GEOL 1313 Notes
GEOL 1313 Notes GEOL 1313 - 001
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Date Created: 06/09/16
Chapter 1 Geology: the science that pursues an understanding of planet Earth. Physical geology: examines Earth materials and seeks to understand the many processes that operate on our planet. Historical geology: understanding of the origin of Earth. People & the Environment More people now live in the city than in rural areas. People are aﬀected by geologic hazards and rely on natural resources. Geologic hazards are the natural processes that adversely aﬀect people. The nature of Earth has been a focus of study for centuries. Catastrophism: Theories that Earth has been shaped by catastrophes. Uniformitarianism: The physical, chemical, and biologic laws that operate today have operated throughout the geological past. The Development of Geology The magnitude of geological time involves millions and billions of years. Earth is 4.6 billion years old. Processes are very gradual. The Nature of Scientiﬁc Inquiry Science assumes the natural world is consistent and predictable. The goal is to discover patterns in nature and use the knowledge to make predictions. How or why things happen are explained using: Hypothesis: A tentative or untested explanation. Hypothesis are accepted, modiﬁed, or rejected. Data and results are shared with the scientiﬁc community. This assumption is proven through tests/experiments. Theory: A well tested and widely accepted view that the scientiﬁc community agrees best explains certain observable facts. A View of Earth Earth is a small, self-contained planet Earth's four spheres are: Hydrosphere: Water portion (seas, lakes) Atmosphere: Gaseous envelope Geosphere: the solid earth (what we study in geology) Biosphere: All plant/animal life Earth as a system: Earth system science: Aims to study Earth as a system composed of numerous interacting parts. Employs an interdisciplinary approach to solve global environment problems. (global warming, overpopulation) Early Evolution of Earth The universe began with the Big Bang. Earth and the other planets formed at the same time out of the same material as the Sun. The Nebular Theory: Proposes that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula. Nebular Theory: The solar nebula consisted of hydrogen and helium, in addition to microscopic dust grains. A disturbance caused the solar nebula to slowly contract and rotate. The solar nebula assumed a ﬂat, disk shape with the protosun (Pro-Sun) at the center. Inner Planets: Formed from metallic and rocky substances. Mercury, Venus, Earth, Mars. Outer Planets: Formed from ice and gases. Neptune, Jupiter, Saturn, Uranus Formation of Earth's Layered Structure Metals sank to the center due to density. Molten rock rose to produce primitive crust. (chemical segregation) The earliest primitive crust was lost to erosion and weathering. A primitive atmosphere evolved from volcanic gases. 3 Basic Divisions of Earth's Interior Crust: Earth's thin, rocky, outer skin, divided into the continental and oceanic crust. Diﬀerences include age, density, and composition. Mantle: Approximately 2,900 kilometers thick and composed of peridotite. Core: Composed of iron and nickel alloy. Earth's Internal Structure Additionally, Earth is divided into two diﬀerent zones based on physical properties. Lithosphere: Rigid, outer layer of Earth that consist of the crust and the upper mantel. Asthenosphere: The soft, weak layer below the lithosphere. Transition zone: A zone marked by a sharp increase in density below the asthenosphere. Lower Mantle: Zone of strong, very hot rock Outer Core: liquid outer layer of the core Inner Core: Solid inner layer This happens due to the pressure that the outer core gives oﬀ to the inner core. Chapter 2 1/25/16 Igneous: First rock, cooling and solidiﬁcation of magma. (molten rock) Sedimentary: Derived from preexisting rock.Accumulate in Earth's surface. Metamorphic rock: Formed by changing rock Density allows the magma to rise. Earth's surface is divided into continents and ocean basins. The diﬀerence between these two areas is relative levels. Elevation diﬀerence is a result of diﬀerences between density and thickness. Continents are relatively ﬂat plateaus approximately 8 kilometers above sea level composed of granite rock. The average depth of ocean basins composed of basaltic rock. Features of continents include mountain belts, crayons, shield, and stable platforms. Mountain belts: the most prominent features of continents. Cartoons: the stable interior of the continents. Shields: the expansive, ﬂat regions of deformed crystalline rocks in the cratons. Stable Platforms: Features of the ocean ﬂoor include continental margins, deep ocean basins, and oceanic ridges. Continental margins are the portion of the sea ﬂoor adjacent to major land masses. The continental shelf is a gently sloping region. Continental slope: steep dropoﬀ Continental rise: thick wedge of sediment. Deep ocean basins are the portions of the sea ﬂoor between the continental margins and the oceanic ridges. Abyssal plain is a ﬂat feature of the deep ocean basin. Deep ocean trenches are deep and relatively narrow depressions. Sea mounts are small volcanic structures that dot the ocean ﬂoor. Oceanic ridges are the most prominent feature on the ocean ﬂoor and are composed of igneous rock that has been fractured and uplifted. Continental Drift: Plate Tectonics Before 1960, many many geologists believe that continents' and ocean basins' positions were ﬁxed. Continental drift, a hypothesis designed to explain continental movement, was ﬁrst proposed in the 20th century, but initially rejected by North American geologists. Alfred Wegener: First proposed continental drift hypothesis in 1915. Published The Origin of Continents and Oceans. Evidence used in support of continental drift hypothesis: Jigsaw Puzzle Evidence: The continents seem to ﬁt together (near match) Fossil evidence: Identical fossil organism are found on continents now separated by vast oceans. (rock types, and geologic features, ancient climates) Objections Wegener incorrectly suggested that the gravitational forces of the Moon and Sun were capable of moving the continents. Incorrect: the continents broke through the ocean crust. Strong opposition to this hypothesis from all areas of the scientiﬁc community. Following World War II, oceanographers learned much about the seaﬂoor. The oceanic ridge system winds through all of the major oceans. There is no oceanic crust older than 180 million years old. Sediment accumulation in the deep ocean was relatively minor. This led to the theory of plate tectonics. Rigid Lithosphere: Overlies weak asthenosphere. The lithosphere is Earth's strong, outer layer. The asthenosphere is a hotter, weaker region of the mantle under