6. Cross cutting age relations indicate that dike A is younger than dike B, whic

Question

6. Cross cutting age relations indicate that dikeA is younger than dike B, which is cut by fault F2 (see below). Dike B yields a K-Ar date of 99.9 +/- 2.3 million years based on analyzing potassium feldspar and Dike A yields a date of 45.1 +/- 3.1 million years based on analyzing amphibole.. Fault F2:

a. is older than 99.9 Ma.

b. Is younger than 45.1 Ma.

c. Is a reverse fault and it must be older than 45.1 Ma, but younger than 99.9 Ma.

d. Dike A is of silicic composition and dike B is of mafic composition.

e. Dike B is Cenozoic in age.

f. None of the above

7. Which of the following statements is true?

a. the core mantle boundary is called the Mohorovicic discontinuity

b. the ocean crust, like the Moon, has a lot of green cheese.

c. the crust is denser than the mantle

d. P and S waves travel faster in the mantle than in the crust

e. The depth to the core mantle boundary is aobut 6400 km f. all of the above

11. In the Dallas area of north Texas

a. heat flow is relatively low

b. nearly flat-lying sedimentary rocks of Cretaceous age, the Austin Chalk, lie very close to the earth’s surface (e.g., they are well exposed in several road cuts, like the North-South Tollway)

c. the soil on top of the Austin Chalk is very rich in organic material (i.e. dark gray to black)

d. a very broad, regional disconformity is in the process of being developed, assuming the depositional environment of the region will change with time and the area will be covered by younger sediments.

e. the crust is between 30 and 45 km thick.

f. none of the above g. all of the above

12. To quantify the flow of heat from the interior of Earth at any specific site, one needs to know

a. only the geothermal gradient at site A.

b. only the thermal conductivity of one rock below site A.

c. just the fact that the temperature of our home increases with depth.

d. Both the geothermal gradient below site A and the thermal conductivities of rocks typical below the area of Site A.

e. The color of the rocks below site A.

f. The age of the rocks below site A.

15. The San Andreas fault system

a. consists of a series of strike slip faults along which the Pacific ocean lithosphere plate is moving northward relative to North America

b. is no longer active

c. consists of several reverse faults, dipping to the west, allowing the western margin of California to fall into the Pacific ocean

d. consists of a series of strike-slip faults along which the Pacific ocean lithosphere plate is moving southeastward relative to North America

e. has resulted in numerous earthquakes with focal depths greater than 500 km.

Explanation / Answer

6. Cross cutting age relations indicate that dike A is younger than dike B, whic

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