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Geology 101

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Carrie B Sanders

Geology 9/16/2012 2:52:00 PM Fundamental Concepts  Spatial arrangement of features on Earth o Global distribution of oceans and continents: continental drift, plate tectonics  Stratigraphic arrangement of earth materials (minerals and rocks) o oldest to youngest: absolute vs. relative age  Uniformitarianism o The present is the key to the past The Science of Geology  Physical Geology o Examines the materials composing Earth to gain an understanding of the surface  Historical Geology o Understand the origin of Earth and its development throughout time  Information comes from outcrops o Where bedrock is exposed at the surface o The study of carious Earth materials provides insight into many basic processes Geology, People and the Environment  Natural hazards o Volcanoes, floods, earthquakes, landslides, tsunami  Resources o Water and soil o Metallic and nonmetallic materials o Energy o Great demands for resources and a growing pressure for people to dwell in environments that have significant geologic hazards o River flooding in natural, but the magnitude and frequency of flooding can be changed significantly by human activities Some Historical Notes about Geology  Catastrophism o Mid seventieth century o Earth’s landscapes had been shaped primarily b great catastrophes o Mountains and canyons o Explained as having been produced by sudden and often worldwide disasters produced by unknown causes that no longer operate  Uniformitarianism o The present is the key to the past o Implies the operation of timeless, changeless laws or principles Relative Dating and the Geologic Time Scale  Relative dating o Events are placed in their proper sequence or order without knowing their age in years  Law of superposition o The youngest layer is on top o Oldest is on the bottom o Sequence of rock layers – not their numeric age  Principle of fossil succession o Fossil organisms succeed one another in a definite and determinable order o Any time span can be recognized by its fossil content Origin of Planet Earth  Nebular hypothesis o Suggests that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula Formation of Earth’s Layered Structure  High velocity impact of nebular debris and the decay of radioactive elements caused the temperature of our planet to steadily increase  Melting produced liquid blobs of heavy metal that sank toward the centre of the planet  Produced Earth’s dense iron rich core  Earth’s largest layer: mantle o Located between the core and crust o Dominated by iron, magnesium, oxygen seeking elements  Consequence o Large volumes of gases were allowed to escape from Earth’s interior o A primitive atmosphere gradually evolved Plate Tectonics: A Geologic Paradigm  Continental drift o Alfred Wegener o The idea that the continents moved about the face of the planet o Proposal contradicted the established view that the continents and ocean basins are permanent and stationary features on the face of the Earth  Paradigms o Wove together the basic processes known to operate Earth o Called plate tectonics Continental Drift: An Idea Before its Time  Single supercontinent called Pangaea once existed  Hypothesized o About 200 million years ago this supercontinent began breaking into smaller continents, which then “drifted” to their present position  Similarity between the coastlines on opposite sides of the South Atlantic  Shorelines are continually modified by erosional, depositional and tectonic processes  Continental shelf o A gently sloping platform of continental material extending from the shore o Continents overlap in a few places, these are regions where streams have deposited large quantities of sediment, thus enlarging continental shelves  Fossil Evidence o Fossil evidence for the existence of a land bridge connecting South America and Africa o Some type of land connection was needed to explain the existence of identical fossils on widely separated landmass o True for late Paleozoic and early Mesozoic life forms o Several fossil organisms that had been found on different oceans presently separating the continents o The idea of land connections was the most widely accepted solution to the problem of migration Rock Type and Structural Similarities  The rocks found in a particular region on one continent should closely match in and type with those found in adjacent positions on the adjoining continent  Evidence exists in the form of mountain belts that terminate at one coastline, one to reappear on a landmass across the ocean  Appalachians trends northeastward through eastern North America and disappears off the coast of Newfoundland and Labrador  When these landmasses are reassembled, the mountain changes forms a nearly continuous belt  Paleoclimatic evidence o Palaios = ancient, climatic = climate o Evidence for dramatic global climatic changes o Indicated near the end of the Paleozoic Era, ice sheets covered extensive areas of the Southern Hemisphere o Layers of ancient glacial rock called tillite, of the same age were found in southern Africa and South America and in India and Australia o Some locations the