• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/32

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

32 Cards in this Set

  • Front
  • Back

· Sketch or describe the various texturesdisplayed by igneous rocks.

The two primary texture terms are phaneritic and aphanitic. Phaneritic textures are textures where the crystals in a rock are easily observable to the unaided eye (think of granite). Aphanitic textures are textures where the crystals in a rock are not easily observable to the naked eye and contain microscopic crystals, fine-grained volcanic ash, volcanic glass without any crystals, or a combination of these (think of Rhyolite).




Beyond that, there are very coarse crystal rocks, which contain centimeter to meter long crystals, and these are called pegmatite rocks. There are also coarsely crystalline rocks that contain crystals larger than several millimeters to centimeter long crystals. Medium-grained rocks have crystals that are easily visible to the naked eye, and are typically millimeter long crystals, but not centimeters across. Igneous rocks that include larger crystals in a finer grained matrix are porphyritic. The crystals in a porphyritic rock are termed phenocrysts. Volcanic rocks that contain small holes called vesicles are called vesicular rocks. Volcanic ash or pumice when still hot, can be compacted by overlying materials, becoming a hard rock with a "welded" texture. Some volcanic rocks contain angular fragments in a finer matrix and are called volcanic breccia (think of the sedimentary breccia).

· Sketch an igneous system and show where the mainigneous textures form.

Vesicles are formed when gases disolved in magma accumulate as bubbles. They can only form under low pressures o the surface or very near to the surface. Many lavas are vesicular and much of the material in volcanic ash forms when the thin walls between vesicles bursts, shattering partially solidified magma into sharp particles. Mosh volcanic ash is broken vesicles (think of the smoke and ash coming from a volcano as a reference point).




Volcanic breccia can form in many ways, including from explosive eruptions of ash and rock fragments from a lava flow that breaks apart as it partially solidifies while flowing, or from volcano triggered mudflows and landslides on the steep unstable slopes of the volcano (think near the top of the volcano on the sides).




Volcanic glass forms when magma erupts on the surface and cools so quickly that crystals do not have time to form. This can happen in a lava flow or in volcanic ash (obsidian is a reference point).




Fine-grained igneous rocks form if the magma only has enough time to grow small crystals. This usually occurs when magma solidifies on the surface in a thick lava flow or at shallow depths beneath the surface because cooling in these settings is fairly rapid. Medium-grained rocks form deeper, where cooling occurs more slowly.




Coarse-grained rocks form at greater depths where magma cools at a rate that is slow enough to allow large crystals to grow.




Some volcanic ash erupts vertically in a column and settles back to earth. This ash cools significantly before accumulating on the surface. Because it is relatively cool and strong, the ash may not become welded; thus it is said to be nonwelded.




Other volcanic ash erupts in thick clouds of hot gas, ash, and rock fragments called pyroclastic flows, that flow rapidly downhill under the influence of gravity. The ash deposited by pyroclastic flows is very hot, and so most parts are welded to some extent.




For a porphyritic texture to form, magma needs sufficient time in a subsurface magma chamber to grow visible crystals. Later, the magma rises closer to the surface, where the remaining magma solidifies rapidly into the fine-grained matrix around the larger crystals (phenocrysts).




Pegmatite may form if magma is water rich. The dissolved water allows atoms to migrate farther and faster and so helps large crystals to grow. This generally occurs near the sides and top of a magma chamber and in local pockets within the magma Most pegmatite forms at moderate to deep levels within the earth's crust.

Sketch and describe how igneous rocks areclassified.

Igneous rocks are classified according to the size of the crystals, and then the kind of minerals. First they are classified as coarsely crystalline (phaneritic) or finely crystalline or glassy (aphanitic). Then, they are organized by the kind of minerals, or more simply, the color of the rock. Felsic rocks contain light colored minerals, abundant amounts of quartz and feldspar. Mafic and ultramafic rocks contain dark colored minerals and abundant amounts of magnesium and iron minerals. Intermediate rocks are in between in mineral and chemical composition.

· List some common igneous rocks and a fewcharacteristics of each.

Granite is a common igneous rock with coarse crystals, and a light color The abundance of felsic minerals feldspar and quartz put it in the Felsic category. Most granites also contain biotite or muscovite and garnet.




Rhyolite is the fine-grained equivalent of granite but it can contain glass, volcanic ash, pieces of pumice, and variable amounts of phenocrysts of quartz, K-feldspar, or biotite.




