Earth Chpt 4 & 5

Bowens Reaction Series -- Andesitic

A geologist sends you a sample that was collected in the field. You find that it is a gray-colored igneous rock containing amphibole and intermediate plagioclase feldspar. Using Bowen's Reaction Series as a guide, how would you describe its composition? Hint 1. Minerals occurring together in an igneous rock share the same temperature regime. Do these minerals reflect a relatively low or high crystallization temperature? How do the various temperature regimes relate to compositional classifications? NOTES: Amphibole and intermediate plagioclase feldspar occur in the andesitic temperature regime.

quiet and effusive eruptions

A hot spot that occurs in oceanic crust is likely to produce which of the they of eruption. Hint 1. Recall the factors that influence the type or style of volcanic eruption. NOTES: The composition of the lava associated with this type of tectonic setting would be basaltic and the type of eruption would be quiet and effusive due to the high temperature and low silica content.

Kilauea in Hawaii

Around which volcano is a scientist likely find pillow basalts?

Basaltic Igneous Rock ==== Pyroxene and calcium-rich plagioclase feldspar.

Basaltic igneous rocks contain which of the following minerals: HINTS Bowen's Reaction Series will be useful here. Minerals in any given igneous rock share the same temperature regime. Pyroxene and calcium-rich plagioclase feldspars reflect a basaltic composition.

Muscovite and pyroxene

Based on the diagram shown in the video, name two minerals that are unlikely to coexist in the same igneous rock. Hint 1. Recall that the left side of the diagram contains minerals rich in Si, K, and Na, while the right side is dominated by Fe-, Mg-, and Ca-rich minerals.

Viscosity - DEFINE

Define viscosity. Hint 1. An Everyday Comparison Honey has a higher viscosity than fruit punch. If both liquids are poured at room temperature, which liquid will flow more easily? ANSWER: Resistance to flow. Magma has a higher viscosity if it has a lower temperature, is rich in silica, and contains very few dissolved gases.

felsic; crystal size

Fill in the blanks in this sentence using the terms below: Granite and rhyolite are both ____, but they differ in ____. Hint 1. The Two Main Characteristics of Classifying Igneous Rocks Remember that the two main characteristics that are used to classify igneous rocks are by their textures and compositions.

Plagioclase feldspar and quartz; pyroxene and olivine

Fill in the blanks using the choices below: ____ are minerals typically found in igneous rocks that have a high silica content, whereas ____ are minerals that are typically found in igneous rocks with a low silica content. Hint 1. Relate Color to Composition Remember that the color of an igneous rock is dependent on the minerals it contains. A light-colored rock results from light minerals, and a dark-colored rock results from dark minerals.

Igneous Rock == by their textures and compositions

How are igneous rocks classified? Hint 1. Classification Versus Interpretation The classification of igneous rocks is based solely on characteristics of the rocks that can be observed. Be careful not to confuse this with interpretation, which compares observations to possible conclusions about a rock's past.

Pahoehoe flows develop cave-like tunnels that were previously used for carrying lava from an active vent to the flow's leading edge.

How do lava tubes form? Hint 1. The Material That Forms the Tubes Think about which type of flow that forms the lava tubes inside volcanic conduits.

Magma exists strictly below Earth's surface, whereas lava is found on Earth's surface.

How does magma differ from lava?

The liquid igneous material cools, the ions within slow in their movement, and they pack more closely together. When sufficiently cooled, ions become confined to a crystalline arrangement.

How does the crystallization of igneous material occur?

Quartz

If an igneous rock is heated, which mineral melts first according to Bowen's reaction series?

Olivine

If an igneous rock is heated, which mineral will be the very last mineral left to melt according to the Bowen's reaction series?

greater silica; lower melting temperature

Igneous rocks of felsic composition have __________ and __________ relative to mafic igneous rocks. Hint 1. Think about the composition and melting temperature of igneous rocks.

