Physical Geology Exam 2
8 most common elements in Earth's crust, abundance order (most to least):
46.6% Oxygen (O) 27.7% Silicon (Si) 8.1% Aluminum (Al), 5.0% Iron (Fe) 3.6% Calcium (Ca) 2.8% Sodium (Na) 2.6% Potassium (K) 2.1% Magnesium (Mg)
What does Crystal mean?
Any natural solid with an ordered, repetitive, atomic structure
Types of sedimentary environments
Continental • Dominated by stream erosion and deposition • Glacial • Wind (eolian) Marine • Shallow (to about 200 meters) • Deep (seaward of continental shelves) Transitional (shoreline) - Tidal flats - Lagoons - Deltas
Sedimentary facies
Different sediments often accumulate adjacent to one another at the same time. Each unit (facies) possesses a distinctive set of characteristics reflecting the conditions of a particular environment. Merging of adjacent facies is a gradual transition.
Turning sediment into rock
Many changes occur to sediment after it is deposited. Diagenesis—chemical, physical, and biological changes that take place after sediments are deposited • Occurs within the upper few kilometers of Earth's crust Includes: • Recrystallization—development of more stable minerals from less stable ones. • Lithification—sediments are transformed into solid rock by: o Compaction and cementation o Natural cements, which include calcite, silica, and iron oxide
4. Neutral atom: electrons 35; mass # 80
# of protons: 35 atomic #: 35 # of neutrons: 45
1. 5 characteristics Earth material needs to be a mineral:
(1) Naturally occurring (2) solid substance (3) orderly crystalline structure (4) well-defined chemical composition (5) generally inorganic.
What factors influence the texture of igneous rocks?
(1) the rate molten rock cools (2) amount of silica (3) amount of dissolved gases in the magma
Describe 4 natural hazards associated w/ volcanoes.
(1)Pyroclastic flows - hot mixtures of gas, ash, and pumice that sometimes exceed 800 degrees celcius. (2)Lahars- which can occur when a volcano is quiet. Mixtures of volcanic debris and water. (3)Explosive eruptions (4)Rapid collapse of volcanic summits and flanks
Rock or slaty cleavage
-Closely spaced planar surfaces along which rocks split -Develops in a number of ways Slate -Very fine-grained -Excellent rock cleavage -Most often generated from low-grade metamorphism of shale, mudstone, or siltstone
Gneissic
-During higher grades of metamorphism, ion migration results in the segregation of minerals. -exhibit a distinctive banded appearance. Gneiss -Medium- to coarse-grained -Banded appearance -High-grade metamorphism -Often composed of light-colored, feldspar-rich layers with bands of dark ferromagnesian minerals
Phyllite
-Gradational between slate and schist -Platy minerals not large enough to be identified with the unaided eye. -Glossy sheen and wavy surfaces -Exhibits rock cleavage -Composed mainly of fine crystals of muscovite and/or chlorite
Facies
-Metamorphic rocks that contain the same assemblage of minerals
Non-Foliated
-Metamorphic rocks that lack foliation -Develop in environments where deformation is minimal -Typically composed of minerals that exhibit equidimensional crystals Marble -Coarse, crystalline -Parent rock was limestone or dolostone -Composed essentially of calcite or dolomite crystals -Used as a decorative and monument stone -Exhibits a variety of colors Quartzite -Formed from a parent rock of quartz-rich sandstone -Quartz grains are fused together.
Schistosity
-Platy minerals are discernible with the unaided eye. -Exhibit a planar or layered structure -Rocks having this texture are referred to as schist. Schist -Medium- to coarse-grained -Platy minerals (mainly micas) predominate -The term schist describes the texture. -To indicate composition, mineral names are used (such as mica schist).
Metamorphic Textures
-size, shape, and arrangement of mineral grains
3 factors that determine the nature of a volcanic eruption and the role they play:
1) the composition of the magma 2) the temperature of the magma 3) the quantity of dissolved gases contained in the magma. The composition and temperature of the magma influence the viscosity (helps determine whether the eruption will be violent or quiet). The gases provide force to propel the liquid rock from the volcano. The quantity of gases present and the ease with which they can escape (dependent upon viscosity) determines the nature of the eruption.
Agents of Metamorphism:
1. Heat • Most important agent • Recrystallization results in new, stable minerals. • Two sources of heat: 1. Contact metamorphism—heat from magma 2. An increase in temperature with depth— geothermal gradient 2. Pressure and differential stress • Increases with depth • Confining pressure applies forces equally in all directions. • Rocks may also be subjected to differential stress, which is unequal in different directions. 3. Chemically active fluids • Mainly water • Enhances migration of ions • Aids in recrystallization of existing minerals • Sources of fluids -Pore spaces of sedimentary rocks -Fractures in igneous rocks -Hydrated minerals such as clays and micas
If Granite and Basalt are exposed at the surface in a hot, wet region...
1.) Which type of weathering will predominate? Chemical 2.) Which rock will weather faster? The basalt will weather faster because granite contains quartz which is not chemically weathered.
Evaporite deposits
A sedi rock formed of material deposited from solution by evaporation of water. Ex. Bonneville Salt Flats in Utah
Shiprock, New Mexico How did it form?
A well-known landmark in NW New Mexico, marks the subsurface "plumbing" system of a former volcano. The igneous rock is much harder than surrounding sedi. strata. Erosion gradually cut into the bedrock, spires and sharp ridges of igneous rock were left towering above the easily eroded sedi rocks. Shiprock is the central magma pipe that once fed magma upward to the volcano. Sharp ridges extending outward from the central spire are dikes representing radial cracks filled with magma injected outward from the central pipe.