striations and grooves indicated that the ice had moved from what is now the sea onto land o During the late Paleozoic Era, large tropical swamps existed in the Northern Hemisphere o More plausible explanation for the late Paleozoic glaciation was provided if the landmass were fitted together as a supercontinent, with South Africa centered over the South Pole Planet of Shifting Plates  Plate Tectonics o Lithosphere: the sphere of rock that consists of the crust and uppermost (brittle) part of the mantle called plates o Plates: mobile and continually change shape and size over time as they interact with other plates o This movement is ultimately driven by the unequal distribution of heat within Earth, resulting in mantel convection o Hot material found deep in the mantle moves slowly upward and serves as one part of our planet’s internal convective system o Cooler, denser slabs of lithosphere descend back into the mantle, setting Earth’s rigid outer shell in motion o Generate earthquakes, create volcanoes and deform large masses of rock into mountains Plate Boundaries  Divergent Boundaries o Plates move apart o Resulting in upwelling material from the mantle o Perhaps create new sea floor o Occurs mainly at a mid ocean ridge o As that part of the plate moves farther away from the mid ocean ridge with seafloor spreading, it becomes older, cooler and thicker  Convergent Boundaries o Plates move together o Resulting in the descent (consumption) of oceanic lithosphere into the mantle o 2 continental margins collide to create a major mountain system o As 2 plates slowly converge, the leading edge of an oceanic slab is bend downward o Allowing it to slide beneath the other slab by a process called subduction o Plate margins at which oceanic crust is being consumed are called subduction zones  Transform Fault Boundaries o Plates slide past each other without the production or destruction of lithosphere o Form in the direction of plate movement Earth’s Internal Structure  Layers Defined by Composition o The crust, Earth’s comparatively thin, rocky outer skin is generally divided into oceanic and continental crust o Composed of dark rocks called basalt o The continental crust consists of many rock types o Upper crust is composed of similar rocks called granite o The composition of the lowermost continental crust is more similar to basalt  Mantle o More then 82% of Earth’s volume is contained in mantle o A solid rocky shell o Represents a marked change in chemical composition o Dominant rock type: peridtite  Core o Nickel alloy o Minor amounts of oxygen, silicon and sulphur o Elements that readily form compounds with iron Layers Defined by Physical Properties  Characterized y a gradual increase in temperature, pressure and density with depth  Gradual increase in temperature and pressure with depth affects the physical properties  Change the mechanical behaviour of Earth materials  Substance is heated, its chemical bonds weaken and its mechanical strength (resistance to deformation) is reduced  Exceeds the melting point the chemical bonds break down  Pressure also increases with depth and tend to increase rock strength  Depending on the physical environment, Earth material may behave like a brittle solid, deform, in a puttylike manner or even melt and become liquid  Earth can be divided into 5 man layers o Lithosphere  Outermost layer  Consists of the crust and uppermost mantle  Forms a relatively cool, rigid and brittle shell  Tends to act as a unit that exhibits rigid behaviour, mainly because it is cool and strong o Asthenosphere  Within ocean basins, sot and weak  Top portion has a temperature/pressure regime that results in a small amount of melting  Mechanically detached from the layer o Mesosphere (lower mantle)  Increased pressure counteracts the effects of higher temperature  Rocks gradually strengthen with depth  Still very hot and capable of very gradual flow  Essential component of heat transfer mechanism that drives plate tectonics o Outer core  Convective flow of metallic iron within this zone that generates Earth’s magnetic field o Inner core  Higher temperature  Material is stronger (because of immense pressure) Hydrosphere  Dynamic mass of water  Continually on the move,  Evaporating from the oceans to the atmosphere  Precipitating on the land  Returning to the ocean again  Global ocean is the most dominant feature Atmosphere  Thin and tenuous  Provides the air that we breathe  Protects us from the Sun’s intense heat and ultraviolet radiation  Energy exchange produce the effects of weather and climate Biosphere  Includes all life on Earth  Zone that extends from the ocean floor upward into the atmosphere  Plants and animals depend on the physical environment for the basics of life  Help maintain and alter physical environment The Face of the Earth  Principal divisions o Continents o Ocean basins  Significant difference is their relative levels  Boundary marked by the outer edge of the continental shelf, a gently sloping platform of continental material that extends seaward from the shore  Boundary between the continents and the deep ocean basin lies along the continental slope  Continents o Linear mountain belts o Located principally in 