HMWK #2
pdf
keyboard_arrow_up
School
Georgia Southern University *
*We aren’t endorsed by this school
Course
1122
Subject
Geology
Date
Apr 3, 2024
Type
Pages
5
Uploaded by DoctorCat8176
Name ChQ\S((A \N Y\\H) Due: See Folio GEOL 1121 Homework # 2 Magma and Igneous Rocks Part A. Bowen’s Reaction Series ) Open Figure 1 Bowen's Reaction Series on Folio and answer the following questions. Notice that in the figure, the temperature scales are unique to each major rock division. I decreases), decreases),)and the sodium and 1. Read the statement below. Circle the correct choice in parentheses. Bowen showed that as basaltic magma cools, the silica content of the magma the iron, magnesium, and calcium content of the magma (increases / potassium content of the magma/ decreases). 2. Listall the possible minerals you would likely find in the following rocks: a. Gabbro from a magma chamber that completely solidified at a temperature of 1080°C. Hint: There are 3. 10 Cl& ENL it P M) 10 clate ferdspor PYI0RENE, fgivinL b. Diorite from a magma chamber that completely crystallized at a temperature of 850°C. Hint: There are 3 p\aqio Clast felds por P\)\Y(\HY\L,MM\K a7 3. If a gabbro completely crystallizes at a temperature of 950°C, will it have olivine in it? ! ig 2 Will it have hornblende in it? !1 ‘ fz 4. Explain why quartz is the last mineral to crystallize in Bowen'’s Reaction Series. Hint: Compare the chemical composition of quartz to what happens to the silica content of magma as the magma cools. Buarrz < yne WY Minra) 10 CyStallize PLOUSA v CrySHINTS aF Liwar o podunes, List the minera.ls in‘peridotite in the order in which they would melt, from first to last. Oliving P;*mum Qayna ¥ First melted Last melted
6. In reality, olivine in mantle peridotite will not melt because the Earth doesn'’t get hot enough tC}l'dO s:‘is?gefr:he when the mantle is fluxed. So, when mantle peridotite partially melts, the magma produqed will con melt from the lower temperature (higher silica) minerals, namely pyroxenes and Ca-plagioclase. a. Ifthe partial melt from peridotite were to migrate away and then erupt at the surface, what is the name of igneous rock that would form? E)O\ SC[ \ Suppose you are hiking along the trail at Yonah Mountain in north Georgia near the town of Cleveland. You stop to look at the beautiful plutonic igneous rocks that make up the mountain. You immediately recognize that the rocks contain about 40% pink microcline (K-feldspar), but you aren’t quite sure about the identities of the other minerals in the rock. a. Based on Bowen’s Reaction Series, list all the other minerals you can expect to find in the rock: QuartZ, sodijum plagioctase, hiotik, A Douw_ b. Whatis the name of this rock? 07 Yanive i Part B. Rock Movies: Note: You MUST watch the videos | posted on Folio. | w your assignment will be considered incomplete. ill check the video logs. If you do not watch the videos, 8. Watch the video on Folio titled Movie 1: Quartz in Basalt. This video shows a fantastic specimen of a vesicular basalt with large crystals of quartz in it. It was collected from a volcanic eruption in central Mexico by a colleague of mine. Answer the following questions. a. Based on Bowen'’s Reaction Series, are the quartz crystals and the versicular basalt genetically related? In other words, did both the quartz crystals and the vesicular basalt form out of the same magma (same temperature and chemical conditions)? Yes or No: n 0 b. Based on your answer to question 8 (a) above, explain how the quartz crystals became embedded within the vesicular basalt. Quatt cyStole are Found in pasal $ic W& Xiogh Saion day - procestes Watch the video on Folio titled Movie 2: Xenolith 1. This video shows a great example of a xenolith embedded within a host rock. Both host rock and xenolith are plutonic igneous rocks. This rock was collected by me within the central mountains of Puerto Rico. Answer the following questions. a. ldentify the two @ks in this sample: YQ “\b Xenolith: D\OV“’C) Host Rock:
b. Explain ; qugstion":e(::;ar:bhowh the xenolith became embedded within the host rock. When you answer this ) er that the host rock was magma and the xenolith was solid when all this happened. e Yenout Yeconus empedded Withiv AN WUSE YoOK vy weing Enguiked ONC () W e AS(oNding cnagma as it Fius oy N caviin c. Notice that the contact between the xenolith and the host rock is very sharp. Does this sharp contact CY Ufi ‘\,, indicate remelting of the xenolith within the host magma? Yes or No. _D_O__'_ ' d. Using your knowledge of Bowen's Reaction Series, explain your answer to 9 (c) above. TIKL & povnidl muddivg o OCEUYS At anowe MOgMa Yo HIow avound and Anow ¢ LAnoinyne, 10. Watch the video on Folio titled Movie 3: Xenolith 2. This video shows another great example of a xenolith embedded within a host rock. Both the host rock and the xenolith are igneous rocks. This rock was coIIectgd by me just north of Phoenix, Arizona, along a hiking trail called Bushnell Tanks. The geology of the area consists of mountains of a plutonic stock cut by a series of mafic dikes. yaran U Intermediate Mafic mafi a. What is the texture of the host rock? b. What is the composition of the host rock? Felsic Lomati e d. What is the texture of the xenolith? P\ U \70 fl (C/ e. What s the composition of the xenolith? Felsic Mafic Ultramafic And eyt b AV h. Does your answer to (g) above suggest the xenolith was remelting in the host magma?r No. c. Identify the host rock. f. Identify the xenolith. s the contact between the host rock and the xenolith sharp or diffuse? Using your knowledge of Bowen's Reaction Series, explain why the contact between the host rock and the xenolith is as you described above. This WS Peause €atn Yock WaS SO AERINE W Y p Liatuye ond SWCA