lithosphere. Earth's Major Plates The lithosphere is broken into approximately two dozen smaller sections called lithospheric plates. Plates are in constant motion. Plate boundaries: most interactions among individual plates occur along their boundaries. Types of plate boundaries: Divergent (MOR) Mid-Oceanic Ridges Oceanic Ridge Rio Grande Rift Valley Convergent Plates: Move together Form subduction zones 1) Continent/Oceanic 2) Continent/Continent 3) Oceanic/Oceanic Transform Conservative Margins (San Andreas Fault) New ocean ﬂoor is generated as two plates move apart. Most divergent plates boundaries are located along the crests of oceanic ridges. Oceanic ridges and seaﬂoor spreading Well developed divergent plate boundaries the seaﬂoor is elevated. Along the crest of the ridge is a canyon like feature called a rift valley. Seaﬂoor spreading is the mechanism that operates along the ridge to create new ocean ﬂoor. Spread Rates AVERAGE 5 cm/year Mid Atlantic Ridge 2cm/year East Paciﬁc Rise 15 cm/year Continental Rifting Occurs when a divergent plate boundary occurs within a continent. A land mass will split into two or more smaller segments. A continental rift, an elongated depression will develop within the region. Convergent Plate Boundaries Two plates move toward each other at these destructive plate margins. Where the older portions of ocean plates are returned to the mantle. Oceanic-Oceanic Convergence One descends beneath the other, partial melting initiates volcanic activity. Continental-Continental Convergence Two continents together, less dense, buoyant continental lithosphere does not subduct. The resulting collision produces mountains. Transform Plate Boundaries Plates slide past one another and no lithosphere is created or destroyed. Most join two segments of an oceanic ridge system along breaks in the oceanic crust known as fracture zones. Transform faults can also move ridge crests toward subduction zones. A few transform faults can cut through continental crust. Examples: The San Andreas Fault plate boundary, Alpine Fault in New Zealand. Evidence from Ocean Drilling Some of the most convincing evidence has come from drilling into the ocean ﬂoor. Age of the deepest sediments: The oldest sediments are the furthest. The thickness of ocean ﬂoor sediments veriﬁes seaﬂoor spreading. Sediments are almost absent on the ridge crest. Hot Spots and Mantle Plumes A mantle plume is a cylindrically shaped upwelling of hot rock. The surface expression of a mantle plume is a hotspot, which is an area of volcanism. Hawaii Islands (hotspot) When a plate moves over a hotspot, there will be a chain of volcanoes. Paleomagnetism Ballistic rocks contain magnetite, an iron rich mineral aﬀected by Earth's magnetic ﬁeld. When the basalt cools below the Curie point, the magnetite aligns toward the position of the North Pole. Apparent Polar Wandering The apparent movement of the poles indicates the continents have moved. The magnetite is "frozen" in position. Magnetic Reversal and Seaﬂoor Spreading During a magnetic reversal, Earth's magnetic ﬁeld periodically reverses polarity. North Pole becomes South Pole. This happens due to the convection generated by the core. Geologic Evidence for Plate Motion By knowing the age of the seaﬂoor and the distance from the spreading center, an average rate of plate motion can be calculated. Mantel plume leads leads to divergent plates Measuring Plate Motion from Space Using GPS to measure various points on Earth's surface. GPS data are collected over various areas repeatedly for many years to establish plate motion. How does plate motion aﬀect plate boundaries? Total does not change despite movement along plate boundaries. Plates can grow or shrink depending on the plate boundaries surrounding each plate. The African Plate is bounded by divergent boundaries and is growing. Researches agree that convective ﬂow in the mantle is the basic driving force of plate tectonics. Density Higher heat ... Less Dense (lighter) Lower heat ... More Dense (heavier) Forces that Drive Plate Motion Subduction Cold Oceanic Lithosphere Slabpull Force Models Convection in the mantle (warm), buoyant rocks rise and cool, dense rocks sink. Underlying driving force of plate tectonics slab pull/ridge push forces of plate tectonics are part of the same system as mantle convection. Convective ﬂow is a major force for transporting heat away from the interior of the Earth. Chapter 10 1/27/16 Crustal Deformation Deformation (physical change): All changes in the shape or position of a rock bod in response to stress. Rock or geologic structure are the features that result from forces generated by the interaction of tectonic plates. This includes: folds, faults, and joints. Stress: Force that Deforms Rocks Flowing, folding, fracturing, or faulting. Magnitude is a function of the amount of force applied to a given area. Stress applied uniformly in all directions is conﬁning pressure. Stress applied unequally in diﬀerent directions is called diﬀerential stress. Types of Stress Compressional stress: squeezes a rock and shortens a rock body. Tensional stress: pulls apart a rock unit and lengthens it. Shear stress: produces a motion similar to slippage that occurs between individual playing cards when the top of the stack is moved relative to the bottom. Strain: a change in shape of a rock caused by diﬀerential stress. Strained bodies lose their original conﬁguration during deformation. Deformation Stress = Force Strain = Change Strain is the result of the stress. Original conﬁguration = size, shape Elastic, Brittle, and Ductile Deformation Elastic: the rock returns to nearly its original size and shape when the stress is removed. Once the elastic limit (strength) of rock is surpassed, it either bends (ductile deformation) or breaks (brittle deformation). Bend = Ductile Break = Brittle Factors that aﬀect rock strength Temperature: Higher = ductile (bend) Cooler = brittle (break) Conﬁning pressure: squeezes rocks, making them stronger and harder to break (ductile) Rock type: Crystalline igneous rocks generally experience brittle deformation (hard rock) Sedimentary and metamorphic rocks with zones of weakness generally experiences ductile deformation. Time: Forces applied over a long period of time generally result in ductile deformation. Ductile vs Brittle Deformation and Resulting Rock Structures Joints are cracks from the rock being stretched and pulled apart. Folds are evidence that rocks can bend without breaking. High temperature usually indicates high pressure. Reversely low temperature signiﬁes low pressure. Folds: Ductile Deformation Rocks are bent into a series of wave like undulations called folds. Most folds are compressional stress that result in shorten and thickening of the crest. 