earth science

Horokanai Ophiolite

Horokanai Ophiolite is a earth 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 Horokanai Ophiolite rather than just read about it. In short: The Horokanai ophiolite is a geological complex located in the Kamuikotan tectonic belt about 30 km northwest of Asahikawa city, Hokkaido, Japan. The ophiolite complex is exposed along either side of a north-dipping anticline in several blocks.

Key takeaways

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

Reference excerpt

The Horokanai ophiolite is a geological complex located in the Kamuikotan tectonic belt about 30 km northwest of Asahikawa city, Hokkaido, Japan. The ophiolite complex is exposed along either side of a north-dipping anticline in several blocks.

Stratigraphy Exact thicknesses of units within the Horokanai Ophiolite complex are not reliably estimable due to differences in stratigraphy and structure between different blocks. However, the basic sequence of units within the complex as a whole has been described in several studies. Overlying, unconformable Cretaceous sediments

Radiolarian chert, shales, sandstones Gabbroic – Basaltic Rocks (intruded by dolerite and plagio-granite dikes)

Metamorphosed basalts exhibiting pillow lava and basaltic tuff flow structures Uppermost portion is the Gokurakudaira Formation: a Type-1-aphyric tholeiite greenstone belt Amphibolites derived from basaltic and gabbroic rocks Metamorphosed massive-gabbro- and layered-gabbro-derived amphibolites Ultra-Mafic Rocks (intruded by dikes and lenses of diorite rocks, olivine gabbro, and hornblende-gabbro pegmatite)

Orthopyroxenite with layered, cumulate structures Serpentinite with relict mineral structures suggesting parental dunite with layered/cumulate structures Serpentinite with relict mineral structures suggesting parental harzburgite (described as massive, homogeneous with thin dunite layers) Underlying layer of Kamuikotan tectonic belt blueschist

Metamorphism The Horokanai ophiolite exhibits metamorphism of the low greenschist (upper Horokanai ophiolite) to low granulite (lower Horokanai ophiolite) facies. Asahina et al. (1979) describes the metamorphic alteration of the complex. The original dunite and harzburgite of the ultra-mafic lower portion of the ophiolite have largely been metamorphosed into serpentinite, with little to none of the original peridotite remaining. The orthopyroxenite is described as “Metagabbro.” What was originally a coarse-to-fine gabbro section is now a sequence of clinopyroxene-, schistose- and epidote-amphibolites. Finally, the upper basaltic pillow lavas and tuff flows have metamorphosed to amphibolite schists and “metabasalt.” Asahina et al. (1979) presents two theories for the metamorphism of the Horokanai complex. The first theory claims that metamorphism takes place at a mid-ocean ridge with a high geothermal gradient, accompanied by shear and plastic flow. The second theory claims that metamorphism takes place within an island-arc complex, where the rocks making up the ophiolite serve as basement rocks.

Origins Ishizuka (1981) proposes an abyssal tholeiitic composition for the Horokanai ophiolite complex, claiming that the chemical composition of the ophiolite more closely resembles that of an oceanic spreading ridge than that of an island arc or hotspot. The distinction was made by examining the Chromium, Nickel and Titanium abundances in the ophiolite, as well as relic spinel chemistry in Horokanai pillow basalts. Takashima et al. (2002) examines the Gokurakudaira Formation - the uppermost mafic portion of the Horokanai ophiolite - in order to determine an origin. The formation exhibits MORB-like tholeiitic composition in agreement with the observations from Ishizuka. However, Takashima et al. (2002) presents other petrologic evidence that suggests a geologic fore-arc setting similar to the Lau Basin. They base this conclusion on the presence of picrite (with back-arc-associated pyroclastic and turbidite deposits) and high-Mg basaltic-andesite (commonly associated with fore-arc and back-arc settings) within the Gokurakudaira Formation. In their model, the formation of a spreading center within a fore-arc basin above a subducting plate constitutes the origin of the Horokanai ophiolite complex.

References

Worked examples

Example 1 — a first encounter with Horokanai Ophiolite

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

In research: Horokanai Ophiolite appears in earth 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 Horokanai Ophiolite 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: Horokanai Ophiolite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geologic formations of Japan, Ophiolites, so understanding it makes those chapters shorter.
In everyday life: Look for Horokanai Ophiolite 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 Horokanai Ophiolite in 20 minutes

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

Frequently asked questions

What is Horokanai Ophiolite in simple terms?

Why does Horokanai Ophiolite matter?

Because it connects several earth 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 Horokanai Ophiolite?

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 Horokanai Ophiolite.