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Introductory Geology

by: Imani Millington

Introductory Geology GEOL 1121K

Imani Millington
GPA 3.8

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About this Document

chapters 2, 4 and interlude C
Introductory Geology 1
Hidalgo Odio
Study Guide
Geology, geology notes, Introtogeology, GeorgiaStateUniversity
50 ?




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This 3 page Study Guide was uploaded by Imani Millington on Saturday October 8, 2016. The Study Guide belongs to GEOL 1121K at Georgia State University taught by Hidalgo Odio in Fall 2016. Since its upload, it has received 14 views. For similar materials see Introductory Geology 1 in Geology (GEOL) at Georgia State University.


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Date Created: 10/08/16
Study Guide: Geology Chpt 2, 4, interlude C Chapter 2: How Plates Work Magnetic fields  Magnetic anomalies are found on the continents and sea floor. they create irregular patterns on continents and distinct  alternating bands on the sea floor.  Earth’s magnetic field is created by the flow of liquid iron in the Earth’s molten outer core (electromagnet)  Polarity chrons have nothing to do with magnetic strength. Time intervals between reversals differ so he lengths of  polarity chrons also differ  Paleomagnetism­ study of fossil magnetism   Anomalies­ a symmetrical relative to mid ocean ridges. Anomaly patterns represent alternating stripes of normal  polarity and reversal polarity seafloor  Positive anomalies­ stronger than expected (dipole points south for both earth and sea floor)  Negative anomalies­ weaker than expected (dipole reverses points to the north for earth and south for seafloor) Mid Ocean Ridge  Gabbro does form along the sides of magma chambers in the crust below the ridge axis but the magma that rises to  become seafloor cools to form basalt   The seafloor is spreading of mid ocean ridge axis is moving at a rate of 5 cm per year  the mid Atlantic ridge is in the middle of its ocean but this is not true for mid ocean ridges in the pacific and Indian  oceans  Oceanic lithosphere attains maximum thickness when it’s about 80 million years old.  Accretionary prisms form due to the process of subduction (as the sediment are the down going slab the overriding  plate scrapes them off and the prisms form  Asthenosphere is part of the mantle not the core it supports the lithosphere, and is warm enough to flow slowly   The center of the mid­ocean ridge is where new oceanic lithosphere is being created. Molten basalt is rising in the  trough of mid ocean ridge. The crust is the hottest here and the youngest less dense of all ocean crust   Ocean crust consists primarily of basalt and does not have the wide variety of rock types of continental crust  Plate tectonics  Contact between lithosphere plates is called a plate boundary passive margins do not occur at plate boundaries  A subducting plate is always oceanic lithosphere   Plates motion ranges from 1­15 cm per year  The Himalayas are growing because a continental plate is colliding with another continental plate India crashed into  Asia 40 million years ago. Neither plate can subduct so the continental crust is forced upward  Mantle plumes are the possible cause for hot spots but they do not affect plate movement in a meaningful way   According to the mantle plume model, hot spot plumes originate deep in the mantle just above the core­mantle  boundary. Alternative explanations of hot spot volcanoes propose plumes at shallow depth or no plumes at all  The chain of volcanoes along the west coast of south America (the Andes mountains) exist because an oceanic plate is  subducting under the western edge of the south American plate  Lithosphere consist of the crust and the upper mantle and behaves like a hard layer that breaks and bend. The  lithosphere and asthenosphere is similar and composition   Divergent boundary­ plates move away from each other   Convergent boundary­ different types of plates colliding   Transform boundary­ move sideways past each other  Wegner plate theory    Apparent polar­ wander paths are created by measuring the paleomagnetism in rocks in rocks of different ages from  the same location­thus the paleopole at each different age can be reconstructed to create a polar wander path through  time for that location.   Ocean crust is primarily young basalt, while continental crust is much older and has a range of compositions. Has been  confirmed, Glomar Challenge, there is a thin package of sediment on top of ocean crust and that it thickens away from  the ridge axis  Wegner could not adequately explain how or why the continents moved.  