3 Kinds of Folds Anticlines are upfolded; arches are the oldest. Synclines are downfolded; troughs are the youngest. Depending on the orientation, anticlines and synclines can be described as: symmetrical: mirrored images asymmetrical: the limbs of the fold are not identical overturned: one or both beyond vertical Plunging the axis Domes & Basins Compressional force (anticline); the oldest is at the center. Basins are downwarped circular features. Youngest rocks are in the center (syncline). Monoclines are large, steplike folds in otherwise horizontal sedimentary strata. As blocks of basement rocks are displaced upward, the ductile sedimentary strata drape over them. Faults are fractures in rocks, along which displacement has occurred. Sudden movement along faults are the cause of most earthquakes. Polished, smooth surfaces called slicken slides; provide evidence for movement along fault. Dip Slip Faults occur when movement is parallel to inclination. There are three kinds of dip slip faults: Normal: hanging wall down, footwall up (tensional stress) Reverse: hanging wall moving up relative to footwall (compressional stress) Thrust: faults have an angle less than 45° so the overlying plate is almost horizontal (shear stress) example: Franklin Mountains Hanging wall is rock surface above the fault. The footwall is the rock surface below the fault. Strike Slip Fault: placement that is horizontal and parallel to the strike of the fault. Right Lateral: As you face the fault, the side of the fault moves to the right. Left Lateral: As you face the opposite side of the fault, the fault moves to the left. Large strike slip faults that cut through the crust to accommodate plate motion are called transform faults. Oblique Slip Faults exhibit both a strike slip and a dip slip movement. This kind of fault exhibits both tensional and shear stress at the same time. Joints are fractures in a rock where there has been no rock movement. Most joints appear in parallel groups. They are parallel due to the direction of the stress. A geologist identiﬁes and describes the dominant rock structures in a region using a limited number of outcrops (sites where bedrock is exposed at the surface.) Work is aided by aerial photography, satellite imagery, GPS, and seismic reﬂection proﬁling. Strike and Dip Sedimentary rocks that are inclined or bent indicate that the layers were deformed following deposition. Strike is deviation from North. For example: 20° from North. Compassion direction of the line produce by the intersection of inclined rock layers or fault with a horizontal plane. Dip The angle of inclination of the surface of a rock unit or fault measured from a horizontal plane. Include both an inclination and a direction toward which the rock is inclined. Minerals Deﬁnition of a Mineral Deﬁnition of a Rock Atoms: Smallest particles of matter that cannot be chemically split Composed of: Protons Charge of +1 Neutrons Charge of 0 Electrons Charge of -1 Atomic Number: Number of protons in the nucleus of an atom Determines the atom’s chemical nature Element: A group of the same kind of atoms Approximately 90 natural elements and several synthesized Ionic Bonding Atoms gain or lose outermost (valence) Covalent Share valence electrons Metallic Bonding Valence electrons are free to migrate Primary Diagnostic Properties Determined by observation or performing a simple test Several physical properties are used to identify hand samples Optical Properties 1. Luster: Appearance of a mineral in reﬂected light (how shiny) Metallic Dark colored Opaque Heavy (high density, speciﬁc gravity) Nonmetallic vitreous glassy luster dull or earthy luster pearly silky Example: Galena displays a metallic luster, submetallic luster on the surface 2. Optical Properties: Ability to transmit light Opaque: No light is transmitted Translucent: light, but no image is transmitted Transparent: light 3. Color: Generally unreliable for mineral identiﬁcation Often highly variable due to impurities to slight changes in mineral chemistry Quartz (rose, smokey, white) Fluorite (yellow, rose, purple, green, etc) Feldspar: ﬂesh colored, always 4. Streak: Color of a mineral in its powdered form Not every mineral produces a streak when rubbed across a streak plate (dash for streak) Although the color of a mineral is not always helpful in identiﬁcation, the streak which is the color 5. Crystal Shape or Habit: Characteristic shape of a crystal or aggregate of crystals Fibrous Bladed Banded Cubic Mineral strength How easily minerals break or deform under stress More descriptive Under pressure how it breaks Hardness Resistance of mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness (1-10) 1. Talc 2. Gypsum 2.5 Fingernail 3. Calcite 3.5 Copper Penny 4. Fluorite 4.5 Wire nail 5. Apatite 5.5 Glass & Knife Blade 6. Orthoclase 6.5 Streak plate 7. Quartz 8. Topaz 9. Corundum 10. Diamond 80x harder than talc Typically ask for more or less than 5.5 Comparison of Mohs scale and an absolute scale Tenacity The mineral’s resistance to break or deforming Brittle minerals (such as those with ionic bonds) will shatter into small pieces Malleable minerals (such as those with metallic bonds) are easily hammered into diﬀerent shapes Sectile minerals, such as gypsum and talc, can be cut into thin shavings Elastic minerals, such as the micas will bend and snap back to their original shape Cleavage Tendency to break along planes of weak bonding Produces smooth, ﬂat, natural surfaces Sometimes so small you cannot see it with your naked eye Described by Number of planes Angles between adjacent planes Resulting geometric planes cleavage in one direction muscovite cleavage in two directions at 90 angle example: feldspar Cleave in two directions not at 90 angle example: hornblende cleavage in three direction at 90 angle example: halite cleavage in three directions not at 90 example: calcite Cleavage in four direction example: ﬂuoride ionic covalent bonds in same mineral Fracture Absence of cleave when a mineral is broken irregular fractures conchoidal fractures **** QUIZ quartz (glass) splintery fractures ﬁbrous fractures feldspar is the most common mineral second is quartz (hardness, conchoidal, common) 6. Density and Speciﬁc Gravity Density is deﬁned as mass per unit volume Speciﬁc gravity is ratio of the weight to the volume 7. Other properties Taste Halite tastes like salt Feel Talc feels soapy Graphite feels greasy Magnetism Magnetite can be picked up by a magnet Lodestone is a natural magnet For quiz, ﬁrst question will be to ﬁnd the most distinguishable characteristic of a list of minerals Sulphur - Smell, rotten egg Halite: Salty Talc: Soapy Graphite: Optical properties Calcite: Double refraction ability to transmit light Reaction to dilute hydrochloric acid Carbonates will eﬀervesce in acid All mineral samples are crystal crystalline solids Mineral structures 1. Unit cells atomic