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Part C. Chemical Analysis of Volcanic Igneous Rocks neous rocks cannot be determined by re microscopic, and two, even under the f this, volcanic igneous rocks must be analyzed for Unlike plutonic igneous rocks, the chemical composition of vo[canlc ig counting mineral crystals, for a couple of reasons. One, the minerals al microscope there are too many minerals to count. Because 0 chemical composition by using a number of different types of mass spectrometers. There are a number of methods used to chemically analyze volcanic rocks. One way is to take a r:)ckt and gr":grg up into a fine powder. This powder is then poured in a platinum crucible and placed in a furnape adg en:p ra e exceeding 1400°C. The powder melts. This melt is taken out of the furnacg,.poured ont.o a 1-1nch—. |an}e;‘ er r|]'out metal plate and cooled quickly to a glass. Then, while still hot and plastic, it is pressed into a flat dISC.. This has to be done rapidly because the melt cools quickly. The round glass disc is placed in an analyzer whereitis bombarded with x-rays in a technique called x-ray fluorescence (XRF) analysis. With .thls. tephmque, geologists can determine the abundances of the eight main cations (Si, Fe, Mg, Ca, Na, K, Al, Mn, Ti) within each rock, and hence determine the type of igneous rock it is. Each element is measured as a weight percent of their oxide _forrp, and Si is by far the most abundant element of the eight listed above. The names of the most common extrusive igneous rocks are determined on the basis of the weight percent SiOz versus the combined weight percentages of NazO and K20 using a Total Alkali and Silica (TAS) diagram. Table 1 below contains the chemical analyses of eight extrusive igneous rocks from different volcanoes ofthe Cascade Range in Oregon (listed as Rock 1 through Rock 8 along the first column). In the row next to each rock is the chemical analysis of that rock. Note that SiO2 is the most abundant oxide, composing ~48 to 74 wt.% of t‘hese' rocks, which is typical for most igneous rocks. As we've learned in class, the amount of SiO2 can be used to identify and name extrusive igneous rocks, which are too fine-grained to identify based on mineral content. Table 1. Chemical analysis of extrusive rocks from the Cascade Range, Oregon. S::::)':e sio2 FeO MgO ca0 Na20 K20 Other 1 486 103 67 107 25 03 210 2 507 93 6.1 97 27 05 211 3 535 83 5.4 76 32 07 212 4 55.9 73 40 68 35 10 215 5 50.9 54 36 6.0 37 13 203 6 638 44 23 456 37 2.0 19.3 7 69.4 23 11 31 39 30 172 8 741 13 02 12 4.1 45 147 11.Using the chemical information from Table 1 above, do the following. a. Calculate Naz0 + K20 and write the answer in the blanks next to each rock on the following page. b. On the TAS diagram on the following page, plot SiOz vs. Na20 + K20 for each rock and then identify the igneous rock by reading the name of the rock from the field in which your point is plotted. c. Write the name of the igneous rocks in the spaces on the following page (Rocks 1-8). d. Finally, connect all the points you plotted with a smooth line. Important! You must plot the data on the TAS diagram. If you don't plot the points, or if you don't plot the points correctly, then your assignment will be considered incomplete. If you skip any of the steps (a-d), then your assignment will be incomplete.
Basa Rock 1: SiO2:48.6 Na20 + K:0 = Name Name:: BG SC\ \ ‘\' S Rock 2: Si02:50.7 Naz20 + Kz0 = name: PO Sa i C fifld(\lfc/ Rock 3: Si02: 535 Naz0 + K20 = name: PCASQ HHC AHNdesit+e Rock 4: Si02:55.9 Na20 + K20 = Name: fi fldfig\\b Rock 5: SiO2: 59.9 Na20 + K20 = El:litfifikt: Rock 6: SiO2:63.8 Naz20 + K20 = Name: O ( 3 Rock7: SiOz 694 Na:O+KiO = Name:___ ALV YT Rock 8: Si0z74.1 NazO + KO = Name: \ Y\U‘l 6 \WC 14 1 e phonolite T14 57.3 1 11, i 256 pres tephriphonolite 1z s trachyte il 10 e 593.30 (g < 20%) 110 F 94 NG trachydacite e phonotephrite trachyandesite\ (q> 20%) d 29.4 69. 8 JeesT i 73 rhyolite T g 8 foxiite :g?zrgtg% ) basaltic | o i 2 trachy- 63.0 o basanite ndesite 16 O (ol > 10%) trachy- 57.0 = basalt 59 E 45.0 52.0 O 4 i f 5.0 5.0 | 1 4 tGN b:a;bh saltic andesite dacite 7=, andesite 1 picro- ] 4 2 basalt 2 B7 45 49 53 57 61 65 69 73 77 SiO, (Wt.%) Total Alkali and Silica (TAS) Diagram. The value for total alkali is the sum of the values of Na2O and K20 for each rock sample. In the diagram, ol = olivine, q = quartz, and the pairs of numbers are the coordinates at the corners of each rock field. 12. Look at the line you plotted on the TAS diagram and the elemental values in Table 1. a. What happens to the Na and K contents in magma as silica increases? ( V(’ (A w b. What happens to the Mg, Fe, and Ca content as silica increases? de( xegsSe C. Based on your answer to (c) above, where does mg, Fe, and Ca go? Hint: See Bowen’s Reaction Series. r‘\th‘r Side of Chavy