Geology 12. Rocks and the Rock Cycle Provincial Exam Questions EXTRA PRACTICE TEST #3 KEY

Transcription

1 Geology 12 Rocks and the Rock Cycle Provincial Exam Questions EXTRA PRACTICE TEST #3 KEY

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3 2003 GEOLOGICAL MAP Drill hole pond T U V 80 S X Y W 50 m Unit T Coal Unit U Shale Igneous rock S Unit V Sandstone Zone of contact metamorphism - i -

4 2003 ROCK AND MINERAL INFORMATION TABLE Photograph 1 Photograph 2 Mineral R Rock S Hand specimen Note: The three specimens on the top right have been cut into gemstones. Mineral R Magnified view This space intentionally blank 4 mm Additional information Properties of Mineral R Hardness can scratch glass Streak white Specific gravity between 3 and 4 Mineral Composition Dark ferromagnesian minerals: 60% Dark gray calcium-rich plagioclase feldspar: 40% - ii -

5 2003 ROCK AND MINERAL INFORMATION TABLE Photograph 3 Photograph 4 Rock V Rock W Hand specimen Shell debris Mineral J Mineral K Magnified view 5 mm 1 mm Additional information Mineral Composition Mineral J: 95% Mineral K: 5% Mineral Composition Mineral J: 0% Mineral K: 100% Mineral J Mineral K A transparent to translucent mineral with well-developed cleavage which can be scratched with a copper penny. Reacts vigorously with dilute hydrochloric acid. A transparent mineral with no apparent cleavage and a conchoidal fracture which can scratch a steel knife. No reaction with hydrochloric acid. - iii -

6 2003 PHOTOGRAPHS Photograph 5 Photograph 6 - iv -

7 Photograph 7 Photograph 8 - v -

8 Photograph 9 Photograph 10 - vi -

9 WRITTEN RESPONSE KEY INSTRUCTIONS: Answer each question in the space provided. You may not need to use all of the space given. REFERENCE DATA BOOKLET For question 1, refer to the table below, and the following in the Data Booklet. page x: Bowen s Reaction Series page xii: Properties of Common and Important Minerals Minerals present Mineral content of granite Mineral content of stream sand potassium feldspar 60% 18% quartz 30% 80% biotite 10% 2% 1. An area of British Columbia that is entirely composed of granite is drained by a single, fast-moving stream. With reference to chemical and physical properties, describe two factors which could be used to explain why the mineral content of the stream sand has become so different from the mineral content of the granite. (2 marks) Any two for 2 marks: Hardness: Quartz, the harder mineral, has become enriched in the sediment because it is better at resisting weathering and erosion, whereas the other two minerals have been worn and washed away. Cleavage: Quartz has no cleavage and thus is more resistant to weathering and erosion. Feldspar has two cleavages and biotite has one excellent cleavage. Mineral stability: According to Bowen s Reaction Series, quartz has more stability than the other two minerals and has thus become enriched in the sediment.

10 REFERENCE DATA BOOKLET For question 2, refer to the following in the Data Booklet. page i: Geological Map 2. A geologist has observed that the crystals in igneous rock unit S are much smaller at points X and Y than they are at a point half way between X and Y. Explain why the crystals are smaller at X and Y than in the middle of the unit. (2 marks) Igneous rock unit S would have been intruded as a magma. The magma in contact with the country rock would have lost heat and cooled much more quickly than the magma in the middle. The faster a magma cools, the smaller the crystals will be. Note: chilled margins is worth 1 mark only Ô 2marks Ô REFERENCE DATA BOOKLET For question 3, refer to the following in the Data Booklet. Geological Map Photograph Sedimentary structures are very useful to geologists because they can give clues about the environment where the sedimentary rock they occur in was deposited. The sedimentary structure shown in Photograph 10 was found in the sandstone T shown on the geological map. a) Identify the sedimentary structure. (1 mark) Ripple marks 1 mark b) Describe how the sedimentary structure would have formed. (1 mark) Moving water, usually shallow, or moving air 1 mark c) Name an environment where the sedimentary structure could have formed. (1 mark) There are many possible answers anywhere there is sand and moving air or water, for example: bottom of a stream shallow marine, even deep marine if there are currents intertidal zone beach desert sand dunes Ô Ô Ô any one for 1 mark

