Geology test #2: Chap. 4-7
What texture describes an igneous rock that has two or more distinctly different-sized populations of mineral grains?
Porphyritic
What are the factors that determine the explosiveness of a volcanic eruption (i.e. composition, temperature and dissolved gases)? How do each of these factors affect the explosiveness of an eruption?
Temperature: strongly influences the mobility of lava Composition: The more silica content, the more viscous the magma becomes Dissolved gases: water vapor in gasses dissolved in magma tend to affect the mobility
The sizes, shapes, and arrangements of mineral grains in an igneous rock is known as ____________
Texture
Volatiles
gaseous components of magma dissolved in the melt. They will readily vaporize at surface pressures
Volcanic tuff
mixture of volcanic ash, bombs, rock fragments
Continental volcanic arc
mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. EX: the Andes and the Cascades
Which of the following igneous rocks has a phaneritic texture? - Andesite Rhyolite Basalt Gabbro
Gabbro
Stock
a pluton similar to but smaller than a batholith
Which igneous rock or magma has the lowest silica content?
basalt
Olivine and quartz commonly crystallize together from mafic or basaltic magmas
false
Flood basalt
flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
Hot spot
a concentration of heat in the mantle capable of producing magma, which rises to Earth's surface
Scoria
vesicular ejecta that is the product of basaltic magma
Know how igneous rocks are classified and named.
1.Texture.-Coarse, Fine, Glassy 2.Chemical Compostion 3.Mineral content -Proportion of light mineral to dark minerals.
Magma
A body of molten rock found at depth, including any dissolved gases and crystals.
Ultramafic
A compositional group of igneous rocks containing mostly olivine and pyroxene.
Mafic
A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar.
Felsic
A compositional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicates.
Granitic
A compositional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicates.
Andesitic
A compositional group of igneous rocks that contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar.
Intermediate
A compositional group of igneous rocks that contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar.
Bowen's Reaction Series
A concept proposed by N. L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks.
Phenocrysts
A conspicuously large crystal embedded in a matrix of finer-grained crystals.
Lahar
A debris flow on the slopes of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels.
What are flood basalts? Where in the U.S. would you find flood basalt today?
A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Idaho Falls
Batholith
A large mass of igneous rock that formed when magma was emplace at depth, crystallized, and subsequently exposed by erosion
Pumice
A light-colored, glassy vesicular rock commonly having a granitic composition.
Laccolith
A massive igneous body intruded between preexisting strata
Conduit
A pipelike opening through which magma moves toward Earth's surface. It terminates at a surface opening called a vent.
crystal settling
A process that occurs during the crystallization of magma, in which the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber.
Cinder cone
A rather small volcano built primarily of ejected lava fragments that consist mostly of pea- to walnut-size lapilli.
Island arc
A string of islands formed by the volcanoes along a deep ocean trench
Pluton
A structure that results from the emplacement and crystallization of magma beneath the surface of Earth.
Dike
A tabular-shaped intrusive igneous feature that cuts through the surrounding rock.
Vesicular texture
A term applied to aphanitic igneous rocks that contain many small cavities called vesicles.
Concordant
A term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock.
Discordant
A term used to describe plutons that cut across existing rock structures, such as bedding planes.
Glassy texture
A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals.
Aphanitic texture (fine-grained)
A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope
Aa flow
A type of lava flow that has a jagged, blocky surface
Composite volcano
A volcano composed of both lava flows and pyroclastic material
Describe the six types of igneous textures (aphanitic, phaneritic, porphyritic, glassy, vesicular, and fragmental/pyroclastic). Under what conditions does each texture form? How is the rate of magma cooling related to the different types of textures?
A. Glassy texture Composed of unordered atoms and resembles dark manufactured glass. (Obsidian is a natural glass that usually forms when highly silica-rich magmas solidify.) B. Porphyritic texture Composed of two distinctly different crystal sizes. C. Phaneritic (coarse-grained) texture Composed of mineral grains that are large enough to be identied without a microscope. D. Vesicular texture Extrusive rock containing voids left by gas bubbles that escape as lava solidies. (Pumice is a frothy volcanic glass that displays a vesicular texture.) E. Pyroclastic (fragmental) texture Produced by the consolidation of fragments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive volcanic eruption. F. Aphanitic (fine-grained) texture Composed of crystals that are too small for the individual minerals to be identified without a microscope.
