Igneous Rocks Flashcards
Granite
is a course-crystalline felsic intrusive rock. The presence of quartz is a good indicator of granite. Granite commonly has large amounts of salmon pink potassium feldspar and white plagioclase crystals that have visible cleavage planes. Granite is a good approximation for the continental crust, both in density and composition.
Rhyolite
Rhyolite is a fine-crystalline felsic extrusive rock. Rhyolite is commonly pink and will often have glassy quartz phenocrysts. Because felsic lavas are less mobile, it is less common than granite. Examples of rhyolite include several lava flows in Yellowstone National Park and the altered rhyolite that makes up the Grand Canyon of the
Diorite
Diorite is a coarse-crystalline intermediate intrusive igneous rock. Diorite is identifiable by it’s Dalmatian-like appearance of black hornblende and biotite and white plagioclase feldspar. It is found in its namesake, the Andes Mountains as well as the Henry and Abajo mountains of Utah
Andesite
Andesite is a fine crystalline intermediate extrusive rock. It is commonly grey and porphyritic. It can be found in the Andes Mountains and in some island arcs (see Chapter 2). It is the fine grained compositional equivalent of diorite.
Gabbro
Gabbro is a coarse-grained mafic intrusive igneous rock , made with mainly mafic minerals like pyroxene and only minor plagioclase. Because mafic lava is more mobile, it is less common than basalt. Gabbro is a major component of the lower oceanic crust.
Basalt
Basalt is a fine-grained mafic extrusive igneous rock. It is commonly vesicular and aphanitic. When porphyritic, it often has either olivine or plagioclase phenocrysts. Basalt is the main rock which is formed at mid-ocean ridges, and is therefore the most common rock on the Earth’s surface, making up the entirety of the ocean floor (except where covered by sediment).
Igneous Rock
Rocks that are formed from liquid rock. i.e. Volcanic processes
Molten material is called _______ when it is in the ground and _____ when it is on the surface.
Molten material is called MAGMA when it is in the ground and LAVA when it is on the surface.
How are igneous rocks classified?
Based on texture and composition.
Texture- Physical characteristics of the minerals
Composition- Refers to the rock’s specific mineralogy and chemical composition
If the magma cools slowly, deep within the crust, the resulting rock is called _______
Intrusive or Plutonic
Phaneritic
Large, easy-to-see crystals within an igneous rock. This is common in intrusive rocks.
Slow cooling processes allows crystals to grow large. Giving a coarse-grained texture
Intrusive
AKA Plutonic
Igneous rock cooling and then forming inside the Earth
Volcanic Glass
Extrusive rock that cools so rapidly it does not develop crystals at all.
Obsidian
Dark colored volcanic glass, with extremely small microscopic crystals or no crystals. Typically form from felsic volcanism
Extrusive
Igneous rock cooling and thus forming outside of the earth.
Phenocrysts
A large crystal within an igneous rock. These can be seen within phaneritic and porphyritic rocks.
Groundmass
Fine-grained, not discernible part of a rock
Pegmatitic
A rock (Or texture within a rock) with unusually-large crystals. Minerals with rare trace element concentrations and/or unusual minerals. Typically forming in veins as the last dredges of magma crystalize.
All magmas contain gases dissolved in solution called _____
All magmas contain gases dissolved in solution called VOLATILES
The gas bubbles in magma become trapped in solidifying lava to create _______
All magmas contain gases dissolved in solution called VESICULAR TEXTURE
The volcanic rock with common vesicles is called __________
The volcanic rock with common vesicles is called SCORIA
An extreme version of scoria occurs when volatile-rich lava becomes meringue-like froth of glass called ________
An extreme version of scoria occurs when volatile-rich lava becomes meringue-like froth of glass called PUMICE
Pumice
Low density, highly vesiculated. Usually white to tan volcanic rock. Typically arises from felsic volcanism.
-Some pumice is so full of vesicles that the density of the rock drops low enough that it will float.
