GEOL 101 Lecture Notes Week 3
GEOL 101 Lecture Notes Week 3 GEOL 101
Western Washington University
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This 4 page Class Notes was uploaded by Sarah Vernier-Dolin on Sunday October 9, 2016. The Class Notes belongs to GEOL 101 at Western Washington University taught by Paul A. Thomas in Fall 2016. Since its upload, it has received 13 views. For similar materials see Introduction to Geology in Geology at Western Washington University.
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Date Created: 10/09/16
GEOL 101 – Lecture Notes Week 3 10/3 – 10/8 Fracture Zones § Run perpendicular to divergent boundary – segments of Mid-Ocean Ridge cross-cut by fraction zones § They occur at transform plate boundaries Fracture zone o Ex. San Andreas Fault Hot Spots/Thermal Plume § Plate moves over the hot spot à the formation of linear islands & seamount chains § Volcano forms over a hot spot § Volcano becomes inactive as area moves away from the hot spot § The plate subsides as it cools so islands become seamounts § The islands are younger when they’re bigger because they get material added to them 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 § A hot spot can be feeding more than one island at a time Earth’s Magnetic Field § The liquid outer core contains convection currents § Normal magnetic polarity occurs when compass needle points true north § Reversed magnetic polarity occurs when compass needle points, considering north to be what truly points south. Polarity flips & reverses completely, no in between s age. Minerals § They’re the building blocks of rocks § Granite – built up of several different minerals, like most rocks § Minerals are made of different minerals all bon ded together o They come together in a specific structure Process of Crystallization § Minerals form by process of crystallization o When atoms come together in specific proportion & crystalline arrangemen § Ways to crystalize: o Cooling of magma/lava o Precipitation from water Distinguishing One Mineral from Another § Crystal form – texture, the size of the minerals or fragments, their shape & how they’re stuck together § Cleavage/no cleavage (cleavage = breaks along flat sides) § Color § Luster (how it shines – metallic, transparent, etc.) § Hardness Chemical Composition of Earth’s Crust Potassium Magnesium All others 2% 2% 1% Sodium 3% Calcium 4% Iron Aluminum Oxygen 5% 8% 47% Silicon 28% § What’s important to notice are not all of the percentages, but that it is made up mostly of oxygen and silicon § Aluminum, sodium, & potassium are typically found together mostly on continental crust § Iron, calcium, & magnesium are typically found together in oceanic crust § Oxygen generally has a negative charge & silicon generally has a positive charge, whi ch is typically what bonds them together Silicate Minerals: SiO4 § These have building block made of silicon & oxygen § Most common family of minerals that make up most rocks § Silicate tetrahedron: one silicon atom bonded with four oxygen atoms o Tetrahedron can bond together & with other elements – can share oxygen in this case, bonding at corners § Not neutral; must bond with others to neutralize it Light Color Silicate Minerals § Sodium, potassium & aluminum together usually make light color § Quartz, muscovite, feldspar Dark Color Silicate Minerals § Iron, calcium & magnesium usually make the dark color § Pyroxene, biotite olivine, amphibole – hornblende Quartz – SiO2 § Hardness = 7 (on scale 1 -10) § Many colors § Conchoidal fracture – does not break along cleavage points o Best way to identify Feldspar § Most common mineral in Earth’s crust § Hardness = 6 § Breaks along cleavage planes § 2 main different types: o Plagioclase feldspar § “plag” Na à Ca o Potassium feldspar § K Mica § 2 varieties: muscovite (light) & biotite (dark) § Breaks as thin sheets à 1 direction of cleavage Others § Amphibole – hornblende (dark) § Olivine (olive green in color) – most iron rich § Pyroxene (dark & greener) How Are Minerals Classified? § Silicates § Carbonates – calcite (CaCO2) calcium carbonite § Oxides § Halides § Sulfides – pyrite, fool’s gold (FeS) § Sulfates – gypsum (CaSO42H2O) § Native minerals (some are just one mineral, ex. silver) Extrusive/Volcanic Igneous Rocks § Make it to the surface to cool, most commonly lava flow § Cools down fast at the surface § Small crystals/mineral grains à fine grained Intrusive Igneous Rocks § Coarse-grained rocks Classification of Igneous Rocks § Based on o Texture – appearance of surface, related to how the rock cools o Chemical composition – elements in the magma, determines what minerals are present Igneous Textures § Coarse-grained – interlocking crystals that can be seen with the naked eye § Fine-grained – small interlocking crystals too small to be seen with the naked eye § Vesicular (when gas escapes as cools) – vesicles are holes in volcanic rock that form as lava solidifies around gas bubbles § Aphantic (fine version) § Porphyritic – composed of 2 different distinct crystal sizes; undergone 2 stages of cooling § Glassy – volcanic glass is called obsidian and lacks crystals. Rocks that are very glassy show a characteristic conchoidal (curved) fracture pattern § Pyroclastic (fragmental) – when molten material erupts from a volcano it can solidify before it hits the ground o Broken up chunks of rock in it o “fire fragment” Chemical Composition § Most common types of magmas & their characteristics: Type of Magma Silica Content Sodium, Potassium, Calcium, Iron & & Aluminum Magnesium Ultramafic < 45 Increase Mafic 45-52 Intermediate 53-65 Felsic >65 Increase § Minerals get darker & turn green as they become ultra -mafic § There are few fine-grained ultramafic rocks – almost all of them are coarse-grained § Ultramafic are mantle rocks Bowens Reaction Series § Not every mineral crystalizes at the same time & same temperature § Bowens Reaction Series describes the order in which they crystalize § Cooling: magma à crystal § Heating up: melting § Magma comes from the mantle § Mantle (therefore magma) starts as ultramafic; this changes in particular rocks as we evolve them § As we cool down ultramafic magma, the high temperature rock (aka the first to cool) is olivine § In the discontinuous series, the next to crystalize is pyroxene, then amphibole, then biotite mica, then potassium feldspar, then muscovite mica, then quartz § The highest temperature minerals are mafic, & the lowest temperature minerals are felsic § In the continuous series, they crystalize in the o rder of calcium rich then sodium rich (continuous series really shows feldspar’s crystallization) The Crystallization of Magma § To create magma you must melt the mantle somehow § Olivine crystalizes first, leaving it behind removed from the magma à now magma just mafic not ultramafic o Deplete magma of different elements o As we deplete it just keeps changing à more intermediate à felsic o The further it moves through the more it evolves o This is how we form felsic rocks from ultramafic