This type of rock contain 45 to 55 % silica content and 4 mafic igneous rocks minerals are pyroxene, amphibole, olivine, and mica. Olivine, pyroxene, amphibole, and biotite are common rock-forming minerals of mafic. Working mostly with basaltic magmas, he determined the order of crystallization of minerals as the temperature drops. Question 16 (1 point) Viscosity is function of temperature and composition, so which magma would have the highest viscosity (least likely to flow)? Lower temperature magmas have higher viscosity than higher temperature magmas (viscosity decreases with increasing temperature of the magma). A magma with low silica (<45%) will be runny and so the eruption will not be explosive. Filed Under: Earth Tagged With: Felsic, Felsic Rocks, Mafic, mafic rocks. Mafic is a kind of igneous rock which are rich in magnesium and iron. This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. The cliche imagery of volcanoes involve lava: majestic, cardinal red geysers spurting a viscous glowing fluid into a river of oozing, crusting, newly forming rock. This type of magma has a high gas and silica content. For an introductory college-level earth sciences class: a review of the impacts of magma viscosity on how crystals form underground and how, above ground, la. Tends to erupt effusively, as lava flows. Viscosity is a liquid's resistance to flow. Silicon dioxide, or silica, is a mineral most commonly known as quartz. Describes magma that contains lower amounts of silica and is generally less viscous and less gas-rich than silicic magma. 3. 1 B. The higher the amount of silica in the magma, the higher is its viscosity. the importance and affect of magma viscosity (how thick it is) in magma movement and shape of whatever structure is formed. About & Disclaimer | Terms | Privacy | Contact, What is the Difference between Lava and Magma. Felsic is a term that is made up of the names of Feldspar and silica. The amount of dissolved gases in the magma can also affect its viscosity, but in a more ambiguous way than temperature and silica content. For example, granite contains around 70% of silica. Like most liquids the higher the temperature the more fluid a substance becomes thus lowering its viscosity. Answer. Viscosity generally increases as the temperature decreases. If any melting takes place, crystal settling will make the magma at the bottom of the chamber more mafic than it was to begin with (Figure 3.14c). Mafic rocks are rich in iron and magnesium, whereas Felsic rocks are rich in silica and aluminum. Required fields are marked *. Viscosity is a liquid's resistance to flow. The effect of temperature on viscosity is intuitive. Where mafic contains 45 to 55% of silica content, the latter contains more than 65% of silica content. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar. The type of lava emitted in an eruption can reveal intimate details of the inner workings of not only the volcano, but also the underlying geological processes governing Earths surface. The theory of plate tectonics, Pangea, and the geothermal energy industry all owe their start to the primal urge of ancient scientists to study and revere Natures most fearsome phenomena. The higher the amount of silica in the magma the higher is its viscosity. Mafic rocks are those types of igneous rocks that consist of magnesium as well as iron. Felsic magma is viscous and does not flow easily. The higher the amount of silica in the magma the higher is its viscosity. A glimpse offered into the fiery subterranean processes that has inspired awe and fear throughout the span of the human race. For all compositions, viscosity decreases with P, rapidly below 5 GPa and slowly above.