Conchoidal
Fractures that have a circular appearance
Tephra
General term for solid, but fragmented, material erupted from a volcano. Has 3 subcomponents Ash (<2 mm), Lapilli (2-64mm), and blocks and bombs (>64mm)
Ash
Volcanic tephra that is less than 2mm in diameter
Lapilli
Volcanic tephra that has a diameter between 2mm and 64mm. Many ciders are within this category.
Bombs (Tephra)
AKA Blocks
Large volcanic tephra greater than 65mm in diameter
Tuff
Rocks made from pyroclastic tephra; either ash, lapilli, and/or bombs. Tephra types can be used as an adjective.
If deposited when hot where material can fuse together while hot, the rock is called welded tuff.
Composition
The mineral make up of a rock. What minerals are found within a rock
Igneous Rock 4 groups by composition
Felsic Intermediate Mafic Ultramafic -These groups refer to differing amounts of silica, iron, and magnesium
Felsic
Predominance of light-colored (felsic) minerals. FELdspar and SILica in the form of quarts.
- Minor amounts of dark-colored minerals
- Rich in silica (65-75% range)
- Poor in magnesium and iron
- Primary felsic rocks are rhyolite (extrusive) and granite (intrusive)
Rocks with 65-75% silica
Felsic
Intermediate
- Composition between felsic and mafic
- Usually contains roughly-equal amounts of light and dark minerals
- Intermediate silica in the range of 55-60%
Rocks with 55-60% Silica
Intermediate
Mafic
- Abundance of ferromagnesian minerals (with magnesium and iron symbols Mg and Fe) plus plagioclase feldspar. Commonly made of dark minerals.
- Low in silica 45-50% range
Rocks with silica range between 45-55%
Mafic
Ultramafic
- Refers to the extremely mafic rocks composed mostly of olivine and some pyroxene
- Poor in silica 40% or less
Rocks with less than 40% silica
Ultramafic
Plutonic
Igneous rock cooling, and thus forming, inside the Earth
General name of a felsic rock that is extrusive. Generally has a white, tan, or pink groundmass color
Rhyolite
General name of a felsic rock that is intrusive
Granite
Intermediate rock that is extrusive. Generally has a grey groundmass
Andesite
Intermediate rock that is intrusive
Diorite
Mafic rock that is extrusive. Generally has a black groundmass color
Basalt
Mafic rock that is intrusive
Gabbro
Intrusive ultramafic rock. Which is the main component of the mantle. The minerals are typically olivine with some pyroxene.
Peridotite
Komatiite
Fine-grained extrusive ultramafic
-Rare because volcanic material that comes direct from the mantle is not common. Although some examples can be found in ancient Archean rocks
Archean
Eon defined as the time between 4 billion years ago and 2.5 billion years ago. Most of the oldest rocks on Earth, including portions of the continents, formed at this time
Phaneritic (What rocks)
Coarse grained.
Granite, Diorite, Gabbro, Peridotite
Aphanitic (Rock types)
Fine-grained
Rhyolite, Andesite, Basalt
Porphyritic
Large crystals in a fine matrix
Porphyritic Rhyolite, Porphyritic Andesite, Porphyritic Basalt
Vesicular
Bubbly or frothy
Pumice, Scoria
Glassy
Obsidian
Pyroclastic
Fragmental
Rhyolitic Tuff or Volcanic Breccia, Andesitic Tuff or Volcanic Breccia, Basaltic Tuff or Volcanic Breccia
Which type of rocks are more common in geological record? And why?
Intrusive because they are formed underground with larger, stronger crystals and are more likely to last. Extrusive crystals are also less durable.
Dike
(Also Dyke) A narrow igneous intrusion that cuts through existing rock. Not along bedding planes.
- Important for dating rock sequences and interpreting the geological history of an area.
- Discordant intrusions
Sills
A type of dike that is parallel to bedding planes within the bedrock
-Concordant intrusion
Country Rock
Term for the lithified rocks that make up the geological record in an area. This term can sometimes refer to only the deeper, crystalline (Non-Layered) rocks.
