GEOL 310 Final, Fall 2005

1 The American University of Beirut Department of Geology Global Tectonics (Geol 310) Fall 2005-2006: Final Examination Dr. Maya El-Kibbi Time: 3 hours Pledge Exam rules apply. I. - Based on the diagrams below, compare proposed driving mechanisms of plate tectonics. (12 pts) - Which mechanism appears to be more significant today? Defend your answer. (8 pts) 2 II. - Give the main characteristics of the mantle transition zone. (7 pts) - Explain the effect of the nature of the mantle transition zone on the vertical extent of mantle convection. (7 pts) - Draw a LABELED diagram to illustrate your explanation. (6 pts) III. - Briefly discuss the geometric model behind the depth-age relationships (given below) and define the variables (d) and (t). (5 pts) t d = 2500 + 350 / 62 8. ) 6400 3200exp( t d − − = - Explain why this model applies to ocean ridges and draw a simple sketch to illustrate your answer. (5 pts) IV. - Explain how seismic tomography of the mantle (including anisotropy modeling) can contribute to our understanding of the motion of the plates. (20 pts) V. - In your opinion, what is the importance of the notion of fixed hotspots in studying plate movements? (7 pts) - What is the significance of using a geomagnetic polarity timescale in studying plate motions? (7pts) - How can you relate the significance of the notion of fixed hotspots to that of reversals of the geomagnetic field? (6pts) 3 VI. Consider the figure below: (10 pts) - Using graph paper, draw a velocity vector diagram showing the configuration of the plates. - Calculate the relative motion between plates A and B. - Draw arrows at each plate boundary to show motion of each plate relative to the other. - Analyze the stability of the triple junction. Label the velocity lines.