Worksheet D. 1 (a) Check and double-click the placemark for Problem 1a in the D.

Question

Worksheet D. 1 (a) Check and double-click the placemark for Problem 1a in the D. Igneous Rocks worksheet folder to fly to the spectacular Half Dome in Yosemite National Park. Given that it is part of an intrusive batholith, what type of rock texture would you expect to see at Half Dome? Select one:

a. fine-grained

b. coarse-grained

c. glassy

d. fragmental

Worksheet D. 1 (b) Visitors commonly note the rounded appearance of the back side of Half Dome. It was not polished by glaciers, but rather fractured off in sheets much like how one might peel layers from an onion. This process occurs because these rocks formed at ~20-25 km depth, but have experienced a removal of confining pressure since they are now exposed at the surface (think of how a sponge expands once you remove your hands pressing down on it). What is this process called? (Hint: Look these words up in your glossary). Select one:

a. stoping

b. assimilation

c. fractional crystallization

d. exfoliation

Worksheet D. 1 (c) Check and double-click on the "North America Batholiths map" in the folder labeled Problem 1. You will see the exposed batholiths of the western United States. Using the transparency slider at the bottom of the Places panel, make the overlay semi-transparent. To get a sense of the size of the Sierra Nevada batholith, determine its length between placemarks for Problem 1c using the Ruler Tool (in km). Select one:

a. 100-130 km

b. 300-340 km

c. 700-720 km

d. 1000-1030 km

Worksheet D. 1 (d) Check and double-click on the red polygon for the Henry Mountains laccolith complex in the folder labeled Problem 1. This complex consists of many blister-like intrusions. Note the size difference between this intrusion and the Sierra Nevada batholith. Estimate how much smaller in length the Henry Mountains laccolith complex is relative to the batholith. Select one:

a. ~1/2

b. ~1/4

c. ~1/6

d. ~1/17

Worksheet D. 1 (e) Placemark Problem 1e highlights a tabular intrusion from the main laccolith that is parallel to the upturned sedimentary layers. What kind of intrusion is this? Select one:

a. sill (a tabular intrusion that inserts between sedimentary layers)

b. dike (a tabular intrusion that cuts across sedimentary layers)

Worksheet D. 2 (a) Check and double-click placemark Problem 2a to fly to the Spanish Peaks, CO area where some prominent volcanic centers are visible. Which of the following statements is incorrect? Select one:

a. igneous rock comprising the dike is more resistant to erosion than the surrounding rock

b. there are no similar dikes in the surrounding area

c. the dike is very linear, implying that magma likely filled a crack

d. the dike's magma source is likely related to the Spanish Peaks volcanic center

Worksheet D. 2 (b) Check and double-click the placemarks for Problems 2b-i, -ii, and -iii. These place marks highlight dikes filling radial fractures from the volcanic neck at Shiprock. Which of the following is the most reasonable explanation for this pattern?

Select one:

a. they filled fractures that existed in the area before the volcano developed

b. the volcanic magma chamber created pressures that fractured the rocks in a radial pattern

c. this fracture pattern is accidental and random

d. the fracture pattern is controlled by the nearly horizontal sedimentary rock layers

Explanation / Answer

Worksheet D. 1 (a) : b.) coarse grained

Worksheet D. 1 (b) : d.) exfoliation.

Worksheet D. 1 (c) : c.) 700-720 km

Worksheet D. 1 (d) : b.) ~1/4

Worksheet D. 1 (e) : a.) sill ( a tabular intrusion that inserts between sedimentary layers).

Worksheet D. 2 (a) : b.) there are no similar dikes in the surrounding area.

Worksheet D. 2 (b) : b.) the volcanic magma chamber created pressures that fractured the rocks in a radial pattern.

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