3. Atmosphere, Ocean

3. Atmosphere, Ocean - Signature class Lecture 3: Plate...

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Unformatted text preview: Signature class Lecture 3: Plate tectonics, Evolution, Atmospheres, Oceans Atmosphere Oceans Plate Tectonics: Unifying theory Evolution 6371 km radius Inner core solid, out core molten Velocities are lower when molten (outer core) or partially molten (asthenosphere) Explains symmetry on ridges of magnetic anomalies; yields a prediction for ages of magnetic anomaly; what is spreading rate in above example Seafloor spreading as a magnetic tape recorder Answer : 400 km/10 Myr = 40 km/Myr = 4 cm/year (half rate; ocean basin opens 8 cm/yr) Age of Seafloor Not only is there symmetry of the magnetic signature on the seafloor but there is also a similar symmetry with respect to age of the volcanic rocks making up the seafloor relative to the MOR Youngest ocean crust is at MOR (red) and the oldest ocean crust is generally furthest from the MOR (blue, green, and cooler colors) Figure 3-11 Age of the Seafloor MORs are extremely young by geological standardsno more than 2 million years old. Rocks of the seafloor become progressively older as one travels away from MORs. Earthquakes: MOR, subduction zones, and transform faults Earthquake studies of oceanic ridges and trenches provided key evidence needed to further support the emerging theory of plate tectonics. In 1965, a Canadian seismologist, J. Tuzo Wilson, made a major contribution by noting lateral sliding movement at faults near MORs connecting the spreading movements taking place at adjacent ridge segments (Fig. 3-12b) = transform faults. FIgure 3-12 Transform Faults (a) At Mid- Atlantic Ridge, long linear breaks connect spreading movements on adjacent MOR segments. (b) Motion of plates toward or away from each other transformed into motion of plates sliding past each other. Transform faults offset ocean ridges Ridge Ridge FZ FZ Transform fault FZ FZ Spreading direction change Spreading direction change You will be asked to draw this figure!! Plate Tectonics Today Figure 3-13 The Geospheres Tectonic Plates Tectonic plates, many of which include both oceanic and continental lithosphere, come in many shapes and sizes. Arrows indicate some relative motions between plates. Modern tectonic plates move slowly, averaging several cm (a few inches) per year fast as your fingernail grows. Basic tenants of plate tectonics 1) rigidity : the earth's lithosphere is broken into a series of rigid plates justified by fit of continents 2) construction/destruction: plates are created at mid ocean ridges and destroyed at subduction zones; steady state 3) relative motion : plates are in relative motion Which is NOT correct about the Earths magnetic field A) Last reversed 780 ka B) Is like a giant bar magnet in the center with compasses point North (normal) C) Is recorded by cooling rocks which yield + anomalies if they cooled in a normal field and anomalies if they cooled in a reversed field D) Is the result of fluid flow in the oceans E) Acts as a magnetic tape recorder/bar code for sea floor spreading Clicker question: Earths magnetic field A)...
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3. Atmosphere, Ocean - Signature class Lecture 3: Plate...

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