How Magma Forms Earth is divided into three general layers. Extrusive igneous rocks are _________, whereas intrusive igneous rocks are _________. Flux MeltingFlux melting occurs when water or carbon dioxide are added to rock. dark colored, more dense and less viscous (not sticky) The cooling behaviour of intermediate magmas lie somewhere between those of mafic and felsic magmas. G) All of these. Magma is a molten and semi-molten rock mixture found under the surface of the Earth. For igneous rock, the composition is divided into four groups: felsic, intermediate, mafic, and ultramafic. An igneous rock with large crystals embedded in a matrix of finer crystals is indicative of a two-stage cooling process, and the texture is porphyritic (Figure 3.15). Lava that cools extremely quickly may not form crystals at all, even microscopic ones. Why are thin sections of rocks used to study igneous rocks? F. dominant rock formed by the eruption of volcanic mountain ranges such as the Andes in western S. America This creates magma in places where it originally maintained a solid structure. The presence of quartz is a good indicator of granite. A) pyroclastic F, During this stage of rsum review, employers use the rsum to guide interview questions: Thus, you can often figure out the relative order in which the minerals crystallized from the magma. = 2 1/4. 2. B. quartz When many plutons merge together in an extensive single feature, it is called a batholith. If vesicular, pummus geothermal gradient Norman Levi Bowen, born in Kingston Ontario, studied geology at Queens University and then at MIT in Boston. Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle. Another is the native rock is melted and consumed into the rising magma or broken into pieces that settle into the magma, a process known as stoping. The fine-grained texture indicates the quickly cooling lava did not have time to grow large crystals. C) The rock is crystalline, but mineral grains are too small to be seen with the unaided eye. There are 3 main agents that cause metamorphism. As a mafic magma starts to cool, some of the silica combines with iron and magnesium to make olivine. 1. andesite B. olivine and pyroxene B. Olivine - pyroxene - amphibole - biotite The word reaction is critical. This section will focus on the common igneous bodies which are found in many places within the bedrock of Earth. Some pumice is so full of vesicles that the density of the rock drops low enough that it will float. These rocks usually have a coarse texture (individual minerals are visible without magnification), because the magma cools slowly underground, allowing crystal growth. The solid parts, called tephra, settle back to earth and cool into rocks with pyroclastic textures. C) intermediate - the intermediate range composition magma makes for strato volcanoes that are mostly passive erupting D) gabbroic, granitic, The classification of igneous rocks is based on __________. B) The magma was rich in volatiles (like water) which aided in fast crystallization of large, but few numbers of crystals. In a porphyritic volcanic rock, which mineral grains are the last to crystallize? Common rock types within the intrusive category are granite and diorite. Working mostly with basaltic magmas, he determined the order of crystallization of minerals as the temperature drops. St. Helens volcano, Washington state Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). D. Heavier crystals float on the top of the magma in the magma chamber producing a layered igneous rock upon complete solidification. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series (Figure 3.3.1 and Figure 3.3.3). B. may be composed of grains of olivine and pyroxene phenocrysts The rock then cools into new crust. B) the magma stays the same temperature, causing ions to slow down and form crystals, mostly Si-O tetrahedra Rhyolite refers to the volcanic and felsic igneous rocks and granite refer to intrusive and felsic igneous rocks. C) andesite Who was Bowen, and what is a reaction series? Pyro, meaning fire, refers to the igneous source of the tephra and clastic refers to the rock fragments. This answer has been confirmed as correct and helpful. Magmas derived from crustal material are dominated by oxygen, silicon, aluminum, sodium, and potassium. E. pyroxene C) rate of cooling When volcanoes erupt explosively, vast amounts of lava, rock, ash, and gases are thrown into the atmosphere. 3.5 Igneous Rocks Charlene Estrada. A) The rock is crystalline, but mineral grains are of distinctly different sizes. 3. rhyolitic pumice 6 2/3 3. rhyolite Figure 3.3.2 shows a zoned plagioclase under a microscope. Cooling history is also related to changes that can occur to the composition of igneous rocks. This reduction in overlying pressure, or decompression, enables the mantle rock to melt and form magma. Typical intermediate rocks are diorite and andesite. Match the rock name with the best description. If the magma has a low viscosity (i.e., its runny)which is likely if it is maficthe crystals that form early, such as olivine (Figure 3.3.6a), may slowly settle toward the bottom of the magma chamber (Figure 3.3.6b). Diorite is a coarse-crystalline intermediate intrusive igneous rock. in Developments in Precambrian Geology (ed. b. C) The extrusive magma, because it is deep below the surface, cools very slowly, producing very small mineral grains. The __________ of an igneous rock involves the mineral content, and/or refers to the magma from which it solidified. To give an example of how large these crystals can get, transparent cleavage sheets of pegmatitic muscovite mica were used as windows during the Middle Ages. This mixture is usually made up of four parts: a hot liquid base, called the melt; minerals crystallized by the melt; solid rocks incorporated into the melt from the surrounding confines; and dissolved gases. solid rock with a fine texture D. muscovite and quartz, According to Bowen's reaction series, which is the proper sequence of ferromagnesian silicate minerals crystallizing from a cooling magma? As long as more magma pools into a volcanos magma chamber, there is the possibility of an eruption and the volcano will remain active. Ignimbrites may be loose deposits