Lecture 13: Melting the Mantle and Volcano Types

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Questions and Answers

What does the equation $FA + FB = 1$ signify in the context of mixing seawater and freshwater?

The total mass of seawater must equal the total mass of freshwater.

The properties of seawater and freshwater remain unchanged.

The concentration of salt in seawater must equal that in freshwater.

The sum of the mass fractions of the components equals the total mass. (correct)

How does the salt content in a mixture of seawater and freshwater relate to the mass fraction of seawater (FA)?

It remains constant regardless of FA.

It is irrelevant to the mixture's composition.

It is inversely proportional to FA.

It is directly proportional to FA. (correct)

Which of the following best describes the makeup of mantle plumes as per the evidence provided?

They are exclusively derived from primitive mantle components.

They are primarily made up of sediments from the ocean floor.

They are a combination of peridotitic mantle material and recycled components. (correct)

They consist solely of recycled oceanic crust material.

In the context of geochemical tracing, what factors determine the concentration of Strontium in a mixture of seawater and freshwater?

The mass of the components and their initial concentrations. Signup and view all the answers

What is the primary property of a mixture of seawater and freshwater based on the given content?

The mixture exhibits properties that are intermediate between seawater and freshwater. Signup and view all the answers

What is the primary formula used to describe the relationship between input and output in geochemical fluxes?

Input = output + change in storage Signup and view all the answers

What role does geothermal energy play in the formation of volcanogenic massive sulfide (VMS) deposits?

It heats seawater, enriching it with metals. Signup and view all the answers

Which of the following metals is NOT typically found in VMS deposits?

Iron (Fe) Signup and view all the answers

How does the flux of hydrothermal vents compare to the total global river flux?

Hydrothermal vent flux is 0.1% of river flux. Signup and view all the answers

What elements are primarily cycled through the ocean's food web before being exported to the seafloor?

Various chemical elements such as C, N, S, and P Signup and view all the answers

What does a high 87Sr/86Sr ratio in mantle derived samples indicate?

Recycling of crustal material Signup and view all the answers

What is the significance of black smoker chimneys in the context of hydrothermal activity?

They indicate high concentrations of sulfide minerals. Signup and view all the answers

What is the half-life of 87Rb, which is important for understanding the decay to 87Sr?

48.8 billion years Signup and view all the answers

Which of the following is the primary question that isotopic analysis can help answer?

How old is the sample? Signup and view all the answers

What is meant by the term 'negligible change in storage' in the context of conservative elements?

No significant changes occur in the long term. Signup and view all the answers

What type of deposits are formed by the precipitation of metals and sulfur at hydrothermal vents?

Volcanogenic massive sulfide (VMS) deposits Signup and view all the answers

What does a linear trend in a plot of 87Sr/86Sr versus 1/Sr indicate?

Mixing of seawater and freshwater Signup and view all the answers

How is the isotopic composition of a mixture calculated in geochemistry?

By a weight-averaged approach based on concentration Signup and view all the answers

Which processes can the analysis of 87Sr/86Sr ratios help track in subduction zones?

Interaction of sedimentary materials with oceanic crust Signup and view all the answers

In a two-component mixing model, what do the slope and intercept of the line represent?

Isotopic and concentration characteristics of the components Signup and view all the answers

What type of geological materials can the 87Sr/86Sr ratio provide insights into regarding their origins?

Both continental and oceanic materials Signup and view all the answers

Study Notes

Lecture 13: 3 Ways to Melt the Mantle and 3 Kinds of Volcanoes

Reduce Pressure Without Losing Heat (MORB Volcanism): Melting occurs when pressure decreases while maintaining heat, typically at mid-ocean ridges where tectonic plates pull apart. Rising mantle material fills the gap, decreasing pressure and causing melting, forming basaltic lava (MORB).
Add Water (Reduce Melting Temperature - Subduction Volcanoes): The addition of water from subducted oceanic plates into the mantle lowers the melting temperature of mantle material. This process generates magma associated with subduction zones, such as the Cascade volcanoes in the Pacific Northwest.
Increase Temperature (Hot Spot Volcanoes): A plume of hot mantle material rising toward the surface increases the temperature of surrounding rock, causing melting and magma formation. Examples include the Hawaiian Islands, which formed over a stationary hotspot.

Key Points: Ways to Melt Mantle

Reduce pressure
Add water
Increase temperature

MORB Melting by Adiabatic Decompression

Plate Spreads: Tectonic plates pull apart at mid-ocean ridges.
Mantle Upwells: Material from the mantle rises to fill the gap.
Pressure Decreases: As mantle rock rises, the pressure on it decreases, though the heat remains mostly the same.
Mantle Rock Melts: This results in the upwelling mantle rock beginning to melt, thus forming magma.
Adiabatic Decompression: Lowering the pressure without losing heat results in the melting of mantle rock, creating magma.
Solidus: The temperature at which the first tiny bit of melt (magma) starts to form in the rock.

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Description

Explore the three main processes that cause the mantle to melt and the three types of volcanoes associated with these processes. From MORB volcanism at mid-ocean ridges to subduction zones and hot spots, understand how pressure, temperature, and water influence magma formation. This quiz will enhance your grasp of volcanic activity and tectonic interactions.