Six different crystal systems
All crystalline materials are assigned to one of the crystal systems, each mineral species occurring in only one of those systems. Crystal Systems: 1. Isometric (or cubic): diamond and spinel 2. Hexagonal: - Beryl( emerald and aquamarine) - Corundum (ruby and sapphire) 3. Tetragonal: zircon 4. Orthorhombic: topaz (pictured) and chrysoberyl 5. Monoclinic: jades (pictured), moonstone - orthoclase feldspar 6. Triclinic: turquoise (pictured) and labradorite feldspar
Foliation
Any planar (nearly flat) arrangement of mineral grains or structural features within a rock. a. Slaty cleavage - literally cleavage made of thin slates of rock. b. Schistosity - when mica and chlorite crystals begin to grow. When these platy materials are large enough to be discernible with the unaided eye and exhibit a layered structure. c. Gneissic - banded in appearance.
Types of igneous textures
Aphanitic (fine-grained) texture • Rapid rate of cooling • Microscopic crystals • May contain vesicles (holes from gas bubbles) Phaneritic (coarse-grained) texture • Slow cooling • Large, visible crystals Porphyritic texture • Minerals form at diff. temperatures. • Large crystals (phenocrysts) embedded in a matrix of smaller crystals (groundmass). Glassy texture • Very rapid cooling of lava • Rock is called obsidian. Pyroclastic texture • Fragmental appearance produced by violent volcanic eruptions • Often appear more similar to sedimentary rocks Pegmatitic texture • Exceptionally coarse-grained • Form in late stages of crystallization of granitic magmas
Ring of Fire
Arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America; composed over 75% of the world's active/dormant volcanoes. This huge ring of volcanic/seismic (earthquake) activity is located at the borders of the Pacific Plate and other major tectonic plates. These volcanoes lie above subduction zones, where plates that comprise the Pacific Ocean floor are sinking beneath other oceanic plates or beneath plates carrying continents.
Silica content
As an indicator of composition • Crustal rocks exhibit a considerable range—45% to 70% As it influences magma behavior. • Granitic magmas have high silica content and are viscous. • Basaltic magmas have much lower silica content and more fluid-like behavior.
Isotope
Atoms with the same number of protons but different number of neutrons.
The largest intrusive igneous bodies? Is it tabular/massive? Concordant/discordant?
Batholith Massive Discordant
How do volcanic bombs differ from pyroclastic debris?
Blocks are made of hardened lava, and bombs are made of incandescent lava.
Andesite/Rhyolite
Both are aphanitic, but Rhyolite has more silica.
Basalt/Gabbro
Both are relatively low in silica, but Basalt is aphanitic/Gabbro is phaneritic.
Granite/Rhyolite
Both contain a relatively high concentration of silica. Granite is phaneritic/Rhyolite is aphanitic
Conglomerate/Breccia:
Both have particles bigger than 2mm. Conglomerate, largely rounded gravels Breccia, large angular particles.
Muscovite/Biotite
Both in Mica family, excellent cleavage; Muscovite is light colored w/ pearly luster; Biotite is dark and iron rich.
Minerals
Building blocks of rocks • Naturally occurring • An inorganic solid • Ordered internal molecular structure • Definite chemical composition
How is carbonic acid (H2CO3) formed in nature?
By rain dissolving some carbon dioxide as it falls through the atmosphere, more amounts released by decaying organic matter acquired as the water goes through the soil. Reacted w/ potassium feldspare? Residual clay minerals form
3 common cements for sedi rocks: How might they be identified?
Calcite, silica, and iron oxide Calcite will fizz with dilute hydrochloric acid; silica is the hardest cement producing the hardest sedimentary rocks, and sedimentary rocks with iron oxide cement have an orange or red color.
Which metamorphic rock is being described?
Calcite-rich and often nonfoliated - Marble Loosely coherent rock composed of broken fragments that formed along a fault zone - Fault Breccia A grade of metamorphism between slate and schist - Phyllite Very fine-grained and foliated; excellent cleavage - Slate Foliated and composed predominately of platy materials - Schist Composed of alternating bands of light and dark silicate minerals - Gneiss Hard, nonfoliated rock resulting from contact metamorphism - Quartzite
Volcanic Landforms
Calderas • Steep-walled depressions at the summit • Size generally exceeds 1 km in diameter Pyroclastic flows • Associated with felsic and intermediate magma • Consist of ash, pumice, and other fragmental debris • Vesuvius AD 79 A deadly Pyroclastic Flow • Material is propelled from the vent at a high speed (e.g., Yellowstone plateau). Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal fractures called fissures (e.g., Columbia River plateau, Columbia River Basalts- 1km of thickness ) Lava domes • Bulbous mass of congealed lava • Most are associated with explosive eruptions of gas-rich magma. Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber to the surface. • Volcanic necks (e.g., Shiprock, New Mexico) are resistant vents left standing after erosion has removed the volcanic cone.
Bondings
Chemical bonding * Formation of a compound by combining two or more elements Ionic bonding * Atoms gain or lose outermost (valence) electrons to form ions. * Ionic compounds consist of an orderly arrangement of oppositely charged ions. (ex. Halite - NaCl) Covalent bonding • Atoms share electrons to achieve electrical neutrality. • Generally stronger than ionic bonds • Both ionic and covalent bonds typically occur in the same compound. Other types of bonding: • Metallic bonding • Valence electrons are free to migrate among atoms. • Weaker and less common than other bonds
Clastic/Nonclastic textures Which is common to all detrital sedi rocks?
Clastic, discrete fragments and particles Nonclastic, Pattern of interlocking crystals and may resemble igneous rock. Clastic
Minerals most common in detrital sedi rocks
Clay and quartz. Why are they so abundant? Clay, from chemical weathering/Granite, resistant to chemical weathering
Most important control of soil formation? Why?