What are cinder cones?
Also called scoria cones, they are built from ejected lava fragments that begin to Harden in flight to produce the vesicular rock scoria.
What is Shiprock, New Mexico?
An example of volcanic necks
Porphyritic texture
An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, whereas the matrix of smaller crystals is termed the groundmass.
Phaneritic texture
An igneous rock texture in which the crystals are roughly equal in size and large enough so the individual minerals can be identified without the aid of a microscope.
Where in the U.S. would you find stratovolcanoes today?
Andes in the south, and Cascade Range of the western US and Canada
Describe Basalt
Aphanitic (fine-grained), Mafic (basaltic), a very dark green to black, finegrained rock composed primarily of pyroxene and calcium-rich plagioclase feldspar, with lesser amounts of olivine and amphibole
Describe Rhyolite
Aphanitic (fine-grained), felsic (granitic), contains light colored silicates
How does temperature affect the viscosity of magma?
As lava cools and begins to congeal, its viscosity increases and eventually the flow halts
What are volcanic domes? Which of the three lava types are typically associated with lava domes?
As the thick lava is squeezed out of the vent, it often produces a dome-shaped mass called a lava dome. Cool, silica-rich rhyolitic lavas are associated with lava domes.
What type of magma, commonly erupted along oceanic ridge systems, originates by partial melting of mantle peridotite?
Basalt
What is the sequence of rock compositions produced during differentiation (i.e. basaltic - andesitic - granitic)?
Basaltic yields andesitic, andesitic yields granitic
Why are rocks of intermediate (andesitic) and felsic (granitic) compositions generally not found in ocean basins? Along which of the three types of plate boundaries are andesitic magmas generated? Describe two ways in which andesitic magma forms. Describe two ways in which granitic magma forms. Where are most granitic rocks found?
Because they are formed from partial melting of the earth crust. Andesitic magmas are generated around Convergent plate boundaries. 1. Magmatic differentiation of basaltic magma 2. Basaltic magma migrating upward through continental lithosphere becomes andesitic by assimilating moresilica-rich components of earth's crust 1. End product of crystallization of andesitic magma 2. Combination of crystallization and assimilation of continental crust 3. Direct partial melting of continental crust Continental crust
Which of the following factors or processes influence the composition of magma?
Composition of the original rock that melted to form the magma Types of minerals that crystallize from magma Mixing of magmas having different compositions Composition of any host rock assimilated by the magma
What materials comprise these types of volcanoes?
Consist of alternating laters if explosively erupted cinders and ash interbedded with lava flows.
All of the following are factors that affect the generation of magma except for _____________ Heat Pressure Crystal size Volatiles
Crystal Size
Describe the different factors that affect magma composition (crystal settling, magma mixing, assimilation, melting of different source rocks, etc.).
Crystal settling: A process that occurs during the crystallization of magma, in which the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber. Magma mixing: The process of altering the composition of a magma through the mixing of material from another magma body. Assimilation: In igneous activity, the process of incorporating country rock into a magma body.
Andesitic magma can form through differentiation of granitic magma
False
Volatiles
Gaseous components of magma dissolved in the melt. Volatiles will readily vaporize (form a gas) at surface pressures.
Describe the characteristics of a basaltic magma in terms of temperature, composition and type of eruption. How does a pahoehoe lava flow differ from an Aa lava flow?
Hot basaltic lavas are usually very fluid, generally flow in thin, broad sheets or stream like ribbons. Aa Laval flows have surfaces of tough jagged blocks with dangerously sharp edges and spiny projections. Pahoehoe flows exhibit smooth surfaces that sometimes resemble twister braids or ropes. "on which one can walk"
Describe a pyroclastic flow (nuée ardente). Why are they so dangerous and destructive?
Hugh cloud of hot ash, dust, and gases - Cascade downhill at speeds up to 200km/hr - Devastating, causing many deaths - Can bury entire towns
How do porphyritic textures form?
If molten rock containing some large crystals moves to a different environment—for example, by erupting at the surface—the remaining liquid portion of the lava cools more quickly. The resulting rock, which has large crystals embedded in a matrix of smaller crystals, is said to have a porphyritic texture
Extrusive
Igneous activity that occurs at Earth's surface.
