Geoworld Tectonics Lab.docx - Name Date Geoworld Plate...

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50 My 100 My 150 My Years past Name ____________________________________________________ Date: _________________ Geoworld Plate Tectonics Lab © 2013 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, which 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 final answers in any blanks provided. Part 1: Analysis of the Present State of Geoworld A. Sea Floor Magnetic Anomalies Geoworld has a magnetic field aligned in a north-south direction. The polarity of this field reverses at random intervals through time, just as the one on Earth does. The history of polarity of the magnetic field is well known for the past 150 million years and is shown by the adjacent magnetic polarity time scale. Shading represents normal polarity (the magnetic field points north) while white represents reverse polarity (the magnetic field points south). Detailed aerial and ship-board magnetic surveys have been conducted over the oceans of Geoworld. Parts of the sea floor have an extra strong magnetic field while other parts have an extra weak magnetic field. Just as on Earth, the areas with anomalously strong magnetic fields are composed of rocks that are magnetized with the same polarity as the current field while areas with anomalously weak magnetic fields are composed of rocks that are magnetized with the opposite polarity as the current field. Portions of the sea floor with an anomalously strong magnetic field are shaded; portions of the sea floor with an anomalously weak magnetic field are unshaded. Note that the magnetic anomalies form a striped pattern on the map of Geoworld. Note also that the pattern in the Elrond Sea is symmetrical while that in the Aragorn Ocean is asymmetrical. This is because there is
an active spreading ridge in the Elrond Sea but not in the Aragorn Ocean. The center of symmetry in the Elrond Sea is right along the spreading ridge.

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