or solid rock, and they can bury entire landscapes. Glazner, A. F., Bartley, J. M., Coleman, D. S., Gray, W. & Taylor, R. Z. Mafic describes a kind of igneous rock or even magma that is relatively high in magnesium and iron content; hence the word 'mafic' which is a combination of the words magnesium and ferric . Many xenoliths are crystals torn from inside the Earth and embedded in magma while the magma was cooling. = 45/20 For example, it is not known what happens to the pre-existing country rock as the diapir intrudes. Andesite is the name of a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color. Physical Geology - 2nd Edition by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. B. variable silica, iron and magnesium content, glassy texture Arndt, N. T. Chapter 1 Archean Komatiites. A __________ texture would be most UNLIKELY to occur in an extrusive igneous rock. B) considered "plutonic" rocks because they form from magma beneath the surface; considered "volcanic" because they form from lava erupted from a volcano. D) The rock contains broken fragments and is volcanic in origin. A. Pyroxene - amphibole - olivine - biotite A. A) Intrusive magma is cooler because it is well insulated by the surrounding rock. C. Al and Si are the least abundant elements in the magma. B. Andes mountains volcanoes As the magma rises to the surface, the drop in pressure causes the dissolved volatiles to come bubbling out of solution, like the fizz in an opened bottle of soda. Basalt is a fine-grained mafic igneous rock. On page 14 of The Call of the Wild, what's meant by the phrase "The _____ is defined as to lose or give up hope that things will 15. The most important factor affecting the mineral composition of an igneous rock is ________. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. There are two reasons for this: one is that in the early analytical procedures, the results were always expressed that way, and the other is that all of these elements combine readily with oxygen to form oxides. D) phaneritic, __________ is named for a prominent, volcanic mountain range in western South 3. Granite commonly has large amounts of salmon pink potassium feldspar and white plagioclase crystals that have visible cleavage planes. Plutons can have irregular shapes, but can often be somewhat round. Batholiths are found in the cores of many mountain ranges, including the granite formations of Yosemite National Park in the Sierra Nevada of California. Because the earth was largely molten at its origin, magma may be considered the beginning of the rock cycle. Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). 20/3 D) felsic - very sticky magma makes for explosive eruptions, Which one of the following rock types contains the greatest amount of quartz? Batholiths and stocks are discordant intrusions that cut across and through surrounding country rock. Examples of rhyolite include several lava flows in Yellowstone National Park and the altered rhyolite that makes up the Grand Canyon of the Yellowstone. This results in a higher gas content and viscosity. What is a likely reason for this phaneritic texture? This hot material rises to an area of lower pressure through the process of convection. For a volcano to erupt, it must have a source of magma. A) mafic - very fluid magma makes for passive (fluid) eruptions seated magma in the magma chamber ascend s due to buoyancy or any tectonic activity and intrudes into the country rock (host rock) or it may come out at the surface and solidify. 2. porphyritic andesite C) solid + melt This was done over and over, each time allowing the magma to cool to a lower temperature before quenching. Obsidian is a rock consisting of volcanic glass. A. C. potassium feldspar The results were studied under the microscope and by chemical analysis. D. glassy and frothy texture A significant exception to this is active volcanoes, which are discussed in a later section on volcanism. Classification of Igneous Rock Series. Decompression melting often occurs at divergent boundaries, where tectonic plates separate. C) the composition Added 2/10/2022 11:11:08 PM This answer has been confirmed as correct and helpful. A. a decrease in the confining pressure (decompression) 1. granite D) solid + crystal. As cooling continues, the various reactions on the discontinuous branch will proceed because silica is abundant, the plagioclase will become increasingly sodium-rich, and eventually potassium feldspar and quartz will form. Young, emerging subvolcanic intrusion cutting through older one, Xenolith (solid rock of high melting temperature which has been transported within the magma from deep below) or roof pendant (fragment of the roof of the magma chamber that has detached from the roof and sunk into the melt), Contact metamorphism in the country rock adjacent to the magma chamber (caused by the heat of the magma), Uplift at the surface due to laccolith emplacement in the near sub-ground, Active magma chamber (called pluton when cooled and entirely crystallized; a batholith is a large rock body composed of several plutonic intrusions), Old pegmatite (late-magmatic dyke formed by aggressive and highly mobile residual melts of a magma chamber). Komatiite is a rare rock because volcanic material that comes directly from the mantle is not common, although some examples can be found in ancient Archean rocks [2]. K.C. 2. rhyolite A. consist of very large grains of quartz, olivine and pyroxene in relatively large bodies of former sedimentary rock Stage 2 When lava is extruded onto the surface, or intruded into shallow fissures near the surface and cools, the resulting igneous rock is called extrusive or volcanic. B) granodioritic Lava is molten rock flowing out of fissures or vents at volcanic centres (when cooled, they form rocks such as basalt, rhyolite, or obsidian). Or carbon dioxide are added to rock xenoliths are crystals torn from inside the Earth was largely molten at origin. To cool, some of the tephra and clastic refers to the composition of igneous?... Extremely quickly may not form crystals at all, even microscopic ones c. and. A porphyritic volcanic rock, which mineral grains are too small to be seen the... 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