Climate Temperature and precipitation
Diagenesis
Collective term for all of the chemical, physical, and biological changesthat take place after sedis are deposited , during and after lithification. Ex. Recrystallization
Where are fissure eruptions most common?
Columbia River plateau
3 factors that control the viscosity of a given magma, which in turn, controls the nature "violence" of an eruption
Composition of the magma Temperature of the magma Dissolved gases in the magma
How is confining pressure different than differential stress?
Confining applies force evenly/Differential applies force in different directions
Nature of magma
Consists of three components: • Liquid portion = melt • Solids, if any, are silicate minerals. • Volatiles are dissolved gases in the melt, including water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2).
Contact metamorphism/Regional metamorphism: Which creates most meta rock?
Contact Metamorphism occurs when a molten igneous body 'bakes' the surrounding rock causing it to morph. Regional is produced during mountain building when large segments of Earth's crust is deformed along convergent plate boundaries. Regional
3 categories of sedimentary environments
Continental, glacial Marine, shallow (to 200m) Transitional, shoreline
Which type of plate boundary is regional metamorphism associated?
Convergent plate boundaries
What does porphyritic texture indicate about an igneous rock?
Cooled at two different rates; magma started to cool deep underground where cooling rates are slow, but before the magma was completely crystallized, it moved towards the surface where the remaining magma crystallized quickly.
Slope orientation
Direction the slope is facing
Cross-bedding/Graded bedding
Cross - layers with in sedimentary rock, inclined horizontally. Graded - single sedimentary layer gradually changes from coarse (bottom) to fine (top)
How do current ripple marks differ from oscillation ripple marks?
Current - steeper sides on the down current direction and gradual slopes on the up current side. Oscillation - back-and-forth movement of surface waves in a shallow near shore environment.
Ferromagnesian minerals in common:
Dark silicates are minerals containing iron and/or magnesium. Examples of these minerals: olivine, augite (pyroxene), hornblende (amphibole), biotite, garnet.
Describe each of the 4 basic intrusive features:
Dike - tabular, discordant pluton Sill - tabular, concordant pluton Laccolith - similar to sill, lens or mushroom shaped, arches overlying strata upward Batholith - largest intrusive body, surface exposure of 100+ square km, frequently form the cores of mountains
Composition of Minerals
Elements • Basic building blocks of minerals • Less than 100 are known (92 are naturally occurring) Atoms • Smallest particles of matter • Retains all the characteristics of an element Atomic structure • The central region is called the nucleus. - Consists of protons (+ charges) and neutrons (- charges) • Electrons - Negatively charged particles that surround the nucleus - Located in discrete energy levels called shells o Atomic Number: # of protons. o Atomic Mass: #protons + # neutrons o Valence Electrons: # e- in the outermost shell. The # of valence e- determine the group number in the periodic table. Eg. F,Cl, Br all have 7 valence e- . First e- shell have max of 2e- and subsequent e- Shells can have up to 8e- (Octect rule).
4. What do chemically active fluids play in metamorphism?
Enhances migration of Ions and aids in recrystallization of existing minerals
Which sedimentary rock is being described?
Evaporite used to make plaster - Rock gypsum Fine-grained detrital rock that exhibits fissility - Shale Primary ex. of organic sedi rock - Coal Most abundant chemical sedi rock - Limestone Dark-colored hard rock made of microcrystalline quartz - Flint or Chert Variety of limestone composed of small spherical grains - Dolostone
Common silicate minerals Light silicates
Feldspar group • Most common mineral group • Exhibit two directions of perfect cleavage at 90 degrees • Orthoclase (potassium feldspar) and plagioclase (sodium and calcium feldspar) are the two most common members. Quartz • Only common silicate composed entirely of oxygen and silicon • Hard and resistant to weathering • Conchoidal fracture • Often forms hexagonal crystals Muscovite • Common member of the mica family • Excellent cleavage in one direction • Produces the "glimmering" brilliance often seen in beach sand Clay minerals • Clay is a general term used to describe a variety of complex minerals. • Exhibit a sheet or layered structure • Most originate as products of chemical weathering.
Volcanos
General features • Openings at the summit of a volcano - Crater—A steep-walled depression at the summit, generally less than 1 km in diameter. - Caldera—A summit depression typically greater than 1 km in diameter and produced by a collapse following a massive eruption. - Vent—An opening connected to the magma chamber via a pipe.
Classification of igneous rocks/Bowen's reaction series:
Igneous rocks are classified in part by the minerals they contain. Bowen's reaction series tells us which minerals are compatible and thus are found together in igneous rocks.
How are gneisses and migmatites related?
Gneiss is heated and melted to where light bands are folded and formed of igneous or igneous looking rock while dark bands remain the same.
Granite/Diortite
Granite and Diorite are both phaneritic, but Granite has more silica.
Igneous Compositions
Granitic versus Basaltic compositions * Granitic composition - Light-colored silicates - Termed felsic (feldspar and silica) in composition - High silica (SiO2) content - Major constituent of continental crust * Basaltic composition - Dark silicates and calcium-rich feldspar - Termed mafic (magnesium and ferrum, for iron) in composition - Higher density than granitic rocks - Comprise the ocean floor and many volcanic islands Other Compositional Groups * Intermediate (or andesitic) composition - Contain 25% or more dark silicate minerals - Associated with explosive volcanic activity * Ultramafic composition - Rare composition that is high in magnesium and iron - Composed entirely of ferromagnesian silicates
What are the agents that change rock?
Heat Pressure and Differential stress Chemically active fluids
Migmatites
Highest grades of metamorphism that is transitional to igneous rocks
Why is highly viscous magma a higher threat to life and property?
