Igneous Rocks and Magma Formation

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Questions and Answers

What are igneous rocks?

Rocks that formed from a melt that cooled (other melted rocks)

What are intrusive rocks called?

Magma

What are extrusive rocks called?

Lava

Where is magma found?

<p>Underground</p> Signup and view all the answers

Where is lava found?

<p>Above ground</p> Signup and view all the answers

Which of these minerals are found in felsic magma?

<p>Quartz (C), Feldspar (D)</p> Signup and view all the answers

What is the silica content of felsic magma?

<blockquote> <p>65% (B)</p> </blockquote> Signup and view all the answers

What is the silica content of intermediate magma?

<p>53-65% (C)</p> Signup and view all the answers

What is the silica content of mafic magma?

<p>45-52% (A)</p> Signup and view all the answers

What is the silica content of ultramafic magma?

<p>&lt;45% (B)</p> Signup and view all the answers

What happens to the concentration of ferromagnesian silicates as silica content decreases?

<p>They rise</p> Signup and view all the answers

Define geotherm.

<p>A line or surface on the Earth that connects two points of equal temperature</p> Signup and view all the answers

What are some examples of geological features associated with geotherms?

<p>Hot springs, geysers, fumaroles, and volcanic activity</p> Signup and view all the answers

What does Bowen's reaction series describe?

<p>The point at which certain minerals crystallize and melt</p> Signup and view all the answers

Describe the continuous branch of Bowen's reaction series.

<p>It describes the evolution of the plagioclase feldspars as they evolve from being calcium-rich to more sodium rich.</p> Signup and view all the answers

Describe the discontinuous branch of Bowen's reaction series.

<p>It describes the formation of the mafic minerals olivine, pyroxene, amphibole, and biotite mica.</p> Signup and view all the answers

Explain the difference in viscosity between magma with high silica content and magma with low silica content.

<p>Magma with high silica content has a much higher viscosity than magma with low silica content.</p> Signup and view all the answers

Which of the following are processes of magma formation in the Earth?

<p>All of the above (D)</p> Signup and view all the answers

Describe decompression as a process of magma formation.

<p>Rock from a higher pressure area rises to a lower pressure area and melts without a significant change in temperature.</p> Signup and view all the answers

Describe the addition of volatiles as a process of magma formation.

<p>Volatile substances, like water vapor, enter a rock, lowering its melting point, allowing it to melt at lower temperatures.</p> Signup and view all the answers

Describe the transfer of heat from adjacent magma or very hot rocks as a process of magma formation.

<p>Heat from a hot rock moves into a cooler rock, melting it if the cooler rock reaches its melting point.</p> Signup and view all the answers

Define pluton.

<p>A deep-seated intrusion of igneous rock</p> Signup and view all the answers

Define batholith.

<p>A large pluton greater than 100 square kilometers</p> Signup and view all the answers

Define laccolith.

<p>A mushroom or lens-shaped pluton</p> Signup and view all the answers

Define dike.

<p>Dikes are tabular intrusions that cut across existing rock layers.</p> Signup and view all the answers

Define sill.

<p>A tabular, concordant pluton</p> Signup and view all the answers

What is a supervolcano?

<p>A volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index</p> Signup and view all the answers

What is the VEI and what does a magnitude 8 on the VEI represent?

<p>The Volcano Explosivity Index (VEI) is a scale used to measure the relative explosivity of volcanic eruptions. A magnitude 8 eruption represents an eruption that releases more than 1,000 cubic kilometers of material.</p> Signup and view all the answers

Give an example of a supervolcano?

<p>Yellowstone Caldera</p> Signup and view all the answers

What are hot-spot volcanoes?

<p>Volcanoes that form over exceptionally hot parts of the Earth's mantle</p> Signup and view all the answers

Where do hot-spot volcanoes occur?

<p>On the overlying crust</p> Signup and view all the answers

What does a hotspot track indicate?

<p>A chain of volcanoes formed as a tectonic plate moves over a plume of hot mantle material</p> Signup and view all the answers

Which of the following are forms of subaerial volcanoes?

<p>All of the above (D)</p> Signup and view all the answers

Describe the characteristics of stratovolcanoes.

<p>They have steep sides formed by alternating layers of thick, nonflowing lava and ash.</p> Signup and view all the answers

Describe the characteristics of cinder cones.

<p>They are small, steep-sided volcanic cones formed by the accumulation of small, solidified lava fragments ejected from a single vent during an eruption.</p> Signup and view all the answers

Describe the characteristics of shield volcanoes.