Diorite contains more mafic minerals than granite, so it is an intermediate between felsic and mafic. It generally contains abundant plagioclase feldspar, and amphibole, and it can contain variable amounts of either biotite or pyroxene.



Andesite is the fine-grained equivalent of diorite. It is commonly gray or greenish, but it can also have a slight maroon or purplish tint. Andesite commonly has phenocrysts of cream-colored feldspar or dark amphibole.




Gabbro is a coarsely crystalline, mafic rock, containing pyroxene and other mafic minerals, along with light-gray, calcium rich plagioclase feldspar. Feldspar-rich varieties are lighter colored, and some gabbro has olivine.




Basalt is a dark mafic lava rock. Most basalt is dark gray to nearly black, and many out-crops have vesicles. Basalts can contain phenocrysts of dark pyroxene, green olivine, or cream-colored plagioclase feldspar.




Peridotite is an ultramaffic rock with coarse crystals. It contains more magnesium and iron minerals, especially green olivine and dark pyroxene. The upper mantle is composed of peridotite.




Ultramafic lavas erupted early in Earth's history, and so such rocks are preserved only in the oldest parts of some continents. The magma was very hot and commonly grew olivine or pyroxene crystals that are unusually long for a lava flow.



· Describe the main differences between felsic andmafic rocks.

Felsic rocks have abundant amounts of light-colored minerals like quartz and feldspar, while mafic rocks have darker minerals like magnesium and iron.

· List the main characteristics of obsidian,pumice, scoria, tuff, breccia, and pegmatite, and indicate where each of theserock types fits into an igneous classification system based on composition.

Obsidian is a shiny volcanic glass that is normally medium-gray to black color. Most obsidian has a composition equivalent to rhyolite and forms when lava cools too rapidly to form crystals. Some obsidian contains phenocrysts or fragments. Obsidian is mostly felsic but some is barely into the intermediate. Most geologists do not call such rocks obsidian if they are intermediate or mafic.




Pumice is a volcanic rock containing many vesicles. Most pumice can float on water, unlike any other rock in the universe so far as we know. Pumice is also light-colored and felsic to intermediate. Highly vesicular basalt is scoria.




Scoria is a dark gray, black, or reddish volcanic rock that also contains many vesicles. It usually has the composition of basalt or andesite. In outcrops, scoria consists of a jumbled mass of rock fragments as large as several meters across. Scoria is vesicular and mafic.




Tuff is a volcanic rock composed of a mix of volcanic ash, pumice, crystals, and rock fragments. If the particles of ash and pumice cool before being buried by overlying materials, the rock remains only weakly consolidated and is nonwelded tuff. If tuff gets buried while it's still hot as within a thick pyroclastic flow, the weight of overlying materials compacts ash and pumice into lenses, forming welded tuff. Tuff commonly contains angular fragments of older rocks, which do not compact. Tuff is usually felsic to intermediate though some basaltic mafic tuff can form but this mostly forms from ash particles that settle out of the air from smaller eruption columns.




Volcanic breccia is formed from broken apart lava that solidifies during flow, or from mixtures of volcanic rock, ash, and mud. This generally occurs during mudflows and landslides. Volcanic breccia can be any composition.




Pegmatite rocks are rocks with very large crystals ranging from serval centimeters to meters across. This is due to their forming within the curst with enough dissolved water that it grows exceptionally large crystals. While pegmatite can be any composition, most are felsic with large crystals of feldspar and quartz. Granitic pegmatite typically also contains one or more mica minerals (muscovite or biotite). Some includes less common minerals, which can form gemstones, like garnet, tourmaline, and beryl (emerald and aquamarine).

· Summarize the main minerals that are present in felsic, intermediate, mafic, and ultramafic rocks.

Felsic rocks generally contain high amounts of silica (SiO^2), commonly 70 to 77%, and they consist mostly of quartz and feldspar. Silica is the also the dominent chemical constituent of maffic rocks, such as basalt and gabbro, but at lower concentrations (44 to 50% SiO^2). These rocks contain more magnesium, iron, and calcium, and these elements cause darker, mafic minerals, such as pyroxene and olivine, to be more abundant. Intermediate rocks, like andesite and diorite, contain intermediate amounts of silica (about 60% SiO^2) compared to felsic and mafic rocks. They also contain intermediate amounts of magnesium, iron, calcium, potassium, and other elements. They contain abundant feldspar, with variable amounts of quartz and mafic minerals, especially amphibole and biotite.

· Describe three ways that heat is transferred from a warmer mass to a cooler one and an example of conduction and convection by plate tectonics.