Highly viscous magma may produce explosive clouds of hot ash and gases that evolve into buoyant plumes called eruption columns, because of the high viscosity of the silica-rich magma, a significant portion of the volatiles remain dissolved until the magma reaches a shallow depth, where tiny bubbles begin to form and grow. The bubbles and pressure create explosive reactions. When fluid lava erupts, the pressurized gases escape with relative ease.
Hawaiian Islands and Yellowstone are associated w/ which 3 zones of volcanism? Cascade Range? Flood basalt provinces?
Hot-spot Composite cones Deep Hot spot
Metamorphic rocks are produced from:
Igneous rocks/ Sedimentary rocks/ other Metamorphic rocks
List possible environmental effects of acid precipitation
Increases of aluminum in lakes, damages roots and leaches nutrients from soil
2 chemical sedi rocks; list and describe:
Inorganic; evaporation and chemical activity produce chemical sediments Organic; water-dwelling organisms form chemical sediments
Ionic and Covalent bonding
Ionic - oppositely charged ions, gain or lose electrons. Covalent - sharing of electrons between atoms
How does mechanical weathering add to the effectiveness of chemical weathering?
It increases the amount of surface area available
3 major components of magma:
Liquid (melt) Solid (silicate minerals that have crystallized from the melt) Gaseous phase (volatiles)
Describe the formation of Crater Lake.
Magma chamber was vacated during the eruption of Mt. Mazama. Magma ejected, leaving a big empty void under the mountain. The mountain collapsed into itself, creating a deep crater, or caldera, eventually filled with water, leaving the 2000ft deep lake we see today, is considered to be possibly active, and many think it will erupt again in the future, like many other volcanoes. Caldera found on shield volcanoes, like Kilauea? Kilauea blew its top, and due to continued eruptions, continues to reshape itself.
Lava/Magma
Magma is a substance in the mantle, under the earth's crust; Lava is that same substance but outside the Earth's crust.
Settings Intrusive/Extrusive originate:
Magma may crystallize at depth, plutonic rocks Lava solidifies at Earth's surface, volcanic rocks
How does mechanical/chemical weathering differ?
Mechanical - breaking rocks down in to smaller pieces w/o changing the composition Chemical - breaking rocks down into different substances, e.g. by dissolving it.
Melt/Volatile
Melt- mobile ions of the 8 most common elements in Earth's crust. Volatile- materials that vaporize at surface pressures.
Decompression melting
Melting that occurs as rock ascends due to drop in confining temperature.
2 ways a parent rock can affect metamorphic process:
Mineral makeup and chemical composition can determine the degree to which each metamorphic agent will cause change.
Metamorphism and Plate Tectonics
Most metamorphism occurs along convergent plate boundaries • Compressional stresses deform the edges of the plate. • Formation of Earth's major mountain belts, including the Alps, the Himalayas, and the Appalachians Large-scale metamorphism also occurs along subduction zones at convergent boundaries. • Several metamorphic environments exist here. • Important site of magma generation
Burial metamorphism
Occurs at subduction zones where one plate moves under another, deforms, melts.
The Canadian Shield
Oldest part of the North American Continent
Common silicate minerals Dark silicates
Olivine group • High temperature Fe-Mg silicates • Individual tetrahedra are linked together by Fe and Mg ions. • Forms small, rounded crystals with no cleavage Pyroxene group • Single-chain structures involving iron and magnesium • Two distinctive cleavages at nearly 90 degrees • Augite is the most common mineral in the pyroxene group. Amphibole group • Double-chain structures involving a variety of ions • Two perfect cleavages exhibiting angles of 124 and 56 degrees • Hornblende is the most common mineral in the amphibole group.
Terms used to describe igneous rock texture
Openings produced by escaping gases - Vesicles Obsidian exhibits texture - Glassy A matrix of fine crystals surrounding phenocrysts - Groundmass Crystals are too small to be seen w/o microscope - Aphanitic A texture characterized by two distinctly diff. crystal sizes - Porphyritic Coarse-grained with crystals of roughly equal size - Phaneritic Exceptionally large crystals exceeding 1 centimeter in diameter - Pegmatitic
Primary basis for distinguishing between various detrital sedi rocks:
Particle size
Chemical sedimentary
Precipitation of material occurs by: • Inorganic processes (Chemical Inorganic) • Organic processes (biochemical origin)
Physical properties of minerals
Primary diagnostic properties 1. Determined by observation or performing a simple test 2. Several physical properties are used to identify hand samples of minerals. • Crystal form • External expression of a mineral's internal structure • Often interrupted due to competition for space and rapid loss of heat • Luster • Appearance of a mineral in reflected light Two basic categories: 1. Metallic 2. Nonmetallic Other descriptive terms include vitreous, silky, or earthy. Color • Generally unreliable for mineral identification • Often highly variable due to slight changes in mineral chemistry • Exotic colorations of certain minerals produce gemstones Streak • Color of a mineral in its powdered form Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness. Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes Fracture • Absence of cleavage when a mineral is broken • Specific gravity • Weight of a mineral / weight of an equal volume of water • Average value = 2.7 Other properties: • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity
Why is heat the most important agent?
Provides the energy needed to drive the chemical reaction
Materials Extruded from a Volcano
Pyroclastic materials—fire fragments Types of pyroclastic debris • Ash and dust—fine, glassy fragments • Pumice—porous rock from frothy lava • Lapilli—walnut-sized material • Cinders—pea-sized material • Particles larger than lapilli - Blocks—hardened or cooled lava - Bombs—ejected as hot lava
Why do the cores of Earth's major mountain chains contain metamorphic rock?
Regional Metamorphism, when the rocks become heated to their boiling point they are buoyant enough to rise.
Difference between soil and regolith?
Regolith is the accumulation of weathered debris/Soil is the combination of mineral and organic matter water, and air; the portion of the regolith that supports the growth of plants.
