Final Exam Review.docx - Final Exam Review Paleomagnetism and geomagnetic pole paths Earth\u2019s magnetic field Flow in the liquid outer core create the

Final Exam Review.docx - Final Exam Review Paleomagnetism...

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Final Exam Review: Paleomagnetism and geomagnetic pole paths Earth’s magnetic field: Flow in the liquid outer core create the magnetic field: o It is similar to the field produced by a bar magnet o The magnetic pole is tilted ~11.5 from the axis of rotation Geographic and magnetic poles are not parallel A compass points to magnetic N, not geographic N The difference between geographic N and magnetic N is called declination, it depends on: o Absolute position of the two poles: Geographic north Magnetic north Longitude Curved field lines cause a magnetic needle to tile Angle between magnetic field line and surface of the Earth is called inclination, it depends on: o Latitude Magnetic poles: The magnetic pole intersects Earth’s surface just like the geographic pole does: o Magnetic N pole and magnetic S pole both exist o Magnetic poles are located near geographic poles o Magnetic poles move constantly Rock magnetism can be measured in the laboratory The study of fossil magnetism is called paleomagnetism Paleomagnetism: Rock magnetism can be measured in the laboratory The study of fossil magnetism is called paleomagnetism Iron (Fe) minerals in rock preserve information about the magnetic field at the time the rocks formed
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o Declination and inclination preserved n rocks often vary from present latitude and longitude o Instruments used in paleomagnetism record changes in position o This data is used to trace continental drift Iron minerals archive the magnetic signal at formation Hot magma o High temperature, no magnetization Thermal energy of atoms is very high Magnetic dipoles are randomly oriented The Juan de Fuca ridge and plate Basic Principles of Plate Tectonics: Divergent Boundary: Tectonic plates move apart Lithosphere thickens away from the ridge axis New lithosphere created at divergent boundary Also called: mid-ocean ridge, ridge Convergent Boundary: Tectonic plates move together The process of plate consumption is called subduction Also called: convergent margin, subduction zone, trench Transform Boundary: Tectonic plates slide sideways Plate material is neither created nor destroyed Also called: transform fault, transform Mid-ocean ridges: Sea-floor spreading opens the axial rift valley Rising asthenosphere melts, forming mafic magma o Pillow basalt: magma quenched at sea-floor o Dikes: preserved magma conduits
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o Gabbro: deeper magma Subduction Zones: Lithospheric plates move toward one another One plate sinks back into the mantle (subduction) The subducting plate is always oceanic lithosphere Continental crust cannot be subducted, too buoyant Subduction is balanced by sea-floor spreading Earth maintains a constant circumference Convergent boundaries are also called Subduction Zones The Juan de Fuca ridge: Tectonic spreading centre located off the coasts of the state of Washington and the province of British Columbia
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