Lab Exercise #2: Magma, Volcanism, and Igneous Rocks Every igneous rock has a st
ID: 114368 • Letter: L
Question
Lab Exercise #2: Magma, Volcanism, and Igneous Rocks Every igneous rock has a story to tell that geologists can unravel by texture and composition. In this exercise, you will briefly tell the story of four of the igne samples you just identified-samples I , 4, 6, and 9. Instructions and Observations considering the rock's ous Write a few lines about each of the rocks listed below, including the following information (1) Rock name (2) Was this rock formed from felsic, intermediate, or mafic magma or lava? How do you know? (3) What type of plate boundary is associated with this type of magma/lava composition? (4) What kind of eruption and volcanic structure is this type of magmaava associated with? (5) Where did this rock solidify? Underground? On Earth's surface from extruded lava? In midair as part of expelled pyroclastic material? How do you know? (6) How relatively quick was this rock's formation? Did it solidify in a one- or two-step process? How do you know? Submit to your instructor as directed. Keep a copy for yourself to use in answering qui questions nomme Sample #1: Ph Sample #4: furn(w Sample #6: abbre- e Sample #9:Explanation / Answer
Granite:
2) The rock is acidic igneous, volcanic rock, of felsic (silica-rich) composition as it contains greater than 66% SiO2. The rock contains assemblage of quartz, feldsper.Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture.
3) Granite containing rock is widely distributed throughout the continental crust. Granitic melt generally erupted in intra-continental plate boundary. Granite often occurs as small stock masses and batholiths which are associated with orogenic mountain ranges. Granitic melthas a felsic composition. Felsic rocks are less dense than mafic and ultramafic rocks. Basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons as they are erupted from subduction. Therefore, granitic rocks form the basement of all land continents.
4) Granite often occurs as small stock masses and batholiths which are associated with orogenic mountain ranges. It is the most abundant basement rock but the outcrops of granite tend to form tors and rounded massifs. Granites generally occur as circular depressions surrounded by a range of hills, which are formed by the metamorphic aureole or hornfels.
5) Granite is a common type of felsic intrusive igneous rock which shows granular and phaneritic in texture. Granite rocks are coarse to medium grained which represents the slow colling of mamga. it indicates subsurface cooling of magma. But some granite formed by assimilation known as granitization.
6) Granite forms in two steps. In the first step, the subducting plate dives into the Earth’s mantle, heats up and begins to melt. This creates magma. Magma rises, and causes melting in the rock above it, making more magma. When this magma cools, it makes igneous rocks like diorite, not granite. In the second step, subduction, melting, and magma formation continue. However, when the magmas formed in this step rise upward, they cause part of the diorite formed in the first step to begin to melt. This, combined with melting of surrounding sedimentary and igneous rocks, makes magma which cools to become granite.
1) Rock name: Rhyolite
2) The rock is acidic igneous, volcanic rock, of felsic (silica-rich) composition as it contains greater than 66% SiO2. The rock contains assemblage of quartz, feldsper. The composition of feldsper varies from sanidine and plagioclase in a ratio of greater than 2:1 in the QAPF diagram.
3) Rhyolite is the extrusive equivalent to the plutonic granite rock, and it occurs as breccias or in volcanic plugs and dikes. Rhyolite is an felsic rocks and it is associated with intra-continental magmatism or continental margin. Most of Rhyolite associated with episodes of continental extension. For example, Basin and Range Province of Western U.S. and Mexico. Most of the preserved volume of Rhyolite is represented by pyroclastic flow deposits. It is known as ash flow tuffs or ignimbrites. Granitic magma and the large volumes of silicic magma erupt in continental rhyolite centers which represents evidence of the existence of rhyolite magma with granitic composition magma.
4) Rhyolite occur as breccias or in volcanic plugs and dikes but some rhyolite is highly vesicular pumice. Due to fast cooling, crystals form a natural glass or vitrophyre, known as obsidian. Slower cooling forms large crystals in the lava and results in textures such as flow foliations, nodular, spherulitic and lithophysal structures. Many eruptions of rhyolite are highly explosive and the are deposited as tephra/tuff or of ignimbrites.
5) The Rhyolite mineral grains are fine which indicates fast cooling or surface cooling and It may have texture from glassy to aphanitic to porphyritic. So, Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock. Rhyolite is solidified volcanic rocks
6) Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock. Rhyolite formed by one step process because subsurface granitic magma may changes its composition when it rises to the surface. Rhyolite usually forms in continental or continent-margin volcanic eruptions where granitic magma reaches the surface and it is rarely produced at oceanic eruptions. So, it indicates rhyolite formed as one step process.
PUMICE:
1) Rock name: Pumice
2) The rock is is a volcanic igneous rock that consists of highly vesicular rough textured. It may be silicic or felsic to intermediate in composition such as rhyolitic, dacitic, pantellerite, phonolite, trachyte or it may be basaltic and other compositions.
3) Pumice is the extrusive igneous rock. It is formed when super-heated, highly pressurized rock is violently ejected from a volcano. It found in all type of settings generally continental or continental margin because pumice is formed by eruption of gases from highly viscous rocks.
4) Pumice is formed dut to ejecting of gases or volatile matters from highly volatile rocks. Such as rhyolite is highly vesicular pumice. Vesicles are formed in two main forms. Tubular microvesicles which form a silky or fibrous fabric due to ductile elongation in the volcanic conduit or, in the pumiceous lavas, during flow of magma. The another form of vesicles are subspherical to spherical due to releasing of high vapor pressure.
5) The Pumice are extrusive igneous rocks indicating surface cooling and It may have rough texture. So, Rhyolite can be considered as the extrusive igneous rock.
6) Pumice can be considered as the extrusive igneous rock. Pumice is formed by one step process because magma rises to the surface and releaseing viscous and gaseous matters formed vesicular structure
Gabbro:
2) It is formed from mafic magma, containing large group of dark, often phaneritic minerals. So, gabbro is plutonic intrusive igneous rocks chemically equivalent to basalt.
3) Gabbro is generally found in oceanic boundary or mid ridge ridge but they do not come out to the surface as they are plutonc rock. Their volcanic equivalent rocks is Basalt. Gabbro is also found as plutons associated with continental volcanism.
4) Gabbro can be formed as a massive, uniform intrusion.
5) Gabbro is coarse grained rocks so they are plutonic or solidified in underground region.
6) Gabbro are formed by one step. They are containg mafic minerals which are formed in bowns reaction series
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