Conduction is heat transferred by direct contact. Convection is a type of heat transfer by flow of a liquid or by a solid but weak material. When convection occurs in a circular path, as in a pan, we use the term convection cell. Radiant heat transfer is the radiation of heat transferring through the air, or thermal radiation.




Convection occurs in plate tectonics when solid asthenosphere rises beneath a mid-ocean ridge, bringing hot rocks upward by convection, adding material to the oceanic lithosphere. Conduction can occur when the cooled oceanic lithosphere subducts back into the asthenosphere. The downward motion, coupled with upward motion of material beneath mid-ocean ridges, completes a kind of convection cell.

· Describe how thermal vibrations and pressure affect a mineral lattice.

Thermal vibrations weaken and break the bonds in a mineral lattice so the atoms separate which causes melting. However, pressure pushes the bonds together in a mineral lattice so that they stay together. Pressure allows for minerals to stay solid at higher temperatures, whereas a lower pressure will cause lower temperatures to melt minerals.

· Draw graphs showing how increasing temperature,decreasing pressure (decompression), or adding water to hot rocks causes melting.

N/A

· Sketch and describe the processes involved in forming igneous rocks.

Magma forms from melting, typically 40-150 km beneath the surface, in the deeper parts of the crust or in the mantle. The place where melting occurs is called the source area. Complete melting is rare, and most magmas result from partial melting, leaving most of the source area unmelted.




Magma rises through the crust because it is less dense than the rocks surrounding it.




Magma that accumulates beneath the surface forms a magma chamber, and some magma chamber represents a large batch of magma emplaced at the same time, but most are the results of small increments. Rocks may also solidify in these subsurface chambers and never reach the surface. These are plutonic rocks in the technical sense.




As magma rises through the crust, it may stop in magma chambers along the way and intrude into the surrounding rocks. Igneous rocks that solidify below the surface are called intrusive rocks or plutonic rocks.




Many magma chambers are only several kilometers below the surface, as beneath the volcano. Magma may be added to the chamber a little at a time and some magma may solidify before the next batch arrives. Some of the magma may crystallize in the chamber too. Some rise to the surface carrying those early formed crystals, forming porphyritic volcanic rocks.




Magma that reaches the surface erupts as lava (molten rock) or as volcanic ash. Volcanic ash forms when dissolved gases in the magma expand and blow the magma apart into small fragments of volcanic glass. Rocks that form on the surface are called extrusive rocks because they formed while extruding from the volcano onto the surface. These are simply called volcanic rocks.





· Sketch or describe how melting can influence magma composition.

The composition of the magma is dependent on whether the source completely melted or partially melted. Completely melted source magma has the same composition as the source, though this is not common. Partial melting occurs because some minerals melt before others. Felsic minerals, for example, melt at lower temperatures than mafic minerals, so partial melting produces a magma that is more felsic than the source. Partial melting of a mafic source can yield an intermediate magma. If a more felsic source area, such as continental crust, is melted, the magma will be felsic. If an intermediate source is almost completely melted, the magma will have an intermediate composition, but partial melting more commonly produces a felsic magma.




The overall composition of the mantle is ultramafic but, due to partial melting, magmas generated in the mantle are mostly mafic. Most mafic magma is derived by partial melting of the mantle.

· Sketch or describe how partial crystallization, assimilation, and magma mixing can change a magma.

Magma cools from the outside in. As magma cools, mafic minerals crystallize first, which makes the composition of the remaining magma less mafic and more felsic. Consequently, partial crystallization of a mafic magma typically produces a magma of more intermediate composition.




Once formed, heavy mafic minerals may settle (sink) through the magma and collect in layers at the bottom of the magma chamber. This process, called crystal settling, will make lower parts of the magma chamber more mafic, leaving the remaining magma more felsic.




Felsic crystals may be less dense than magma and so may float upward. This makes the top of the magma chamber more felsic.




If two different magmas come into contact, they may mix, a process called magma mixing. Magma mixing produces a magma that has a composition intermediate between the two magmas that mixed.




Mafic magma is hotter than the melting temperature of felsic rocks, so mafic magma can melt felsic wall rocks. if wall rocks around a magma melt, they may be incorporated into the magma, a process called assimilation.

· Explain the factors that control the viscosity of a magma.