Intrusive
Igneous rock that formed below Earth's surface.
Plutonic
Igneous rocks that form at depth. Named after Pluto, the god of the lower world in classical mythology.
Assimilation
In igneous activity, the process of incorporating country rock into a magma body.
Nuée ardente
Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion.
Pillow lava
Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens
How does magma differ from lava? Describe a pyroclastic type of eruption.
Magma is composed of molten rock and is stored in the Earth's crust. Lava is magma that reaches the surface of our planet through a volcano vent.
Lava
Magma that reaches Earth's surface.
Decompression melting
Melting that occurs as rock ascends due to a drop in confining pressure.
Describe decompression melting
Melting that occurs as rock ascends due to a drop in confining pressure.
What are the roles of pressure and heat in generating magma from solid rock? What magma composition is produced within this environment?
Melting, which is accompanied by an increase in volume, occurs at progressively higher temperatures with increased depth. This is the result of the steady increase in confining pressure exerted by the weight of overlying rocks. Conversely, reducing confining pressure lowers a rock's melting temperature.
How does rhyolitic lava differ from andesitic lava and basaltic lava in terms of temperature, composition, viscosity, and type(s) of eruptions? Which two of the three lava types are most likely to erupt explosively? Why?
More than 90% of the total volume is estimated to be basaltic in composition. Andesitic lavas and other lavas account for most of the rest, while Rhyolitic flows make up as little as 1% of the total. Silica-rich Rhyolitic lava may be too slow to perceive, and seldom travel more than a few kilometers from they vents. Andesitic flows are between the two.
Describe composite/stratovolcanoes.
Most picturesque, yet danger volcanoes; located in the ring of fire, large, nearly symmetrical structures consisting of alternating laters of explosively erupted cinders and ash interbedded with lava flows.
How does a caldera differ from a volcanic crater? How does a caldera form?
Most traders are formed by one of the following processes: (1) the collapse of the summit of a large composite volcano following an explosive eruption of silica-rich pumice and ash fragments (Crater Lake) (2) the collapse of the top of a shield volcano caused by subterranean drainage from a central magma chamber (Hawaiian) or (3) the collapse o a large area, caused by the discharge of colossal volumes of silica-rich pumice and ash along ring fractures (Yellowstone)
Glass
Natural glass that is produced when molten lava cools too rapidly to permit recrystallization. Volcanic glass is a solid composed of unordered atoms.
Consider Bowen's reaction series. Which mineral would you expect to see as a phenocryst in a porphyritic basalt?
Olivine
How does the composition of a melt produced by partial melting compare with the composition of the parent rock?
Partial melting occurs in rocks because the different minerals that compose rocks have different melting points. The melt take the compostion of the heated minerals, while the solid parent rocks remains with the solid minerals that did not melt.
__________ is thought to be common in the Earth's mantle but rare in the crust.
Peridotite
Volcanic
Pertaining to the activities, structures, or rock types of a volcano.
Describe Granite
Phaneritic (coarse-grained), Felsic (granitic)
Describe Gabbro
Phaneritic (coarse-grained), Mafic (basaltic) tends to be dark green to black in color and composed primarily of pyroxene and calcium-rich plagioclase feldspar. Although gabbro is uncommon in the continental crust, it makes up a significant percentage of oceanic crust.
What are volcanic pipes and necks?
Pipes: a rare type of conduit that carries magma that origniated in the mantle Volcanic necks (plugs):
What are plutons? How does a batholith differ from a stock? Give two examples of batholiths found today in the U.S.
Plutons: a structure that results from the emplacement and crystallization of magma beneath the surface of earth. Batholiths are the largest intrusive igneous bodies, typically composed of felsic (granitic) and intermediate rock types, produced by hundreds of discrete injection of magma that form smaller intrusive bodies (plutons) that crowd against or penetrate each other Smaller plutons are terms stocks because they are smaller, but would be classified as batholiths if they were fully exposed
Describe the characteristics of a shield volcano. What lava type typically constructs shield volcanoes? Where are shield volcanoes found today?