Magma - The amount of Gas in the Magma

In addition to viscosity, which of the following parameters has an influence on whether a volcanic eruption will be effusive or violent? Hint 1. Effusive eruptions release pressure slowly, while violent eruptions release internal pressure much more rapidly. NOTES: In addition to the viscosity, the amount and type of gas in the magma or lava can influence the eruption of a volcano. As pressure on the magma or lava is reduced, the gas can escape violently, causing a large eruption.

the surface of a lava flow

In what type of igneous feature would you find rocks with a vesicular texture? Hint 1. Vesicular textures can look "frothy" or jagged and rough. Rocks with this texture often have many interior cavities. What would form such cavities? Because escape of gas from lava is possible only at or close to the surface of Earth, lava flows may possess vesicular texture.

Basaltic (2)

In which of the following lava types would you expect to see the development of pahoehoe? Hint 1. Recall how viscosity impacts the flow of lavas. What is pahoehoe and how is it produced? NOTES: When very fluid basaltic lavas flow, the thin skin that solidifies on the surface of the flow produces a feature known as pahoehoe.

Two Plate Tectonic -- at a mid-oceanic ridge and at an oceanic-continental convergent boundary

In which two plate tectonic settings would one expect magma to be generated? Hint 1. Three Ways Magma Is Generated Remember the three basic ways in which magma can be generated: by a decrease in pressure, by the lowering of temperature due to the addition of water, and by the heating and melting of crustal rocks.

Magma - Defined

Molten rock found at depth that contains dissolved gases and some crystals

silicate minerals.

Most igneous rocks are primarily composed of: Hint 1. What are the most common minerals in Earth's crust? Silicate minerals are the most common minerals in Earth's crust and therefore make up the bulk of most igneous rocks, though minerals from many other important groups may also be present.

They formed at depth and have been exposed by uplift and erosion.

Most igneous rocks never reach the surface. However, igneous rocks other than those formed in volcanoes are found exposed on many parts of Earth. How do you account for this phenomenon?

Sill

Part complete A ________ is a tabular, concordant pluton that is nearly horizontal and forms when magma exploits a weakness between sedimentary layers.

the mantle and crust

Part complete As a result of partial melting, magma originates in __________. Tectonic forces act in the mantle and crust to cause rocks to melt and form magma.

Quartz, K-feldspar, and plagioclase feldspars, with relatively fewer biotite and amphiboles

Part complete Based on what you learned in this video, what minerals make up rhyolite? Hint 1. Recall that rhyolite is compositional equivalent to granite, but has a different texture.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

Part complete Contrast pahoehoe and aa lava flows. Hint 1. How Lava Characteristics Relate to Each Other Consider the relationships between lava temperatures and the surface features that result. Is a hot lava flow more fluid or less fluid than a cool lava?

the order in which specific minerals cool and form within melted magma, from hottest to coolest

Part complete What is Bowen's reaction series? Hint 1. Order within the Series Bowen's reaction series is in the order of first to last.

Lava cools rapidly.

Part complete What is one way a glassy texture forms? Hint 1. Think about how crystal size relates to cooling rate.

granitic, andesitic, basaltic, ultramafic

Part complete Which of the choices below lists the four basic compositional groups of igneous rocks, ranging from the highest silica content to the lowest silica content? Hint 1. Group Name Synonyms Three of the igneous composition group names have the synonyms intermediate, mafic, and felsic.

Mafic igneous rocks are rich in Fe, Mg, and Ca.

Part complete Which of the following is true about mafic igneous rocks? Think about the characteristics (composition and melting temperature) of mafic igneous rocks.

Continental margins

Part complete Which of the following regions will primarily erupt silica-rich lavas?

Quartz and potassium feldspar

Part complete Which two minerals define a felsic composition?

The dark crystals formed first, undergoing slow cooling, and the remainder cooled quickly.

