earth science

Wrangellia terrane

Wrangellia terrane 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 Wrangellia terrane rather than just read about it. In short: The Wrangellia terrane (named for the Wrangell Mountains, Alaska) is a crustal fragment (terrane) extending from the south-central part of Alaska and along the Coast of British Columbia in Canada. Some geologists contend that Wrangellia extends southward to Oregon, although this is not generally accepted.

Key takeaways

Wrangellia terrane 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 Wrangellia terrane to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Wrangellia terrane from memory before moving on to harder problems.

Reference excerpt

The Wrangellia terrane (named for the Wrangell Mountains, Alaska) is a crustal fragment (terrane) extending from the south-central part of Alaska and along the Coast of British Columbia in Canada. Some geologists contend that Wrangellia extends southward to Oregon, although this is not generally accepted.

Extent and terminology The term Wrangellia is confusingly applied to all of:

The Wrangell(ia) Terrane alone; A composite terrane (CT) consisting of the Wrangell Terrane, Peninsular Terrane, and other rock units that were not originally part of the North American craton; A composite terrane which also includes the Alexander Terrane. Earlier geologists sometimes used the term "Talkeetna Superterrane" to describe Wrangellia.

Origin There are two conflicting hypotheses about whether the Wrangellia Superterrane originated at polar or equatorial latitudes:

That Wrangellia accreted at a northerly latitude near its current location (when North America, or Laurentia, was farther east as part of Pangaea). That Wrangellia originated c. 3,000 km (1,900 mi) south of its current location, approximately where Baja California is now. This hypothesis is not favoured in tectonic plate reconstructions favoring an Andean subduction model, specifically since it introduces allegedly large and rapid displacements of Wrangellia across the Panthalassic Ocean.

Northern hypothesis Geological evidences indicate that the Caledonide closure of the Iapetus and Rheic Oceans along the Laurentian westcoast (modern coordinates) also opened an ocean between the northern margin of Laurentia and Baltica on one side and Siberia on the other. This effectively dispersed continental fragments—the Alexander, Eastern Klamath, Northern Sierra and Okanagan terranes—westward along the shores of this ocean in a back-arc process similar to that of the present-day Scotia Plate between the South America Plate and the Antarctic Plate. During the Carboniferous, the Alexander terrane migrated westward into the northern Panthalassic Ocean where it merged with Wrangellia in the late Carboniferous—the two continental fragments remained isolated in the open ocean until they were accreted to Laurentia in the Middle Jurassic.

Southern hypothesis Rocks of Wrangellia (the individual terrane, not the composite terrane) were originally created in the Pennsylvanian to the Jurassic somewhere, but probably near the equator, in the Panthalassic Ocean off the west coast of Laurentia (North American craton) as island arcs, oceanic plateaus, and rock assemblages of the associated tectonic settings. It is composed of many rocks types, of various composition, age, and tectonic affinity, but the Late Triassic flood basalts are the defining unit of Wrangellia. These basalts, extruded onto land over 5 million years about 230 million years ago, on top of an extinct Pennsylvanian and Permian island arc, constitute a large igneous province, currently exposed in a 2,500 km (1,553 mi) long belt. Wrangellia collided and amalgamated with the Alexander Terrane by Pennsylvanian time. By the end of the Triassic, the Peninsular Terrane had also joined the Wrangellia composite terrane. A subduction zone existed on the west side of Wrangellia. Seafloor rocks too light to be subducted were compressed against the west edge of Wrangellia; these rocks are now known as the Chugach Terrane. A complex fault system, known as the Border Ranges Fault, is the modern expression of the suture zone between Wrangellia and Chugach Terranes. Over time, plate tectonics moved this amalgamation of crust generally northeastward into contact with the North American continental margin. The Wrangellia composite terrane collided with and docked to North America by Cretaceous time. Strike-slip displacement, with Wrangellia travelling northward, continued after docking, although the amount of post-accretion displacement is controversial.

See also List of Cascade volcanoes List of Northern Cordilleran volcanoes List of volcanoes in the United States Volcanology of Canada – Volcanic activity in CanadaPages displaying short descriptions of redirect targets Volcanology of Western Canada

References

Citations

General sources

External links Google search for maps of Wrangellia Large Igneous Provinces Commission: December 2008 LIP of the Month: The Accreted Late Triassic Wrangellia Oceanic Plateau in Alaska, Yukon, and British Columbia

Illustrations

Worked examples

Example 1 — a first encounter with Wrangellia terrane

Start with the simplest possible case. Write down what Wrangellia terrane 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 Wrangellia 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 Wrangellia 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 Wrangellia terrane

In research: Wrangellia terrane 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 Wrangellia 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: Wrangellia terrane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coast of British Columbia, Flood basalts, Large igneous provinces, so understanding it makes those chapters shorter.
In everyday life: Look for Wrangellia 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 Wrangellia terrane in 20 minutes

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

Frequently asked questions

What is Wrangellia terrane in simple terms?

Why does Wrangellia terrane 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 Wrangellia 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 Wrangellia terrane.