Strata
Discernible layers of rock, typically from sedimentary rock
Magma Chamber
A reservoir of magma below a volcano
Diapir
The path of rising magma
- Domed rock formation in which a core of rock has moved upward to pierce overlying strata
- , geological structure consisting of mobile material that was forced into more brittle surrounding rocks, usually by the upward flow of material from a parent stratum.
Stoping
The process of surrounding bedrock being broken off and passed through a magma
When a diapir cools it forms a mass of intrusive rock called a ____________
When a diapir cools it forms a mass of intrusive rock called a PLUTON
Pluton
A coherent body of intrusive rock (which is formed underground) which is now at (or near) the surface
-Can be irregular shapes, but can often be somewhat round
Where do igneous rocks with a coarse-grained (phaneritic) texture form?
Phaneritic (coarse grain) igneous rocks cool slowly deep underground.
How does the silica content affect the behavior of magma?
Increasing silica in the transition from ultramafic to felsic composition makes the magma more viscous.
Which rock composition has the most amount of iron and magnesium?
ultramafic
What causes igneous rocks to develop a fine-grained (aphanitic) texture?
Fast cooling Fine grain (aphanitic) igneous rocks cool rapidly on the surface.
A basaltic intrusion that cuts across layers of sedimentary rocks is called a _______.
A basaltic intrusion that cuts across layers of sedimentary rocks is called a DIKE.
___________ describes the temperature at which minerals crystallize when cooled, or melt when heated.
BOWEN’S REACTION SERIES describes the temperature at which minerals crystallize when cooled, or melt when heated.
The most important aspect of Bowen’s Reaction Series is to notice the relationships between ____ and ____
The most important aspect of Bowen’s Reaction Series is to notice the relationships between MINERALS and TEMPERATURE
Examine Bowen’s Reaction Series diagram. If a rock contains amphibole, potassium feldspar (orthoclase), and quartz, if the rock is heated, which mineral would melt first?
The Bowen diagram shows that quartz both crystallizes from cooling magma and melts from heated rock at the lowest temperature.
Examine Bowen’s Reaction Series diagram. Which mineral has the highest temperature of crystallization?
The Bowen diagram shows that olivine both crystallizes from cooling magma and melts from heated rock at the highest temperature.
Examine Bowen’s Reaction Series diagram. As a felsic magma cools, which mineral would be the last to crystallize?
The Bowen diagram shows that quartz both crystallizes from cooling magma and melts from heated rock at the lowest temperature.
The rate at which temperature increases with depth is called the _____________
The rate at which temperature increases with depth is called the GEOTHERMAL GRADIENT.
Magma is created at mid-ocean ridges via _______
Magma is created at mid-ocean ridges via DECOMPRESSION MELTING.
What is the process by which decompression melting produces magma at divergent plate boundaries?
reduction of pressure at constant temperature
-Decompression melting takes place when pressure is reduced on rising asthenospheric material which remains at the same temperature at divergent boundaries.
If volatiles such as water vapor and carbon dioxide are added to a rock, what will happen to the melting temperature?
The melting temperature of a rock will decrease
Volatiles added to hot rock act as a flux reducing the melting point and causing the rock to melt at that same temperature.
What does a P-T diagram of the mantle show?
It shows how pressure and temperature increase with depth.
A P-T diagram plots temperature against pressure, both of which increase with depth.
The unmelted country rocks within an igneous rock mass are called _________
The unmelted country rocks within an igneous rock mass are called XENOLITHS
Why felsic magmas are much more common within continents?
When mafic magma rises through thick continental crust, it does so slowly, more slowly than when magma rises through oceanic plates. This gives the magma lots of time to react with the surrounding country rock. The mafic magma tends to assimilate felsic rock, becoming more silica-rich as it migrates through the lithosphere and changing into intermediate or felsic magma by the time it reaches the surface
The crystallization process in which a rising magma diapir incorporates some of the surrounding country rock so that the chemistry of the magma changes is called _____.
