Geology Chapter on Earth's Temperature and Core
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Questions and Answers

What are the two primary approaches used to estimate the Earth's temperature distribution?

Models of the Earth's thermal history and models involving redistribution of radioactive heat sources.

What is the estimated temperature range at the center of the Earth's core?

Between 6700 to 7000 °C.

What significant temperature change occurs at the 660-km discontinuity?

It marks the boundary between shallow and deep convection systems.

Who proposed the theory of seafloor spreading and in what year?

<p>Vine and Matthews proposed it in 1963.</p> Signup and view all the answers

How does seafloor spreading contribute to the formation of new lithosphere?

<p>New lithosphere is formed from upwelling mantle at ocean ridges as plates move away from the ridge axis.</p> Signup and view all the answers

What evidence was recognized in the 1950s that helped popularize the concept of seafloor spreading?

<p>Linear magnetic anomalies on the ocean floor.</p> Signup and view all the answers

Describe the temperature gradient observed in the LVZ and the D'' layer.

<p>Both layers exhibit significant temperature gradients.</p> Signup and view all the answers

What kind of geological features can disrupt the continuity of linear magnetic anomalies?

<p>Fracture systems can interrupt these anomalies.</p> Signup and view all the answers

What effect does a submarine plateau have when it encounters a subduction zone?

<p>It resists subduction and may produce a cusp in the arc system.</p> Signup and view all the answers

What type of earthquakes are mostly associated with the India-Asia boundary?

<p>Earthquakes are chiefly less than 100 km deep.</p> Signup and view all the answers

What dominates near sutures in collisional boundaries?

<p>Thrust fault mechanisms generally dominate near sutures.</p> Signup and view all the answers

What percentage of the Earth's volume and mass does the core comprise?

<p>The core comprises about sixteen percent of the Earth's volume and thirty-two percent by mass.</p> Signup and view all the answers

What geological feature is formed in response to the India collision?

<p>The Baikal rift in southern Siberia appears to have formed due to this collision.</p> Signup and view all the answers

What region is known for the flattening of velocity and density gradients?

<p>The D'' layer is known for the flattening of velocity and density gradients.</p> Signup and view all the answers

How does the volume of the accretionary prism get affected during an arc-continent collision?

<p>The volume decreases by more than seventy-five percent.</p> Signup and view all the answers

What is the thickness range of the lithosphere?

<p>The lithosphere ranges from 50 to 300 km in thickness.</p> Signup and view all the answers

What kind of faulting is common in the overriding plate during the collision illustrated in the content?

<p>Transcurrent faulting is common in the overriding plate.</p> Signup and view all the answers

Why is the Low Velocity Zone (LVZ) important for plate tectonics?

<p>The LVZ is important because it decouples the tectonic plates from the mantle, enabling plate movement.</p> Signup and view all the answers

What happens to the landward slope of the trench in a collision zone?

<p>The landward slope of the trench steepens and narrows.</p> Signup and view all the answers

What does the outer core's inability to transmit S-waves suggest about its state?

<p>The outer core's inability to transmit S-waves suggests that it is in a liquid state.</p> Signup and view all the answers

What important geological process does the Sunda arc system illustrate in its early stages?

<p>It illustrates a plate boundary in the early stages of an arc-continent collision.</p> Signup and view all the answers

What elements influence the temperature distribution within the Earth?

<p>The initial temperature distribution, heat generation with depth and time, mantle convection, and core formation all influence temperature distribution.</p> Signup and view all the answers

At what discontinuity does the inner core extend from?

<p>The inner core extends from the 5200-km discontinuity to the center of the Earth.</p> Signup and view all the answers

What occurs in the D'' layer that is significant to mantle dynamics?

<p>The D'' layer may be the site where mantle plumes are generated.</p> Signup and view all the answers

What is the average age of oceanic crust before it begins to subduct?

<p>The average age of oceanic crust before subduction is about 120 million years.</p> Signup and view all the answers

What geological events preceded the velocity maxima of continental plates?

<p>Velocity maxima in continental plates occurred just after the fragmentation from a supercontinent, such as Pangea.</p> Signup and view all the answers

What do ophiolites represent in the context of oceanic crust?

<p>Ophiolites are fragments of oceanic crust that are older than Jurassic found in continental orogenic belts.</p> Signup and view all the answers

How do calculated seafloor spreading directions help in paleogeographic reconstructions?

<p>They allow researchers to reconstruct past plate positions and estimate rates of plate separation.</p> Signup and view all the answers

What does the average age of oceanic crust on most continents indicate about its lifecycle?

