Igneous Rocks and Geotherm Concepts

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Questions and Answers

What is the primary characteristic that distinguishes magma from lava?

Magma is found underground while lava is found above ground. (correct)

Magma is formed from solid rocks.

Magma has a higher temperature than lava.

Magma is always more viscous than lava.

Which type of volcanic rock is characterized by having high silica content over 65%?

Intermediate

Felsic (correct)

Ultramafic

Mafic

What does a hotspot track signify in geological terms?

A series of volcanic eruptions at the same location.

A single volcano that erupts continuously.

An area of the mantle where no volcanism occurs.

A chain of volcanoes formed as a tectonic plate moves over a hotspot. (correct)

Which type of subaerial volcano is known for having steep sides and is formed by alternating layers of lava and ash?

Stratovolcano Signup and view all the answers

Which type of lava flow is described as having a ropey, smooth surface?

Pahoehoe Signup and view all the answers

What is the maximum size classified as ash in pyroclastic material?

64 mm Signup and view all the answers

What forms pillow lavas?

Lava that cools quickly underwater. Signup and view all the answers

Which of the following statements is true about basaltic lavas?

They are mafic with low silica content. Signup and view all the answers

What is the primary difference between weathering and erosion?

Weathering involves transformation of rocks, while erosion involves their movement. Signup and view all the answers

Which of the following processes leads to the formation of sedimentary rocks?

Diagenesis and lithification Signup and view all the answers

How are chemical and biochemical sedimentary rocks classified?

By their mineral composition Signup and view all the answers

What does transgression refer to in geological terms?

The rise of sea level that floods previously dry land. Signup and view all the answers

What is a characteristic of metamorphism?

It transforms rocks into denser materials with new mineral compositions. Signup and view all the answers

Which of the following best describes lithification?

The process of sediment compaction and cementation into rock. Signup and view all the answers

What distinguishes regional dynamothermal metamorphism from thermal or contact metamorphism?

Regional involves large areas affected by pressure, while contact is localized around heat sources. Signup and view all the answers

What is a common characteristic of foliation in metamorphic rocks?

An aligned arrangement of mineral grains creating distinct banding. Signup and view all the answers

Study Notes

Igneous Rocks

Igneous rocks form from melted rock that cools.
Magma is intrusive (plutonic) rock.
Lava is extrusive (volcanic) rock.
Magma is underground, lava is above ground.
Felsic rocks have high silica content (>65%).
Intermediate rocks have 53-65% silica.
Ultramafic rocks have <45% silica.
Mafic rocks have 45-52% silica.
As silica content decreases, ferromagnesian silicates increase.

Geotherm

A line or surface showing equal temperature points.
Used to track hot springs, geysers, and volcanic activity.

Bowen's Reaction Series

Describes the sequence of mineral crystallization/melting during magma cooling.
The continuous branch shows the evolution of plagioclase feldspar.
The discontinuous branch shows olivine, pyroxene, amphibole, and biotite mica formation.

Magma Viscosity and Silica Content

Magma with high silica content has higher viscosity.
Magma with low silica content has lower viscosity.

Magma Formation

Decompression causes rocks to melt at lower temperatures.
Addition of volatiles lowers the melting point of rocks.
Transfer of heat from adjacent magma raises temperatures.

Plutons

Intrusive igneous rock masses.
Batholiths are the largest plutons (>100km^2).
Laccoliths are mushroom-shaped plutons.
Dikes are tabular, discordant plutons.
Sills are tabular, concordant plutons.

Supervolcanoes

Volcanic centers with massive eruptions (VEI 8).
Yellowstone Caldera is a notable example.

Hot Spot Volcanoes

Volcanoes formed over rising plumes of hot mantle material (hotspots).
Hotspot tracks show plate movement over time.

Subaerial Volcanoes

Stratovolcanoes: Steep sides, alternating layers of lava and ash.
Cinder cones: Small, steep-sided cones formed by solidified lava fragments.
Shield volcanoes: Gently sloping, wide volcanoes formed by runny lava.

Pyroclastic Debris

Ash: <2mm
Lapilli: 2-64mm
Bomb: >64mm

Pillow Lavas

Lava cools quickly underwater, forming pillow shapes.

Basaltic vs Rhyolitic Lavas

Basaltic has low silica, rhyolitic has high silica.

Weathering, Erosion, and Transportation

Weathering: the breakdown of rocks.
Erosion: the removal and transportation of weathered material.
Transportation mediums (biggest to smallest): ice, water, wind.

Lithification and Diagenesis

Lithification: compactions and cementation of sediments into rock.
Diagenesis: chemical, biological, and physical processes that alter sediment after deposition.

Metamorphism

Metamorphism changes rocks into denser, more compact forms.
Metamorphism from regional dynamothermal changes vs thermal/contact metamorphism.

Protolith

The original rock before metamorphism.

Aureole

The zone around an intrusion that shows metamorphism change.
Non-foliated metamorphic rocks lack a layered texture. Quartzite, marble, and hornfels are examples.

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Description

Test your understanding of igneous rocks, their formation, and the principles of geotherm. Explore Bowen's Reaction Series, magma viscosity, and silica content to deepen your geological knowledge. This quiz covers essential concepts for geology students.