At about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize. This is one of the important types if we igneous rocks are classified on the basis of silica content and it contains 45 to 55% of silica. Low viscosity means that mafic magma is the most fluid of magma types. In some cases, however, partially cooled but still liquid magma, with crystals in it, will either move farther up into a cooler part of the crust, or all the way to the surface during a volcanic eruption. Viscosity describes a fluid's resistance to flow, or how thick or sticky the fluid is. They are dark in colour ( whereas felsic rocks are light in colour). The most common examples of rocks classified as Mafic are gabbro, dolerite, and basalt. What is the tendency of the magma with high silica content. Although there are many exceptions to this trend, mafic magmas typically have 1% to 3% volatiles, intermediate magmas have 3% to 4% volatiles, and felsic magmas have 4% to 7% volatiles. Tends to erupt effusively, as lava flows. Commonly even very felsic rocks will not have biotite or muscovite because they may not have enough aluminum or enough hydrogen to make the OH complexes that are necessary for mica minerals. How is felsic magma formed? Earth Sciences. Viscosity is determined by its composition and temperature: Felsic lava is more viscous than mafic lava. Your email address will not be published. The higher the amount of silica in the magma the higher is its viscosity. Mafic rocks are darker in color than Felsic rocks. Felsic magmas usually have higher gas contents than mafic magmas. How does an increase in silica content affect viscosity? Source: Physical Properties of Magma The anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 GPa, while the P dependence of viscosity beyond this remains to be measured. A high viscosity magma will flow more readily and easily than a low viscosity magma. Mafic magma also has high mean temperatures, between 1000o and 2000o Celsius (1832o and 3632o Fahrenheit), which contributes to its lower viscosity. Volcanoes are one of the most fascinating phenomena that grace Earths surface; they are the windows into the nether region, a brief glimpse into the underlying processes governing our world. The amount of silica influences the magmas viscosity in such a way that if the silica content is low, the magma would have low viscosity, whereas a high content of silica would make the magma more thick and sticky. Compare these with those in the table above to determine whether each of these samples is felsic, intermediate, or mafic. Common examples of mafic rocks are basalt, CBSE Previous Year Question Paper for Class 10, CBSE Previous Year Question Paper for Class 12. Mafic Describes magma that contains lower amounts of silica and is generally less viscous and less gas-rich than silicic magma. Physical Geology by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Shield Volcanoes. Mafic magma has a low content of silica because of which before cooling, mafic lava has a low viscosity. What aspects is most important to increase or decrease viscosity? How does silica affect viscosity? 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). Which magma is more viscous quizlet? A magmas viscosity is largely controlled by its temperature composition and gas content (see downloadable programs at the bottom of this page). The higher the amount of silica in the magma, the higher is its viscosity. In turn, felsic magma is associated with the volatile stratovolcano characterized by Plinian eruptions (mushroom cloud) followed by a deadly pyroclastic flow of hot ash, gas, and lava. Most felsic magma will stay deeper in the crust and will cool to form igneous intrusive rocks such as granite and granodiorite. Higher SiO 2 (silica) content magmas have higher viscosity than lower SiO 2 content magmas (viscosity increases with increasing SiO 2 concentration in the magma). Temperature Inversion - Types, Conditions, Effects and FAQs, Jet Stream - Layers, Formation, Types, Facts and FAQs, Forest Fire - Types, Effects, Natural Disaster and Management, Fly Ash - Concrete, Bricks, Sources, Relation and Facts, Rivers - Origin, History, Formation and Uses, Typhoon - Formation, Structure, Differences and FAQs, Relation Between Temperature and Humidity. In conclusion, you have seen the most significant points in mafic vs felsic. Magma mixing is also sensitive to the mineral assemblage (influencing the shape ratio): for instance, a mafic magma with plagioclase (aspect ratio ~4) has a higher viscosity than a similar magma . Felsic magma or lava is higher in viscosity than mafic magma/lava. Which magma is more viscous quizlet? There are two types of felsic lava: rhyolite and dacite. On the basis of the texture of rocks, different names of mafic rocks are given below in the table: To sum up we can say that mafic is a term which is made up of magnesium and ferric thus used to describe the rocks which are rich in two whereas now it is also used to describe the igneous rocks which are rich in high content of magnesium as well as iron. Mafic lava before cooling has a low viscosity in comparison with felsic lava due to the lower silica content in mafic magma. When viscosity is high, flow rate (velocity) is low. Want to create or adapt OER like this? Question3. As long as there is silica remaining and the rate of cooling is slow, this process continues down the discontinuous branch: olivine to pyroxene, pyroxene to amphibole, and (under the right conditions) amphibole to biotite. A number of processes that take place within a magma chamber can affect the types of rocks produced in the end. - Lexico definition. What is the difference between mafic and felsic? The Bowen