Factors that cause different soils from same parent material or same soils from different parent material.
Residual/Transported soil
Foliated textures
Rock or slaty cleavage Schistosity Gneissic
Difference between rock and mineral:
Rocks are aggregates of 2 or more minerals
Volcanism at divergent plate boundaries is associated with which rock type? What causes rocks to melt in these regions?
Seafloor spreading, as rock rises it experiences a decrease in confining pressure and undergoes melting without the addition of heat. Constant pressure.
Compare/contrast 3 main type of volcanoes. (size, composition, shape, eruptive style):
Shield, largest on Earth. Gently sloping domes, quiet eruptions of fluid basaltic lava, contain very little pyroclastic material. Ex. Mauna Loa Cinder cones are composed almost exclusively of pyroclastics, steep-sided, and the smallest of the volcanoes. Ex. Paricutin Composite cones are alternating layers of lava (andesitic or rhyolitic in composition) and pyroclastic debris. Slopes are steeper than those of a shield volcano but gentler than a cinder cone. Associated with violent volcanic activity. Ex. Vesuvius
How does rate of cooling influence crystal size?
Slow has fewer but larger crystals/Fast has many but smaller crystals.
Soil
Soil = mineral and organic matter + water + air • Rock and mineral fragments produced by weathering (regolith) that support the growth of plants • Humus (decayed animal and plant remains) is a small, but essential component.
Igneous activity along plate margins
Spreading centers - The greatest volume of volcanic rock is produced along the oceanic ridge system. - Mechanism of spreading » Lithosphere pulls apart » Less pressure on underlying rocks » Results in partial melting of mantle » Large quantities of basaltic magma are produced. Subduction zones - Occur in conjunction with deep oceanic trenches - Descending plate partially melts. - Magma slowly moves upward. - Rising magma can form either: » An island arc if in the ocean » A volcanic arc if on a continental margin - Associated with the Pacific Ocean basin » Region around the margin is known as the "Ring of Fire" » Most of the world's explosive volcanoes are found here.
How does topography influence the development of soil?
Steep slope, more weathering less water. Bottomland, too much water.
Metamorphic Zones
Systematic variations in the mineralogy and textures of metamorphic rocks are related to the variations in the degree of metamorphism.
Igneous Rocks are classified based on
Texture and Composition • Composition can be Felsic, Intermediate,Mafic and Ultramafic. • Texture is the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals.
2 criteria used to classify igneous rock
Texture and Mineral composition
Where does hydrothermal metamorphism occur?
The emplacement of magma, when magma bodies cool and solidify, silica rich fluid (water) are driven into the hosts rocks. When host rocks are highly fractured, mineral matter contained in these hydrothermal solutions may precipitate to form more minerals.
Geothermal gradient
The gradual increase in temperature with depth in the crust. The average is 30C per km in the upper crust.
Eruptions that created Columbia Plateau differ from eruptions that create large composite cones. How?
The greatest volume of volcanic material is extruded from fractures in the crust called fissures. Rather than building a cone, these long narrow cracks tend to emit low- viscosity basaltic lavas that blanket a wide area.
Partial melting
The process most igneous rocks melt. Individual minerals have diff. melting points; most igneous rocks melt over a temp. range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.
Magmatic differentiation. How does this lead to several different igneous rocks from a single magma?
The process of generating more than one rock type from a single magma. As magma cools, the first minerals to crystallize are low in silica but rich in metals, so the residual melt will become enriched in silica and depleted in metals. If the early formed minerals are separated from the residual melt by crystal settling or "squeezing", then they will not be able to react with the melt and they will remain low silica/ high metal minerals. These early formed minerals will form a rock with a lower concentration of silica than that of the parent magma, but the residual melt will eventually crystallize to form a rock with a higher concentration of silica than that of the parent magma. Thus, rocks of different compositions can be formed from the same parent magma.
Sorting and rounding related to transported sand grains
The smaller and rounder the more mature and further it has traveled
How do tuff/volcanic breccia differ from other igneous rocks?
They are both pryoclastic and their names do not imply mineral composition.
How do geologists use index minerals?
To describe the type of metamorphic environment they belong to.
Metamorphism
Transition of one rock into another by temperatures and/or pressures unlike those in which it formed. • Progresses incrementally from low grade to high grade. • During metamorphism, the rock must remain essentially solid.
Metamorphism
Transition of one rock to another by temp and/or pressure diff from how it formed.
Scoria and how is it different from pumice?
Vesicular ejecta that is a product of basaltic magma. Pumice is lighter in color and less dense than scoria.
Compare volcanic crater to caldera:
Volcanic crater is a small depression marking the vent/exit site of erupting lava or pyroclastic material, excavated by the boring or drilling action of the erupting magma and gases. Caldera is a much larger volcanic depression, forms during or following a large outpouring of lava or pyroclastic debris.
Name the main gases released during a volcanic eruption and the role they play.
Water vapor (70%) Carbon dioxide (15%) Nitrogen (5%) Sulfur compounds (5%) Smaller amounts of Chlorine, Hydrogen, and Argon.
3 most common volatiles in magma:
Water vapor (H2O) Carbon dioxide (CO2) Sulfur dioxide (SO2)
Role of external processes in rock cycle
Weathering, Mass wasting, and erosion
Hot-spot volcanism
a concentration of heat in the mantle capable of producing magma that rises to Earth's surface; The Pacific Plate moves over a hot spot, producing the Hawaiian Islands
Viscosity
a measure of a material's resistance to flow (e.g., higher viscosity materials flow with great difficulty).