The crystallization process in which a rising magma diapir incorporates some of the surrounding country rock so that the chemistry of the magma changes is called ASSIMILATION
Assimilation is the process by which rising magma incorporates country rock and composition changes.
Unmelted pieces of country rock incorporated within the igneous rock mass are called _______.
Unmelted pieces of country rock incorporated within the igneous rock mass are called XENOLITHS
Xenoliths are bits of country rock that are incorporated within a mass of igneous rock.
Crystal settling would be another name for ______.
Crystal settling would be another name for FRACTIONAL CRYSTALLIZATION
Fractional crystallization by crystals settling out under gravity is one way that magmas can change in composition while cooling.
Partially melting an ultramafic rock produces a magma with a(n) _________ composition.
Partially melting an ultramafic rock produces a magma with a(n) MAFIC composition.
Partial melting produces a magma a step lower on the Bowen diagram than the rock from which it melts.
As magma travels up from the asthenosphere through the lithosphere into continental crust, how will fractional crystallization change the chemistry of an ultramafic magma?
The ultramafic magma will become more mafic.
Referring to the Bowen diagram and fractional crystallization, the ultramafic magma will become more mafic.
Place the following minerals in order of crystallization from highest temperature (1) to lowest temperature (7).
\_\_\_\_ Muscovite \_\_\_\_ K-spar (orthoclase feldspar) \_\_\_\_ Olivine \_\_\_\_ biotite \_\_\_\_ amphibole \_\_\_ Pyroxene \_\_\_\_ Quartz
\_\_1\_\_ Olivine \_\_2\_\_ Pyroxene \_\_3\_\_ amphibole \_\_4\_\_ biotite \_\_5\_\_ K-spar (orthoclase feldspar) \_\_6\_\_ Muscovite \_\_7\_\_ Quartz
The first plagioclase to crystallize from a mafic melt will be richer in what element?
Calcium (Ca)
If a mantle rock that is peridotite (ultramafic) completely melts, what kind of magma will be produced?
Ultramafic
If a mantle rock that is peridotite (ultramafic) partially melts, what kind of magma will be produced?
Mafic
Partial melting of rocks produces melts that are….
More felsic than the original rock
if a mafic magma is rising through the crust and is able to assimilate more felsic materials, the magma will become more…
Felsic
unmelted chunks of country rock found within igneous intrusions are called…
Xenoliths
If you have a bucket of salt water and remove some of the water by evaporation, what will happen to the water in the bucket?
it will become saltier
Fractional crystallization produces magmas that are….
More Felsic than the original magmas
What are the three ways magma is generated?
Flux melting
Decompression melting
Heat induced melting
How does magma form at a hotspot?
At a hotspot the magma forms due to above normal amounts of heat.
At a subduction zone, how does magma form?
At a subduction zone magma forms by addition of water to the mantle
Flux melting
Where does magma come from?
Magma is formed in certain tectonic environments due to the conditions in those areas that promote melting.
Primary felsic rocks are….
Rhyolite (extrusive) and granite (intrusive)
What is the main component of the mantle?
Peridotite
When many plutons merge together in an extensive single feature, it is called a _____________
When many plutons merge together in an extensive single feature, it is called a BATHOLITH
Batholiths
Used to describe a large mass or chain of many plutons and intrusive rocks.
- Found in cores of many mountain ranges (Including the granite formations of Yosemite National Park)
- Typically more than 100 KM^2 and associated with subduction zones
- Mostly felsic in composition
- Discordant intrusion
Stock
A type of pluton with less surface exposure than a batholith. May represent a narrower neck of material emerging from the top of a batholith
discordant intrusion
Batholiths and stocks are _________ that cut across and through country rock
Batholiths and stocks are DISCORDANT INTRUSIONS that cut across and through country rock
Laccoliths
Large Igneous intrusion that is wedged between sedimentary layers, bulging upwards
Lopolith
Large igneous intrusions that are wedged between sedimentary layers bulging down
Bowen’s Reaction Series
A series of mineral formation temperatures that can explain the minerals that form specific igneous rocks
-Describes the temperature at which minerals crystallize when cooled or melt when heated.