arrangement that results in the basic building blocks of a mineral crystal 2. Minerals can be constructed of the same unit cells and have diﬀerent external forms examples of minerals with cubic unit cells include: Fluorite: crystals are cubes Magnetite: Crystals are octahedrons Garnets: crystals are dodecahedrons Mineral Structures Steno’s Law or Law of Constancy pf Interfacial Angles Regardless of crystal size, the angles Compositional Variations in Minerals Ions of similar size can substitute for one another without disrupting the mineral’s internal framework examples include olivine: (Magnesium, Iron)SiO 2 Compositional Variations in Minerals Other minerals have trace variations in their chemical compositions Examples include quarts (SiO2) and Fluorite (CaF2) The trace variations can signiﬁcantly inﬂuence the mineral’s color Polymorphs Minerals with the same composition but diﬀerent crystalline structures Diamond - Strong bonds (carbon atoms) Graphite - Weak bonds (carbon atoms) Transforming one polymorph into another is called a phase change Diﬀerent internal structure, burial process and pressure Nearly 4000 minerals have been named Rock Forming Minerals Only a few dozen Common minerals that make up most of the rocks of Earth’s crust Composed mainly of the eight elements that make up most of the continental crust Igneous Processes From Magma to Crystalline Rock Crystallization is the cooling of magma which results in the systematic arrangement of ions into orderly patterns. Silicon and oxygen atoms link together ﬁrst to form a silicon-oxygen Magma that crystallizes at depth forms plutonic or intrusive igneous rocks these rocks are observed at the surface following periods of uplifting and erosion of overlying rocks The solidiﬁcation of lava or volcanic debris forms volcanic or extrusive igneous rocks. Above the crust cools fast Below the crust cools slow (protected, no wind, rain to come in contact) Igneous rocks are composed primarily of silicate minerals Dark or ferromagnesian silicates Rich in iron or magnesium examples include olivine, pyroxene, amphibole, and biotite mica more dense Light (or nonferromagnesian) silicates Contain more potassium, sodium, or calcium than iron and magnesium Examples include quarts, muscovite, mica, and felspar less dense Igneous Compositions Basaltic (Maﬁc) Compositions (DARK) 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 Granitic or felsic composition (LIGHT) light colored silicates composed almost entirely of quartz and potassium feldspar Termed felsic (feldspar and silica) in composition High silica (SiO2) content Major constant of continental crust Other compositional groups Andesitic or intermediate composition contain 25% or more dark silicate minerals (amphibole, pyroxene, and biotite mica) Associated with volcanic island arcs Ultramaﬁc Composition Rare composition of mostly olivine and pyroxene Composed almost entirely of ferromagnesium minerals Peridotite is an example 90% olivine Also the main constituent of the upper mantle Felsic (granite) - Muscovite, quartz, potassium diﬀerence between granite and rhyolite is the grain size, granite is coarser grain, under the surface rhyolite is smaller grain size, above the surface Silica content as an indicator of composition The chemical makeup of an igneous rock can be inferred from the silica content Silica content inﬂuences magma behavior Granite magmas have high silica content, are viscous (thick), and erupt at a lower temperature - move slow Basaltic magmas have much lower silica content, more ﬂuid like behavior, and erupt at a higher temperature - move faster Texture: The overall appearance of a rock based on the size, shape, and arrangement of mineral grains Factors aﬀected crystal/grain size: Rate of cooling Slow rate: fewer but LARGER crystals under the surface Fast rate: many SMALL crystals on the surface Amount of silica Amount of dissolved gases Types of Igneous Textures Aphanatic (ﬁne grained) texture Rapid rate of cooling Microscopic crystals Phaneritic (coarse grained) texture Slow cooling Large, visibile crystals Porphritic Texture Some minerals ca grow large before others form from the magma The magma can move to a diﬀerent environment (moving from deep to shallow places) which causes the remaining minerals to form quickly deep - larger shallow - smaller Large crystals (phenocrysts) are embedded in a matrix of smaller crystals (groundmass) Vesicular texture Rocks contain voids left by gas bubbles in the lava Common feature of an extrusive igneous rock Very light Glassy Texture Very rapid cooling (eruption, water) Obsidian (felsic dark rock NOT maﬁc, because of impurities) Ions are frozen in place before they can unite in an orderly crystalline structure Pyroclastic (fragmental) texture Forms from the consolidation of individual rock fragments ejected during explosive eruptions Pegmatitic Texture Exceptionally coarse grained form in late stages of crystallization of magmas rocks with this texture are called pegmatites El Paso - Transmountain Igneous Rocks Classiﬁcation Based on texture and composition Texture is inﬂuenced by cooling history Mineralogy is inﬂuenced by the chemical composition of the parent magma Granitic (Felsic) Igneous Rocks Granite Coarse grained (phaneritic) One of the best known igneous rocks Very abundant because they are made from the most abundant minerals Natural beauty, especially when polished 10-20%quartz, roughly 50% potassium feldspar Small amounts of dark silicates Some granites have a porphyritic texture contain elongated feldspar crystals Rhyolite Extrusive equivalent of granite (ﬁne grains) Composed essentially of light colored silicates Typically buﬀ to pink or light gray in color less common and less voluminous than granite rate of cooling is high, highly fractured, less common Obsidian Dark colored, glassy rock Forms when silica rich lava cools quickly at Earth’s surface (underwater) Usually black to reddish brown in color Similar chemical composition to granite (SiO2 not SiO4) Dark color is the result of small amounts of metallic ions in an otherwise clear, glassy substance Pumice Glassy textured rock that forms when large amounts of gas escape from the lava Voids are quite noticeable Resembles ﬁne shards of intertwined glass Typically found in deposits with obsidian Will ﬂoat when placed in water Andesitic (intemediate) igenous rocks Andesite medium gray, ﬁne grained rock Volcanic origin Commonly exhibits a porphyritic texture Diorite Intrusive equivalent of andesite coarse grained rock looks like gray granite but lacks visible quartz crystals can have a salt and pepper appearance easily see the grains Basaltic (Maﬁc) Igenous Rock Basalt Very dark green to black, ﬁne grained rock Composed mostly of pyroxene and calcium rich plagioclase feldspar When porphyritic, contains small, light