plate tectonics worksheet.v3.doc - u201cGeoworldu201d...

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“Geoworld” Plate Tectonics Lab © 2003 Ann Bykerk-Kauffman, Dept. of Geological and Environmental Sciences, California State University, Chico * Purpose: To better understand the principles of the plate tectonics theory by applying them to the past, present and future analysis of a theoretical planet. Reading Assignment : Any passages on plate tectonics in your textbook. Introduction During this lab exercise, we will analyze the plate tectonics of part of a mythical planet called Geoworld; a tectonic map of the area is shown on p. 9. Geoworld has a plate tectonics system just like ours on Earth, only Geoworld is flat instead of spherical. In answering the questions below, you may assume that the movement rates for plates (both relative and absolute) are constant throughout the time between your past and future reconstructions (they were, however, quite different at one time - see Part 1, A., questions 6 and 7). All questions are in bold face. Please put your answers in any blanks provided. A. Sea FloorMagnetic AnomaliesGeoworld has a magnetic field aligned in a north-south direction. Thepolarity of this field reverses at random intervals through time, just as theone on Earth does. The history of polarity of the magnetic field is wellknown for the past 150 million years and is shown by the adjacent magneticpolarity time scale. Shading represents normal polarity (the magnetic fieldpoints north) while white represents reverse polarity (the magnetic fieldpoints south).Detailed aerial and ship-board magnetic surveys have been conductedover the oceans of Geoworld. Parts of the sea floor have an extra strongmagnetic field while other parts have an extra weak magnetic field. Just ason Earth, the areas with anomalously strong magnetic fields are composedof rocks that are magnetized with the same polarity as the current field whileareas with anomalously weak magnetic fields are composed of rocks that aremagnetized with the opposite polarity as the current field. Portions of thesea floor with an anomalously strong magnetic field are shaded; portions ofthe sea floor with an anomalously weak magnetic field are unshaded.Note that the magnetic anomalies form a striped pattern on the map ofGeoworld. Note also that the pattern in the Elrond Sea is symmetrical whilethat in the Aragorn Ocean is asymmetrical. This is because there is an activespreading ridge in the Elrond Sea but not in the Aragorn Ocean. The centerof symmetry in the Elrond Sea is right along the spreading ridge. *Permission is granted to reproduce this document for classroom use. Copies may not be distributed for profit. Please notify the author ([email protected]) that you are using this material and please describe where and how you are using it. Thank you!Part 1: Analysis of the Present State of Geoworld 1
2 “Geoworld” Plate Tectonics Lab

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