Part complete Working in the field, you come upon a light-colored, fine-grained igneous rock that contains some very large dark-colored crystals. How do you account for this complex mineralogy? Hint 1. What do the two distinct sizes of crystals imply about the crystallization history of this rock? The compositional differences imply that the dark-colored, coarser-grained minerals formed first, at a slow cooling rate, and the light-colored, finer-grained minerals cooled later and more quickly.

Pumice

Part complete ________ has a large percentage of voids and is lightweight, so therefore has the ability to float in water.

Upper mantle

Peridotite is the main constituent of which part of the Earth?

Pyroclastic Debris -- ash and cinders

Pyroclastic debris from a volcanic eruption can include _____. Along with bombs and lapilli, ash and cinders are common components of pyroclastic debris ejected from volcanoes.

Dikes are discordant igneous intrusions; sills are concordant igneous intrusions; both are tabular.

Select the correct description of dikes and sills. Hint 1. Discordant Versus Concordant A discordant igneous body cuts across bedding surfaces in the country rock, whereas a concordant igneous body is found between bedding surfaces.

FALSE

TRUE / FALSE The more the silica in magma, the lower the viscosity.

False

TRUE OR FALSE Temperatures will decrease with increasing depth into the Earth.

False

TRUE or FALSE Concordant plutons cut across existing structures while discordant plutons are parallel to existing features.

Laccolith

A ________ is a mushroom-shaped pluton that forms by injecting magma between sedimentary strata, forcing the upper layers to arch upward.

muscovite, orthoclase feldspar, plagioclase feldspar, and quartz

The light silicate minerals include __________. Hint 1. An abundance of these light minerals would give rock a "felsic" composition. These are all light-colored minerals and are found in granitic rocks.

Potassium feldspar quartz

The most abundant minerals found in granitic (felsic) igneous rocks include ______. CHOOSE ALL THAT APPLY. Hint 1. Granitic (felsic) igneous rocks are composed almost entirely of light (nonferromagnesium) silicates.

violent and explosive eruptions

The subduction of oceanic crust under continental crust predominantly produces which of the following types of volcanic eruption? Hint 1. What are the parameters that influence the type or style of volcanic eruption? What type of magma would result from mixing of melted oceanic and continental crust? NOTE: Lava of medium-to-high silica content at low temperature would be produced at this tectonic setting and would be quite likely to cause a violent and explosive eruption at some point.

the appearance of a rock based on the size(s), shape(s), and arrangement on the mineral grains it contains.

The texture of an igneous rock describes Hint 1. Two Meanings for One Word Although everyday usage of the word "texture" generally refers to how something feels, the definition of the texture of an igneous rock is much different.

olivine; mantle

Ultramafic rocks contain __________ and are commonly found in __________. Hint 1. Think about the composition of ultramafic igneous rocks and in what setting they are found.

Rock fragments that erupted from the volcano

Welded tuff consists of ash surrounding large, jagged, irregularly-shaped pieces of material. What is this material and where does it come from?

ROCK TEXTURES -- aphanitic, phaneritic, porphyritic, vesicular, glassy, and pyroclastic

What are the six major igneous rock textures? Hint 1. Textures Are Results of Cooling The six major igneous textures are created as results of different rates of cooling, the release of gases during cooling, and sudden volcanic eruptions.

the liquid portion (mobile ions of the eight most common minerals found in the Earth's crust) called melt, the solid portion which consists of silicate mineral crystals, and the gaseous portion called volatiles

What are the three components of magma?

Volatiles

What creates the small holes found in a vesicular texture?

They both exhibit a vesicular texture.

What do pumice and scoria have in common? Hint 1. Recall the classification scheme and what two major factors are used to categorize igneous rocks.

The rock began cooling under the Earth's surface, but then was moved to above the Earth's surface where it finished cooling.

What does a porphyritic texture indicate about the cooling history of an igneous rock? Hint 1. Compare the Groundmass to the Phenocrysts In a porphyritic rock, the phenocrysts solidify before the groundmass solidifies.