colored feldspar phenocrysts most common extrusive igneous rock upper layers of oceanic crust are composed of basalt Gabbro intrusive equivalent of basalt veyr dark green to black ﬁne grained rock composed mostly of pyroxene and calcium rick plagioclase feldspar uncommon on the continental crust but makes up a signiﬁcant portion of the oceanic crust z Chapter 4: Pyroclastic Rocks Composed of Tuﬀ common pyroclastic rock composed of ash sized fragments cemented together Welded Tuﬀ Ash particles are hot enough to fuse together Earth’s crust and mantle are primarily composed of solid rock Magma is generated in the uppermost mantle Greatest amounts are produced at divergent plate boundaries (mid ocean rift) Lesser amounts are produced at subduction zones Can also be generated when crucial rocks heated Generating magma from solid rock Geothermal gradient: temperatures in the upper crust increase about 25 degrees Celsius per kilometer rocks in the lower crust and upper mantle are near their melting points Minerals have diﬀerent melting points (geothermal gradient) Decompression melting melting occurs at higher temperatures with increasing depth reducing pressure lower the melting temperature inner core temperature is higher but melting is not happening because of the pressure Generating Magma from Solid Rock Addition of water Occurs mainly at subduction zones ocean collides with continental continental sinks As an oceanic plate sinks, heat an pressure driver water from the crust and overlying sediments Fluids migrate into the overlying wedge of mantle The addition of water lowers the melting Temperature increase: melting crustal rocks heat from nearby magma sources can melt the surrounding crustal rocks Can also form melt from heat generated during continental collisions In summary, there are three ways to create magma Decrease in pressure (outer core liquid, inner core solid) Introduction of water Heating crustal rocks above their melting temperature (magma source or colliding of plates) How Magmas Evolve A single volcano may extrude lavas that vary in composition Bowen’s Reaction Series Minerals crystallize in a systematic fashion based on their melting points Rocks are made out of minerals, those minerals do not form at the same time Minerals form at diﬀerent times Olivine, high melting points 1200 Quartz, Feldspar melting point 600 form one after the other As minerals crystallize, the composition of the liquid portion of the magma continually changes First mineral crystallizes, then remaining magma is diﬀerent from the original magma and the minerals that will come will be diﬀerent in composition that the ﬁrst mineral olivine is rich in magnesium, quartz is rich in silicon Magmatic Diﬀerentiation and Crystal Settling Crystal Settling Earlier formed minerals are denser than the liquid portion of the magma and sink to the base of the magma chamber Magmatic Diﬀerentiation The formation of one or more secondary magmas from a single parent magma Maﬁc Magma - rich in iron and magnesium ﬂow eruption Magma - not rich in iron and magnesium explosive eruption Assimilation and Magma Mixing Assimilation As magma migrates through the crust, it may incorporate some of the surrounding rock Magma Mixing During the ascent of two chemically diﬀerent magma bodies, the more buoyant mass may overtake the slower-rising bodies Possible to have magmas with two diﬀerent densities Partial melting produces most magmas During partial melting, the melt is enriched in ions from minerals with the lowest melting temperature Partial melting of ultramaﬁc rocks yields maﬁc magmas minerals to melt ﬁrst are the low melting ones such as quartz, muscovite, feldspar Partial melting of maﬁc rocks yields intermediate magmas Partial melting of intermediate rocks yields felsic magmas Formation of Basaltic Magmas Most magma that erupts is basaltic (maﬁc) magma Most originate from partial melting of mantle rocks at oceanic ridges Mixing is with dark colored rock Formation of Andesitic and Granitic Magmas Andesitic magma Magmatic diﬀerentiation of mantle derived basaltic magma Granitic magmas Most form when basaltic magma ponds beneath eh continental crust Melted crustal rocks after the magma composition Can form from magmatic diﬀerentiation of andesitic magma Nature of Intrusive Bodies A pluton is cooled, emplaced magma into preexisting rocks Classiﬁcation of plutons Plutons are classiﬁed by their orientation to the surrounding rock Those plutons are either horizontal or vertical They can be small or huge Tabular - table-like Discordant - cut across existing structures (vertical) Concordant - are parallel to features like sedimentary strata (horizontal) Massive - irregular shaped Tabular Intrusive Bodies: Dikes and Sills Dikes: a tabular discordant pluton Sill: a tabular, concordant pluton Maybe exhibit columnar jointing pillar like columns with 6 sides cool from the center to the outside Massive Intrusive Bodies: Batholiths, Stocks, and Laccoliths Batholiths Largest intrusive body Laccoliths Forcibly injected between sedimentary strata Causes the overlying strata to arch upward QUIZ know the ways to diﬀerentiate igneous rocks (color, grain size) how to create magma Decrease in pressure (outer core liquid, inner core solid) Introduction of water Heating crustal rocks above their melting temperature (magma source or colliding of plates) sills and dikes massive - laccolith (mushroom like), baccolith, stock Chapter 5 All eruptions involve magma Magma is molten rock that usually contains some crystals and varying amounts of dissolved gases Lava is erupted magma (above the surface) Viscosity of a magma controls the nature of an eruption Silica - high silica, high viscosity Sticky magma keeps its gasses trapped, high pressure within the magma Viscosity is a measure of a material’s resistance to ﬂow The more viscous the material, the greater its resistance to ﬂow Factors aﬀecting viscocity Temperature - hotter magmas are less viscous Composition - silica (SiO2) content Higher silica content magmas are more viscous (rhyolitic, and andesitic magmas) Lower silica content magmas are less viscous (basaltic lavas) Hot magma is less viscous higher temperature, deeper source (mantle) ultramaﬁc rock more rich with aluminum, iron and magnesium less silica lower temperature shallow source more silica content DIssolved gases The violence of an eruption is related to how easily gases escape from magma Quiescent Versus Explosive Eruptions Involves ﬂuid basaltic lavas Eruptions are characterized by outpourings of lava that can last weeks, months, or even years Explosive Eroptions Associated with high viscous magmas Eruptions expel particles of fragmented lava and gases at supersonic speeds that evolve into eruption columns Lava Lava ﬂows about 90% of lava is basaltic lava less than 10% of lava is