Question

The transition from spinel to perovskite structure occurs between _____.

• A. lower mantle and outer core
• B. outer core and inner core
• C. upper mantle and lower mantle
• D. lower crust and upper mantle

Answer 1

The Correct Option is C

The question asks us to identify between which layers the transition from a spinel to a perovskite structure occurs. This is a topic within the field of geology, specifically relating to mantle mineralogy. To determine the correct answer, let's analyze the structural changes that occur within Earth's layers.

The Earth's structure is divided into several layers: the crust, mantle, and core. The mantle itself is further divided into the upper mantle, lower mantle, and the transition zone between them. Understanding these layers is crucial:

1. The **upper mantle** extends from the bottom of the crust to about 660 kilometers deep and includes the lithosphere and the asthenosphere.
2. The **lower mantle** extends from 660 kilometers down to about 2900 kilometers, reaching the outer core.

Now, let's explore the chemical process:

• Spinels are a class of minerals characterized by their crystal structure. In the mantle, spinel structures can transition into more dense structures as pressure increases with depth.
• Perovskite is a more compact mineral structure often found in the lower mantle. It is primarily comprised of MgSiO₃ in these regions.

The transition from a spinel to a perovskite structure occurs in response to increasing pressure and temperature conditions. This transition marks the boundary between the upper mantle and the lower mantle, often referred to as the mantle transition zone.

Let us evaluate the options:

• Lower mantle and outer core: This boundary does not involve the transition from spinel to perovskite.
• Outer core and inner core: This boundary is primarily liquid-solid transition, irrelevant to spinel or perovskite structures.
• Upper mantle and lower mantle: Correct. This is where the transition from spinel to perovskite occurs, at the depth of the transition zone (approx. 660 km).
• Lower crust and upper mantle: The boundary involves crust-mantle transition without involving spinel structures.

Based on these explanations, the correct answer is: **upper mantle and lower mantle.** This is where the spinel-perovskite transition occurs due to increasing pressure and temperature. Understanding this transition helps geologists infer the dynamics and composition of Earth's mantle under immense pressure.