According to Bowen’s Reaction, the low end where all minerals crystallize into solid rock is approximately ______ (at standard sea level, 1 bar)
Low end where all minerals crystallize into solid rock is approximately 700’ C (1292’ F) at standard sea level (1 bar(
According to Bowen’s Reaction, the upper range where all minerals exist in a molten state is approximately at what temperture?
All minerals exist in a molten state at approximately 1250’ C (2282’ F) at sea level (1 bar)
Norman L. Bowen
(1887-1956)
Notice relationship between minerals and temperature
Book - The Evolution of the Igneous Rocks (1928)
Magma and lava contain three components….
Melts, solids, and volatiles
Melt (Component of Magma/Lava)
made of ions from minerals that have been liquified.
Solids ((Component of Magma/Lava)
Made of crystallized minerals floating in the liquid melt.
-This minerals may be minerals that have already cooled
Volatiles (Component of Magma/Lava)
Gaseous components such as water vapor, carbon dioxide, sulfur, and chlorine. Dissolved in the magma
The three components of magma/lava affect the __________ of the magma/lava
The three components of magma/lava affect the BEHAVIOR of the magma/lava
Geothermal Gradient
The average change in temperature that is experienced as material moves into the Earth. Near the surface, this rate is about 25’C/KM (For every km of depth, the temp increases about 25’C)
-The geothermal gradient changes with depth (which has a direct relationship to pressure) through the crust into the upper mantle
3 Principle ways rock behavior crosses to the right of solidus line to create molten magma
- Decompression
- Flux Melting
- Heat Induced Melting
Decompression Melting (definition)
Caused by lowering pressure
-Melting that occurs as material is moved upward and pressure is released. Typically found at divergent plate boundaries or hot spots
Flux Melting (Definition)
The process in which volatiles enter the mantle wedge and the volatiles lower the melting temperature causing volcanism
Heat Induced Melting (Definition)
Cause by increasing temperature
Partial Melting
The process of some material being derived from a heterogenous mixture when melting. Because all rocks are made of many different components they have many different melting points. As they are heated, certain easy-to-melt components will be melted first. 0
Magma is create at mid-ocean ridges via___________
Magma is create at mid-ocean ridges via DECOMPRESSION MELTING
How does decompression melting work?
-Strong convection currents cause solid asthenosphere to slowly flow beneath the lithosphere.
The lithosphere is a poor heat conductor so temps remain about the same through underlying mantle
Where convection currents cause mantle to rise the pressure decreases which causes the melting point to drop.
In this situation the rock at geothermal gradient is rising toward the surface, thus hotter rock is now more shallow and a lower pressure. (The rock is still at the temp of geothermal at its old location) It shifts pasts the melting point and partial melting starts. As this magma rises it cool and crystallizes to form new crust.
How does flux melting work?
Occurs in island arcs and subduction zones when volatile gases are added to mantle material.
-Produces many volcanoes in the Pacific ring of fire
-Subducting slab contains oceanic lithosphere and hydrated minerals.
As slab descends into hot mantle the increased temp causes hydrated minerals to emit water vapor and other volatile gases. Which are expelled from the slab. Volatiles dissolve into overlying asthenosphere mantel and decreases its melting point.
-Applied pressure and temp have not changed, the mantle melting point has been lowered by volatiles. Melting begins
(Like salt on a icy roadway. Salt lowers the freezing temp of solid ice so it turns to water)
How does Heat-Induced Melting work?
Least common process for generating magma
- Transforms solid mantle into liquid magma by simply applying heat
- Occurs at mantle plumes and hotspots.
Mantle Plume
Rising material and heat derived from the mantle.
Crystallization
The process of liquid rock freezing into solid rock. Because liquid rock is made of many components, the process is complex as different components freeze at different temps.