The rock was likely formed by a violent volcanic eruption.

What does an igneous rock with a pyroclastic texture tell a geologist? Hint 1. Recall from the video that pyro means fire, and clastic means broken.

Iron

What element is principally responsible for making olivine, pyroxene, amphibole, and biotite dark? Hint 1. These minerals occur in mafic igneous rocks. What does mafic mean? Iron is common in mafic rocks and minerals; in fact, "mafic" refers to the high iron and magnesium content of these materials.

the rate at which the rock cools, the amount of silica that is present in the magma from which it forms, and the amount of dissolved gases present in said magma

What factors influences the texture of an igneous rock? Hint 1. Why Rock Textures Are Useful The texture of an igneous rock in part illustrates the history of that rock.

Gases dissolved in a magma

What is a volatile?

Accessory Mineral --- A mineral that makes up a relatively small portion of the total rock composition

What is an accessory mineral? Hint 1. Recall the mineral composition vs. texture classification chart from the video.

Scoria is a vesicular ejecta that is produced from mafic magma. Although pumice is also vesicular, it differs from scoria in that pumice is felsic.

What is scoria, and how does it differ from pumice? Hint 1. How Some Pyroclastic Materials Are Identified Although several pyroclastic materials are identified by their sizes, scoria and pumice are identified by their texture and composition.

Extrusive igneous rocks cool and solidify on the Earth's surface, whereas intrusive igneous rocks cool and solidify beneath the Earth's surface.

What is the difference between extrusive igneous rocks and intrusive igneous rocks?

Size, shape, and arrangement of mineral grains in the sample

What is the geologic definition of texture?

Vesicles

What is the name of the small holes created by gas bubbles on the surface of scoria?

Granitic - Magmas - A basaltic pond of magma becomes trapped below continental crust and partially melts this silica-rich crust into a granitic magma.

What is the process that is thought to generate most granitic magmas? Hint 1. Differences Between Magma Compositions Remember that granitic magma has a high silica content and a low iron content, basaltic magma has a high iron content and a low silica content, and andesitic magma is fairly balanced in its content of iron and silica.

Granitic Magmas -A basaltic pond of magma becomes trapped below continental crust and partially melts this silica-rich crust into a granitic magma.

What is the process that is thought to generate most granitic magmas? Hint 1. Differences Between Magma Compositions Remember that granitic magma has a high silica content and a low iron content, basaltic magma has a high iron content and a low silica content, and andesitic magma is fairly balanced in its content of iron and silica.

Intermediate Rock --- Andesite porphyry

What is the rock name of an intermediate rock with two distinct grain sizes? Hint 1. Think about what is used to classify an igneous rock as intermediate in composition, and what texture is associated with two different grain sizes.

Batholith

What is the term used to describe a very large, widespread, and deep intrusive body of igneous rock? Hint 1. This type of intrusion has lead to the formation of entire mountain ranges. A deep, large-sized igneous intrusion fits the description of a batholith.

Geothermal gradient

What is the term used to describe increased temperature with depth in the Earth?

Water lowers the melting temperature of the rock, allowing it to melt.

What role does water play in generating magma?

Liquid portion, solid portion, gaseous portion

What three components make up most magmas?

Fast because it was erupted from a volcano

What was the rate of cooling and the environment of formation for an extrusive igneous rock and why?

Extrusive

When lava erupts at Earth's surface, what type of rock is produced? Magma that reaches the surface cools quickly, has fine-grained texture, and produces extrusive rocks.

It is less dense.

When magma forms, it rises up through the crust. Why does magma rise?

Phaneritic

Which igneous texture has visible crystals that are a few millimeters across?

Silicates

Which mineral group makes up most igneous rocks?

Large crystals that form in a fluid-rich environment late in crystallization

Which of the following best describes a pegmatitic texture?

Granite is phaneritic and rhyolite is aphanitic.

