Fina Tuuholoaki's Quiz History_ Laboratory 2 _ Plate Tectonics and the Rock Cycle

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Laboratory 2 : Plate Tectonics and the Rock Cycle Results for Fina Tuuholoaki  Answers will be shown after your last attempt Score for this attempt: 14 out of 15 Submitted Jan 18 at 11:40pm This attempt took 10 minutes.  Question 1 0.2 / 0.2 pts True False   Cheating or plagiarism of any kind will not be tolerated in ESS 101. This includes copying answers from a friend or classmate, copying answers verbatim found on the internet or other literary sources, or copying any work that may answer the question being asked. Make sure you always use your own words when answering the questions in the homework and cite appropriate references if you use them to help you answer the question. Violations the academic code of conduct (https://www.washington.edu/cssc/for-students/academic- misconduct/) will will be reported to the UW Academic Misconduct representative for investigative review. I acknowledge that I have carefully read and understand the above statement regarding the consequences of cheating and plagiarism, and promise to complete my work in this class with honesty and integrity. Answer "True" below supporting your acknowledgement. Learning Goals: By completing this lab, students will become more familiar with: The three types of plate boundaries: convergent, divergent, and transform The different types of magma associated with each type of plate boundary The plate tectonic map of the Circum-Pacific Basin The relationship between plate tectonics, volcanoes, and earthquakes The Hawaii-Emperor Seamount chain and using distance-time relationships of the volcanic islands to describe historical tectonic movement Plate Tectonics Overview

Plate tectonics links together many aspects of geology. Plate tectonics describes how the earth’s thin, outer lithosphere is broken into plates that slowly move over the asthenosphere (Figure 2-1). These brittle rock plates have thicknesses of 10 to 100 km and move over the ductile rock of the asthenosphere at rates of 1 to 10 cm/year. This is about the same rate at which your fingernails grow! The forces that drive plate motion are primarily ridge-push and slab-pull gravity forces. See Incorporated Research Institutions for Seismology video on the forces that drive plate tectonics (select animation tab). (https://www.iris.edu/hq/inclass/animation/what_are_the_forces_that_drive_plate_tectonics) Figure 2-1: Earth’s tectonic plates. The black lines indicate the boundaries between plates, and the red arrows indicate the relative motions at plate boundaries . Chemical and physical layers of the earth Earth’s structure can be classified by chemical composition or by physical properties. The chemical layers of the Earth are the crust, mantle, and core. The crust is mainly composed of igneous rocks (that is, rocks that formed when hot magma cooled at earth’s surface). Continental crust is made of felsic (silica-rich) rocks like granite, and oceanic crust is made of mafic (silica-poor) rocks such as basalt. Below the crust is the mantle , which is made of silicate minerals that are rich in iron and magnesium. Generally, rocks that are silica-rich tend to have relatively lower iron-magnesium (Fe-Mg) content. The physical layers of the outer earth are the lithosphere and the asthenosphere (Figure 2-2). Tectonic plates are pieces of the lithosphere , a layer of brittle rock. The plates slide over the asthenosphere, a layer of ductile, mantle rock. 1

  Figure 2-2: Cross-section of the outer solid Earth . The lithospheric plates slide over the asthenosphere . Oceanic lithosphere forms at mid-ocean ridges (divergent margins) and descends back into the asthenosphere in subduction zones (convergent margins). 2 Plate Boundaries Volcanoes and mountains form at plate boundaries, and plate boundaries produce strong earthquakes. There are three types of plate boundary: 1. Divergent , where two plates are moving apart. 2. Convergent , where two plates are moving together. There are three different types of convergent margins: Ocean-ocean , where oceanic crust converges with oceanic crust. At this type of margin, the denser of the two plates will dive beneath the other, and create a subduction zone (e.g. the Marianas Trench). Ocean-continent , where oceanic crust converges with continental crust. At this type of margin, the denser oceanic crust will dive beneath the less dense continental crust and create a subduction zone (e.g. the Cascadia subduction zone). Continent-continent , where continental crust converges with continental crust. At this type of margin, both plates are relatively buoyant and do not want to sink down. Therefore, subduction does not occur and the two plates collide together to form mountain ranges such as the Himalaya Mountains (formed by the collision of the Indian and Eurasian plates). 3. Transform , where two plates with ocean and/or continental crust are sliding past each other. Volcanoes Volcanoes are places where liquid rock erupts onto the surface of the earth. Volcanoes often form at divergent and convergent boundaries, but they can also form in the middle of plates due to mantle hot spots or rifting. Some important concepts and distinctions for volcanic systems include:

Magma is liquid rock found beneath the surface of the Earth. Lava is liquid rock found on the surface of the Earth. Igneous rocks form when magma or lava cools into a solid. Volcanic rocks are igneous rocks that form on the surface (where cooling of lava is rapid), and plutonic rocks are igneous rocks that form underground (where cooling of magma is slow). Plate Boundary Volcanoes: (1) Divergent Margins As two plates move apart, the space that was once occupied by the plates is replaced by upwelling mantle asthenosphere. As this mantle material ascends, it experiences decreasing pressures, which causes it to melt. This process is known as decompression melting. Eventually, this melt either reaches the surface as basaltic lava and cools to create a new crust, or it cools as basaltic magma beneath the surface to create new mantle lithosphere. All oceanic lithosphere is created in this way at mid-ocean ridges (Figure 2-3). Figure 2-3: Divergent plate margin and zone of upwelling of magma. Oceanic lithosphere is generated at the ridge axis, cooling and increasing in thickness as it moves away from the plate margin. [From Igneous Petrogenesis by M. Wilson.] (2) Convergent Margins At convergent margins, if one plate is denser than the other it will subduct beneath the less dense plate, forming a subduction zone. Subduction zone magmas form when the downgoing plate is heated and thus dehydrated. The water squeezed out of the subducting plate lowers the melting point of the rocks in the overlying mantle and initiates melting. This is like how adding salt to ice lowers the melting point of the ice, allowing the ice to melt at a colder temperature. This magma rises and erupts on the surface of the Earth, resulting in volcanic activity. At ocean-ocean subduction zones, this volcanic activity creates an arcuate chain of volcanoes on the overlying plate known as an island arc (e.g. the Philipine and Aluetian islands, Figure 2- 4A). At ocean-continent subduction zones, this same feature is called a continental arc (e.g. the Cascades and Andes volcanoes, Figure 2-4B). Island arc magmas only pass through oceanic lithosphere (which is predominantly basaltic) on their way to the surface, so their composition tends to be more mafic, ranging

from basalt to andesite . Continental arc magmas pass through and mix with continental lithosphere, which is more felsic. As a result, continental-arc magmas are on average andesitic and range in composition from basaltic to rhyolitic. Figure 2-4: A Schematic of an island arc at an ocean-ocean convergent margin. B Schematic of a continental arc at a continent-continent convergent margin. Table 2-1 provides an overview of the different magma generation processes, magma compositions, and landforms found at each type of plate boundary. Intraplate Volcanoes: (1) Hot spot Volcanism A hotspot is caused by the upwelling of hot, buoyant material in the deep mantle. The upwelling rock melts as it nears the earth’s surface and causes a volcano to form. As the tectonic plate moves over the stationary hot spot, a line of volcanoes is created over the course of millions of years. If a hotspot is located beneath oceanic crust, then it can produce a chain of basaltic islands erupted onto the ocean floor, such as the Hawaii-Emperor Seamount Chain (the Hawaii hotspot, Figure 2-5C). If a hotspot is located beneath continental crust, then it can produce a chain of volcanoes on land, such as the eastern Snake River Plain (the Yellowstone hotspot). Hot spot volcanism is typically basaltic. See this video about hot spots. (https://www.iris.edu/hq/inclass/animation/hotspot_volcanism_thermal_plume) Figure 2-5: Schematic of hot spot volcanism. A Rising plume of hot mantle rock B Hot spot with a large pool of magma under plate, causing lava to flood onto the surface and cool to form basalt. C Formation of an island chain as the plate moves over the stationary hot spot . 3 4

  Table 1 : A Synthesis of plate boundaries, magma formation processes, magma compositions, plate tectonic landforms, and real-world examples Plate Boundary Magma generation Magma composition Landforms produced Examples DIVERGENT decrompression of mantle basaltic (mafic) mid-ocean ridge; continental rift Mid-Atlantic Ridge, Juan de Fuca Ridge, East African Rift CONVERGENT (ocean-continent subduction) dehydration of subducting slab, hydration melting of mantle, and mixing with continental crust andesitic to dacitic (intermediate) continental volcanic arc Cascadia Subduction zone (PNW), Andes Mountains (South America) CONVERGENT (ocean-ocean subduction) dehydration of subducting slab, hydration melting of mantle basaltic to andesitic island arc Aleutian Islands, Philippines CONVERGENT (continent-continent collision) partial melting of continental crust due to collision thickening granitic (plutonism) high non-volcanic mountain range (interior of continent) Himalayas Alps, Appalachian Mountains (ancient collision mountain range) TRANSFORM uncommon N/A small mountains and basins along "bends in fault" San Andreas Fault, California Note: We do not discuss continent-continent convergence in this lab. For questions 1 to 28, open up the large JPEG file of the Plate Tectonics Map of the Circum- Pacific Region (https://canvas.uw.edu/courses/1699809/files/113584913/download? download_frd=1) and/or look at the cropped figures provided below The map title is located in the upper left corner of the map. Directly below the map's title, the bathymetry ( ocean depth ) scale is shown. Use this information to answer question 1 (a-c).

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