2 zones  Surrounding the Pacific Ocean  Eastward from the Alps o Formerly lofty peaks are now worn low, the result of millions of years of erosion o Shields, extensive and relatively flat expanses composed of largely of crystalline  Ocean Basins o Wide diversity of features (linear chains of volcanoes, deep canyons, large plateaus) o Deep ocean trenches are relatively narrow, represent only a small fraction of the ocean floor Earth as a System  System o A group of interacting, or interdependent, parts that form a complex whole o A change in one part can produce changes in any or all parts o When a volcano erupts, lava from Earth’s interior may flow out at the surface and block a nearby valley o Influences region’s drainage system by creating a lake or causing streams to change course o Large quantities of volcanic ash and gases can be emitted during an eruption might be blown high onto the atmosphere and influence the amount of solar energy o Powered by 2 sources  Sun  Drives external processes that occur in the atmosphere in the hydrosphere, circulation and erosional processes are driven by the sun  Earth’s interior  Heat remaining from when our planet formed, and heat that is continuously generated by radioactive decay powers the internal mountains The Rock System  Cycle that involves the processes by which one type of rock changes to another is called the rock cycle  Magma o Molten material that forms in certain environments of Earth’s interior where temperatures and pressures are such that rock melts o Once formed migrates upward into Earth’s crust o Cools before Earth’s surface results in crystals and minerals o Resulting in igneous rocks (once cooled on surface of Earth)  Exposed at the surface, they will undergo weathering  Influences the atmosphere slowly disintegrate and decompose rocks o Sedimentary rocks  Compacted the wright of overlying layers  When cemented as percolating water fills the pores with mineral matter o Metamorphic rock  Sedimentary rock will react to the changing environment and turn into metamorphic rock  Additional pressure changes or to still higher temperatures, it will melt, creating mama which will eventually crystallize into igneous rock LECTURE NOTES Physical Properties  Cleavage  Fracture  Hardness  Malleability  Ductility  Septicity  Flexibility  Brittleness  Elasticity: does it return to its original shape  Specific gravity: heavy or light?  Lustre: metallic, nonmetallic (vitreous, adamantine, waxy, pearly, silky)  Colour: usually not diagnostic, except for gold  Streak: what colour does it leave on a streak plate  Optical properties: double refraction  Magnetic  Crystalline form: shapes of crystals (hexagonal, rhombohedral, pyramidal)  Association with other minerals  Diagram page 64-65 o Olivine - Pyroxene - Amphibole - Mica -K-Feldspar Quartz o CA-Rich Plagioclase Feldspar - NA-rich Plagioclase Feldspar o Basalt - Gabbro o Andesite - Diorite o Rhyolite - Granite Numerical and Verbal Terms for Classic and Proclastic Sediments Size Verbal Size Pyroclastic Description >256 mm Boulder Block Volcanic breccia 64-256 mm Cobble Bomb Volcanic breccia 4-64 mm Pebble 4-32 mm Lapilli 2-4 mm Granule 0.25 – 4mm Coarse ash 0.062 – 2 mm Sand … Coarse ash 0.039 – 0.062 Silt <0.25mm Fine ash mm <0.0039 Clay … Fine ash Bedding planes  Strike and dip (angular amount) Cross – stratification Minerals: the building blocks of rocks 9/16/2012 2:52:00 PM  Mineralogy  Minerals are the building blocks of rocks  Minerals  Orderly internal structure and a definite chemical composition  Characteristics o It must occur naturally o It must be a solid at surface temperatures and pressures o It must posses an orderly internal structure that is, its atoms must be arranged in a definite pattern o It must have a definite chemical composition that can vary within specified limits o It is usually inorganic (although mineral formation can, in some cases be mediated by biological process)  Synthetic diamonds and other useful materials produced by chemists are not considered minerals  Rock o Any solid mas of mineral or mineral like matter that occurs naturally as part of our planet  Limestone is composed of impure masses of the mineral calcite  Granite occur as aggregates of different minerals o Aggregate implies that the minerals are joined in such a way that the properties of each mineral are retained  Obsidian and pumice, composed of noncrystalline, glassy substances; coal which consists of organic matter The Composition of Minerals  Elements o Every sample of the same mineral contains the same elements joined together in a consistent, repeating pattern o Gold and sulphur consist entirely of one element o More elements are joined to form chemically stable and electrically neutral compounds o Atom  The smallest part of matter that cannot be chemically split  Atomic Structure o Central part of an atom, the nucleus consists of particles called protons and neutrons o Each proton has a positive electrical charge while each neutron has no charge o Equal in size and density o Negatively charged particles are called electrons  Occupy what may be visualized as concentric, spherically shaped energy level shells o The number of electrons equals the