<p>The average age is about 60 million years, indicating a relatively young and dynamic lifecycle compared to continental crust.</p> Signup and view all the answers

What historical evidence is shown by paleomagnetic data from Archean rocks?

<p>Paleomagnetic data indicate that plates were moving at slower rates of about 2 cm/y between 3.5 and 2.4 billion years ago.</p> Signup and view all the answers

What illustrates the direction of plate movement in seafloor spreading reconstructions?

<p>Flow or drift lines illustrate the relative directions of plate movement in seafloor spreading reconstructions.</p> Signup and view all the answers

What significant historical tectonic event is associated with the opening of the North Atlantic?

<p>The opening of the North Atlantic is marked by seafloor spreading, which is illustrated through calculated reconstruction methods.</p> Signup and view all the answers

What does the term 'episodic heat transfer' refer to in the context of the lower mantle?

<p>Episodic heat transfer refers to the irregular and intermittent process of heat movement from the lower mantle to the Earth's surface.</p> Signup and view all the answers

What possible implications can episodic heat loss have on the Earth's geological activity?

<p>Episodic heat loss could lead to fluctuations in volcanic activity and tectonic movements.</p> Signup and view all the answers

How might the heat transfer from the lower mantle be measured or observed?

<p>Heat transfer can be measured through geological surveys and monitoring of seismic activity.</p> Signup and view all the answers

What factors could contribute to the episodic nature of heat loss from the mantle?

<p>Factors may include variations in mantle convection, tectonic activity, and changes in material properties.</p> Signup and view all the answers

What are the two primary minerals responsible for rock magnetization?

<p>The two primary minerals are magnetite and hematite.</p> Signup and view all the answers

Why is it significant to understand the process of heat transfer from the lower mantle?

<p>Understanding this process is crucial for predicting geological phenomena and comprehending Earth's thermal dynamics.</p> Signup and view all the answers

What technique must be used to identify primary magnetization in rocks?

<p>Demagnetization techniques must be used to remove secondary magnetization.</p> Signup and view all the answers

What does NRM stand for in paleomagnetic studies?

<p>NRM stands for natural remanent magnetization.</p> Signup and view all the answers

What is thermal remanent magnetization (TRM) and how is it acquired?

<p>TRM is acquired by igneous rocks as they cool through a blocking temperature for magnetization.</p> Signup and view all the answers

What range does the Curie temperature for iron oxides fall within?

<p>The Curie temperature for iron oxides ranges between 500 °C and 600 °C.</p> Signup and view all the answers

Which plate driving force is chiefly responsible for plate motion according to most models?

<p>Slab-pull forces are chiefly responsible for plate motion.</p> Signup and view all the answers

What is the impact of ocean-ridge push forces on plate movement?

<p>Ocean-ridge push forces have a very small impact on plate movement.</p> Signup and view all the answers

Explain why rock magnetization varies and does not follow simple geometric relationships.

<p>Variations in the shapes, sizes, and velocities of plates lead to complex magnetization patterns.</p> Signup and view all the answers

Flashcards

What is the Earth's crust?

The thin, outermost layer of the Earth, composed of relatively light, rigid rock. It's thinner beneath oceans and thicker under continents.

What is the LVZ?

The region within the Earth where seismic waves travel at anomalously low speeds. It's located at the base of the lithosphere and is crucial for plate tectonics.

What is the D'' layer?

The boundary layer between the Earth's mantle and core. It's characterized by steep temperature gradients and may be where mantle plumes originate.

What is the lithosphere?

The rigid, outermost layer of the Earth, composed of the crust and the uppermost part of the mantle.

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What is the mantle?

The region within the Earth between the crust and the core. It's mostly solid but behaves like a very viscous fluid over long periods.

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What is the outer core?

The outermost layer of the Earth's core. It's liquid and plays a critical role in generating the Earth's magnetic field.

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What is the inner core?

The innermost layer of the Earth's core. It's solid and extremely hot, composed primarily of iron.

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What is plate tectonics?

The process of Earth's internal heat causing the lithospheric plates to move and interact, shaping the Earth's surface.

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Seafloor Spreading

A process where new oceanic crust is formed at mid-ocean ridges as magma rises from the mantle and solidifies.

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Linear Magnetic Anomalies

Linear magnetic anomalies on the seafloor, with alternating positive and negative magnetic signatures.

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Low Velocity Zone (LVZ)

A region of the Earth's upper mantle characterized by a low velocity of seismic waves.

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Core-Mantle Interface

The boundary layer between the Earth's mantle and its outer core.