Produced by the accumulation of fluid basaltic lavas and exhibits the shape of broad, slight some structure that resembles a warrior's shield. Constructed of a myriad of thin basaltic lava flows, averaging a few meters thick intermix with relatively minor amounts of ejected pyroclastic materials. The Hawaiian islands, the Canary Islands, Iceland, and Galapagos islands.
What is the name of a volcanic rock that is extremely vesicular and glassy?
Pumice
Describe Volcanic tuff
Pyroclastic,
What criteria are used to classify and name pyroclastic material and pyroclastic rocks?
Pyroclasts are the loose fragments associated with explosive eruptions: Bombs (> 64mm): twisted shapes due to solidification from fluid while airborne. Blocks (> 64mm): large chunks of rock broken from within and around the volcanic conduit. Lapillus (2-64mm): individual fragments of minerals, glass or rock 2 - 64 mm in diameter. Ash grains (< 2 mm): mineral, glass and rock fragments less than 2 mm in diameter
What are the first minerals to crystallize from a basaltic magma? What are the last minerals to crystallize at low temperature in Bowen's Reaction Series?
Pyroxene, biotite mica
Which of the following pairs of igneous rocks have the same composition? - Rhyolite and gabbro Rhyolite and granite Andesite and peridotite Basalt and diorite
Rhyolite and Granite
Which of the following igneous rocks has a pyroclastic texture? - Porphyritic basalt Intrusive diorite Andesitic lava Rhyolitic tuff
Rhyolitic tuff
Volcanic breccia
Rock formed from large pieces of volcanic rock (cinders, blocks, bombs).
What is the name of a famous cinder cone in Arizona?
SP Crater
How are dikes and sills similar?
The difference between a dike and a sill is that dykes are formed across or vertical to the rock while sill are on horizontalcracks. However, they are both sedimentary in nature. Both are intrusive, where magma flows through the outer crust. They arerelatively thin
Lava flows are typically finer grained than intrusive rocks. Why?
The extrusive magma cools quickly so the mineral grains do not have time to grow
Crystallization
The formation and growth of a crystalline solid from a liquid or gas.
Describe how magmatic differentiation changes the composition of magma during crystallization.
The formation of a magma body having a mineralogy or chemical composition that is different than the parent magma is called magmatic differentiation. One mechanism that causes this to happen is called crystal settling. This process occurs when the earlier-formed minerals are denser (heavier) than the liquid portion and sink toward the bottom of the magma chamber. When the remaining melt solidifies—either in place or in another location, if it migrates into fractures in the surrounding rocks—it will form a rock with a mineral composition that is different than the parent magma.
How do volcanic eruptions affect climate? How does volcanic material ejected into the atmosphere affect incoming solar radiation?
The gases and dust particles thrown into the atmosphere during volcanic eruptions have influences on climate. Most of the particles spewed from volcanoes cool the planet by shading incoming solar radiation. The cooling effect can last for months to years depending on the characteristics of the eruption.
. What are fissure eruptions? What type of lava is typically associated with fissure eruptions?
The greatest volume of volcanic materials is extruded from fractures in Earth's crust called fissures. Fissure eruptions usually emit fluid basaltic lavas that blanket wide areas.
Melt
The liquid portion of magma excluding the solid crystals.
Groundmass
The matrix of smaller crystals within an igneous rock that has porphyritic texture.
How does composition (silica content) affect the viscosity of magma?
The more silica content, the more viscous = sticky, slower
How is viscosity related to the explosiveness of an eruption?
The more viscous the material, the greater its resistance to flow.
Stratovolcano
The most common volcano. Known for its layers of lava flows and cinder. Built up by violent eruptions that leave the tephra followed by calm eruptions that leave lava flows. They build tall and steep volcanoes.
Partial melting
The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.
Describe partial melting. How is Bowen's Reaction Series used to predict the order in which different minerals melt? What magma composition does partial melting of peridotite produce?
The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results. Recall from Bowen's reaction series that rocks with a granitic composition are composed of minerals with the lowest melting (crystallization) temperatures—namely, quartz and potassium feldspar (see Figure 4.21). Also note that as we move up Bowen's reaction series, the minerals have progressively higher melting temperatures and that olivine, which is found at the top, has the highest melting point. Yields a melt with a chemical composition that is richer in silica and nearer the felsic (granitic) end of the spectrum than the rock from which it formed.
magma mixing
The process of altering the composition of a magma through the mixing of material from another magma body.
magmatic differentiation
The process of generating more than one rock type from a single magma.