Which of the following best describes the difference between granite and rhyolite? Hint 1. Recall the classification scheme and what two major factors are used to categorize igneous rocks.

Vesicular

Which of the following describes a texture containing bubble-shaped cavities? Hint 1. The voids in this texture are the result of gas bubbles.

Scoria

Which of the following eruptive materials can be described as basaltic, vesicular ejecta found around cinder cone volcanoes?

obsidian

Which of the following igneous rocks contains no mineral crystals? Hint 1. What is the relationship between igneous rock texture and mineral composition? Which texture could develop without well-formed minerals? limestone basalt gneiss granite obsidian NOTES: Obsidian cools so quickly that the individual ions in the lava do not have time to organize into a crystalline structure.

Phaneritic texture

Which of the following is a characteristic of an igneous rock found in a batholith? Hint 1. Batholiths are large, intrusive bodies that cool slowly and are typically found within continental crust.

Aa flows have sharp, jagged edges.

Which of the following is a feature of an aa flow? Hint 1. Aa flows move very slowly, advancing as a mass of lava blocks.

rhyolite

Which of the following is an aphanitic igneous rock? Hint 1. Igneous rocks are classified based on texture and mineral composition. The texture of an igneous rock depends on where and how it formed.

Basaltic

Which of the following lavas make up 90 percent of the total volume of lava on Earth?

Potassium feldspar

Which of the following minerals is not a ferromagnesian mineral?

O2

Which of the following substances is not a volatile found in magma?

Pegmatitic

Which of the following textures describes an igneous rock with anomalously large crystals? Hint 1. The larger grains of this texture result from the cooling of a wet magma.

Phaneritic 2

Which of the following textures indicates that a rock is of intrusive origin?

Volcanic in Origin -- Aphanitic

Which of the following textures indicates that a rock is volcanic in origin?

Porphyritic

Which of the following textures indicates two stages of cooling and crystallization? Hint 1. Think about the effect that two episodes of cooling would have on grain size.

Basaltic

Which of the following types of lava will most likely lead to a volcanic eruption of an effusive nature? Hint 1. How does silica content influence volcanic eruptions? Consider what affects the ability of lava to flow. NOTE: The low silica content of basaltic lavas produces low viscosity and tends to make volcanic eruptions quiescent and effusive.

Rhyolitic or Felsic

Which of the following types of magma has the highest viscosity? NOTES: In general, the higher the silica content of a magma or lava, the greater its viscosity, or resistance to flow.

Viscosity --- an increase in temperature

Which of the following would decrease the viscosity of magma? Hint 1. Viscosity is a measure of a material's resistance to flow.

Pyroxene

Which of these minerals would be the first to crystallize in a body of magma? Hint 1. Recall Bowen's reaction series; ferromagnesium minerals are the first to crystallize in a magma chamber.

It is less dense than the surrounding rock.

Why does magma have a tendency to rise after its formation? As rock melts, the density decreases. This process causes the magma to rise.

fine-grained

Working in the field, you see a thin, dark-colored igneous sill across the valley. Without seeing the sill up close, what texture would you expect it to possess? Hint 1. What possible implications does the size of an intrusion have on texture? Because rock is a relatively poor conductor of heat, smaller intrusions would tend to cool more quickly than large intrusions.

Gabbro

You have found a mafic rock with a phaneritic texture. What is a potential rock name? Hint 1. Recall the minerals that make up mafic rocks and how "phaneritic" is defined in terms of grain size.

Bowen's reaction series

________ describes how an entire suite of silicate minerals can form from a single basaltic magma as it cools and crystallizes.

Pumice 2

________ is a felsic igneous rock with a meringuelike vesicular texture, consisting of very small holes, created by small shards of volcanic glass.

Viscosity

________ is a material's resistance to flowing.

Magma

________ is molten rock that is below the Earth's surface and retains most of its volcanic gases.

Pyroclastic material

________ is pulverized rock, lava fragments, and ash erupted from a volcano.