The viscocity of a magma is controlled by temperature (low temperature is more viscous than high temperature), composition (abundant silicate chains are more viscous than few silicate chains though water dissolved in magma disrupts long chains and decreases viscocity [called volatiles]). The percentage of crystals also get in the way f flowing magma and cause the magma to flow more slowly (abundant crystals make a more viscous magma)

· Describe what factors might be combined to form very high-viscosity magma or very low-viscosity magma.

A high-viscosity magma will have a low temperature, abundant silicate chains, and many crystals. It will not be near water which can disrupt chains. A low-viscosity magma will have a high temperature, few amount of silicate chains, and few crystals. Chains may also be disrupted by water.

· Explain the order in which minerals crystallize from a magma (Bowen’s Reaction Series), and compare it to the order in which they melt.

High temperature mafic minerals like olivine and pyroxene are the first to crystallize from a mafic magma.



Amphibole and biotite are the most common in rocks of intermediate composition but are also present in mafic or felsic rocks. They crystallize at a slightly lower temperature than mafic rocks, but before most of the felsic minerals.




Plagioclase feldspar may be calcium-rich or sodium rich or somewhere in between. Calcium-rich plagioclase feldspar crystallizes at a higher temperature than sodium-rich plagioclase feldspar.




Light-colored felsic minerals like quartz, K-feldspar, and muscovite crystallize at the lowest temperatures. These minerals along with sodium-rich plagioclase may be the only minerals formed from felsic magmas, which lack the chemical components required to grow abundant mafic minerals. Felsic minerals rarely grow from mafic magmas, which lack sufficient silicon. While mafic magmas crystallize first, felsic minerals melt first (remember they are opposites).

· Describe how the rate of magma cooling affects the size of crystals.

Minerals that crystallize very early (mafic) can grow unimpeded in the magma and so commonly have well-defined crystal shapes. Minerals that crystallize later must grow around pre-existing crystals, and so they grow in irregular and poorly defined shapes.

· Explain how the crystallization of minerals can change the composition of remaining magma.

As magmas crystallize, they extract the mineral components from a magma, like magnesium, iron, and calcium (because mafic minerals crystallize first). As a result, the remaining magma is actually more felsic or intermediate, because it no longer contains those mafic minerals.

· Sketch or describe why melting occurs along mid-ocean ridges and why the resulting magmas are basaltic (mafic).

Magma begins in the mantle, as mostly solid and crystalline rocks. The mantle's high pressures and temperatures allow these rocks to flow as a weak solid while maintaining a crystalline strucuture. Parts of the asthenosphere are close to the melting temperature.




As the plates seperature, solid asthenosphere rises to fill the area between the plates. As the asthenosphere rises, pressure decreases and the rock partially melts (decompression melting).




The buoyant, mafic magma rises away from the unmelted residue in the mantle and accumulates in magma chambers in the crust and upper mantle.



Magma moves upward through magma-filled fractures that form as the plates pull apart. Some magma erupts as lava within the rift.




Older oceanic crust moves away as the magma cools and forms new oceanic crust.

· Describe the types of igneous rocks that form along mid-ocean ridges.

Mafic rocks are the main type of rocks that form along mid-ocean ridges. While the oceanic crust itself consists of basalt, gabbro can be found in magma chambers beneath the rift. Below the base of the gabbro is the mantle, which contains ultramafic rocks.

· Discuss how an ophiolite compares to a section through oceanic crust.

Ophiolites are identical to the sequence of newly formed oceanic crust except that it also contains an additional layer of oceanic sediment on top. Such sediment accumulates on top of the pillow basalts, and the sedimentary cover gets thicker with time.

· Describe and sketch how magma is generated in a subduction zone.

Pressure and temperature increase as an oceanic plate (oceanic crust and lithospheric mantle) converges with an oceanic or continental plate during a subduction period. The process of metamorphism occurs as existing minerals are converted into new ones because of the pressure and temperature change. Water-bearing minerals, like mica, break down and forces the water out of the crystalline structures. The water liberated from minerals then rises into the overlying asthenosphere. The added water lowers the melting temperature of the mantle above the subducting plate. If the temperature is high enough, melting occurs, and mantle-derived magmas rise into the overriding plate. The magma then may crystallize at depth or eventually erupt at the surface.

· Describe what happens when subduction-derived magma encounters overlying crust.

Mafic or intermediate magma formed from partial melting of the mantle is slowed by thick continental crust. The magma heats the surrounding rocks, causing partial melting, and produces felsic or intermediate magma. Subduction related magma generally never reaches the surface but some erupt forming volcanos. On continental crust, the volcanos are usually part of a mountain belt. If the overlying crust is oceanic, it island arcs. It generally has an intermediate composition (andesite). Island arcs can erupt mafic magma, and continental magma can be felsic. In both cases, magmas added at depth and on the surface thicken the crust.