Foliation
any planar arrangement of mineral grains or structural features within a rock
Rock
any solid mass of minerals
Sedimentary rocks
are products of mechanical and chemical weathering. They comprise about 5% (by volume) of Earth's outer 10 miles. Contain evidence of past environments: • Provide information about sediment transport • Often contain fossils Are important for economic considerations because they may contain: • Coal • Petroleum and natural gas • Sources of Fe, Al, and Mn
Magmatic Differentiation
causes different lava-ash compositions from the same volcano at different times.
valence electrons
determines the group number in the periodic table
Sediment originates
from mechanical and/or chemical weathering
Origin of Magma
from solid rock • Role of heat - Temperature increases in the upper crust (geothermal gradient) average between 20 oC to 30 oC per kilometer. - Rocks in the lower crust and upper mantle are near their melting points. - Additional heat may induce melting. • Role of pressure - Increases in confining pressure increases a rock's melting temperature. - When confining pressures drop, decompression melting occurs. • Role of volatiles - Volatiles (primarily water) cause melting at lower temperatures. - Important factor where oceanic lithosphere descends into the mantle
Magma
melting that occurs at various levels w/in the Earth's crust and upper mantle to depths of 250 km (150 m)
Igneous rocks form as
molten rock cools and solidifies
List and describe 3 mechanism mineral develop a preferred orientation:
rotation recrystallization change in grain shape
Evolution of Magmas
• A single volcano may extrude lavas exhibiting very different compositions. • Bowen's reaction series • Minerals crystallize in a systematic fashion based on their melting points. • During crystallization, the composition of the liquid portion of the magma continually changes. • Processes responsible for changing a magma's composition • Magmatic differentiation • Separation of a melt from earlier formed crystals • Assimilation • Changing a magma's composition by incorporating surrounding rock bodies into a magma • Processes responsible for changing a magma's composition • Magma mixing • Two chemically distinct magmas may produce a composition quite different from either original magma.
Rock
• A solid aggregate of minerals
Intraplate volcanism
• Activity within a tectonic plate • Associated with plumes of heat in the mantle • Form localized volcanic regions in the overriding plate called a hot spot • Produces basaltic magma sources in oceanic crust (e.g., Hawaii and Iceland) • Produces granitic magma sources in continental crust (e.g., Yellowstone National Park)
Igneous rocks—intermediate rocks
• Andesite - Volcanic origin - Aphanitic texture • Diorite - Plutonic equivalent of andesite - Coarse-grained
Igneous rocks—basaltic rocks
• Basalt - Volcanic origin - Aphanitic texture - Composed mainly of pyroxene and calcium-rich plagioclase feldspar - Most common extrusive igneous rock
Other metamorphic environments
• Burial metamorphism o Associated with very thick sedimentary strata o Required depth varies depending on the prevailing geothermal gradient. • Metamorphism along fault zones o Occurs at depth and high temperatures o Pre-existing minerals deform by ductile flow. • Impact metamorphism o Occurs when high-speed projectiles, meteorites, strike Earth's surface; are called impactiles.
Index minerals and metamorphic grade
• Changes in mineralogy occur from regions of low-grade metamorphism to regions of high-grade metamorphism. • Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form.
Two major textures are used in the classification of sedimentary rocks:
• Clastic o Discrete fragments and particles o All detrital rocks have a clastic texture. • Nonclastic o Pattern of interlocking crystals o May resemble an igneous rock
Chief constituents of detrital rocks include:
• Clay minerals • Quartz • Feldspars • Micas Particle size is used to distinguish among the various rock types.
Igneous rocks—pyroclastic rocks
• Composed of fragments ejected during a volcanic eruption • Varieties - Tuff = ash-sized fragments - Volcanic breccia = particles larger than ash
Metamorphic Environments/Settings:
• Contact or Thermal Metamorphism—driven by a rise in temperature within the host rock o The zone of alteration (aureole) forms in the rock surrounding the magma. o Most easily recognized when it occurs at or near Earth's surface • Hydrothermal metamorphism—chemical alterations from hot, ion-rich water circulate through fissures and cracks that develop in rock o Most widespread along the axis of the mid-ocean ridge system • Regional metamorphism - occurs during mountain building o Produces the greatest volume of metamorphic rock o Rocks usually display zones of contact and/or hydrothermal metamorphism.
Differences in crystallization of magma results in different textures
• Cooling of magma results in the systematic arrangement of ions into orderly patterns. • Silicate minerals result from crystallization in a predictable order. (Bowen's Reaction Series) • Texture is the size and arrangement of mineral grains.
Igneous rocks are composed primarily of silicate minerals.
• Dark (or ferromagnesian) silicates - Olivine, pyroxene, amphibole, and biotite mica • Light (or nonferromagnesian) silicates - Quartz, muscovite mica, and feldspars
3 types of Sedimentary Rocks, with classification are based on the source of the material.
• Detrital rocks—transported sediment as solid particles • Chemical Inorganic rocks—sediment/precipitated material that was once in solution • Biochemical rocks: rock material of biological origin (fossils)
Types of intrusive igneous features
• Dike—a tabular, discordant pluton • Sill—a tabular, concordant pluton (e.g., Palisades Sill in New York) • Laccolith - Similar to a sill - Lens or mushroom-shaped mass - Arches overlying strata upward • Batholith - Largest intrusive body - Surface exposure of 100+ square kilometers (smaller bodies are termed stocks) - Frequently form the cores of mountains
Igneous rocks—mafic rocks
• Gabbro - Intrusive equivalent of basalt - Phaneritic texture consisting of pyroxene and calcium-rich plagioclase - Significant percentage of the oceanic crust
Sedimentary Environments
• Geographic setting where sediment is accumulating • Determines the nature of the sediments that accumulate (grain size, grain shape, etc.)
Plate Tectonics and Igneous Activity
• Global distribution of igneous activity is not random. • Most volcanoes are located within or near ocean basins (at subduction zones). • Basaltic rocks are common in both oceanic and continental settings, whereas granitic rocks are rarely found in the oceans.