number of protons, resulting in an electrically neutral state o Characterized by a certain number of protons o Atomic number o Atomic weight  Corresponds to the total number of protons and neutrons in its nucleus o Stability of their atoms is dictated by the number of electrons present in their energy level shells o Innermost shell can hold a maximum of 2 electrons o The outer shells can hold a maximum of 8 electrons o Nobel gases  The least chemically active elements o Combine with other atoms to achieve stable configuration o Combination is achieved through the interaction of the outermost electrons called valence electrons  Bonding o The strong attractive force linking atoms together is called a chemical bond o Chemical bonding joins two or more elements together (compound) o Ionic bonds  One or more electrons is transferred from one atom to another  One atom gives up some electrons and the other receives them  Giving up one electron- becomes positively charged  Receiving one electron - becomes negatively charged  Atoms that have an electrical charge are called ions  Negatively charged ion is called an anion  Positively charged ion is called a cation  Ionic bond is the attraction of oppositely charged ions to one another, producing an electrically neutral compound  Arrangement maximizes the attraction between ions with unlike charges, while minimizing the repulsion between ions with like charges  Ionic compounds consist of an orderly arrangement of oppositely charged ions assembled in a definite ratio that provides overall electrical neutrality  The properties of a chemical compound are dramatically different from the properties of the elements composing it  Most minerals are chemical compounds with unique properties that are very different from the elements that compose them  Most rocks, however are mixtures of minerals with each mineral retaining its own identity  Covalent Bonds o Share electrons o Silicon, readily forms covalent bonds with oxygen The Structure of Minerals  Composed of an ordered array of atoms chemically bonded to form a particular crystalline o Regularly shaped objects - crystals  Internal atomic arrangement is determined partly by the charges on the ions and by the size of the ions involved  Stable compounds - each positively charged ion is surrounded by the largest number of negative ions  Some elements are able to join together in more than one type of geometric arrangement o Two or more minerals can share the same chemical composition o Exhibit very different physical characteristics (polymorphs) o Graphite and diamond Physical Properties of Minerals  Crystal Habit o External expression of a mineral that reflects the orderly internal arrangement of atoms o When a mineral can form without space restrictions, it will develop individual crystals with well formed crystal faces o Example: quartz o The growth of individual crystals is interrupted by  Competition for space  Resulting in an intergrown mass of crystals lacking obvious crystal habit  Lustre o Is the appearance or quality of light reflected from the surface of a mineral crystal o Example: pyrite  Polished metal o Metallic lustre, nonmetallic lustre o Vitreous (glassy, silky, resinous, earthy)  Colour o Of a mineral specimen is often obvious, it is not always diagnostic o Quartz is clear and colourless o Addition of slight impurities cause colour  Streak o The colour of a mineral in its powdered form and it obtained by rubbing the mineral across a piece of unglazed porcelain known as a streak plate  Hardness o A measure of a minerals resistance to abrasion or scratching o Mohs Scale of hardness o 1 (softness) - 10 (hardest)  Cleavage o The tendency of a mineral to break along planes of weak bonding o Identified by the distinctive smooth surfaces produced when the minerals are broken o Simplest type of cleavage occurs in micas  Weak bonds in one planar direction, they cleave to form thin flat sheets o When minerals break even in multiple directions, cleavage is described as the number of planes exhibited and the angels at which they meet  Fracture o Chemical bonds of similar strength in all directions o Lacking the ability to cleave along certain planes within their crystals o Still may break or fracture in a distinctive manner o Break into splinters or fibres  Specific Gravity o A number representing the ratio of the weight of a mineral to the weight of an equal volume of water o Some metallic minerals have a specific gravity two or three times that of common rock forming minerals o Example: Glena (lead)  Specific gravity of 7.5 where as the specific gravity of 24 karat gold is 20  Other properties o Halite is ordinary salt - identify by taste o Thing sheets of mica will bend and elastically snap back o Gold is malleable and can be easily shaped o Talc feels soapy o Graphite feels greasy o Magnetite has high iron and attracted to a magnet o Transparent piece of calcite is placed over printer material, the letters appear twice -double refraction  Reacts vigorously when brought into contact with acid Mineral Classes  Minerals: Building blocks of rocks o Make up most rocks of Earth’s crust o Rock forming minerals o Eight elements make up the bulk of these minerals o Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium o Silicon and oxygen combine to form the framework of the most common mineral class - silicates  Silicates o Contains the elements oxygen and silicon o Includes one or more other common element that are needed to produce electrical neutrality o Can be extremely useful to humans o potentially hazardous to our health  The Silicon Oxygen Tetrahedron o Have the same fundamental building block - silicon oxygen tetrahedron o Tetrahedron join together to become neutral compounds through the addition of cations o Then a chemically stable structure is produced, consisting of individual tetrahedra linked by cations  More Complex Silicate Structures o Tetrahedra can link with other tetrahedra (by sharing oxygen ions) o Form single or double chains or sheet structures o Joining results from the sharing of a different number of oxygen atoms between silicon atoms in adjacent tetrahedra o In the single chain, the oxygen to silicon ratio is 3:1 o In the 3 dimensional framework this ratio is 2:1 o As more of the oxygen ions are shared, the percentage of silicon in the structure increases o Described as having a high or low silicon content based on their ratio of oxygen to silicon o Most silicate have a negative charge  Metal cations are required to bring the overall charge into balance and to serve as the mortar that holds these structures together  Common Silicate Minerals o Feldspars  The most abundant silicate minerals, composing of more than 50 percent of Earth’s crust o Quartz  The second most abundant mineral in the Earth’s crust o Each mineral group has a particular silicate structure and that a relationship exists between the internal structure of a mineral and the cleave it exhibits o Since the bond is strong, tend to cleave between the silicon oxygen structures rather than across them o Silicate minerals readily form (crystalize) when magma cools and solidifies o Cooling occurs at or near Earth’s surface o Can be formed under the extreme pressures associated with mountain building o Indicate the conditions under which they form  Ferromagnesian (Dark) Silicates o Minerals containing ions of iron or magnesium or both in their structure o Dark in colour, have a greater specific gravity o Example: olivine, pyroxenes, amphiboles, dark mica, dark garnet o Olivine  High temperature  Black to olive green, gloomy lustre  Important components of Earth’s mantle  When oxygen are linked to iron and or magnesium ions by ionic bonds  Lacks a distinct cleavage o Pyroxenes  Important components of dark igneous rocks  2 directions of cleavage  single chains of tetrahedra bonded by ions of ion and magnesium o Amphibole  A chemically complex group of minerals whose most common member is hornblende  Dark green to black  Has 2 direct cleavage  Cleavage angles in amphibole minerals reflect preferential breakage along ionic bonds between the silica chains o Biotite  Dark iron rich member of the mica group  Possesses a sheet structure that gives it excellent cleavage in one direction o Garnet  Similar to olivine in that its structure is composed of individual tetrahedra linked by metallic ions  Glassy lustre, lacks cleavage, possess conchidal fracture  Crystals that are most commonly found in metamorphic rock  Nonferomganesian (Light) Silicates o Generally light in colour o Have a specific gravity of 2.7 which is considerably less than the ferromagnesian silicates o Contain varying amounts of aluminum, potassium, calcium and sodium o Muscovite  Mica group  Light in colour and has a pearly lustre  Thin sheets  Transparent or translucent  Identified by the sparkle it gives a rock o Feldspar  Form under a very wide range of temperatures and pressures  All feldspars have similar physical properties: have 2 planes if cleavage, relatively hard, lustre that ranges form glassy to pearly  Crystals can be identified by their rectangular shape and rather smooth, shiny faces  Orthoclase  Contains potassium ions in its structure  Called potassium feldspar  Light cream to salmon pink  Plagioclase  Contains both sodium and calcium ions that can freely substitute for each other during crystallization  White to grey to blue green  Striations  Fine, parallel scratch like lines  Quartz  Silicate mineral  Silicon and oxygen  Resistant to weathering  Lacks cleavage  Exhibits conchidal fracture  Clear and colourless  Coloured by the inclusion of various ions  Forms without developing good crystal faces  Milky white, smoky grey, rose oink, amethyst purple, rock crystal clear  Clay  Used to describe a variety of complex minerals that have a sheet structure  Fine grained and can be studied only microscopically  Products of the chemical weathering of other silicate minerals  Role as a supporting material for buildings, clay inerals are extremely important to humans  Kaolinite: used to manufacture of fine chinaware and in the production of high gloss paper (textbook)  Important Nonsilicate Minerals o Carbonate minerals are much simpler structurally than silicates o Difficult to distinguish from each other o Have vitreous lustre, a hardness of 3 to 4, nearly perfect rhombic cleavage o Distinguished by using dilute hydrochloric acid o Example: Limestone  Numerous economic uses as road aggregate, building stone and main ingredient in Portland cement o Example: balite, sylvite, gypsum Igneous Rock 9/16/2012 2:52:00 PM Magma: The Parent Material of Igneous Rock  Igneous Rock o Form as molten rock cools and solidifies rocks o Magma  Is formed by the process called partial melting o Partial melting  Occurs at various levels within Earth’s crust and upper mantle to depths of 250 km o Once formed, magma body rises toward the surface because it is less dense than the surrounding rocks o Molten rock breaks through, producing volcanic eruption o Magma that reaches Earth’s surface is called lava o Lava fountain is produced when escaping gases propelled molten rock from a magma chamber o Igneous rocks that form when magma solidifies at the surface is called extrusive or volcanic  Abundant in western portions o Magma that loses its mobility before reaching the surface eventually crystalizes at depth o Igneous rocks that form at depth are called intrusive or plutonic  Body of plutonic rock is called a pluton Generating Magma from Solid Rock  Most magma originates from melting in Earth’s mantle  Plate tectonics play a major role in the generation of most magma  Greatest amount of igneous activity occurs at divergent plate boundaries, often in association with seafloor spreading  Also produced at subduction zones where oceanic lithosphere descends into mantle  Earth’s crust and mantle are composed primarily of solid, not molten, rock  Magma originates when essentially solid rock, located in the crust and upper mantle, melts  Raise the temperature above the rock’s melting point  Role of heat o Temperatures get higher as they go deeper o Average between 20 and 30 per kilometer in the upper crust o This change in temperature with depth is known as the geothermal gradient o Rocks in the lower crust and upper mantle are near their melting points, they are very hot but still essentially solid o Produce some magma o Subduction zones, friction generates heat as huge slabs of lithosphere slide past one another o Crustal rocks are heated as they descend into the mantle during subduction o Hot mantle rocks can ride and intrude crustal rocks o Rock that is near its melting point can begin to melt if the confining pressure drops or if volatiles are introduced  Role of pressure o Pressure also increases with depth o Occurs at higher temperatures at depth because of greater confining pressure o Cause a rise in the rock’s melting temperature o Reducing confining pressure lowers a rock’s melting temperature o When confining pressure drops, decompression melting is triggered o Occur when rock ascends as a result of convective upwelling, thereby moving into zones of lower pressure o Process is responsible for generating magma along ocean ridges where plates are rifting apart  Role of Volatiles o Water content and gases cause rock to melt at lower temperatures o Effect of volatiles is magnified by increased pressure o Wet rock buried at depth has a much lower melting temperature than dry rock of the same composition and under the same confining pressure o Its temperature depth, and water content determine whether it exists as a solid or liquid o Play an important role in generating magma in regions where cool slabs of oceanic lithosphere descend into the mantle o Oceanic plate sinks, both heat and pressure drive water from the subducting crustal rocks o Migrate into the wedge of hot mantle that lies above o Process is believed to lower the melting temperature of mantle rock sufficiently to generate some melt o When enough mantle derived mafic magma forms (rise toward the surface) o Have a lower density and are already near their melting temperature o Can result in some melting of the crust and the formation of a secondary silica rich or felsic magma o Magma can generate by  Heat can be added  By a magma body from a deeper source intruding and melting crustal rocks  A decrease in pressure  Without the addition of heat  Can result in decompression melting  Introduction of volatiles  Mainly water  Can lower the melting temperatures of mantle rock sufficiently to generate magma The Nature of Magma  Completely or partly molten material that, on cooling, solidifies to form an igneous rock  Consist of 3 parts o A liquid component o A solid component o A gaseous phase  Liquid portion o Called melt o Composed of mobile ions of those elements commonly found in Earth’s crust o Made up of silicon and oxygen o Has less amounts of aluminum, potassium, calcium, sodium, iron and magnesium  Solid portion o Magma are silicate minerals that have already crystallized from the melt o As magma body cools, the size and number of crystals increase  Water vapor o Carbon dioxide and sulphur dioxide are the most common volatile components of magma o Confined by the immense pressure exerted by the overlying rocks o Dissolved within the melt and will readily vaporize From Magma to Crystalline Rock  As magma cools, the ions in the melt begin to lose their mobility and arrange themselves into orderly crystalline structures  Process is called crystallization  Silicon and oxygen atoms that link t
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