11 Use the following graph which shows relationships between temperature, depth, and types of coal, to answer question 4. Temperature in degrees Celsius Peat 40 60% carbon Lignite coal 60 70% carbon Depth in kilometres Bituminous coal 70 90% carbon Anthracite coal (hard coal) 90 95% carbon 9 4. a) Describe a type of environment where a potential coal deposit could accumulate on the earth s surface and the type of material that would accumulate to eventually become coal. (2 marks) Type of environment: usually a swamp, marsh or delta where there is abundant plant growth and decomposition. 1 mark Type of material: plant material, vegetation organic previously living material 1 mark 12 mark 12 mark b) According to the graph, at what temperature and depth would lignite change to bituminous coal? (1 mark) Temperature: approximately > 62 C 12 mark Depth: km 12 mark < 75 C > 2.5 km < 3 km

12 c) Choose one type of coal and describe a use for it. (1 mark) Any one for 1 mark: Peat: used for heating, power generation, soil enhancer, absorbent for liquids Lignite: used for heating, power generation, source for organic chemicals Bituminous: used for heating, power generation, source for organic chemicals, coking in steel manufacture Anthracite: heating, power generation d) Why is anthracite (hard coal) often found in association with slate rather than shale or mudstone? (1 mark) Anthracite (hard coal) forms at the highest temperature and pressure of all the coals and is in fact metamorphic. At this temperature and pressure, the sedimentary rock shale or mudstone will have been metamorphosed to slate because of the higher temperature and pressure. Ô 1 mark Ô

13 Use the following cross section diagrams of coal deposits to answer question 4e). Note the different scales of the cross sections. X Y coal seam 2 m coal seam 100 m e) The two coal deposits X and Y were discovered in British Columbia, however neither of them will be mined at this time. i) Describe any geological or economic reason why deposit X will not be mined. (1 mark) Any one for 1 mark: The coal seam is too thin (about 50 cm) and would be too difficult to extract using machinery. The coal seam is too thin and too much rock would have to be removed for every ton of coal obtained. The price of coal is too low to make it worthwhile mining this deposit. Dip of the seam makes it too deep. Environmental reason connected to economical or geological reasons. ii) Describe a different geological or economic reason why deposit Y will not be mined. (1 mark) Any one for 1 mark: The coal seam is too deep. It would be difficult to extract the coal using cheaper open pit methods. The coal seam is too deep and too much rock would have to be removed for every ton of coal obtained. The price of coal is too low to make it worthwhile mining this deposit. Dip of the seam makes it too deep. Any other good geological or economic reason.

14 REFERENCE DATA BOOKLET For question 5, refer to the following in the Data Booklet. Photograph 6 5. Photograph 6 shows sandstones and siltstones in a cliff section. Using the information visible in the photograph, name and describe (in order from youngest to oldest) three geological processes that have been important in the development of the rock sequence in the cliff section. (3 marks) Youngest Process 3 Process 2 Oldest Process 1 weathering of structure erosion of structure folding of sedimentary layers uplift of sedimentary layers deposition of sand lithification of sediments 1 mark 1 mark 1 mark Note: Part marks if out of order (deduct 1 mark)

15 2004 PHOTOGRAPHS Photograph 1 Photograph 2-4 -

16 GEOLOGICAL MAP Moose Lake L Drill hole P K H J C Granite intrusion G Fossils not to scale 5 metres Unit C Conglomerate (with graded bedding) Unit L sandstone Unit P Fault Unit K Lava layers (fine-grained with vesicles) Unit G Unit H Igneous intrusion Contact metamorphism ~ 20 m.y. (Miocene) ~ 30 m.y. (Oligocene) - 1 -

17 2004 ROCK DATA TABLE Rock Sample H Hand sample Thin section mm 5 cm Description Light material is plagioclase feldspar Coarse-grained 40% dark ferromagnesians Rock Sample J Hand sample Thin section mm 5 cm Description Mostly made of quartz grains Crystals appear to be fused - 2 -

18 2004 ROCK DATA TABLE Rock Sample K Hand sample Thin section mm 10 cm Description Composed of shell fragments cemented by a fine-grained matrix Rock Sample P Hand sample Thin section mm 10 cm Description Fine-grained mafic material Mostly dark ferromagnesians Some plagioclase feldspar Abundant gas holes (vesicles) - 3 -

19 WRITTEN RESPONSE KEY INSTRUCTIONS: Answer each question in the space provided. You may not need to use all of the space given. REFERENCE DATA BOOKLET For question 1, refer to the diagram below and the following in the Data Booklet. page 10: Percentage of Minerals in Igneous Rocks Siltstone High temperature and pressure Formation of light and dark bands Rock X Compaction and cementation Weathering and erosion to silt Rock Y Melting Slow cooling inside the earth Felsic/silicic magma 1. a) What type of rocks are rocks X and Y shown in the diagram above? (1 mark) Rock X: gneiss/schist mark Rock Y: granite/diorite/syenite mark OR OR metamorphic or recrystallized igneous, plutonic, intrusive b) Describe a plate tectonic situation that would cause the high-grade metamorphism of the siltstone. (1 mark) Any one for 1 mark: Large scale metamorphism, characteristic of mountain building. Deep burial, as in accretionary prism. Tectonic settings, i.e. converging boundaries, subduction zones.