Magmatic Differentiation
The process of change a magma’s composition, usually through assimilation or fractionation
Partial melting creates magma with composition that is _________
Partial melting creates magma with composition that is DIFFERENT THAN THE ORIGINAL MANTLE MATERIAL.
Most important example of magmatic differentiation when peridotite (ultramafic) starts melting.. Explain
When ultramafic rock starts melting the silicates melts first due to lower melting point. If it continues the magma becomes increasingly silica-rich. Turning ultramafic mantle into mafic. Mafic to intermediate. As it rises to the surface it is more buoyant than the mantle.
Shields
the old granite cores of the continents
Magmatic differentiation happens via two main components….
Assimilation
Fractionation
Liquid magma is less dense than the surrounding solid rock. So, what does it do?
The less dense liquid magma rises through the mantle and the crust
As magma begins to cool and crystallize (magma differentiation) changes of chemistry of rock towards a more ______ composition
As magma begins to cool and crystallize (magma differentiation) changes of chemistry of rock towards a more FELSIC composition
Assimilation
Bedrock around the magma chamber being incorporated into the magma. Sometimes changing the composition of the magma.
-Often more felsic added to magma
Xenoliths
A piece of foreign rock that has been incorporated into a magma body.
Magma Mixing
Two different magmas come into contact and mix.
Magmatic Rejuvenation
Happens when a cooled and crystallized body of rock is remelted and pieces of the original rock may remain xenoliths
Fractionation
AKA Fractional Crystallization
The process of a magma changing from mafic to felsic via cooling. As the magma cools, higher temp mafic minerals crystallize and more felsic magma is left.
-As the temp drops with a magma diapir rising through the crust, some minerals will crystallize and settle to the bottom of the magma chamber. Leaving the remaining melt depleted of those ions
-This means the remaining melt becomes more silica-rich and more felsic
Highly evolved felsic magmas are largely confined to ________ regions where there is longer time to the surface which allows more fractionation to occur.
Highly evolved felsic magmas are largely confined to CONTINENTALregions where there is longer time to the surface which allows more fractionation to occur.
stratovolcano
Volcano with steep sides, made of a composite of many types of eruption styles, from low viscosity mafic magma, higher viscosity felsic lava, but most commonly, intermediate andesite lava.
-A stratovolcano, also called a composite cone volcano, has steep flanks, a symmetrical cone shape, distinct crater, and rises prominently above the surrounding landscape.
Caldera
Hole left behind after a large volume of material erupts out of a volcano. This depression is often tuned into a valley or lake after the eruption is over.
viscosity
The resistance of a fluid to flow, where a high value means a fluid which does not like to flow (like toothpaste), and a low value means a fluid which flows easily (like water).
shield volcanoes
They are characterized by broad low-angle flanks, small vents at the top, and mafic magma chambers. The name comes from the side view, which resembles a medieval warrior’s shield. They are typically associated with hotspots, mid-ocean ridges, or continental rifts with rising upper mantle material. The low-angle flanks are built up slowly from numerous low-viscosity basaltic lava flows that spread out over long distances. The basaltic lava erupts effusively, meaning the eruptions are small, localized, and predictable.
Are shield volcanoes a hazard to human life?
They are not much of a hazard to human life
Aa
- A more viscous and has a crumbly blocky appearance.
- A blocky, stubby, rubble-like lava
pahoehoe
- Rope-like, flowing basaltic lava
- might come from low-viscosity lava that flows easily into ropey strands.
Fissures
cracks that commonly originate from shield-style eruptions. Lava emerging from fissures is typically mafic and very fluid
What type of lava do Stratovolcanoes normally have?
Felsic to intermediate. But can some times produce mafic
What type of lava do caldera volcanoes have?
Caldera volcanoes are typically formed by eruptions of high-viscosity felsic lava having high volatiles content.
Composite volcanoes
Volcano with steep sides, made of a composite of many types of eruption styles, from low viscosity mafic magma, higher viscosity felsic lava, but most commonly, intermediate andesite lava.
