Lab 4 Volcanoes and Igneous Rocks Online Supplement

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University Of Georgia *

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Geology

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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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