Igneous rocks—granitic rocks
• Granite - Phaneritic texture; Over 25% quartz, about 65% or more feldspar - Very abundant—often associated with mountain building - The term granite includes a wide range of mineral compositions. • Rhyolite - Extrusive equivalent of granite - May contain glass fragments and vesicles - Aphanitic texture - Less common and less voluminous than granite • Obsidian - Dark colored - Glassy texture • Pumice - Volcanic - Glassy texture - Frothy appearance with numerous voids
Partial melting and magma formation
• Incomplete melting of rocks is known as partial melting. • Formation of basaltic magmas - Most originate from partial melting of mantle rocks at oceanic ridges - Large outpourings of basaltic magma are common at Earth's surface. • Formation of andesitic magmas - Produced by interaction of basaltic magmas and more silica-rich rocks in the crust - May also evolve by magmatic differentiation • Formation of granitic magmas - Most likely form as the end product of crystallization of andesitic magma - Granitic magmas are more viscous than other magmas—tend to lose their mobility before reaching the surface. - Produce large plutonic structures
Common chemical sedimentary rocks
• Limestone o Most abundant chemical rock o Composed chiefly of the mineral calcite o Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms). o Inorganic limestones include travertine and oolitic limestone. • Dolostone o Typically formed secondarily from limestone. • Chert o Microcrystalline quartz o Varieties include flint and jasper. • Evaporites o Evaporation triggers deposition of chemical precipitates. o Examples include rock salt and rock gypsum. • Coal o Different from other rocks because it is composed of organic material. o Stages in coal formation (in order): 1. Plant material 2. Peat 3. Lignite 4. Bituminous
Emplacement of magma
• Magma at depth is much less dense than the surrounding rock. - Increased temperature and pressure causes solid rock to deform plastically. - The more buoyant magma pushes aside the host rock and forcibly rises in the Earth as it deforms the "plastic" host rock. • At more shallow depths, the host rock is cooler and exhibits brittle deformation. - Movement of magma here is accomplished by fractures in the host rock and stoping. • Melting and assimilation of the host rock is greatly limited by the availability of thermal energy.
Structure of Minerals
• Minerals consist of an orderly array of atoms chemically bonded to form a particular crystalline structure. • The internal atomic arrangement in ionic compounds is determined by ionic size. • Ions can be replaced in a crystal structure by other ions with similar ionic charge and ionic size • Polymorphs • Minerals with the same composition but different crystalline structures • Examples include diamond and graphite » Phase change is when one polymorph changes into another.
Silicates
• Most important mineral group • Comprise most rock-forming minerals • Very abundant due to large percentage of silicon and oxygen in Earth's crust • Silicon-oxygen tetrahedron • Fundamental building block • Four oxygen ions surrounding a much smaller silicon ion
Intrusive Igneous Activity
• Most magma is emplaced at depth in the Earth. • An underground igneous body, once cooled and solidified, is called a pluton. • Classification of plutons • Shape - Tabular (sheet-like) - Massive • Orientation with respect to the host (surrounding) rock - Discordant—cuts across sedimentary rock units - Concordant—parallel to sedimentary rock units
Parent Rock
• Most metamorphic rocks have the same overall chemical composition as the original parent rock. • Mostly, mineral makeup determines the degree to which each metamorphic agent will cause change.
Metamorphism at subduction zones
• Mountainous terrains along subduction zones exhibit distinct linear belts of metamorphic rocks. -High-pressure, low-temperature zones nearest the trench -High-temperature, low-pressure zones further inland in the region of igneous activity
Mineral Groups
• Nearly 4000 minerals have been named • Rock-forming minerals • Common minerals that make up most of the rocks of Earth's crust • Only a few dozen members • Composed mainly of the eight elements that make up more than 98% of the continental crust.
Examples of foliation:
• Parallel alignment of platy and/or elongated minerals • Parallel alignment of flattened mineral grains and pebbles • Compositional banding • Slaty cleavage where rocks can be easily split into thin, tabular sheets
Factors controlling soil formation
• Parent material • Residual versus transported soil • Time • Amount of time for soil formation varies depending on geologic and climatic conditions. • Climate • Most influential control of soil formation • Key factors are temperature and precipitation. • Plants and animals • Influence the soil's physical and chemical properties • Topography • Steep slopes often have poorly developed soils. • The optimum terrain is a flat-to-undulating upland surface.
General Characteristics of Magma
• Parent material of igneous rocks • Forms from partial melting of rocks • Magma at surface is called lava. • Rocks formed from lava are extrusive, or volcanic rocks. • Rocks formed from magma at depth are intrusive, or platonic rocks.
Soil erosion
• Part of the natural recycling of all Earth materials • Natural rates of soil erosion depend on: - Soil characteristics - Climate - Slope - Type of vegetation • In many regions, soil erosion is much greater than the rate of soil formation. • Sedimentation and chemical pollution - Related to excessive soil erosion - Occasionally, soil particles are contaminated with pesticides.
Sedimentary Structures
• Provide information useful in the interpretation of Earth's history • Types of sedimentary structures • Strata, or beds (most characteristic of sedimentary rocks) • Bedding planes that separate strata • Cross-bedding • Graded beds • Ripple marks • Mud cracks • Fossils
Factors affecting crystal size:
• Rate of cooling • Slow rate = fewer but larger crystals • Fast rate = many small crystals • Very fast rate forms glass. • Percentage of silica (SiO2) present • Dissolved gases
Foliation can form in various ways, including:
• Rotation of platy and/or elongated minerals • Recrystallization of minerals in the direction of preferred orientation • Changing the shape of equidimensional grains into elongated shapes that are aligned
Common detrital sedimentary rocks
• Shale o Mud-sized particles in thin layers that are called lamina o Most common sedimentary rock • Sandstone o Sand-sized particles o Forms in a variety of environments o Predominant mineral = quartz • Conglomerate and breccia o Both are composed of particles greater than 2 millimeters in diameter. o Conglomerate consists largely of rounded gravels. o Breccia is composed mainly of large angular particles.