reaction series is one of the results of his work, and even a century later, it is an important basis for our understanding of igneous rocks. Mafic magma does not erupt explosively but it instead flows out of volcanoes and moves quickly on the surface. The crystals that settle might either form an olivine-rich layer near the bottom of the magma chamber, or they might remelt because the lower part is likely to be hotter than the upper part (remember, from Chapter 1, that temperatures increase steadily with depth in Earth because of the geothermal gradient). There are several formulas and equations to calculate viscosity, the most common of which is Viscosity = (2 x (ball density liquid density) x g x a^2) (9 x v), where g = acceleration due to gravity = 9.8 m/s^2, a = radius of ball bearing, and v = velocity of ball bearing through liquid. This combination is explosive because the gases cannot easily boil out. Of course, this factor also allows it to be one of the most fluid types of magma, and it both moves very quickly and erupts in a non-aggressive manner. Chemical data for four rock samples are shown in the following table. Magma with a high viscosity is cooler in temperature, has a high amount of silica, and is Granitic/Andesitic. Lava made up of Felsic rocks is slow moving and has a higher viscosity than Mafic lava. These results imply that. Intermediate Magma . Soon after that, all of the magma is used up and no further changes takes place. Viscosity is a liquid's resistance to flow. A magma with high silica (>60%) will be quite viscous and so the eruption will be violent. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar. Modeled by Bowen's reaction series. And yes, it is true that felsic magma is more viscous than mafic magma yet less dense. Compare the Difference Between Similar Terms. Why is it important to determine the viscosity of magma? This topic will be helpful to understand one of the types of igneous rocks which are formed from magma and which we usually study in Geography, Geography, Earth Sciences, Physical Geography, etc. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz. The results were studied under the microscope and by chemical analysis. When we divide the igneous rocks on the basis of silica content, mafic rocks stand at 3rd rank in terms of it i.e 45 to 55% silica content and they are dark colour rocks in which most common mafic minerals are Olivine, pyroxene, amphibole, and biotite. In this article, we will talk about this type of rock. Rocks are said to be the hard matter which forms after the solidification of the magma and because of various other geographical phenomena. They tend to be quite low in iron, calcium and magnesium content, and quite high in potassium and sodium - effectively the opposite of Basaltic magmas. It is the silica content that controls the viscosity of the magma, and hence the nature of the volcanism that is seen. Common examples of mafic rocks are basalt, gabbro, diabase, etc. . Mafic rocks are denser and heavier than Felsic rocks. The main determination of lava classes is the amount of silica content in the lava. Olivine, pyroxene, amphibole, and biotite are considered to be common rock-forming mafic minerals. If we talk about Igneous rocks, these are formed after the solidification of magma and can be of two types i.e. Viscosity of Magmas Viscosity is the resistance to flow (opposite of fluidity). Mafic is a kind of igneous rock which are rich in magnesium and iron. All Felsic rocks contain a high percentage of silica. The lava flow has a medium viscosity as well, and once cooled, the resulting rock is known as Andesite. as magma rises thru the lithosphere, pressure decreases and the amount of gas escaping from a magma _____ . What affects the viscosity of magma quizlet? The Earth, by weight, mostly consists of mafic or ultramafic rocks, but silicic rocks are considered to be more abundant on the surface of the Earth. The thicker magma is, the higher the viscosity. Earth Sciences questions and answers. Mafic magma is not viscous and will flow easily to the surface. Common mafic rocks include basalt and gabbro. Viscosity determines what the magma will do. As the temperature continues to drop, olivine becomes unstable while pyroxene becomes stable. The magma slows down. Mafic magma produces high volume, slow moving, effusive eruptions. High-silica (basalt) magma has a much lower viscosity. Mafic lava flows more easily than felsic lava, and the former has a lower risk of exploding. The more mafic the lava (the less silica in it), the lower the viscosity. The magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the Ca end-member within pyroxene melts. Tends to erupt effusively, as lava flows. Hawaiians worshiped volcano gods; Pliny the Younger reverently documented the destruction of Pompeii. Chemically, these rocks are consist of magnesium, iron, and calcium. Gray bar represents the range of viscosity of mafic magmas in the three studied natural outcrops at T = 1480 k. Liquidus temperatures of mafic magmas were calculated at P = 5000 bars using the software MELTS (Ghiorso and Sack 1995 ); b variation of \log (V_\mathrm {R}) with temperature. The silica content of the magma determines how thick the magma is, how easily it flows and how easily dissolved gases within the magma can escape; therefore the silica content determines the characteristic of the volcanic eruption and the shape and size of the resulting volcanic cone. Mafic magma is not viscous and will flow easily to the surface. Mafic is a term used to describe the densest lava flows. All rights reserved. Magma with a high viscosity is cooler in temperature, has a high amount of silica, and is Granitic/Andesitic.