andesitic lava about 1% of lava is rhyolitic Aa and Pahoehoe Flows Composed of basaltic lava Aa ﬂows hava surfaces of rough jagged blocks Pahoehoe ﬂows have smooth surfaces and resemble twisted braids of ropeLava Block Lavas Composed of andesitic and rhyolitic lava Upper surface consists of massive, detached blocks Pillow lavas Composed of basaltic lavas extruded underwater Flow is composed of tubelike structures stacked one atop the other Gases Gases make up 1%-6% of the total wight of a magma As the magma reaches the surface and the pressure is reduced, the gases expand and escape Pyroclastic Materials Volcanoes eject pulverized rock and lava fragments called pyroclastic materials Particles range in size from ﬁne dust, to sand sized ash to very large rocks Tephra rock fragments and particles ejected by a volcanic eruption Volcanic ash - ﬁne, glassy grafments welded tuﬀ - fused ash Lapilli - walnut sized material Cinders - pea sized material Blocks - hardened or cooled lava Bombs - ejected as hot lava Pumice - light gray or pink porous rock from frothy andesitic and rhyolitic lava (more shallow source, felsic) Scoria - reddish-brown porous rock from frothy basaltic and andesitic lava (deeper source, more basaltic) Magma is composed of LAVA, GASES, and PYROCLASTIC MATERIALS Anatomy of a volcano General features Condult - a ﬁssure that magma moves through to reach the surface Vent - the surface opening of a condult Volcanic cone - A cone of material created by successive eruptions of lava and pyroclastic material Crater - a funnel shaped depression at the summit of most volcanic cones, generally less than 1 KM in diameter Caldera - a volcanic crater that has a diameter of >1 kilometer and is produced by a collapsed following a massive eruption Parasitic cones - a flank vent that emits lava (lateral vent, on the side) Fumaroles -a ﬂank vent that emits gases Shield Volcanoes Broad, slightly dome shaped Covers large areas Produced by mild eruptions of large volumes of basaltic lava Most begin on the seaﬂoor as seamounts; only a few grow large enough to form a volcanic island Examples include the Hawaiian Islands Mauna Loa is the largest shield volcano on Earth Cinder Cones Built from ejected lava fragments Steep slope angle Rather small size Frequently occur in groups Sometimes associated with extensive lava ﬁelds Paricutin (located 320 km west of Mexico City) is an example of a cinder cone Composite Volcanoes Also called stratovolcanoes Large, classic shaped volcano (symmetrical cone, thousands of feet high and several miles wide at the base) Composed of interbedded lava ﬂows and layers of pyroclastic debris Mount St. Helens and Mount Etna are examples Volcanic Hazards Pyroclastic Flows A mixture of hot gases and lava fragments that ﬂows down a volcanic slope Lahars Mudﬂow on an active or inactive volcano Other Hazards Volcano related tsunamis Volcanic ash - a hazard to airplanes Volcanic gases - a respiratory health hazard Eﬀects of volcanoes on climates Pyroclastic Flows Also called a nuee ardente Propelled by gravity and move similarly to snow avalanches Material is propelled form the vent at high speeds can exceed 60 mph Lahars AMudﬂow on an active or inactive volcano Volcanic debris becomes saturated with water and rapidly moves down a volcanic slope In 1985, lahars formed during the eruption of Nevada del Ruiz, killing 25,000 Volcano related tsunamis can form after the sudden collapse of a ﬂank of a volcano Volcanic ash Jet engines can be damaged when ﬂying through a cloud of volcanic ash Volcanic gases Volcanoes can emit poisonous gases, endangering humans and livestock Eﬀects of volcanoes on climate Ash particle released from volcanoes can reﬂect solar energy back into space The ash from the eruption of Mount Tambora in 1815 led to the year without summer 1816 Caldera Calderas are circular, steep-sided depressions with a diameter >1KM Three Diﬀerent types Crater lake type calderas: form from the collapse of the summit of a large composite volcano Hawaiian Type Calderas: form gradually from the collapse of the summit of a shield volcano Yellowstone Type Calderas: form from the collapse of a large area Large Igneous Provinces Large igneous provinces cover a large area with basaltic lava Basaltic lava extruded from ﬁssures blanket a large area, called a large igneous provinces or basalt plateaus The colombia plateau and the deccan traps are two examples Lava Domes A lava dome is a small dome shaped mass composed of rhyolitic lava Collapse, gravity and weather conditions work on them Volcanic Necks and Pipes A volcanic rock is the remains of magma that solidiﬁed in a volcanic condult Shiprock, New Mexico, is an example Plate Tectonics and Volcanic Activity Volcanism at convergent plate boundaries Exam Review Chapter 16 Running Water Chapter 17 Ground Water Chapter 19 Wind and Desert Area Chapter 4 Igneous Rocks Chapter 5 Volcanoes Chapter 2 Plate Tectonics Chapter 11 Earthquakes Hydraulic Cycle: Describes the movement of water through diﬀerent regions Inﬁltration - Water soaking into the ground Upstream zone of production: produces sediments in the middle is the zone of transporation at the end is the zone of deposition Channel dig a channel through shale Meandering System - Snake like system Base River coarse sediments at beginning or mouth of river ﬁne sediments at end of river or base river Groundwater unsaturated: little water and air saturated: 100% water can go up and down based on the recharge and discharge (precipitation and drought) when the water go up and down the shape it makes is cone of depression Permeability and porosity Permeability how well a water transmit Porosity how much space A good aquifer has high permeability, high porosity Need space for the water, and water needs to move Aquifer: Water moves mainly made of sand or gravel Aquitard: Sealed, impermeable made of clay or shale ﬁne grain size Saltwater contamination in a coastal area and goes into the well Desert: Dry climate, where yearly precipitation is not as great as the potential for evaporation latitude for desert (20-30) Mountain, Playas Lake Basin and Range structures of the three stages Saltation: Deﬁne Sand Dune: the geometry of sand dunes shape and size is inﬂuenced by wind strength, consistency, sand amount, ALL OF THE ABOVE Diamond: where do we ﬁnd diamonds? what kind of igneous rock? Kimberlite Volcanic/Island Arc Convergent collision between oceanic and oceanic Continental Volcano - ocean and continental Mountain range: continent and continent Pangea - German geologist name of supercontinent Flow of magma high viscosity more sticky, more silica content low viscosity, less silica continent Volcanoes under water sea mound Liquefaction - solid acts as a liquid Amplify vibration or lessen vibration? Liquefaction ampliﬁes vibration Convergent plate