GL 107 Earth Systems Science
K. Hannula
Discussion questions for 10/8/07
1. What is the difference between ductile and brittle deformation? At what conditions do rocks deform in a brittle manner?
Brittle deformation: rocks crack and break, forming faults. Brittle deformation occurs at cold temperatures, near Earth's surface.
Ductile deformation: rocks bend and flow, forming folds and foliations. Ductile deformation occurs at warm temperatures (but below the melting point of rocks), deeper in the crust and in the mantle.
2. Define the following terms:
anticline: A fold warped upward in the middle. (Technically, a fold with the oldest rocks found in the middle.)
syncline: A fold warped downward in the middle. (Technically, a fold with the youngest rocks in the middle.)
monocline: A step-like fold, with one horizontal limb and one steep limb.
dome: A circular or elongate upwarp. (The San Juan Mountains are a structural dome.)
basin: A circular or elongate downwarp. (There is a basin south of Durango called the San Juan Basin.)
3. (Specific answer is not in book) Durango lies on the northern edge of the San Juan Basin. What does that mean about the shape of the local rock layers?
The rock layers in Durango all tilt downwards to the south, and dive underneath younger rocks in the San Juan Basin in southern Colorado and northern New Mexico.
4. Define the following terms:
dip-slip fault: Fault with vertical (up and down) movement.
normal fault: Dip-slip fault in which the hanging wall moves down and the foot wall moves up.
reverse or thrust fault: Dip-slip fault in which the hanging wall moves up and the foot wall moves down.
strike-slip fault: Fault with horizontal movement.
joint: Crack in rock along which no movement occurs.
5. In what tectonic setting do normal faults typically form?
Divergent plate boundaries and continental rifts.
6. In what tectonic setting do thrust faults typically form?
Convergent plate boundaries.