science

Trondhjemite

Trondhjemite 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 Trondhjemite rather than just read about it. In short: Trondhjemites are leucotonalites, a variety of leucocratic tonalite in which the modal mineralogy mostly consists of plagioclase in the form of albite to andesine, >20% quartz, and <10% alkali feldspar. Trondhjemites that occur in the oceanic crust or in ophiolites are usually called plagiogranites.

Key takeaways

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

Reference excerpt

Trondhjemites are leucotonalites, a variety of leucocratic tonalite in which the modal mineralogy mostly consists of plagioclase in the form of albite to andesine, >20% quartz, and <10% alkali feldspar. Trondhjemites that occur in the oceanic crust or in ophiolites are usually called plagiogranites. Trondhjemites are common in Archean terranes, occurring in conjunction with tonalite and granodiorite as the TTG (tonalite-trondhjemite-granodiorite) orthogneiss suite. Trondhjemite dikes also commonly form part of the sheeted dike complex of an ophiolite. The rock type was first described by Victor Goldschmidt in 1916. The name of the rock type is derived from the city of Trondheim, Norway. Despite the name and locality, the Trondheim trondhjemites are not considered ideal type specimen because greenschist metamorphism has erased their original mineralogy. Other well-known trondhjemite localities include the Rio Brazos quartz-eye trondhjemite in the Brazos Mountains, New Mexico, the Twilight Gneiss of the Needle Mountains, Colorado, trondhjemites of the Wind River Range, Wyoming, the Trinity Alps of California, and areas near Riggins, Idaho.

Formation Generation of trondhjemite-tonalitic magmas are understood be caused by fractionation of wet basaltic and/or dry low-K tholeiitic-andesitic magmas caused by partial melting of quartz eclogites, amphibolites or gabbros.

Notes

References Jackson, Julia A., ed. (1997). Glossary of geology (4th ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349. Philpotts, Anthony R.; Ague, Jay J. (2009). Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. ISBN 9780521880060. Barker, Fred (1979). Developments in Petrology: Trondhjemites, Dacites, and Related Rocks. Elsevier. ISBN 0-444-41765-6.

Further reading Best, Myron G. (2002) Igneous and Metamorphic Petrology, Blackwell Publishing, 2nd ed. ISBN 1-4051-0588-7

Illustrations

Worked examples

Example 1 — a first encounter with Trondhjemite

Start with the simplest possible case. Write down what Trondhjemite 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 Trondhjemite 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 Trondhjemite 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 Trondhjemite

In research: Trondhjemite 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 Trondhjemite 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: Trondhjemite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Granitic rocks, Igneous petrology, Igneous petrology stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Trondhjemite 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 Trondhjemite in 20 minutes

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

Frequently asked questions

What is Trondhjemite in simple terms?

Why does Trondhjemite 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 Trondhjemite?

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 Trondhjemite.