GEOL 101 Exam 1 Study Guide
GEOL 101 Exam 1 Study Guide GEOL 101
Western Washington University
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This 8 page Study Guide was uploaded by Sarah Vernier-Dolin on Wednesday October 5, 2016. The Study Guide belongs to GEOL 101 at Western Washington University taught by Paul A. Thomas in Fall 2016. Since its upload, it has received 56 views. For similar materials see Introduction to Geology in Geology at Western Washington University.
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Date Created: 10/05/16
GEOL 101 – Exam 1 Study Guide Introduction § Earth is ~ 4.5 Ga (Giga Annum = billions of years) o 1000 years seems like a long time, but in the scheme of things it’s really just a small fraction § Earth’s Interior o Crust § Rigid, brittle, varies in thickness, thin nest in oceans & thickest in mountain ranges o Mantle § Majority behaves like plastic o Outer Core § Believed to be liquid o Inner Core § Solid metal core, because there’s so much pressure keeping it solid (less pressure à melting) § Lithosphere & Asthenosphere o Lithosphere = crust & uppermost mantle § Brittle & strong o Asthenosphere = Uppermost part of mantle § Deformable (plastic) & weak o The lithosphere moves independently over the top of the Asthenosphere o The lithosphere is what is broken up into plates § Oceanic vs. Continen tal Lithosphere Continental Oceanic Thick Thin Old Young Light Dense Many rock types Basalt Plate Tectonics • Original idea of continental drift: 200 million years ago Pangea existed, where all of the continents fit together as one big jigsaw puzzle § Evidence: rocks on South America & Africa (which once touched) had similarities; fossils found on South America & Africa matched • Seafloor spreading § Divergent plate boundary § As plates/seafloor spread material rises from below, mantle expands & melts. Because the seafloor spreads it releases pressure allowing magma to rise & solidify to create new ocean floor. § As time goes on & the seafloor spreads, the oldest seafloor moves to the edges where it is eventually destroyed. • Divergent plate boundary § Plates move away from each other § Where new ocean floor is constantly being created & destroyed § Where seafloor spreading takes place • Transform plate boundary § Plates move side to side of each other along transform faults § Where fracture zones occur § In between the sliding plates creates a fault, creating a zig zag patter between vertical divergent boundaries & horizontal transform boundaries, as the plates slip past each other • Convergent plate boundary § Plates come together § THERE ARE 3 TYPES OF CONVERGENT BOUNDARIES § Oceanic-Continental Convergent Boundary Ø The oceanic plate subducts (dives under) beneath the continental plate because the oceanic plate is thinner & more dense, sending it under Ø After it is subducted it is then destroyed Ø Oceanic plate bends down, creating an ocea nic trench right along the plate boundary Ø Water is driven from the subducting plate & interacts with the magma below, melting it. The magma then rises to the surface where most of it solidifies within the crust. Sometimes it erupts in a volcanic eruption à linear chain of volcanoes (volcanic arc) or islands (island arc) § Oceanic-Oceanic Convergent Boundary Ø One plate, the older one, subducts beneath the other Ø A trench & island arc result, usually with a curved path Ø The process is similar to oceanic -continental § Continental-Continental Convergent Boundary Ø First, the oceanic part of the plate subducts, bringing the continents closer Ø When the continents hit, subduction stops (can’t shove a continent under another continent) Ø Continent collision = a wide zone of def ormation à you get faults, mountains, etc. Ø Basically: shorten crust horizontally & thicken vertically Ø Volcanism stops • Continental Rifting § Initial uplift from rising mantle § Collapses downward, stretching & faulting to form rift § Can lead to seafloor spreadin g & new ocean basins (ex. Red Sea) 2 § Ocean widens with spreading (ex. Modern Atlantic) • Thermal Plume/Hot Spot § Plates move over hot spot à formation of linear islands & seamount chains § Volcano forms over the hot spot § Volcano becomes inactive as the area move s away from the hot spot § The plate subsides as it cools so islands become seamounts § Islands are bigger when they’re younger because they get material added due to volcanic activity faster than it gets eroded & destroyed, but when volcanic activity stops there’s no more activity to add material to the island § One hot spot can be feeding more than one island at a time • Plates & Volcanoes & Earthquakes § 99% of seismic energy is released at plate boundaries § Same thing goes for volcanoes, mostly occur along plate b oundaries • Earth’s Magnetic Field § The liquid outer core contains convection currents § Normal magnetic polarity – when compass needle points true north § Reversed magnetic polarity – when compass points, considering north to be what really is south. Polarity flips & reverses completely, no in between stage Minerals & the Rock Cycle § Minerals – Basics o They are the building blocks of rocks o Made of different elements all bonded together § They come together in a specific structure each time § Process of crystallization o Minerals form by process of crystallization o When atoms come together in specific proportions & crystalline arrangements o There are 2 main methods to crystalize: Ø Cooling of magma/lava Ø Precipitation from water § Distinguishing One Mineral From Another o Crystal form – texture, the size of the minerals or fragments, their shape & how they’re stuck together o Cleavage/no cleavage (cleavage = breaks along flat sides) o Color o Luster (how it shines – metallic, transparent, etc.) o Hardness § Classification of Minerals o Silicates o Carbonates – calcite (CaCO2) calcium carbonite o Oxides o Halides o Sulfides – pyrite, fool’s gold (FeS) o Sulfates – Gypsum (CaSO42H20) o Native minerals (some are just one mineral, ex. silver) 3 § Chemical Composition of Earth’s Crust a. Percentage of Crust by Weight Sodium sium ium Calci3% 3% 2% 4% Iron 5% Aluminum 8% Oxygen 47% Silicon 28% Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium All others o What’s important to note are not all the percentages, but that it is made up mostly of oxygen & silicon o Aluminum, sodium, & potassium are typically found together mostly on continental crust o Iron, calcium, & magnesium typically found together in oceanic crust o Oxygen generally has a negative charge & silicon generally has a positive charge, which is typically what bonds them together § Silicate Minerals: SiO4 o These have building block made of silicon & oxygen o Most commonly found minerals, making up majority of rocks o Silicate tetrahedron: one silicon atom bonds with four oxygen atoms Ø Tetrahedron can bond together (sharing oxygen, bonding & corners) or with other elements o Not neutral; must bond it with others to neutralize it § Light Color Silicate Minerals o Sodium potassium & aluminum together generally make light color o Quartz, muscovite, feldspar § Dark Color Silicate Minerals o Iron, calcium & magnesium together generally make dark color o Pyroxene, biotite, olivine, amphibole – hornblende § Quartz: SiO2 o Hardness: 7 (on scaled 1 -10) o Many colors o Conchoidal fracture – does not break along cleavage points Ø Best way to identify 4 § Feldspar o Most common mineral in Earth’s crust o Hardness: 6 o Breaks along cleavage planes o 2 main different types of feldspar: Ø Plagioclase feldspar “plag” Na à Ca Ø Potassium feldspar K § Mica o 2 varieties: muscovite (light) & biotite (dark) o Breaks as thin sheets à 1 direction of cleavage § Others o Amphibole – hornblende (dark) o Olivine (olive green in color) – most iron rich o Pyroxene (dark & greener) § Fracture Zones o Run perpendicular to diverg ent boundary – segments of Mid-Ocean Ridge cross-cut by fraction zones o They occur at transform plate boundaries § Ex. San Andreas Fault Fracture zone § Extrusive/Volcanic Igneous Rocks o Make it to the surface to cool, most commonly lava flow o Cools down fast at the surface o Small crystals/mineral grains à fine grained § Intrusive Igneous Rocks o Coarse-grained rocks § Classification of Igneous Rocks o Based on § Texture – appearance of surface, related to how the rock cools § Chemical composition – elements in the magma, det ermines what minerals are present § Igneous Textures o Coarse-grained – interlocking crystals that can be seen with the naked eye o Fine-grained – small interlocking crystals too small to be seen with the naked eye o Vesicular (when gas escapes as cools) – vesicles are holes in volcanic rock that form as lava solidifies around gas bubbles o Aphantic (fine version) o Porphyritic – composed of 2 different distinct crystal sizes; undergone 2 stages of cooling 5 o Glassy – volcanic glass is called obsidian and lacks crystals. Rocks that are very glassy show a characteristic conchoidal (curved) fracture pattern o Pyroclastic (fragmental) – when molten material erupts from a volcano it can solidify before it hits the ground § Broken up chunks of rock in it § “fire fragment” § Chemical Composition o Most common types of magmas & their characteristics: o Minerals get dark & turn green as they become ultramafic Type of Magma Silica Content Sodium, Potassium, Calcium, Iron & & Aluminum Magnesium Ultramafic < 45 Increase Mafic 45-52 Intermediate 53-65 Felsic >65 Increase o Minerals get dark & turn green as they become ultramafic o There are few fine-grained ultramafic rocks – almost all of them are coarse -grained o Ultramafic are mantle rocks § Bowens Reaction Series o Not every mineral crysta lizes at the same time & same temperature o Bowens Reaction