Tectonics Spring 2012  General Questions

The following questions cover important aspects of Earth tectonics.  Sketches are essential to most of the answers.  Wherever possible, try to provide some references to key workers (and papers) who have made important contributions.

(1)  Whole Earth

(a)   Draw a cross section of Earth and locate the boundaries of the continental crust, ocean crust, lithosphere, asthenosphere, mantle, outer core and inner core. Keep the depth to scale, but use an inset if necessary.

(b)   Show a P-wave seismic profile through the sketch, and define the major discontinuities and gradients, particularly the mantle discontinuities.

(c)   In words and diagrams, define the adiabatic gradient, geothermal gradient, and mantle solidus.  Use these curves to illustrate the general behavior of mantle plumes, particularly those that originate near the core-mantle boundary.

(3) Ocean Crust and Ridges

(a) Draw a cross-section of ocean crust showing the major seismic domains and a geologic interpretation for these domains.  Discuss the difference(s) between the seismic or geophysical MOHO and the petrological MOHO.

(b) What is the classical "infinite onion" model for the generation of ocean crust.  How have modern studies modified this picture (For example, what is the AMC reflector and LVV, how big is it and what does it imply)?

(c) Contrast the physical structure of fast ocean ridges and slow ocean ridges.  Give an example of each.  Discuss along-strike variations along a ridge system.