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Outer Core

The outermost layer of the Earth's core, composed of liquid iron and nickel.

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660-km Discontinuity

A boundary in the Earth's mantle located approximately 660 km deep, marking the transition between the upper and lower mantle.

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Accretionary Plate Boundaries

Convergent plate boundaries where two tectonic plates collide, resulting in the formation of mountain ranges, volcanoes, and earthquakes.

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Convection

A process in which hot, less dense material rises and cooler, denser material sinks, driven by thermal energy.

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Episodic Heat Transfer

Heat transfer from the lower mantle is not continuous, but happens in bursts or pulses.

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Episodic Heat Loss

The source of these episodic heat bursts from the lower mantle.

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Episodic Heat Source

A possible source for episodic heat bursts from the lower mantle.

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Subduction Zone Collision with Ridges

When a submarine plateau or aseismic ridge encounters a subduction zone, it resists subduction and creates a cusp-like feature in the arc system. This is often accompanied by volcanic and seismic gaps in the arc.

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Collisional Boundaries

Areas of intense deformation resulting from the collision of two continental plates. This often leads to the formation of mountain ranges and significant geological activity.

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Thrust Faulting in Collision Zones

Dominant fault mechanism near sutures (zones where plates collide). These faults cause rocks to slide over each other, causing uplift and mountain formation.

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Transcurrent Faulting in Collision Zones

Large-scale strike-slip faults that occur in the overriding plate during a continental collision. This can lead to significant crustal displacement and movement.

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Extensional Faulting in Collision Zones

Extensional faults can occur in the overriding plate during a collision event. These faults allow for stretching and thinning of the crust, forming rift valleys and graben structures.

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Sunda Arc System Collision

Example of an arc-continent collision in its early stages. Here, the Sunda arc system in Indonesia is colliding with the Eurasian Plate, resulting in significant geological activity.

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Effects of Ridge-Trench Collision

Changes observed in a subduction zone during a collision with a ridge. The trench narrows, the accretionary prism shrinks, and parts of the subducting plate can be eroded away.

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Baikal Rift Formation

The Baikal Rift is an example of extensional faulting caused by the India-Asia collision. This rift formed far from the collision zone and illustrates the far-reaching effects of these tectonic events.

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What is subduction?

The process of one tectonic plate sliding beneath another, typically occurring at convergent plate boundaries.

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What are the average ages of oceanic crust?

The average age of oceanic crust is about 60 million years (My), while the average age at which it begins to subduct is about 120 My.

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Where are older oceanic crust fragments found?

Fragments of oceanic crust older than Jurassic (ophiolites) are found in continental orogenic belts, where they were tectonically emplaced during mountain formation.

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How can we reconstruct past plate movements?

By analyzing seafloor spreading directions and rates, it's possible to reconstruct past plate positions and estimate plate separation rates over the last 200 million years (My).

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What are 'flow lines' in plate reconstruction?

Flow lines are used to illustrate plate reconstruction, depicting the relative movement of plates over time. They show the path and direction of plate movement throughout geologic history.

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What were plate speeds like in the Archean?

Paleomagnetic data from Archean rocks in southern Africa indicate that plates moved at slower rates, about 2 cm/y, between 3.5 and 2.4 billion years ago.

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Did continental plates always move slowly?

Continental plates have moved as fast as modern oceanic plates for periods of 30 to 70 million years. These peak velocities often occur after continental fragmentation from supercontinents.

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What is the relationship between continental breakup and plate speed?

The peak velocities for Australia and India occurred after their separation from Gondwana, suggesting a connection between plate fragmentation and increased movement.

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Slab-pull force

The primary force driving plate movement, caused by descending plates pulling on the rest of the lithosphere at subduction zones.

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Ocean-ridge push force

Forces exerted at mid-ocean ridges pushing plates apart, considered relatively weak compared to slab-pull.

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Demagnetization

The process of removing secondary magnetization from rocks to isolate the original, primary record of Earth's magnetic field.

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Thermal remanent magnetization (TRM)

Natural magnetization acquired by rocks as they cool from molten to solid states, reflecting the Earth's magnetic field at the time.

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Curie temperature

The temperature at which a magnetic mineral loses its ability to retain magnetization. It's crucial for understanding TRM.

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Primary magnetization

The magnetic field of the Earth, recorded within rocks, providing a snapshot of the past magnetic field.

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Secondary magnetization

Magnetization acquired by rocks after their initial formation, often due to exposure to changing magnetic fields.

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Natural remanent magnetization (NRM)

The magnetization measured in rocks in a laboratory setting, encompassing both primary and secondary components.

