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?

Vine and Matthews proposed it in 1963. Signup and view all the answers

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

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

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

Linear magnetic anomalies on the ocean floor. Signup and view all the answers

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

Both layers exhibit significant temperature gradients. Signup and view all the answers

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

Fracture systems can interrupt these anomalies. Signup and view all the answers

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

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

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

Earthquakes are chiefly less than 100 km deep. Signup and view all the answers

What dominates near sutures in collisional boundaries?

Thrust fault mechanisms generally dominate near sutures. Signup and view all the answers

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

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

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

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

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

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

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

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

What is the thickness range of the lithosphere?

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

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

Transcurrent faulting is common in the overriding plate. Signup and view all the answers

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

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

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

The landward slope of the trench steepens and narrows. Signup and view all the answers

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

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

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

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

What elements influence the temperature distribution within the Earth?

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

At what discontinuity does the inner core extend from?

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

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

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

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

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

What geological events preceded the velocity maxima of continental plates?

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

What do ophiolites represent in the context of oceanic crust?

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

How do calculated seafloor spreading directions help in paleogeographic reconstructions?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

What are the two primary minerals responsible for rock magnetization?

The two primary minerals are magnetite and hematite. Signup and view all the answers

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

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

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

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

What does NRM stand for in paleomagnetic studies?

NRM stands for natural remanent magnetization. Signup and view all the answers

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

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

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

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

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

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

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

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

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

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

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.