Series describes the order in which they crystalize o Cooling: magma à crystal o Heating up: melting o Magma comes from the mantle o Mantle (therefore magma) starts as ultramafic; this changes in particula r rocks as we evolve them o As we cool down ultramafic magma, the high temperature rock (aka the first to cool) is olivine o In the discontinuous series, the next to crystalize is pyroxene, then amphibole, then biotite mica, then potassium feldspar, then musco vite mica, then quartz o The highest temperature minerals are mafic, & the lowest temperature minerals are felsic o In the continuous series, they crystalize in the order of calcium rich then sodium rich (continuous series really shows feldspar’s crystallizati on) § The Crystallization of Magma o To create magma you must melt the mantle somehow o Olivine crystalizes first, leaving it behind removed from the magma à now magma just mafic not ultramafic § Deplete magma of different elements § As we deplete it just keeps chan ging à more intermediate à felsic § The further it moves through the more it evolves § This is how we form felsic rocks from ultramafic § Sedimentary Environments & Rocks o Most of earth’s exposed surfaced is covered by sediment & sedimentary rocks o Loose sediment hardens, lithifies, into sedimentary rock 6 o Sizes of clasts § Largest clasts are boulders § Cobbles are smaller than boulders § 3 largest is sand, smaller than 2 mm § The smallest clasts are clay & silt, together they compose mud o Sediment consists of loose fragmen ts of rocks & minerals, or clasts § When clastic sediment becomes sedimentary rock, the name assigned to the rock depends on the size & shape of the clasts o Sorting is the term used to describe the size range of clasts in a sedimentary deposit § Poorly sorted contains a wide range of clast sizes § Moderate sorting could contain sand & small pebbles, or silt & clay; like an assortment § Well-sorted consists of clasts that all have the same size; like sand -dunes o Common Clastic Sedimentary Rocks § Gravel-Sized Clasts • Conglomerate has rounded pebbles, cobbles, or boulders with sand & other fine sediment between the large clasts ; cobbles are well- rounded • Breccia similar to conglomerate, but the clasts are angular § Sand-Sized Clasts • Sandstone consists of sand-sized grains • Arkose, a rock composed of at least 25% sand -sized feldspar grains • Quartz sandstone, a sandstone composed mostly of quartz grains • Graywacke, contains grains of several different compositions. o They typically include quartz, feldspar, iron -oxide minerals, mica minerals, & small fragments of other rocks § Mud-Sized Clasts • Siltstone consists of silt-sized particles, generally quartz • Shale consists mostly of very fine -grained clay materials. Materials are aligned so the rock breaks in sheetlike pieces or chips § How Carbonate Rocks Form o Limestone & related sedimentary rocks are called carbonate rocks, because they consist of a carbonate ion combined calcium, magnesium, or other elements § Characteristics of Carbonate Rocks o Limestone & dolostone commonly occur together o Limestone is a common rock & exists in many varieties, all of which consist mostly of the mineral calcite (CaCO3). Calcite can convert to dolomite by the addition of magnesium, which produces rock dolomite o Limestone is typically a gray color, but can also hav e shaded of yellow, tan or brown o Dolostone made mostly of mineral dolomite, resembles limestone but is more resistant to weathering & erosion because it is less soluble § Can be grey but more commonly tan, light brown, pinkish or even slightly orange § Where Do Clasts Come From? o Most sediment is pieces of other rocks (clasts) formed by weathering & transport. Other sediment is extracted from water when dissolved material is precipitated by chemical reactions 7 § How Do Physical & Chemical Weathering Produce Sedime nt o Most sediment forms by weathering § Physical Weathering • The physical breaking apart of rocks that are exposed to the environment § Chemical Weathering • Includes several types of chemical reactions that affect a rock by breaking down minerals, causing new mi nerals to form, or by removing soluble material from the rock • Attacks both solid rock & loose rock fragments § What Happens When Environments Shift Through Time o Environments that move across Earth’s surface over time can result in a sequence of different sedimentary rock o One common change – seas to advance across a region, covering more land with time, due to either rise in sea level or lowering of the land à this is called transgression o A different type of sediment is deposited in each environment, & each ty pe of sediment is called a sedimentary facies o A retreat of the sea is called a regression & occurs when sea level becomes lower or the land is uplifted o 8
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