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Study Notes

Plate Tectonics: A Perspective

  • Plate tectonics is a unifying geological model, developed in the 1970s, that explains the Earth's crust and mantle evolution.
  • Plate tectonics seeks to explain various phenomena including crustal deformation, earthquake patterns, continental drift, and mid-ocean ridges.
  • Two major premises of plate tectonics are: the lithosphere (outermost layer) behaves as a rigid substance sitting on the weaker asthenosphere, and the lithosphere is broken into plates that move and change shape.
  • Seafloor spreading, a parental theory, proposes that new lithosphere forms at ocean ridges and moves away, like a conveyor belt.
  • Scientists often view the acceptance of plate tectonics as a revolution, shifting from data collection to unifying theories.
  • The Earth's crust is formed from magma produced by partial melting of the mantle.
  • Continents rise through isothasy and are subjected to weathering and erosion, with materials being recycled through subduction.
  • The physical and chemical properties of the crust are understood via a growing data base.

Plate Boundaries

  • Earthquakes occur along plate boundaries, marking the division between plates.
  • Four types of plate boundaries are identified: ocean ridges, subduction zones, transform faults, and collisional zones.
  • Ocean ridges are divergent boundaries where new lithosphere forms.
  • Subduction zones are convergent boundaries where one plate is forced beneath another.
  • Transform faults are boundaries where plates slide past each other.
  • Continental margins are of two types: active margins where subduction or transform faults coincide with continental edges, and passive margins which are found in opening ocean basins.
  • Earthquakes along plate boundaries may be large or small. Large earthquakes tend to be along 'locked' segments of continental transforms and they release stress.

Seafloor Spreading

  • Linear magnetic anomalies on the seafloor are explained by seafloor spreading and associated magnetic field reversals.
  • These anomalies, recognized in the 1950s, have steep gradients and provide evidence for seafloor spreading.
  • Vine and Matthews (1963) proposed that the anomalies result from seafloor spreading and magnetic field reversals.
  • Ocean ridges are areas where new oceanic lithosphere is created.
  • Seafloor spreading results in the production of new ocean floor at a rate of approximately 3.5 km²/y.

Structure of the Earth

  • The Earth's internal structure is revealed by seismic waves.
  • The crust, mantle, and core are differentiated by seismic discontinuities (Moho, 660-km discontinuity, core-mantle interface, inner-core/outer- core interface).
  • The crust is the outermost layer, ranging from 3 km to 70 km thick.
  • The lithosphere (50-300 km thick) is the strong, rigid part of the Earth's surface.
  • The asthenosphere is located below the lithosphere and is a layer with low seismic wave velocities.
  • The mantle extends from the Moho to the core- mantle boundary.

Plate Motions

  • Plate motions are described by a pole of rotation and a spherical cycloid path.
  • Relative plate motions can be calculated using magnetic anomalies, hotspot tracks, and other data.
  • Plate velocities vary from 1 to 20 cm/year.

Triple Junctions

  • Triple junctions are points where three plate boundaries meet.
  • Different combinations of plate boundaries exist at triple junctions.

Convergent Boundaries

  • Convergent boundaries are marked by earthquakes beneath arc systems.
  • The seismic zone or Benioff zone dips steeply beneath arc systems.
  • Earthquakes often occur at depths of 30 km or greater along these zones.

Divergent Boundaries (Ocean Ridges)

  • Ocean ridges are areas of new lithosphere formation.
  • Rift zones are frequently associated with shallow earthquakes.
  • Rift earthquakes often occur in swarms associated with magma intrusion and extrusion.

Stress Distribution within Plates

  • Stress in plates is often related to large-scale features and is influenced by the interaction of plates and mantle processes.
  • Stress provinces show variations in stress orientations and magnitudes.

Paleomagnetism

  • Paleomagnetism studies rock magnetization to infer past Earth's magnetic fields (directions and strengths).
  • The two major problems associated with reconstruc- tion include separating multiple magnetizations in same rocks and dating these magnetizations.

Hotspots and Plumes

  • Hotspots are areas of volcanic activity thought to be associated with mantle plumes.
  • Hotspot tracks are trails of volcanic activity, which can help to determine plate movement directions and rates.
  • Hotspots are thought to remain relatively fixed in the mantle, but this is a still-debated issue.

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Description

Test your knowledge on the internal structure of the Earth with this quiz covering temperature distribution, seismic activities, and geological theories like seafloor spreading. Explore key concepts including the Earth's core temperature, significant discontinuities, and geological features formed by tectonic interactions.

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