Geology - EARTH Chpt 4

the mantle and crust

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

laccolith

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

Sill

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

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.

Muscovite and pyroxene

Based on the diagram shown in the video, name two minerals that are unlikely to coexist in the same igneous rock. [page 111 text book] 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.

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

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.

FALSE

Temperatures will decrease with increasing depth into the Earth.

FALSE

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

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.

felsic; crystal size

Granite and rhyolite are both ____, but they differ in ____.

by their textures and compositions

How are igneous rocks classified?

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?

The rock was likely formed by a violent volcanic eruption.

What does an igneous rock with a pyroclastic texture tell a geologist?

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.

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?

silicate minerals.

Most igneous rocks are primarily composed of: Hint 1. What are the most common minerals in Earth's crust? NOTES: 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? HINT: Volcanism is only one source of igneous rock. A different process is responsible for emplacing the largest volumes of igneous rock on Earth.

pyroxene and calcium-rich plagioclase feldspar.

Part complete Basaltic igneous rocks contain which of the following minerals: Hint 1. Bowen's Reaction Series will be useful here. Minerals in any given igneous rock share the same temperature regime. NOTES: Pyroxene and calcium-rich plagioclase feldspars reflect a basaltic composition.

the surface of a lava flow Submit

Part complete 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? NOTE: Because escape of gas from lava is possible only at or close to the surface of Earth, lava flows may possess vesicular texture.

Rock fragments that erupted from the volcano

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

Iron

Part complete 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? NOTE: Iron is common in mafic rocks and minerals; in fact, "mafic" refers to the high iron and magnesium content of these materials.

Phaneritic 2

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

Upper Mantel

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

ASH & CINDERS

Pyroclastic debris from a volcanic eruption can include _____. HINT: As a volcano erupts, particles are ejected into the atmosphere. How do these particles differ from those formed by other processes? NOTE: 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.

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. NOTES: 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.

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 __________.

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?

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 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.

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

What is Bowen's reaction series?

Gases dissolved in a magma... Gas Component

What is a volatile?

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

What is an accessory mineral?

Lava cools rapidly.

What is one way a glassy texture forms?

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?

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?

Andesite porphyry

What is the rock name of an intermediate rock with two distinct 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. NOTES: 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? NOTES: 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?

granitic, andesitic, basaltic, ultramafic

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?

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?

Vesicular

Which of the following describes a texture containing bubble-shaped cavities?

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? 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?

rhyolite

Which of the following is an aphanitic igneous rock?

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

Which of the following is true about mafic igneous rocks? Hint 1. Think about the characteristics (composition and melting temperature) of mafic igneous rocks.

Potassium feldspar

Which of the following minerals is not a ferromagnesian mineral?

Continental margins

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

O2

Which of the following substances is not a volatile found in magma? CO2 SO2 ===> O2 H2O

Pegmatitic

Which of the following textures describes an igneous rock with anomalously large crystals?

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?

pyroxene

Which of these minerals would be the first to crystallize in a body of magma?

Quartz and potassium feldspar

Which two minerals define a felsic composition?

It is less dense than the surrounding rock.

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

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

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? NOTES: 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.

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? NOTES: 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

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

Pumice

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

Magma

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