4. You are out in the field and stumble upon an aesthetically pleasing rock; you

Question

4. You are out in the field and stumble upon an aesthetically pleasing rock; your colleague tells you that it is part of a large mafic dike and it has been dated using U-Pb zircon methods as 450 +/-1.3 million years; what geologic EON does it belong to? _____________________________

5. In the vertical cross section BELOW, fault F3 is a moderate angle reverse fault. What relationship demonstrates this? ______________________________________________________. Assume you look to the north in this cross section, in which direction does the fault dip? _________________. What is the strike of the fault? ________________________ In a relative sense, when did motion along this fault occur? __________________________________________.

8. Most earthquake foci in continents are located at depths less than about 20 km. Why? ______________________________________________________________________________ ____________________________________________. Earthquakes with foci at depths greater than about 20 km are typically referred to as “deep focus” earthquakes. Where do these occur, and why? _________________________________________________________________ ________________________________________________________________________________.

9. How was the boundary between the crust and mantle initially discovered? __________ _________________________________________________________________________________. In the middle of a continent (e.g., Kansas), about how thick is continental crust? _____________________. Have we ever drilled to the crust mantle boundary in any continent? _____________________.

10. Generalizing, what three general plate tectonic environments are responsible for most earthquakes? ______________________________________________________________ ____________________________________________________________________________.

11. BELOW, please draw a cross section, looking north, of a syncline oriented such that the east limb dips about 20 degrees to the west and the west limb dips 60 degrees to the east. Label the relative ages of the rocks involved. If the syncline does NOT plunge, what is the orientation of the strikes of the beds that are folded? ___________________________.

Explanation / Answer

4.

Answer: Pleistocene

Explanation: The age of the rock is 1.3 million years by U-Pb zircon method, so this rock must belongs to a period of Cenozoic and with a period of Pleistocene.

8.

The thickness of continental crust is 30-35 km and below it’s a semi liquid asthenosphere presented. Asthenosphere is very hot and generates convection currents. The impact of asthenosphere upon the crust is high because it is tightly bounded by the crust. Hence, the chance of expulsion of hot magma is high. Thus, the rocks which are less than 20 km, has less compaction and does not stay more time. If the forces of upper layers and down layers on the crust is high then the rocks come out.

Deep focus earthquakes generally occur at plate boundaries of oceanic and continental. The depth of deep focus Earthquakes is nearly 150 km to 700 km.

9.

The boundary between the crust and mantle is discovered by using of seismic waves. Seismic waves get refracted at the boundary of crust and mantle and also the velocity of seismic waves increase suddenly. Due to the phenomena of seismic wave reflection gives evidence of boundary of crust and mantle.

10.

The following three are the main reason for the plate tectonic environments:

Extensional plate boundary

Transform plate boundary

Compressional plate boundary

Related Questions

Navigate

• Browse (All)
• Browse 4
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.