20 Use the following map to answer question 2. Kohala Direction of lithospheric plate movement Mauna Kea Hualalai Older rocks Younger rocks Mauna Loa Kilauea LEGEND Older rocks Younger rocks Seismic station Zulu 50 km x Recent earthquake epicentre magnitudes >5.4 Recent volcanic eruptions Site of lava flow 2. The map above shows the island of Hawaii, and the locations of several recent volcanic eruptions which are building shield volcanoes. The island is over a hot spot. a) What is the likely composition of the lava from these eruptions? (1 mark) mafic, or basaltic, or 60% dark ferromagnesians, 40% plagioclase 1mark b) Explain why a pyroclastic flow (nuée ardente) is unlikely in this area. (1 mark) Any one for 1 mark: The mafic lava is thin (has low viscosity) and unlikely to trap the large amounts of gas associated with pyroclastic eruptions. gas was able to escape low viscosity/thin lava/low silica 1 mark for nuée ardentes occur with composite volcanoes 2 c) Place an X on the map in an area where you would expect the volcanic activity to increase over the next several hundred years. (1 mark) See diagram. X can be anywhere to the southeast of Kilauea. 1mark

21 d) Sketch and describe the likely cross-sectional shape of the shield volcanoes in this area of Hawaii. (2 marks) Sketch Description Shield volcanoes: shallow-sloped, extremely wide volcanoes. REFERENCE DATA BOOKLET For question 2e), refer to the following in the Data Booklet. page 10: Percentage of Minerals in Igneous Rocks page 12: Bowen s Reaction Series e) A sample of coarse-grained rock was collected from a Kilauea lava flow, and geologists think it is an ultramafic xenolith brought up from the mantle. The rock has the following mineral composition. Mineral Percent by volume plagioclase feldspar 5% pyroxene 70% olivine 25% How can geologists tell that the material in the xenolith must have formed at a temperature above 1000 C? (1 mark) Bowen s Reaction Series shows the materials found in the xenolith crystallize above 1000 C, i.e.: pyroxene, olivine, plagioclase feldspar. 1mark

22 WRITTEN RESPONSE KEY INSTRUCTIONS: Answer each question in the space provided. You may not need to use all of the space given. Use the following partial, simplified, rock cycle diagram to answer question 1. Metamorphic Rock PROCESS 3 Magma PROCESS 2 PROCESS 4 Sedimentary Rock Igneous Rock PROCESS 1 Sediment Example Process 5 1. Choose any two processes from the diagram above. For each process, describe the process and its probable plate tectonic location. An example is given. (4 marks) Process # Description of Process Plate Tectonic Location Example: Process Igneous rocks in volcanic mountains are weathered and eroded to become sediments. Sediment is carried to the ocean by streams and deposited in layers that are then lithified to become sedimentary rock. Sedimentary rocks are heated near plutons or under extreme pressure in collision zones, which causes them to become metamorphic. Volcanic mountain range at converging plates. Ocean trenches at subduction zones. Near plutons or tectonic collision zones. 3 Rocks are melted at depth to become magma. Subducting plate at a depth of km. 4 Magma cools as it exits the earth, becoming an igneous rock. Volcano or spreading ridge.

23 Use the following diagram of ripple marks and cross-bedding to answer question 2. west east 2. Describe how this structure might have formed. Include direction of flow in your answer. (2 marks) Fluid transporting sand-sized sediment travelled from east to west. Sediment was transported up the gentle slope of the first ripple, then deposited over and down the slip face in a tilted layer. Ô Ô 2 marks

24 Use the following photograph of an igneous layer to answer question 2. X GSC 2. Describe two pieces of evidence that could be found in or near the dark igneous layer at X to establish that it was a sill, and not a buried lava flow. (2 marks) Any two for 1 mark each: inclusions on top and bottom of feature in a sill, but only on bottom of lava flow no sign of weathering on top of feature in a sill contact metamorphism of country rock above and below feature a sill would have a lack of vesicles a sill would have a lack of pahoehoe and aa textures