AKA Straovolcanoes
Cinder cones
Cinder cones are small volcanoes with steep sides, and made of pyroclastic fragments that have been ejected from a pronounced central vent. The small fragments are called cinders and the largest are volcanic bombs. The eruptions are usually short-lived events, typically consisting of mafic lavas with a high content of volatiles.
Flood basalts
- A rare volcanic eruption type, unobserved in modern times, is the flood basalt.
- are some of the largest and lowest viscosity types of eruptions known. They are not known from any eruption in human history, so the exact mechanisms of eruption are still mysterious.
Carbonatites
- An igneous composition or rock containing more than 50% carbonate minerals (e.g. calcite). Magma of this composition is very low temperature (500-600 C) relative to other magmas.
- Arguably the most unusual volcanic activity are carbonatite eruptions.
- Only one actively erupting carbonatite volcano exists on Earth today, Ol Doinyo Lengai, in the East African Rift Zone of Tanzania.
pyroclastic flow
A collapsed part of the eruption column that travels down at very hot temperatures and very fast speeds. They are the most dangerous immediate volcanic hazard.
-These flows are a mix of lava blocks, pumice, ash, and hot gases between 200°C-700°C (400°F-1,300°F). The turbulent cloud of ash and gas races down the steep flanks at high speeds up to 193 kph (120 mph) into the valleys around composite volcanoes.
Lahar
-is an Indonesian word and is used to describe a volcanic mudflow that forms from rapidly melting snow or glaciers.
A type of volcanic mudslide, in which rain or snowmelt accumulates volcanic ash of the slopes of steep volcanoes or other mountains and then wash downhill, causing damaging flooding.
Explosive silica-rich volcanoes will be located mostly at ______.
Explosive silica-rich volcanoes will be located mostly at convergent plate boundaries with subduction zones
-Explosive volcanism is commonly associated with the Ring of Fire which is a ring of subduction zones.
Deep-sea hydrothermal vents (black smokers) are most commonly located at what plate boundary?
divergent boundaries of the mid-ocean ridge
Black smokers are associated with the mid-ocean ridge.
The largest type of volcano is called a _______ volcano and is characterized by broad, low-angle flanks, a small vent or groups of vents at the top, and basaltic magma.
shield volcano
-Shield volcanoes are the largest type with these characteristics.
A __________ is a volcanic hazard arising from a collapsing eruption column that runs downhill at high speeds (>100 mph). These are associated with explosive eruptions and a mix of lava lapilli, pumice, ash, and hot gases.
A PYROCLASTIC FLOW is a volcanic hazard arising from a collapsing eruption column that runs downhill at high speeds (>100 mph). These are associated with explosive eruptions and a mix of lava lapilli, pumice, ash, and hot gases.
-A pyroclastic flow is hot gases containing ash and small rock particles called lapilli that rush at tremendous speeds down flanks of volcanoes
A _______ volcano has steep flanks, symmetrical cone shapes, distinct crater at the top, and a silica-rich magma that results in an explosive eruption style
A STRAVOLCANO (OR COMPOSITE VOLCANO) volcano has steep flanks, symmetrical cone shapes, distinct crater at the top, and a silica-rich magma that results in an explosive eruption style -Stratovolcanoes are symmetrical and picturesque volcanic mountains resulting from explosive silica-rich magmas
What kind of volcanoes make up the Hawaiian Island Chain?
shield volcanoes
-They are shield volcanoes that build up to tall mountains on the sea floor extending above sea level by repeating lava eruptions over many millennia.
Most volcanoes on the sea floor erupt ________.
Quietly with basaltic magma
-Magma that rises at interplate divergent boundaries like at midocean ridges melts by decompression melting and erupts quietly as basaltic lava.
Why does partial melting occur?
-Because some minerals have lower melting points than others
Partial melting occurs when minerals with a lower melting point melt out of a solid rock that also contains minerals with a higher melting point that remain solid
What does the Bowen Reaction Series show about the mineral composition of igneous rocks?
The minerals in igneous rocks form in separate groups that depend on the temperature at which they crystallize.