boundaries: Destructive Divergent plate boundaries: Constructive Transform: Seismic Waves Body Waves: P and S waves Surface Waves: rayleigh and surface waves are the most destructive and slowest P waves are the fastest Streams carry the sediments suspended, and bed load suspended load is the most abundant geysers - fountain of hot steam this is not an artesian system artesian well: water underground under pressure aquifer and aquitard composite volcanoes also called stratovolcanoes examples are mount st. helens and mount etna antartica biggest desert true biggest sign of a tsunami is a rapid retreat of water true Weathering Weathering involves the physical breakdown and chemical alteration of rock at or near Earths surface mechanical weathering - physical forces breaking rocks into smaller pieces chemical weathering - chemical transformation of rock into new compounds Both types work simultaneously and reinforce each other Sediments to sedimentary rock lithiﬁcation compaction As mechanical weathering breaks rock into smaller pieces, more surface area is exposed to chemical weathering. Increased area, increases the exposed area which increases the chemical reaction. 4 square units 6 sides 1 cube 24 square units 1 square unit 6 sides 8 cubes 48 square units .25 square unit 6 sides 64 cubes 96 square units Types of Mechanical Weathering Frost wedging Salt Crystal Sheeting/Unloading (igneous rock, some overlap) Biological Activity Frost Wedging, two methods (mechanical process) Water works its way into cracks (fractures) in rocks and the freezing enlarges the cracks in the rocks (expands) Lenses of ice grow larger as they attract liquid water from surrounding areas Water expands and pushes rock Salt Crystal Growth (mechanical process) Sea spray or salty groundwater penetrates crevices and pore spaces in rocks As the water evaporates, salt crystals form and enlarge the crevices When precipitation begins, the fracture increases Salt attracts to each other and creates structure and that expands as well Sheeting/Unloading (mechanical process) Large masses of igneous rock are exposed by erosion and concentric slabs break loose An exfoliation dome is formed after continued weathering causes the slabs to separate and spall oﬀ Joints are fractures produced by contraction during the crystallization of magma Biological Activity (mechanical process) Plant roots grow into fractures in a rock, causing the cracks to expand Burrowing animals break down rocks by moving fresh material to the surface, enhancing physical and chemical weathering Human impacts (rock blasting) is very noticeable Types of Chemical Weathering Dissolution Oxidation Hydrolisis Spheroidal Weathering The most important agent is water, responsible for transport of ions and molecules involved in chemical processes Dissolution (chemical process) Certain minerals dissolve in water Halite is one of the most water soluble minerals Calcite is the second most soluble mineral Small amount of acid in water increases the corrosive force of water, causing dissolution Carbonic acid (CO2 and water) is created when carbon dioxide dissolved in raindrops (acid rain) Calcite is easily attacked by weakly acidic solutions Acidic waters create caves Oxidation (chemical process) Oxygen combines with iron to form iron oxide Process is slow in dry environments Water increases the speed of the reaction Important in decomposing ferromagnesium minerals like olivine, pyroxene, hornblende, and biotite iron oxides add color lighter on top, darker on bottom limonite on top, hematite on bottom Hydrolysis (chemical process) The reaction of any substance with water A hydrogen ion attacks and replaces another ion Silicates primarily decompose by hydrolysis Clay minerals are the most abundant product of weathering Clay minerals are very stable under surface conditions Spheroidal Weathering (chemical process) Weathering attacks edges form two sides and corners from three sides Sharp edges gradually wear down and become rounded Water involved in the beginning of the process The rate of weathering is inﬂuenced by rocks type (composition) and climate Diﬀerent minerals weather at diﬀerent rates Silicate minerals weather in the same order as crystallization (Bowen’s Reaction Series) Warm, moist climates enhance (and cold, dry climates inhibit) chemical weathering Variations in local climate and the composition of the rock formation will produce uneven weathering of rock called diﬀerential weathering Soil is the bridge between life and the inanimate world The bridge between the various Earth systems Earth’s land surface is covered by a layer of rock and mineral fragments produced by weathering, called regolith Soil is a combination of mineral and organic matter, water, and air and is the portion of the regolith that supports the growth of plants sediments and sedimentary rock are diﬀerent, has to go through compaction and lithiﬁcation Controls of Soil Formation Parent material, (hard rock v soft rock) time, (long time more developed soil, less time less developed) climate, plants and animals, (organic material is a component, when they die they become a part of soil) topography, interact to control soil formation steep slopes no soil river transported soil ﬂat residual soil Parent material The source of weathered material that forms soil residual soil - soils form from the underlying bedrock transported soil soils that form in place from unconsolidated sediment Time Weathering over a short period of time forms thins soils that closely resemble the parent material Soils that have weathered for a long period of time are generally thick and do not resemble the parent material Climate The most inﬂuential control of soil formation Key factors are temperature and precipitation starts from the top then goes down, thickness of the soil increases Plants and Animals Inﬂuence the soil chemistry Remains are converted into humus which is an important part of the organic component of soil Soil where there are trees, the parent material comes from the tree so the soil is of very poor soil Desert has very thin soil, no support for trees If we have water, organic material, there will be a very good fertilized soil Topography Steep slopes have poorly developed soils or no soil Moisture content of these areas is often insuﬃcient for plant growth Flat and undulating surfaces are optimal for soil formation good drainage and minimal erosion Slope orientation is also important in soil formation Southern facing slopes in the Northern Hemisphere receive the most sunlight and optimal for soil formation Soil forming processes operate from the surface downward Soil is divided into horizontal layers called horizons A veritcal section through all the soil horizons is called a soil proﬁle A mature soil has well developed horizons An immature soil may lack