XIII. Active Margins (25 Points)

2. Briefly discuss the growth of an accretionary prism at an active continental margin. Include in your discussion the sediment types contained in an accretionary wedge and the depositional environments in which these sediments were deposited. (5 pts.)

3. Why is there a positive free-air gravity anomaly over the outer high and a negative free-air gravity anomaly over the trench and inner trench wall? Use sketches if you wish. (5 pts).

4. Briefly discuss the variation of K2O across an active continental margin in terms of what the variation is & why it occurs. Use sketches if you wish. (5 pts.)

V. Active Margins (25 Points)

(10 points) A. Draw a schematic structure section across an island arc showing lithospheric and crustal thickness, sites of sediment accumulation, and the accretionary wedge.

B. Briefly describe the manner in which a remnant arc forms in a marginal basin. Use sketches if you wish. (10 pts.)

A. Below is a schematic topographic profile across a well-developed accretionary prism, trench, and outer high. Complete a cross-section here showing: 1) location and orientation of imbricate thrust faults, and 2) distribution of: a) undeformed pelagic sediments, b) undeformed hemipelagic sediments, c) undeformed turbidites, and d) deformed sediments. (15 pts).