Fractional crystallizationsettling early formed crystals. Some of the standard definitions are given below: "In Geology, of or relating to rocks rich in dark, ferromagnesian minerals." Rising mafic magma may have sufficient momentum to simply intrude right into overlying silicic magma (Bergantz and Breidenthal, 2001). How does temperature and silica content affect the viscosity of magma? It is a dark coloured rock that consists of silica content less than felsic and intermediate whereas more than ultramafic igneous rocks. Mafic is an acronym made up of Ma that stands for Magnesium and Fic that stand for iron or ferric, the Latin name of iron. the four major types of magmas: felsic, intermediate, mafic, and ultramafic. Viscosity determines what the magma will do. GAS: In a volcano with low silica content gas escapes easily from the surface of the lava. VISCOSITY is directly related to the amount of silica (sand) in the magma. On the basis of silica content, igneous rocks can be classified into various types. Hence, lower viscosity and low gas content mean higher temperature of magma. 2017 Actforlibraries.org | All rights reserved The means that the overall composition of the magma near the top of the magma chamber will become more felsic, as it is losing some iron- and magnesium-rich components. Granite is a great example of Felsic rocks and muscovite, quartz, and some feldspar are the best examples of Felsic minerals. For a quick summary, the disparity between them is obvious in their levels of viscosity. Non explosive eruptions are favored by low gas content and low viscosity magmas . What happens to the viscosity of magma when the temperature increases? Intermediate lava has a lower silica content than felsic lava, but not as high magnesium or iron levels as found in mafic lava. Mafic magmas have 45% to 55% SiO2, about 25% total of FeO and MgO plus CaO, and about 5% Na2O + K2O. Copyrights By Li Creative Technologies - 2022, How Does Silica Content Affect The Viscosity Of Magma Related Questions. It forms within the upper mantle, much deeper than felsic magma. Higher silica content means higher viscosity. The mafic magmas are somewhat more viscous than the ultramafic magmas, but they are still fairly fluid. Typical intermediate rocks are diorite and andesite (Figure 3.13). Mafic magma also has high mean temperatures, between 1000o and 2000o Celsius (1832o and 3632o Fahrenheit), which contributes to its lower viscosity. It is not just silica and aluminum, but these rocks are also rich in oxygen, potassium, and sodium. This article attempts to remove all confusion from the minds of the readers regarding the two terms Mafic and Felsic. Most felsic magma will stay deeper in the crust and will cool to form igneous intrusive rocks such as granite and granodiorite. Viscosity depends on primarily on the composition of the magma, and temperature. The magma that causes quiet eruptions is low in viscosity and is is classified as mafic magma. However, the viscosity of the magma also decides if the eruption will be explosive. Most of the igneous rocks can be classified as Mafic or Felsic. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series (Figure 3.10 and Who was Bowen). Using the diagram shown here, predict what phenocrysts might be present where the magma cooled as far as line a in one case, and line b in another. shield volcano example. On this basis, igneous rocks can be divided into four major types i.e felsic, intermediate, mafic, and ultramafic ( written as per the silica content in decreasing order). This process is known as fractional crystallization. Figure 3.11 shows a zoned plagioclase under a microscope. Mafic and Felsic are categories into which igneous rocks are classified. Felsic magma can evolve from mafic magma. What is the process of minerals crystallizing and evolving mafic compositions into intermediate felsic compositions? Magmas that have a high silica content will therefore exhibit greater degrees of polymerization, and have higher viscosities, than those with low-silica contents. Because the mafic rocks are enriched in Fe and Mg, they tend to be darker colored than the felsic rock types. Question 16 options: a) mafic b) low. Higher viscosity (felsic) lava is typically less hot than the lower viscosity (mafic) lava. Quartz has a relatively low melting temperature, so magma with a higher silica content can form at much cooler temperatures relative to magma that contains denser elements such as iron or magnesium. As geologists have classified different lava flows and volcanic eruptions over the centuries, the mechanics of the Earth has become clearer. Which of the following increases the viscosity of magma? How does temperature and silica content affect the viscosity of magma? The viscosity of a liquid is related to the ease with which the molecules can move with respect to one another. They are dark in colour and these rocks are consist of magnesium, iron, and calcium. Additionally, they contain somewhat more gas than do the ultramafic magmas, but not nearly so much as the felsic magmas. Mafic magma is not viscous and will flow easily to the surface. Felsic magmas tend to be cooler than mafic magmas when crystallization begins (because they dont have to be as hot to remain liquid), and so they may start out crystallizing pyroxene (not olivine) and plagioclase.
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