soil horizons Soil proﬁle - VERTICAL, all soil horizons Soil Horizon - HORIZONTAL, one section of soil proﬁle O Soil horizon organic matter the lower portion is composed of humus this horizon includes bacterial, fungi, algae, and insects A Soil Horizon organic and mineral matter high biolical activity O and A horizons make up the top soil E Soil Horizon little organic matter light colored layer eluviation (washing out ﬁne soil components to lower soil layers) is common in this layer Soluble inorganic components are washed to lower layers in a process called leaching B Horizon (subsoil) zone of accumulation Material washed down from the E horizon accumulates in this layer Mainly iron oxides, makes the soil dark No organic material Collectively, the O, A, E and B horizons make up the solum, or true soil C Horizon Parent rock Partially altered parent material Parent material is diﬃcult to identify in the O, A, E and B horizons 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 Look @ basic soil orders We look at longitude to see change in climates, to group the soils by region Impact of Human Activity of Soils The agricultural productivity of soils can be improved through fertilization and irrigation Soils can be damaged or destroyed by careless activities Soils are crucial for providing food, ﬁber, and other basic materials Soils are one of the most abused resources Clearing the Tropical Rain Forest - A Case Study Tropical forests are cleared for logging and agricultural use Soils in tropical forests are poor in nutrients and unsuitable for agriculture Most of the nutrients in tropical rain forests are found in trees Clearing tropical rain forests also promotes soil erosion If you remove the trees, it is exposed for erosion and it will be a poor soil Soil Erosion Soil erosion is a natural process in the rock cycle Erosion rates are dependent on climate slope type of vegetation Sediments Sediments and sedimentary rocks cover approximately 75% of Earth They comprise about 5 percent (by volume) of Earth’s outer 10 miles Contain evidence of past environments Sedimentary rocks are an important resource coal, oil, and other fossil fuels groundwater resources Sedimentary rocks are products of weathering Sediments and soluble constituents are typically transported downslope by gravity The sediments are then deposited and subsequently buried As depositions continues, the sediments are lithiﬁed into sedimentary rocks (compaction and cementation) There are three types of sedimentary rocks: Detrital/Mechanical, Chemical/Biochemical, and Organic Sedimentary rocks Some people just use chemical and biochemical (chemical and organic sedimentary) Three Types (Detailed) Detrital Sedientary Rocks: form from sediments that have been weathered and transported The chief constituents of detrital rocks include clay minerals quartz feldspars micas Particle size/grain size is used to distinguish among the various rock types Almost the same chemical composition, but do not look at that Classiﬁcation of the detrital sedimentary rocks Shale Silt and clay sized particles (small) Form from the gradual settling of sediments in quiet, non turbulent environments Sediments form in thin layers that are called laminae ﬁner grain low energy coarse grain higher energy Has ﬁssility (meaning the rock can be split into thin layers) Crumbles easily and tends to form gentles slopes Most abundant sedimentary rocks Common Metamorphic Rocks Most important factor for metamorphism is temperature Foliated - Pressure 1. Contact or Thermal Metamorphism 1. results from a rise in temperature when magma involves a host rock 2. Occurs in the upper crust (low pressure, high temperature) 3. The zone of alteration (aureole) forms in the rock surrounding the magma. 4. mid oceanic ridge 5. temperature is the main factor 2. Hydrothermal Metamorphism 1. chemical alteration caused by hot, ion rich ﬂuids circulating through pore spaces and rock fractures 2. mid oceanic ridge 3. black smokers are the result of the ﬂuids 3. Regional Metamorphism 1. produces the greatest quantity of metamorphic rock 2. Associated with mountain building and the collision of continental blocks 3. convergent boundary 4. mountain 4. Burial Metamorphism 1. Associated with very thick sedimentary strata in a subsiding basin 1. gulf of mexico is an example 5. Subduction Zones Metamorphism 1. Sediments and oceanic crust are subjected fast enough that pressure increases before temperature 2. More pressure related not temperature related 6. Metamorphism Along Fault Zones 1. Occurs at depth and high temperatures pre-existing minerals deform by ductile ﬂow 2. Mylonites form in these regions of ductile deformation 3. Shallow and low temperature brittle deformation 7. Impact Metamorphism 1. Occurs when meteorites strike Earth’s surface 1. product of these impacts are fused fragmented rock plus glass rich ejecta that resemble volcanic bombs 1. called impactiles Textual Variations Slate is associated with low grade metamorphism Gneiss is associated with high grade metamorphism Phyillite and schist are intermediate Slate is low SEDIMENTARY most abundant detridant Phyillite is medium Schist is medium Gneis is high pressure and temperature increase not always at a uniform rate 1. Index Minerals and Metamorphic Grade 1. Changes in mineralogy occur from regions of low grade metamorphism to regions of high grade metamorphism 2. Index minerals are good indicators metamorphic environments 2. Metamorphic Facies 1. Metamorphic rocks that contain the same minerals assemblage and formed in similar metamorphic environments 2. same assembly equals same or similar metamorphic environment 3. High pressure low temperature 1. metamorphis is associated with the upper section of subduction zones 2. Regional metamorphism is associated with colliding continental blocks 1. examples include the Appalachian Mountain too shallow - sediment too deep - igneous Mineral Stability and Metamorphic Environments 1. Some minerals are stable at certain temperature and pressure regimes 1. Examples include the polymorphs andalusite, kyanite, and sillimanite 2. Knowing the range of temperatures and pressures associated with mineral formation can aid in interpreting the metamorphic environment MINERALS used to predict metamorphic events high temperature high pressure minerals are stable and tolerate high temperature high pressure (Andalusite, Kyanite, and Silimanite) what kind of region is it? Exam 3 Review Weathering Chapter 6 Sedimentary Chapter 7 Metamorphic Rock Chapter 8 30 Multiple Choice 10 True/False CHEAT SHEET!!!!! Weathering: Chemical Oxidation what does this mean Hydrolisis what does this mean Dissolution Spheroidal Physical/Mechanical To expose metamorphic rock under sediments pressure needs to be reduced
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