-The beauty of Bowen’s work is showing that igneous minerals always form in specific mineral groupings depending on their temperature of crystallization.
Bowen’s Reaction Series has been expressed as a Y-shaped diagram containing how many minerals?
The Bowen diagram is a simple Y-shape with 8 minerals and a temperature scale.
A rock with aphanitic texture and dark color is best identified as a
basalt
-Since mineral composition of aphanitic rocks is difficult without special equipment, dark color is associated with mafic composition and basalt is a reasonable identification.
A porphyritic igneous rock has what defining characteristic?
Larger crystals in a finer grained groundmass
-Porphyritic rocks have different larger crystals (phenocrysts) in a fine grained groundmass representing different stages of cooling.
Interplate Volcanoes
Are located at active plate boundaries. Created by volcanism at mid-ocean ridges, subduction zones, and continental rifts
Most volcanoes are __________ volcanoes
Interplate
Intraplate Volcanoes
Located within tectonic plates.
Most volcanism is where?
Mid-ocean ridges
All volcanoes on the ocean floor are ___?
Basaltic
pillow basalts
When basaltic lava erupts underwater it emerges in small explosions and/or forms pillow-shaped structures
black smokers
Mineral chimneys that form at hydrothermal vents.
The second most commonly found location for volcanism is ______________
The second most commonly found location for volcanism is adjacent to SUBDUCTION ZONES
A zone of actively erupting volcanism connected to a chain of extinct volcanoes indicates intraplate volcanism is located_______
A zone of actively erupting volcanism connected to a chain of extinct volcanoes indicates intraplate volcanism located over a hotspot.
The two main types of basaltic volcanic rock have Hawaiian names ___________
pahoehoe and aa
Caldera volcanoes
Caldera volcanoes are typically formed by eruptions of high-viscosity felsic lava having high volatiles content.
The most dangerous volcanic hazard are __________
The most dangerous volcanic hazard are PYROCLASTIC FLOWS
3 Different types of detecting changes or indications that an eruption is imminent
- monitoring earthquake frequency, especially special vibrational earthquakes called harmonic tremors, can detect magma movement and possible eruption.
- gas monitoring may be used to predict an eruption. A rapid increase of gas emission may indicate magma that is actively rising to surface and releasing dissolved gases out of solution, and that an eruption is imminent.
- how a GPS unit and tiltmeter can detect land surface changes, indicating the magma is moving underneath it.
Deep-sea hydrothermal vents (black smokers) are most commonly located at what plate boundary?
divergent boundaries of the mid-ocean ridge
Black smokers are associated with the mid-ocean ridge.
Which of these relatively recent volcanic eruptions formed a caldera? Mauna Loa Paracutín Mt. St. Helens Mt. Fuji Yellowstone
Yellowstone
A pegmatite is characterized by __________ that forms from __________.
A pegmatite is characterized by Very large crystals of felsic composition that forms from very slow cooling of residual material expelled from cooling magma
Where do igneous rocks with a coarse-grained (phaneritic) texture form?
deep under the surface.
Phaneritic (coarse grain) igneous rocks cool slowly deep underground.
The crystallization process in which a rising magma diapir incorporates some of the surrounding country rock so that the chemistry of the magma changes is called _____.
Assimilation
Assimilation is the process by which rising magma incorporates country rock and composition changes.
Phaneritic Rocks
Granite, Diorite, Gabbro, peridotite
Aphanitic Rocks
Rhyolite, Andesite, Basalt,
Porphyritic Rocks
Porphyritic Rhyolite, Porphyritic Andesite, Porphyritic Basalt
Vesicular rocks
Felsic- Pumice
Mafic- Scoria
Glassy Rocks
Felsic- Obsidian
Pyroclastic Rocks
Rhyolitic Tuff
Andesitic Tuff
Basaltic Tuff
What type of fault?
Right Lateral Strip Slip
What type of fault?
Right Lateral Strike Slip
What kind of fault?
Reverse Fault
What type of fault?
Normal fault