How does a dike differ from a sill in terms of concordance versus discordance?
The term sills synonymous with concordant intrusive sheet. This means that the sill does not cut across preexisting rocks,in contrast to dikes, discordant intrusive sheets which do cut across older rocks
Pyroclastic
The volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks.
A feldspar crystal where a calcium rich interior is surrounded by a sodium rich rim indicates that there was incomplete reaction between the crystal and surrounding magma
True
The formation of a secondary magma of different composition from a parent magma is called magmatic differentiation
True
Veins & Pegmatites
Veins are intrusions injected into rock fractures and range from several millimeters to several meters wide; Pegmatites are coarse-grained veins that cut across finer-grained rock, typically felsic in composition.
What is the role of volatiles in generating basaltic magma within subduction zones?
Water lowers the melting temperatures. At a Subduction Zone, the oceanic plate descends into the mantle;water is driven from the plate and lowers the melting temperature, creating melt
What type of volcanic eruption produces pyroclastic material?
When volcanoes erupt energetically, they eject pulverized rock, lava, and glass fragments from the vent.
Shield volcano
a broad, gently sloping volcano built from fluid basaltic lavas
Lava dome
a bulbous mass associated with an old-age volcano produced when thick lava is slowly squeezed from the vent, lava domes may act as plugs to deflect subsequent gaseous eruptions
Volcanic island arc
a chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another
Pyroclastic flow
a highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground
Caldera
a large depression typically caused by collapse or ejection of the summit area of a volcano
Pahoehoe flow
a lava flow with a smooth-to-ropy surface
Mantle plume
a mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity
Viscosity
a measure of a fluid's resistance to flow
Describe Volcanic breccia
a rock composed predominantly of angular fragments resulting from brecciation or emplacement due to volcanic action
Sill
a tabular igneous body that was intruded parallel to the layering of preexisting rock
Fumarole
a vent in a volcanic area from which fumes or gases escape
Pipe
a vertical conduit through which magmatic materials have passed
Fissure eruption
an eruption in which lava is extruded from narrow fractures or cracks in the crust
Porphyry
an igneous rock that has a porphyritic texture
Xenolith
an inclusion of unmelted country rock in an igneous pluton
Volcanic neck
an isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano
Changing the composition of magma by incorporating surrounding host rock is known as __________
assimilation
Cinder cones are primarily constructed of what material?
basaltic composition
Describe Diorite
coarse-grained rock that looks somewhat like gray granite. However, it can be distinguished from granite because it contains little or no visible quartz crystals and has a higher percentage of dark silicate minerals. The mineral makeup of diorite is primarily plagioclase feldspar and amphibole.
Describe Obsidian
dalk colored Volcanic glass, noncrystalline glassy substances, and coal, which consists of solid organic debris.
Describe Peridotite
dark-colored igneous rock consisting mostly of olivine and pyroxene. It is an important rock type because the Earth's mantle is predominantly composed of it.
What type of plate boundary would you expect decompression melting to occur?
decompression melting in the upper mantle.
Describe Pumice
glassy volcanic rock with a vesicular texture that forms when large amounts of gas escape through silica-rich lava to generate a gray, frothy mass.
What are pyroclastic deposits?
idk
Which of the three types of plate boundaries is characterized by composite/stratovolcanoes?
idk
How is Bowen's Reaction Series used to predict the order in which minerals crystallize as temperature decreases?
if solid components of a magma remain in contact with the remaining melt, they will chemically react and change mineralogy. -they know minerals that form in the same general temp are found together in igneous rocks
Intraplate volcanism
igneous activity that occurs within a tectonic plate away from plate boundaries
How does a volcanic neck form?
is a volcanic landform created when lava hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure if volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption.
Describe Andesite
medium-gray, fine-grained rock typically of volcanic origin. Andesite commonly exhibits a porphyritic texture
Decompression melting in the generation of magma is common along...
mid-oceanic ridge
Crater
the depression at the summit of a volcano or that which is produced by a meteorite impact
Vent
the surface opening of a conduit or pipe
Pyroclastic material
the volcanic rock ejected during an eruption. Includes: ash, bombs and blocks
