranulite facies occur at high temperatures and a range of pressures

Sedimentary rocks, facies classification is also accompanied by textural changes

If a sedimentary rock were to undergo progressive metamorphismfrom greenschichst through to granulite facies, the textural changes would include slate at the zeolite facies, phyllite at greenschist, mica schist at amphibolite facies and a gneiss texture at granulite facies

The diagram shows where the different metamorphic grades generally occur in a subduction zone

Ex: blueschist occurs near the plate boundaries, where eclogite occur at depth

Contact Metamorphism:

A less common form of metamorphism is contact metamorphism, also referredto as thermal metamorphism

This process involves an igneous body rising through the crustand baking adjacent rocks that are in contact with the intruding body

The thermal aureole, or zone recrystallized rock surrounding igneous body, is rock that experienced higher temperature as a result recrystallizedThe aureole of alerted rock is called hornfels

Heat transfer from the magma body affect rocks that are withinseveral hundreds of meters to several km of the intrusion depending on the size of the intruding igneous body

The new metamorphic rock that crystallized depends on the parent rock that was intruded

Ex: let us consider a sequence of sedimentary rocks- limesome will recrystallize to marble- a rock made up of interlocking crystals of calcite or dolomite with no foliation, sandstone will recrystallize to quartzite and shale will bake to a hornfels

Since contact metamorphism normally takes place within one or two km of the surface, the rocks affected are not subject to significant pressures, not to very high temperatures

Diagram shows the thermal metamorphic change of sedimentary parent rocks to their metamorphic equivalent (i.e. limestone to marble)

The mineral recrystallizations associated with hornfels results in the growth of minerals which show no preferred orientation due to the lack of metamorphic stress

As the grade of metamorphism decreases away from the igneous body, a sequence of metamorphic minerals may be observed

o For ex: the minerals garnet or staurolite might crystallize right next to the hot igneous body- whereas biotite or chlorite may be crystallized further away in the cooler zones

In some cases, large grains of metamorphic minerals (cordierite, garnet, staurolite) form in the rock, giving the rock a coarse-grainedspotted texture called porphyroblastic texture

The large grains are called porphyroblasts

Hydrothermal Fluids:Metamorphism can cause the release of water and other fluids such are carbon dioxide

These fluids can become superheated and travel great distancesaway from the rock undergoing metamorphism

They can remove elements from mineral structures (similar to weathering processes) and can carry them as dissolved loads

When these fluids infiltrate lower temperature rocks the initiate metamorphism that is called hydrothermal alterationSometimes the hydrothermal change can happen kilometers away from the original source of the hydrothermal fluid

When these hydrothermal fluids carry metals, uranium, and dissolved other economic, they form ore deposits

As the fluid temperature decreases, dissolved elements are no longer soluble and minerals crystallize

Metamorphic Rock Textures:Schist and gneiss are important terms used to describe the metamorphic textures of rocks that contain different compositionsA schist is a medium to coarse grained metamorphic rock that is dominated by platy mica minerals

These mica minerals have an obvious preferred orientation thatdefines a distinctive foliation or in this case schistosity

For geologists to differentiate the rock composition, particularly schists, rocks are described as the dominant mineral (i.e. biotite) followed by the texture (biotite-schist)

A gneiss is a term applied to medium to coarse grained banded metamorphic rocks where elongated minerals are dominate

Gneissic texture represents high grade metamorphism During intense metamorphism, the light and dark components

separate into layers giving the rock gniessosity Granits and rhyolites are largely composed of quartz and feldspar

These minerals are stable over a wide range of temperatures, they will not be affected by metamorphism until very high-grade conditions are reached

The diagram shows the metamorphic textures (fabric) from, left to right, low grade to high grade

These textures are correlated to the approximate location theywould occur within a regional metamorphic stetting

This table lists the rock names of the different metamorphic rocks, and their individual textures, grain size, and original parent rock