science

Subcontinental lithospheric mantle

Subcontinental lithospheric mantle is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Subcontinental lithospheric mantle rather than just read about it. In short: The term subcontinental lithosphere mantle is an erroneous term [Stuwe, 2007]. The scientifically correct term is continental lithospheric mantle (CLM), which is the uppermost solid part of Earth's mantle associated with continental mantle lithosphere, also known as continental lithospheric mantle that resides below the crust and above the asthenosphere.

Key takeaways

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Reproduce the core statement of Subcontinental lithospheric mantle from memory before moving on to harder problems.

Reference excerpt

The term subcontinental lithosphere mantle is an erroneous term [Stuwe, 2007]. The scientifically correct term is continental lithospheric mantle (CLM), which is the uppermost solid part of Earth's mantle associated with continental mantle lithosphere, also known as continental lithospheric mantle that resides below the crust and above the asthenosphere. The term subcontinental lithospheric mantle is incorrect because it implies a continent does not include lithospheric mantle. However, continents are lithospheric and lithosphere includes both crust and mantle lithosphere. The modern understanding of the Earth's upper mantle is that there are two distinct components - the lithospheric part and the asthenosphere. The lithosphere consists of crust and lithospheric mantle and behaves mostly in a plate-like fashion [Stuwe, 2007] whereas the asthenosphere is hotter and weaker due to the presence of partial melt and mantle convection. The boundary between these two layers is rheologically based and is not necessarily a strict function of depth. Specifically, oceanic lithosphere (lithosphere that comprises the oceanic tectonic plates) and continental lithosphere (lithosphere that comprises the continental tectonic plates), are defined as a thermomechanical boundary layer that conducts heat via conduction and the sublithospheric mantle, including the asthenosphere, conducts heat by convection such that the sublithospheric mantle is convecting adiabatic. In contrast to oceanic lithosphere, which experiences quicker rates of recycling, continental lithosphere is chemically distinct, cold, and older. This difference is translated into the differences between the CLM and the oceanic lithospheric mantle. There are two different types of continental lithospheric mantle that formed at different times in Earth's history: Archaean and Phanerozoic continental lithospheric mantle.

Archaean continental lithospheric mantle Archaean lithospheric mantle is strongly depleted in fertile melt indicators such as CaO and Al2O3. This depletion in major-elements should then be consequence of the Archaean lithosphere's formation. Trace-elements are abundant in Archaean lithosphere relative to MORB (which samples modern upper mantle) and have been sampled by Re-Os isotope dating of peridotites and ophiolites. The trace element composition of these xenoliths suggest mixing between the two different layers of subcontinental mantle. Particularly, the theory for the removal of Archaean continental lithospheric mantle below Archaean continental crust via delamination helps to explain mantle-peridotite xenoliths found in the extinct Sierra Nevada arc. Though there is evidence for the preservation of the Archaean lithosphere, there is controversy over the preservation of the Archaean mantle, for which the Archaean lithosphere would have been derived. The formation of the Archaean CLM is enigmatic. One early theory that komatiite melts formed the Archaean CLM does not explain how komatiites, which form in hot and deep environments, creates a reservoir that is shallow and cool. Another model of Archaean CLM formation suggests that the CLM formed in a subduction environment in which new Archaean crust was created through slab melting. If the primitive mantle is the starting composition for this CLM formation event, subducting slab would be composed of TTG crust, then the removal of basaltic melt and the enrichment of the mantle wedge with felsic melts could explain the formation of the depleted Archaean subcontinental lithosphere. For more information, see Archaean subduction.

Phanerozoic continental lithospheric mantle The mechanism of arc subduction is well understood to be the location where new continental crust is formed and is presumably also the site of continental lithospheric mantle genesis. Firstly, hydrated oceanic crust slabs begin subducting which releases fluids (subduction zone metamorphism) to the mantle wedge above. Continued subduction of the slab leads to further hydration of the mantle which causes partial melting in the mantle wedge. It is expected then that the modern continental lithospheric mantle is a former, melt-depleted mantle wedge. If the connection between continental crust and the continental lithospheric mantle does not exist, and rather a different Earth process formed both reservoirs, then it further complicates the mechanisms for how the Archaean subcontinental mantle formed.

References

Illustrations

Worked examples

Example 1 — a first encounter with Subcontinental lithospheric mantle

Start with the simplest possible case. Write down what Subcontinental lithospheric mantle claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Subcontinental lithospheric mantle before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Subcontinental lithospheric mantle ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Subcontinental lithospheric mantle

In research: Subcontinental lithospheric mantle appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Subcontinental lithospheric mantle in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Subcontinental lithospheric mantle is common in secondary-school and first-year university syllabi. It links to neighbouring topics Earth's mantle, so understanding it makes those chapters shorter.
In everyday life: Look for Subcontinental lithospheric mantle outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Subcontinental lithospheric mantle in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Subcontinental lithospheric mantle means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Subcontinental lithospheric mantle out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Subcontinental lithospheric mantle in simple terms?

Why does Subcontinental lithospheric mantle matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Subcontinental lithospheric mantle?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Subcontinental lithospheric mantle.