· Explain and sketch how magma forms during continental collisions.

During a continental collision, one continental plate may slide beneath another continental plate. The descending continental gets hotter and experiences increased pressure. Water may be released by metamorphism of water-bearing minerals, and, if descending continental crust gets hot enough, it undergoes partial melting, producing felsic magmas.




Magmas produced by continental collisions typically do not reach the surface, party because they have to pass through thick continental crust. Also, some magmas produced have a relatively high water content compared to mantle-derived magmas and so pass through the wet solidus (and therefore they solidify) as they rise. So, continental collisions, unlike other convergent boundaries, do not have many volcanoes.

· Sketch or explain a mantle plume and its magmatic expression in both oceanic and continental plates.

Mantle plumes are large pieces of mantle that may begin at the core-mantle boundary and ascend all the way through the lower mantle and into the asthenosphere. The movement of the mantle plume is due to the fact that it rises because it is hotter and less dense than the material around it.




In oceanic plates, the magma generated by a mantle plume causes melting of the overlying lithosphere and additional melting occurs by decompression. Magma from the lithosphere and plume can reach the surface, creating large volcanoes on the seafloor. This is occurring on the Big Island in Hawaii and on the seafloor farther to the southeast. As the plate moves, the hotspot can break through the crust and create a succession of volcanoes along a linear chain of islands.




On continental plates, the high temperatures cause melting in the continental lithosphere. If the melting occurs in the lower part of the lithosphere (in the mantle), it produces mostly mafic magma. If the mantle-derived magma causes melting in the upper part of the lithosphere (in the crust), it can generate felsic magma.




Mafic and felsic magma can mx in the crust and produce intermediate magmas. Crustally derived magmas that reach the surface as felsic magma tend to be more explosive and form large volcanic depressions called calderas, where as mafic magma is less explosive.

· Sketch or describe how a hot spot can form a sequence of volcanic islands on a moving oceanic plate.

As the plate moves, the hotspot can break through the crust and create a succession of volcanoes along a linear chain of islands.

Describe what a magma chamber is and the processes that occur in one.

A magma chamber is an underground body of molten rock containing one or more type of magma.




Crystal settling is a common process that occurs in a magma chamber where crystallization occurs and minerals are extracted from the magma and settle to the bottom of the chamber.




New pulses of magma may move into the chamber and mix with existing magmas or remain distinct.




Crystallized minerals could melt due to hotter pulses of magma heating the minerals.




The magma can heat and partially melt the wall rocks, forming a magma with a different composition. This melting is aided by heat brought into the chamber by new batches of magma.




Differences in magma can create well-mixed magma or form a patchwork of different magma types.

· Sketch the different geometries of large magma chambers and summarize how these are expressed in the landscape.

Not sure

· Sketch the difference between a dike and a sill, and explain why each has the orientation that it does.

A dike is a sheetlike intrusion of magma that cuts across vertically any layers present in the host rocks. Most dikes are steep because the magma pushes apart the rocks in a horizontal direction as it rises veritcally and fills the resulting crack to form a dike In some dikes, magma flows into the dike horizontally, and the dike grows sideways with time. Dikes are also common with large plutons.




Sills are intrusions that are parallel to layers in the host rocks. Most sills are subhorizontal and form by pushing adjacent rocks upward rather than sideways.

· Sketch or discuss the geometry of a laccolith.

A laccolith is an inflated lump of magma that forms from a sill due to the magma encountering gently inclined layers. As the layers over the laccolith tilt outward, they eventually form a dome-shaped feature.

· Sketch and explain two ways that a volcanic neck can form.

A volcanic neck mainly forms through the erosion of the volcano, revealing a cross-section of the volcano consisting of resistant harder rocks that solidified inside the magmatic conduit of the volcano.




Other necks can form beneath the volcano where erosion removes the excess rock and reveals the harder, more resistant rock.

· Describe how columnar joints form.

Columnar joints form when a hot but solid igneous rock contracts as it cools. They're common in basaltic lava flows, felsic ash flows, sills, dikes, and some laccoliths. In a tabular unit, like a flow, sill or dike, columnar joints tend to be perpendicular to the tabular unit - they are vertical in a horizontal lava flow, ash flow, or sill, but horizontal in a vertical dike.