GSU GEOL 1122K - Chapter 4 Visual Quiz (8 pages)

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Chapter 4 Visual Quiz



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Chapter 4 Visual Quiz

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Pages:
8
School:
Georgia State University
Course:
Geol 1122k - Introductory Geosciences Ii
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Certain minerals are commonly found together in different igneous rocks According to the following figure which two minerals are you unlikely to find forming in the same rock quartz and olivine pyroxene and amphibole amphibole and k feldspar k feldspar and plagioclase Quartz is a felsic mineral that forms only at relatively low temperatures Olivine on the other hand is a mafic mineral that forms at very high temperatures and is unstable at lower temperatures As a result olivine and quartz will not usually form in the same rock Geologists use composition mineral content and texture grain size to classify igneous rocks Use the chart below to provide the name of a mafic rock that cooled slowly granite rhyolite obsidian gabbro The composition of gabbro is primarily olivine pyroxene and plagioclase these are all mafic minerals Texturally gabbro is coarse grained as a result of slow intrusive cooling Geologists use mineral composition to help categorize igneous rocks From the information provided in the chart which minerals would you expect to find in granite olivine pyroxene and biotite plagioclase pyroxene and quartz k feldspar biotite and olivine quartz k feldspar and plagioclase Bowen s reaction series tells us which minerals tend to form together Quartz k feldspar and plagioclase are commonly found in granite and other felsic igneous rocks Igneous rocks are formed by cooling magma or lava Whether the rock cools intrusively or extrusively has a profound impact on a rock s texture Which statement BEST describes the texture and depositional environment of the rocks shown in the figure glassy to fine grained from cooling intrusively coarse grained from cooling intrusively glassy to fine grained from cooling extrusively coarse grained from cooling extrusively The lava flow and pyroclastic rocks cooled quickly at the Earth s surface When igneous rocks cool quickly crystals do not have time to form and the resulting rocks are glassy or very fine grained In this image volatiles that were driven off of the subducting slab have caused the mantle to melt What kind of melting does this figure show decompression melting compression melting heat transfer melting flux melting During flux melting organic materials water and carbon dioxide are driven from the subducting slab decreasing the melting temperature of the surrounding mantle This process can initiate the upward migration of magma and eventual volcanic eruptions The following four figures show several different tectonic settings where volcanism is active Which of the following images shows a tectonic environment where magmas were produced by flux melting A B C D Figure B shows a subduction zone In this type of tectonic setting volatiles like water and carbon dioxide are driven off the subducting plate into the surrounding mantle This addition of volatiles reduces the melting temperature of the affected mantle area leading to melting Volatile initiated melting is called flux melting The following image shows samples both in hand sample and in microscope thin section views The textures are the result of their emplacement mechanism intrusive extrusive or pyroclastic Match the texture term with the appropriate picture set A Crystalline B Glassy C Fragmental A Glassy B Fragmental C Crystalline A Crystalline B Fragmental C Glassy A Fragmental B Glassy C Crystalline In hand sample crystalline samples appear to be made of large interlocking crystals while glassy rocks are much smoother and vitreous In thin section under a microscope crystalline rocks show intergrowth of many types of mineral crystals while glassy rocks are generally black since volcanic glass does not transmit light The texture of an igneous rock is dependent on its emplacement mechanism how and where the lava or magma cooled Match the following images with their emplacement mechanism A Intrusive B Extrusive C Pyroclastic A Intrusive B Pyroclastic C Extrusive A Pyroclastic B Extrusive C Intrusive A Extrusive B Pyroclastic C Intrusive Rocks that cool intrusively cool more slowly which results in coarse crystalline rocks Extrusive rocks cool very quickly which results in glassy or very fine grained rocks Pyroclastic rocks are explosively emplaced through violent eruptions so the rocks comprise a mixture of volcanic rock fragments This is a picture of a basalic Lava flow Choose the letter on the image that BEST approximates how a rock like this would form A B C D Intrusions form when magma squeezes up through cool rock In this case the basalt made it to the surface and started flowing Viscosity is a material s resistance to flow The pictures below show two types of volcanic eruptions In the first lava is fountaining and flowing freely making a gently sloping volcano In the second eruption a thick plug of lava called a dome has emerged in a volcanic crater Which of the following statements BEST describes the relative viscosity of these two eruptions The lava dome 2 is lower viscosity than the fountaining lava 1 The two lavas have similar viscosities Nothing about relative viscosity can be determined from the images The lava dome 2 is higher viscosity than the fountaining lava 1 If viscosity is a material s resistance to flow then something with high viscosity is going to be much thicker and less runny The lava dome does not flow so it must be higher viscosity than the freely flowing lava fountain


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