Types of volcanoes
• Shield volcano - Broad, slightly dome-shaped - Composed primarily of basaltic lava - Generally covers large areas - Produced by mild eruptions of large volumes of lava - Mauna Loa in Hawaii is a good example. • Cinder cone - Built from ejected lava (mainly cinder-sized) fragments - Steep slope angle - Rather small size - Frequently occur in groups • Composite cone (stratovolcano) - Most are located adjacent to the Pacific Ocean (e.g., Mount Fujiyama and Mount St. Helens). - Large, classic-shaped volcano (thousands of feet high and several miles wide at base) - Composed of interbedded lava flows and layers of pyroclastic debris - Most violent type of activity (e.g., Mount Vesuvius) - Often produce nueé ardentes • Fiery pyroclastic flows made of hot gases, infused with ash and other debris • Move down the slopes of a volcano at speeds up to 200 km per hour - May produce a lahar, which is a volcanic mudflow
Joining silicate structures
• Single tetrahedra are linked together to form various structures including: • Isolated tetrahedra • Ring structures • Single- and double-chain structures • Sheet or layered structures • Complex three-dimensional structures
Soil profile
• Soil-forming processes operate from the surface downward. • Vertical differences are called horizons, which are zones or layers of soil. • O horizon—organic matter • A horizon—organic and mineral matter • High biological activity • O and A horizons make up the topsoil • Soil-forming processes operate from the surface downward. • Vertical differences are called horizons, which are zones or layers of soil. • O horizon—organic matter • A horizon—organic and mineral matter • High biological activity • O and A horizons make up the topsoil • E horizon—little organic matter • Zone of eluviation and leaching • B horizon—zone of accumulation • C horizon—partially altered parent material • Collectively, the O, A, E, and B horizons make up the solum, or "true soil."
Rates of Weathering/Factors affecting weathering
• Surface area • Rock characteristics - Rocks containing calcite (marble and limestone) readily dissolve in weakly acidic solutions. - Silicate minerals weather in the same order as their order of crystallization. • Climate - Temperature and moisture characteristics - Chemical weathering is most effective in areas of warm, moist climates. • Differential weathering - Rocks do not weather uniformly due to regional and local factors. - Results in many unusual and spectacular rock formations and landforms
Factors affecting viscosity
• Temperature—hotter magmas are less viscous. • Composition—silica (SiO2) content - Higher silica content = higher viscosity (e.g., felsic lava such as rhyolite). - Lower silica content = lower viscosity or more fluid-like behavior (e.g., mafic lava such as basalt) • Dissolved gases - Gases expand within magma as it nears Earth's surface due to decreasing pressure. - The violence of an eruption is related to how easily gases escape from magma. • In summary, factors affecting viscosity: • Fluid basaltic lavas generally produce quiet eruptions. • Highly viscous lavas (rhyolite or andesite) produce more explosive eruptions.
Crystal Systems and their function in determination
• The optical, physical and all other properties of a mineral are determined by its chemical composition and crystal structure. Minerals having a definite crystal structure are called crystalline, while those with no regular internal arrangement are known as amorphous. One of the few natural amorphous substances used as a gem is opal, but glass and several other imitations are also amorphous.
Weathering
• Two types: 1. Mechanical—breaking of rocks into smaller pieces (increase of surface area) • Types of mechanical weathering - Frost wedging - Unloading (Old Man of the Mountain) - Thermal expansion (Desert environments) - Biological activity (Root wedging) 2. Chemical weathering---Breaks down rock components and internal structures of minerals. • The most important agent is water. - Responsible for transport of ions and molecules involved in chemical processes • Major processes of chemical weathering - Dissolution - CaCO3 + (H+ +HCO3-) -- Ca2+ + 2 HCO3- Aided by small amounts of acid in the water - Oxidation - 4Fe + 3O2 - 2Fe2O3(Hematite) Any reaction when electrons are lost from one element - Hydrolysis - K-Feldespar + carbonic acid + water - Kaolinite (clay) + K ion + Bicarbonate ion + silica o The reaction of any substance with water. o A hydrogen ion attacks and replaces other ions. • Alterations caused by chemical weathering Decomposition of unstable minerals Formation or retention of stable materials Physical changes such as the rounding of corners or edges
Non-silicate minerals
• Typically divided into classes based on anions • Comprise only 8% of Earth's crust • Often occur as constituents in sedimentary rocks • Carbonates • Primary constituents in limestone and dolostone • Calcite (CaCO3) and dolomite CaMg(CO3)2 are the two most important carbonate minerals. • Many nonsilicate minerals have economic value. • Examples: • Hematite (oxide mined for iron ore) • Halite (halide mined for salt) • Sphalerite (sulfide mined for zinc ore) • Native copper (native element mined for copper)
Classifying soils
• Variations in soil formation over time and distances has led to a great variety of recognized soil types. • Groups have been established using common characteristics. • In the United States, a system was devised, and called the Soil Taxonomy. • Soil Taxonomy • Emphasis is placed on physical and chemical properties. • Six hierarchical categories exist. • Descriptive names are derived from Latin and Greek. • 12 basic soil orders are recognized.
Earth's External Processes
• Weathering—the physical breakdown and chemical decomposition of rock • Mass wasting—the transfer of rock and soil downslope under the influence of gravity • Erosion—the physical removal of material by water, wind, ice, or gravity