<p>They are gently sloping, wide volcanoes formed by very runny lava.</p> Signup and view all the answers

Describe the characteristics of pahoehoe lava flows.

<p>They are characterized by ropey, smooth, or billowy surfaces.</p> Signup and view all the answers

Describe the characteristics of a'a' lava flows.

<p>They have rough surfaces and thick interiors.</p> Signup and view all the answers

Which of the following are examples of pyroclastic debris?

<p>All of the above (D)</p> Signup and view all the answers

What are pillow lavas?

<p>Formations that occur from lava erupting underwater and cooling quickly, causing a pillowy appearance.</p> Signup and view all the answers

Which of the following types of lava has a higher silica content?

<p>Rhyolitic (A)</p> Signup and view all the answers

Which transport medium carries the largest particles?

<p>Ice (A)</p> Signup and view all the answers

Define weathering.

<p>The breaking down of rocks where they are in place.</p> Signup and view all the answers

Which of the following are types of physical weathering?

<p>All of the above (D)</p> Signup and view all the answers

Which of the following are types of chemical weathering?

<p>All of the above (D)</p> Signup and view all the answers

Define biological weathering.

<p>The action of living organisms on rocks</p> Signup and view all the answers

Define erosion.

<p>The movement of rock, soil, and dissolved material by agents like water, wind, or ice from one location to another</p> Signup and view all the answers

Define transportation.

<p>The movement of sediment by agents like wind, water, or ice</p> Signup and view all the answers

What is the difference between lithification and diagenesis?

<p>Lithification is the process by which sediments are compacted and cemented together to form sedimentary rock, while diagenesis is the chemical, biological, or physical process by which sedimentary rocks change after sediments are deposited.</p> Signup and view all the answers

How do you classify chemical and biochemical sedimentary rocks?

<p>They are classified by their mineral composition, rather than grain size</p> Signup and view all the answers

Define transgression.

<p>When the sea level rises relative to land, causing the sea to flood previously dry land.</p> Signup and view all the answers

Define regression.

<p>When the sea level falls relative to land</p> Signup and view all the answers

What is the difference between metamorphism and diagenesis?

<p>Metamorphism transforms rocks into a much denser, more compact rock with different mineral compositions and textures, while diagenesis transforms sediment into sedimentary rock through dissolution or compaction.</p> Signup and view all the answers

Give examples of foliation in metamorphic rocks.

<p>Schistosity and compositional banding</p> Signup and view all the answers

What is the difference between regional dynamothermal metamorphism and thermal or contact metamorphism?

<p>Regional dynamothermal metamorphism occurs when rocks are exposed to high heat and pressure over large areas, while thermal or contact metamorphism occurs when rocks are heated by magma or other hot rocks.</p> Signup and view all the answers

Define protolith.

<p>The original rock, before undergoing metamorphosis</p> Signup and view all the answers

A protolith may belong to any of the primary rock types.

<p>True (A)</p> Signup and view all the answers

What are the pressure and temperature conditions for the formation of a blueschist?

<p>High pressure, low temperature (200-500 degrees Celsius)</p> Signup and view all the answers

Define aureole.

<p>The zone surrounding an intrusion, which is a mass of igneous rock that solidified between other rocks</p> Signup and view all the answers

Describe the characteristics of non-foliated metamorphic rocks.

<p>They typically do not have a plated texture and grow crystals in no particular direction.</p> Signup and view all the answers

Which of the following are examples of non-foliated metamorphic rocks?

<p>All of the above (D)</p> Signup and view all the answers

Flashcards

Igneous Rocks

Rocks formed from cooled melt (magma or lava).

Magma

Molten rock beneath the Earth's surface.

Lava

Molten rock above the Earth's surface.

Felsic Magma

Magma rich in feldspar and quartz, high silica content (>65%).

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Intermediate Magma

Magma with silica content between felsic and mafic (53-65%).

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Ultramafic Magma

Magma with very low silica content, high in iron and magnesium.

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Mafic Magma

Magma with low silica content, rich in iron and magnesium.

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Pluton

Large body of intrusive igneous rock.

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Laccolith

Mushroom or lens-shaped pluton.

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Dike

Tabular, discordant pluton.

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Sill

Tabular, concordant pluton.

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Supervolcano

Volcanic center with VEI 8 eruptions.

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Hot-spot Volcanoes

Volcanoes formed over hot mantle plumes.

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Hot-spot track

Chain of volcanoes formed as a plate moves over a hotspot.

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Stratovolcano

Steep-sided volcano with alternating layers of lava and ash.

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Cinder Cone

Small, steep-sided volcano from solidified lava fragments.