Evidence from climate, fossils distributions  and land shapes supported plate tectonics theory   The theory of plates tectonics, which was derived from Wegner’s proposal of continental drift in the 1920’s was not  accepted till the 1960’s  Study Guide: Geology Chpt 2, 4, interlude C  Inclination­ tilt of a campus needle from the horizontal depends on latitude (north or south) the longitude (east and  west)  Declination­ difference between magnetic north and geographic north. Changes with   The global occurrence of earthquakes reveals that they usually occur on the boundaries of plates or at hot spots   It was not until world war II that scientist produced maps of earthquakes distribution, which indicated the presence of  seismic zones along trenches, mid ocean ridges and fracture, mid ocean ridges and fracture zones long after wegner’s  time Chapter 4: Magma and igneous rocks Igneous Rocks  “wet” igneous rocks melt at a lower temperature than “dry” igneous rocks because the additions of volatiles in “wet”  rocks lower their melting temperature. Volatiles break down chemical bonds.  Pumice is a felsic (high in SiO2) vesicular (air bubbles) rock that contains abundant vesicles which makes it less dense  than water   Water quenching igneous rocks create a glassy texture   Tectonic settings for igneous activity  o Hot spots o Continental rifts  o Volcanic arcs bordering ocean trenches  Granite is a felsic, intrusive, coarse grained igneous rock. Often found in plutons.  Flux melting (addition of volatiles) occurs when a down going slab adds water to the surrounding asthenosphere.  Creates a rising melt   Vesicles­ air pockets or bubbles frozen igneous rocks as gas escaped during cooling  The batholith is light colored granite­an intrusive, coarse grained, igneous rock. Dark colored fine grained basalt is an  extrusive igneous rock  Magma and Lava  Magma compositions evolves as rock as rock melts due to partial melting and assimilation process  Hotter the magma the viscous it is and the faster it flows  Magma will cool and freeze when its volatile content decreases. Cools faster in the presence of circulating ground  water not slower and it will cool faster if the surface area is higher. Deeper the magma the longer the cooling time  Magmas formed at different locations under different conditions can meet and mix which can affect the compositions  of the resulting magma  Pillow basalts are bulbous flows of molten basalt low in silica that cool and harden as they are expelled into seawater  Large igneous provinces may occur on the seafloor or on land along margins or in the interiors of oceanic plates or  continents   Pillow lava forms by extrusive flows at mid ocean ridges where seawater rapidly cools basaltic lava into pillow shaped  blobs   Batholiths are immense regions where several plutons intrude laccoliths are domed injections of magma and sills are  tabular intrusions  Felsic magma is more viscous because the silicon tetrahedral link up in chains, tangle and impede smooth flow  (microscopic level)  Igneous rocks are only coarse grained if they cool slowly beneath the earth’s surface  Mafic minerals­basalt and gabbro  Volcanic arcs formed at convergent plate boundaries as a result of subduction Minerals and composition   Pegmatites have cooled quickly but are coarse grained because they form in water­rich melts that allow atoms to move  around quickly and develop large crystals   Radioactive decay was a heat source for early earth, there are many radioactive elements left and they’re still decaying  and heating earth’s interior  Study Guide: Geology Chpt 2, 4, interlude C  A black, fine grained tabular intrusion between two layers of horizontal sedimentary rock must logically be a basaltic  sill  Dikes cut across existing layers   Bowen’s reaction series allows geologist to predict what minerals will be found in a given igneous rock. Was  established by laboratory experiments in which mafic melt was quenched in mercury. Forms sequence of which  different silicate mineral form from a mafic melt   Pyroclastic refers to fragments that have been exploded out of a volcano  Any fine grained material making up the majority of the rock could be the groundmass and plagioclase could be  phenocryst  Interlude C: Rock cycle    Atoms that move through the rock cycle do not move at the same rate  Rocks found at the earth’s surface are all different ages   A new material can enter the rock cycle as magma rises from the mantle and enter the crust  At one time or another a rock will be subducted to make igneous rocks  The moon has no atmosphere, oceans or active plate tectonics system, the rock cycle does not exist   Rock types within the rock cycle can become either another rock type or the same rock type the same processes  Plate interactions as a result of plate tectonics ultimately generate the various geologic settings where material can melt, metamorphose, and/or weather to become sediments  1. Weathering/transport/deposition/lithification 2. Heat and pressure 3. Melting


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