HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.

HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.

HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.

HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.On the syllabus, one of the goals stated for this course is for you to be able to interpret how arock or outcrop (rock exposure) that you observe around Boulder, CO may have formed.This homework continues to work on that goal by taking you to two localities around Boulder,Chasm Lake on Longs Peak and Coal Creek Canyon, between Boulder and Golden and askingyou to identify the rocks present, interpret how those rocks have formed.The rocks presented from these two localities are dated to be between 1.7 billion and 1.8 billionyears old.Tip! Compile all of your homeworks and notes in order to complete this homework. You will bereferring back to the rock cycle, characteristics of minerals (homework#2), igneous andsedimentary rocks (homework #3) and the conditions that they form under, in addition to themetamorphic rocks and the conditions they form under we just discussed.Pre homework questions (1 pt):Below are statements that reflect some of what you should be getting out of this assignment.1. Before you complete the assignment, rate how true each of the following statements is foryou using a scale of 1-5, where.These answers for the pre-question are graded only for being complete (1 pt all or nothing)and not what your answers are.Your rating(1 through 5)1. I can identify the common rock forming minerals based on theirphysical appearance and provided diagnostic properties2. I am comfortable identifying if a rock is igneous, sedimentary, ormetamorphic based on appearance and description.3. I can identify igneous and metamorphic rocks based on mineralogyand texture4. Based on the rock type (e.g. sedimentary, igneous, or metamorphic,and its appearance. I can infer the conditions under how that rockformed.Location 1: Coal Creek Canyon, ColoradoCoal Creek Canyon is south of Boulder, near the intersection of Highway 93 and Highway 72.The rocks that we are going to be reviewing are off of Highway 72 towards the Front Range.Some of these rocks can also be seen in Golden Gate State Park near Golden.Rock Sample #1This crystalline rock has Interlocking,visible crystals of one type of mineral.The individual crystals are large andappear to have grown to become tightlypacked. There does not appear to be anyalignment of the recrystallized minerals,though faint lines that resemble bidirectional cross bedding can be seen.The mineral is clear or whitish in color,hard, and does not react to acid.5. What is the mineral seen in this sample?6. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?7. What is the name of this rock?8. What was the original rock (e.g. the protolith) of this sample?9. Based on the picture and the description of rock sample #1, what process did the protolithexperience in order to become the rock it is now?Increase in heatIncrease in pressureIncrease in heat and pressurePartial meltingFractional crystallization10. Down below are the possible steps through the rocks cycle that created rock sample #1 inCoal Creek Canyon. Using your knowledge of the rock cycle, place the events in the best order.(Note: online the order of the choices will change, 1 is the oldest).The rock is uplifted and brought up to the surface, where it is exposedSediments are deposited on a beach where the waves move back and forth.Eventually the sediment is buried and lithifiedMagma body intrudes the rock and assimilates some of the rock into its magmacomposition and bakes the rocks at its edgesOlder rock is uplifted and exposed at the surface and weathered. The sediment hastraveled a long distance from its original source and has become well rounded and wellsorted.Rock Sample #2Near Highway 72, there is a shiny rock thatbreaks into plates. Layering is easily seen andthere are three visible minerals that can bemade out.A. A shiny mineral that is dark in color thatcan easily be peeled off into sheets.B. A second shiny mineral that can also bepeeled off into sheets but is light in colorC. A translucent mineral that is glassy andfractures.11. What is mineral A in this sample?12. What is mineral B in this sample?13. What is mineral C in this sample?14. What is the rock type of this sample? Sedimentary, Igneous, or Metamorphic?15. What is the name of this rock sample?16. Based on the picture and the description of rock sample #2, what processes did theprotolith experience in order to become the rock it is now? Choose oneoooooIncrease in heatIncrease in pressureIncrease in heat and pressurePartial meltingFractional crystallizationRock Sample #3Further west on the road, heading deeper into the canyon,there are rocks with alternating light and dark bands.The lighter bands consist of mineral A that is clear orwhitish in color, hard, and does not react to acid.The dark color bands are made of mineral B that is black ordark green in color, rectangular in shape (long compared totheir width) and is a silicate that cleaves in a nonperpendicular way17. What is mineral A in this sample?18. What is mineral B in this sample?19. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?20. Based on the picture and the description of rock sample #3, what processes did the protolithexperience in order to become the rock it is now? Choose oneoooooIncrease in heatIncrease in pressureIncrease in heat and pressurePartial meltingFractional crystallization21. What is the name of this rock?22. Considering both Rock Sample #2 and Rock Sample #3 from Clear Creek Canyon, whattype of metamorphism occurred here 1.7 billion years ago (contact or regional)? And whatgeologic processes could have created those metamorphic events? Answer in one to twosentences.Location 2: Chasm LakeLocation 2 is Chasm Lake in Rocky Mountain National Park, close to Longs Peak. It is possibleto hike up to this locationRock Sample #4This rock is exposed on east facing side ofLong Peak, known as the "Diamond". It hasinterlocking, randomly oriented, visiblecrystals of three mineral typesMineral A: Black, shiny, and breaks intosheetsMineral B: Pink in color, opaque, with arectangular crystal shapeMineral C: Translucent and very hard. Doesnot have any cleavage planes.23. What is Mineral A?24. What is Mineral B?25. What is Mineral C?26. What is the rock type of this sample? Sedimentary, Igneous, and Metamorphic?27. What is the name of this rock?28. Based on the picture and description of rock sample #4, what processes did the protolithexperience in order to become the rock it is now? Choose oneooooooIncrease in pressureIncrease in heat and pressureSlow crystallization deep in the continental crustRapid crystallization deep in the continental crustSlow that rapid crystallization in the continental crustWeathering, deposition, and then lithificationRock Sample #5Interlocking, aligned minerals, give a layered appearanceto the rock and a nice shine. Three different types ofminerals are easily visible.Mineral A: Red in color and a well formed 12 sided crystalshape. Has a glassy luster to it.Mineral B: Black, shiny and breaks into sheets.Mineral C: Silver, shiny, and breaks into sheets.29. What is mineral A?30. What is mineral B?31. What is mineral C?32. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?33. What is the name of this rock?34.Based on the picture and description of rock sample #5, what processes did the protolithexperience in order to become the rock it is now? Choose oneooooooIncrease in pressureIncrease in heat and pressureSlow crystallization deep in the continental crustRapid crystallization deep in the continental crustSlow that rapid crystallization in the continental crustWeathering, deposition, and then lithification35. In some areas around Chasm Lake, you can see where Rock Sample #4 intrudes or cutsinto Rock Sample #5. Using this information along with you knowledge of the rock cycle andhow rocks form, place the following possible events in order to explain what happened to therocks of Chasm Lake. (note: the order of the choices will vary online, 1 is the oldest)A mountain building event occurred, placed the rocks of Ancient Colorado undertremendous amounts of pressure and in some cases burying them deeperThe magma body does not erupt at the surface. Instead stays at depth and the magmaslowly crystallizesA magma body intrudes the preexisting rock and through assimilation become morefelsic.Another unknown geologic event occur that uplifts rocks sample #4 and rock sample#5 to the surface.Minerals in the older rocks were unstable at the new temperature and pressureconditions. Neocrystallization occurs creating new minerals over long periods of time.An unknown rock, older than 1.8 billion years was part of an ancient continental crust.36. Reviewing your answers for the five rock samples seen at these two location, what is thepossible geologic event that occurred in Colorado 1.7 -1.8 billion years ago? Justify youranswer by explaining how that event could create the rocks seen here.Pre homework questions (1 pt):Below are statements that reflect some of what you should be getting out of this assignment.Before you complete the assignment, rate how true each of the following statements is foryou using a scale of 1-5, where.These answers for the pre-question are graded only for being complete (1 pt all or nothing)and not what your answers are.Your rating(1 through 5)37. I can identify the common rock forming minerals based on their physicalappearance and provided diagnostic properties38. I am comfortable identifying if a rock is igneous, sedimentary, ormetamorphic based on appearance and description.39. I can identify igneous and metamorphic rocks based on mineralogyand texture40. Based on the rock type (e.g. sedimentary, igneous, or metamorphic,and its appearance. I can infer the conditions under how that rockformed.41. In the space down below, write a sentence on what skills or knowledge you are feelingmore confident on now after completing this exercise OR what questions you may still haveafter completing this exercise.

 

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