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Shield Volcano

Gently sloping, wide volcano formed by very runny lava.

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Pahoehoe

Lava flow with a smooth, ropey surface.

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‘A’a’

Lava flow with a rough, jagged surface.

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Weathering

Breaking down of rocks in place, without movement.

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Erosion

Transport of weathered material.

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Transportation

Moving sediment from one place to another.

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Lithification

Compaction and cementation of sediments to form rock.

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Diagenesis

Chemical, biological, or physical changes in sediments after deposition.

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Study Notes

Igneous Rocks

  • Igneous rocks form from a melted substance that cools.
  • Magma is intrusive/plutonic rock.
  • Lava is extrusive/volcanic rock.
  • Magma is underground, lava is above ground.
  • Felsic magma has high silica content (>65%).
  • Intermediate magma has 53-65% silica.
  • Ultramafic magma has <45% silica.
  • Mafic magma has 45-52% silica.
  • As silica content lowers, ferromagnesian silicates rise.

Geotherm

  • A line or surface depicting equal temperature points (e.g., hot springs, geysers).

Bowen's Reaction Series

  • Describes the sequence minerals crystallize/melt at various temperatures.
  • Continuous branch relates to plagioclase feldspar evolution (calcium to sodium-rich).
  • Discontinuous branch relates to olivine, pyroxene, amphibole, and biotite mica formation.

Magma and Viscosity

  • Magma with high silica content has higher viscosity than magma with low silica content.

Magma Formation

  • Three processes: decompression, addition of volatiles, transfer of heat.
  • Decompression: Rock melts at lower pressure (e.g., at divergent plate boundaries).
  • Addition of volatiles: Water vapor lowers melting point, allowing melting at lower temperatures.

Plutons

  • Pluton: Deep-seated intrusions.
  • Batholith: >100km^2, largest pluton.
  • Laccolith: Mushroom-shaped pluton.
  • Dike: Tabular, discordant pluton.
  • Sill: Tabular, concordant pluton.

Supervolcanoes

  • Supervolcano - large volcanic center with VEI 8 eruptions.
  • Example: Yellowstone Caldera.

Hotspot Volcanoes

  • Hotspots - areas of the Earth's mantle with plumes, creating volcanoes.

Hotspot Tracks

  • Chain of volcanoes formed as a tectonic plate moves over a hotspot plume.

Subaerial Volcanoes (forms)

  • Stratovolcanoes: Steep sides, alternating lava and ash layers.
  • Cinder cones: Small, steep-sided cones from solidified lava fragments (cinders/scoria).
  • Shield volcanoes: Gently sloping sides, formed by runny lava.
  • Differences between Pahoehoe and ‘a’a’ lava flows are in surface texture.

Volcanic Debris

  • Ash: <2mm, smallest particle.
  • Lapilli: 2-64mm.
  • Bomb: >64mm.

Pillow Lavas

  • Form when lava erupts underwater and cools quickly.

Lava Type Differences

  • Basaltic lava - low silica content.
  • Rhyolitic lava - high silica content.

Weathering, Erosion, and Transportation

  • Weathering: Breakdown of rocks in place (physical and chemical).
  • Erosion: Removal and transportation of rock material.
  • Transportation: Process of moving sediment (e.g., water, wind, ice).

Lithification and Diagenesis

  • Lithification: Compaction and cementation of sediments into rock.
  • Diagenesis: Chemical, biological, and physical processes after sediment deposition.

Classifying Sedimentary Rocks (chemical and biochemical)

  • Classified by their mineral composition, rather than grain size, unlike clastic rocks.

Transgression and Regression

  • Transgression: Sea level rises, flooding land.
  • Regression: Sea level falls, exposing land.

Metamorphism and Diagenesis

  • Metamorphism: Rocks transform into denser, more compact rocks with different mineral compositions.
  • Diagenesis: Sedimentary rocks change due to dissolution or compaction.

Types of Foliation / Metamorphic Rocks

  • Foliation (schistosity, compositional banding): Layered appearance in metamorphic rocks (slate, schist, gneiss).
  • Regional dynamothermal metamorphism: High pressure and heat over large areas.
  • Thermal or contact metamorphism: Changes due to heat from magma.

Metamorphic Rocks (protolith)

  • Protolith: Original rock before metamorphism.
  • A protolith can be any of the primary rock types.
  • Examples of non-foliated metamorphic rocks include quartzite, marble, and hornfels.

Aureoles in Metamorphism

  • Aureole: Zone surrounding an intrusion of igneous rock, altered by heat.

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