Lab 4 Volcanoes and Igneous Rocks Online Supplement
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Feb 20, 2024
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Lab 4: Spring 2024
Lab 4: Born of Fire: Volcanoes and Igneous Rocks Online Supplement
Student Name: Emily Matthews
(For TA Use) Raw score_____/37
Points______/100
To complete this lab, find supplied materials in eLC (where you got this file) in the folder Assignment Lab 4: Volcanoes and Igneous Rocks Due Thursday at 6 pm. Use a word processor to modify this file and type in your responses. Whatever word processor you use,
save your work as a PDF or Word Doc and upload it to eLC.
Write down questions that develop and ask your TA during your lab meeting time or via email. Familiarize yourself with the slides in eLC
and watch any videos linked
. Linked videos are in your slideshows AND on this worksheet. Answer the questions below to receive credit. Items are not necessarily in order, so you will have to do some searching and remember where you have found things and go back to them.
Many processes that result in the formation of new rocks require significant amounts of heat, and often a lot of pressure. Rocks formed from heat are often related to volcanoes: the ejecta that erupts from volcanoes is molten rock, and its’s obviously quite hot. Underneath a volcano, other rocks crystallize from magma deep underground, in similarly hot environments with varying amounts of (but generally high) pressure. These rocks that are born of fire are called igneous rocks. 1)
Igneous rocks are basically distributed into two groups: volcanic and plutonic. Volcanic rocks are more obvious – these ooze or explode out of volcanoes, having once been liquid magma. What does “plutonic” mean in terms of rock?S (3 points)
Plutonic rocks are created when magma slowly cools under the earth’s surface which gives the minerals time to crystallize and grow big. 2)
One thing that controls whether or not we would classify a rock as volcanic vs plutonic is cooling time. Which rock type cools faster, a volcanic rock or a plutonic rock? (1 point)
A volcanic rock
3)
If we were to run a field trip to the side of an erupting volcano, what rock textures would you expect to see in the brand new rocks? (2 points)
A vesicular texture would be seen in brand new rock.
4)
From the video with minerals at the Mica Mine, the igneous rock called pegmatite has intruded into older metamorphic rocks called schist. https://www.youtube.com/watch?v=wa4_bC4tgc8
Is a pegmatite a plutonic rock or a volcanic rock? (1 point)
Plutonic rock
Lab 4: Spring 2024
5)
What does it mean for a rock to intrude into another rock? (use both the Mica Mine video and slides) (2 points)
It means that the magma intruded with other rocks and the temperature of it pressurized the rock, heating it, crystallizing it, and then it cooled down. 6)
What does the term “pegmatite” mean? (1 point) Pegmatite means that it is a type of granite with large crystals
Enchanted Rock
(photo from Texas Parks and Wildlife)
Enchanted Rock is an immensely large, pink granite batholith in the Llano Uplift of Central
Texas. At present the granite emerges 425 feet above the surrounding land. Legend states that
it was given its name when the Tonkwa Native American tribe believed a Spanish conquistador
had cast a spell on it, making magical ghost fires seemingly appear to burn at the top. Today,
however, it serves as a staple of Texas geology.
Please watch this video before proceeding: https://www.youtube.com/watch?
v=hZg6faPBHaA
Lab 4: Spring 2024
7)
According to the video, Enchanted Rock initially formed when a bubble of relatively low-density magma intruded into the overlying metamorphic material. The metamorphic material that now surrounds the eroded granite is known as the Packsaddle Schist.
A.
What name do scientists call this granite at Enchanted Rock? (1 point)
Town Mountain Granite
B.
List three minerals you would expect to find in the granite. (3 points)
Quartz, Potassium Feldspar, Sodium Feldspar
C.
Describe the most important texture you would typically look for in a schist
like the Packsaddle schist. (2 points)
Schistosity of foliation 8)
Out of the Town Mountain Granite and Packsaddle Schist, which would you expect to be the older
of the two? (1 point)
Packsaddle Schist
9)
Like an onion or an ogre, Enchanted Rock has layers. When this granite rose to the surface these
layers began to “peel” away due to release on stress on the rock as overlying rocks eroded away. What is the word for the process scientists use to describe the layers “peeling off”? It’s a specific type of weathering, which we also talked about last week.
(1 point)
Exfoliate
10) In many parts of the Texas hill country you can find chunks of granitic batholith emerging up from the ground, though none quite as impressive as Enchanted Rock.
A.
What variety of igneous rocks would you expect to see in a batholith? Extrusive or Intrusive?
(1 point)
Intrusive
B.
What is the cooling rate associated with the kinds of rocks commonly observed in a batholith? (1 point)
Slow Cooling
C.
What crystal sizes would you expect to see? (1 point)
Large crystal size
11)
Wind
and Water
are the two key agents of erosion most prevalent at a place like Enchanted Rock. (2 points)
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Lab 4: Spring 2024
12) As you learned in the video, erosion is constantly happening at Enchanted Rock. Despite this, some minerals in rocks tend to erode away faster or slower than others. Say, for instance, you went to a Texas beach nearby to Enchanted to cool off after the long hike. What is the primary mineral you would expect to find in the sandy beach? Why is this? (1 point)
Quartz because it is difficult to weather or erode
13) The origins of Enchanted Rock can be traced as far as approximately 1.4 billion years ago in a region of primitive tectonic plates that would ultimately collide and form the supercontinent known as Rodinia, which was a super continent BEFORE the more well-known Pangaea. Their inevitable collision was as a result of a subducting plate forming between the continents, drawing one towards the other. As the southern continent crashed into its northern counterpart, the crust thickened to about 90 kilometers with temperatures as high as 750 degrees Celsius. This spawned massive terrestrial deformation and regional metamorphism. At some point the subducting slab broke off, thus causing some asthenosphere to thrust past the melt zone. Melted rock began to rise through the crust with some larger plutonic bodies known as _____ rising as well. (1 point)
a)
Batholiths
b)
Dikes
c)
Sills
d)
Laccoliths
The following questions are about Yosemite National Park:
Lab 4: Spring 2024
14) Why are the rocks at Yosemite National Park typically very strong? (from the slides, you should have watched this video) https://www.youtube.com/watch?v=Y5RQp77uVPA
(1 point)
The rocks at Yosemite National Park are typically strong because they are mostly granite, which is typically at high temperatures which causes the grains to become very tightly compacted and removing the cracks. Once the rock starts to slowly cool the grains into their tight compaction
15) What minerals forms the large knobs that many rock climbers use when climbing cliffs in Yosemite National Park? (1 point)
Feldspar
16) Why are the granite surfaces polished in some part of Yosemite? (1 point)
Glaciers
General Igneous Rock Questions
17) What is the age relationship between a rock 1 that is intruded by rock 2? (2 points)
a.
Rock 1 is older than rock 2
b.
Rock 2 is older than rock 1
c.
Rock 1 and 2 are the same age
d.
There’s no way to tell if rock 1 or rock 2 is older.
18) Rock ID: What is the name of this rock? (1 point)
Lab 4: Spring 2024
Basalt
19) What is the name of this rock (below)? (1 point) Diorite
20) Is this rock volcanic or plutonic? (1 point) Plutonic
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Lab 4: Spring 2024
21) What is the name of this rock (below)? (1 point) Obsidian
22) Is this rock volcanic or plutonic? (1 point) Volcanic
23) What type of rock is this? (1 point) Granite
24) Is this rock igneous, metamorphic, or
sedimentary? (1 point) Igneous