chemistry

Lunar terrane

Lunar terrane is a chemistry 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 Lunar terrane rather than just read about it. In short: A lunar terrane is a major geologic province on the Moon. Three terranes have been identified on the Moon: the Procellarum KREEP Terrane, the Feldspathic Highlands Terrane, and the South Pole–Aitken Terrane.

Key takeaways

Lunar terrane belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lunar terrane to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lunar terrane from memory before moving on to harder problems.

Reference excerpt

A lunar terrane is a major geologic province on the Moon. Three terranes have been identified on the Moon: the Procellarum KREEP Terrane, the Feldspathic Highlands Terrane, and the South Pole–Aitken Terrane. Each terrane has a unique origin, composition, and thermal evolution.

Procellarum KREEP Terrane The Procellarum KREEP Terrane, or PKT, is a large province on the near side of the Moon that has high abundances of KREEP. KREEP is an acronym built from the letters K (the atomic symbol for potassium), REE (rare-earth elements) and P (for phosphorus), and is a geochemical component of some lunar impact breccia and basaltic rocks. Notably, it is high in the KREEP element thorium, at a level of 4.8 ppm. This is a major factor distinguishing it from the other terranes. The PKT is on the near side of the moon, and covers 10% of the lunar surface, or 16% if one includes the maria lying within the FHT. Despite this, it contains 60% of all basaltic flows. KREEP has been shown to lower the melting point of rocks similar to those found on the Moon, and is expected to have contributed to volcanism in the region. The Oceanus Procellarum and Mare Imbrium regions lie within the PKT. In general, many maria, such as (but not limited to) Mare Frigoris and Mare Cognitum are members of the PKT. Not all maria are in the PKT, however - Mare Crisium and Mare Orientale are located within the outer Feldspathic Highlands. The PKT is the only terrane to lie exclusively in the near side of the Moon. Human and robotic missions have been done to this terrane, and samples have been returned to Earth for further study.

Felspathic Highlands Terrane The Felspathic Highlands Terrane (alternatively Feldspathic), or FHT, is composed predominantly of ancient anorthositic materials. It has low iron oxide and thorium levels. The FHT can be split into an inner and outer felspathic highlands. The outer FHT has comparatively higher levels of iron oxide and thorium. It is thought to be part of the FHT, with the differences being due to modification by ejecta from impacts in other terranes. The FHT covers 65% of the lunar surface. Overall, 6% of the lunar surface (and hence 9% of the FHT) consists of maria within the FHT, such as Mare Moscoviense. FHT maria have on average only 2.2 ppm of thorium, which is twice as much as the lunar average but significantly less than the levels seen in the PKT maria. Outer FHT non-maria regions contain 1 ppm of thorium, and only 0.3 ppm of thorium in the inner FHT. The inner FHT lies exclusively in the far side of the Moon, whereas the outer FHT spans both sides and is the one of two terranes on the near side of the Moon, along with the PKT. No spacecraft have landed on the inner FHT, as the only lander to the far side touched down in the South Pole-Aitken Terrane. In contrast, the outer FHT has been the subject of human landings and sample return.

South Pole-Aitken Terrane The South Pole-Aitken Terrane, or SPAT, may simply represent deep crustal materials of the Feldspathic Highlands Terrane. It has thorium levels between those of the PKT and FHT. The SPAT can be divided into two terranes, an outer and an inner SPAT. The outer SPAT has less iron oxide and thorium than its inner counterpart, although the thorium levels are still between those of the PKT and FHT. The terrane has its origins in a large impact that occurred early in the Moon's history and which had a major impact on the Moon's thermal evolution.

The inner and outer SPAT cover 5.3% and 5.7% of the lunar surface, respectively. Despite collectively covering 11% of the surface, SPAT contains only 5.8% of the thorium in the lunar crust. The SPAT lies exclusively in the far side of the moon, and contains the South Pole-Aitken basin. Chang'e 4, the first and only far-side lander, has landed in the region. It is not a sample return mission, and thus no samples have been directly taken from this terrane yet.

Historical terranes In the 1600s, the Moon was divided into two terranes, terra and maria. The terra terrane was thought to be landmass, and the maria terrane was thought to be the Moon's ocean, although this is now known to be false. The maria terrane is lower in elevation and younger in age than the terra terrane, and was formed by lava. The terra terrane is higher and older, and hence more cratered. Visually, the maria correspond to the dark regions of the Moon, and the terra to the light.

Map of lunar terranes

Illustrations

Worked examples

Example 1 — a first encounter with Lunar terrane

Start with the simplest possible case. Write down what Lunar terrane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Lunar terrane 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 Lunar terrane 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 Lunar terrane

In research: Lunar terrane appears in chemistry 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 Lunar terrane 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: Lunar terrane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geochemistry, Geology of the Moon, Terranes, so understanding it makes those chapters shorter.
In everyday life: Look for Lunar terrane 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 Lunar terrane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lunar terrane 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 Lunar terrane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lunar terrane in simple terms?

Why does Lunar terrane matter?

Because it connects several chemistry 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 Lunar terrane?

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 Lunar terrane.