What tectonic produced the Olympic Peninsula, Mt. Rainier, and deep “implosion” earthquakes?

Question

BlackTom AI · Accepted Answer

Because the Juan de Fuca plate is being forced beneath the North American plate, the region is governed by compressional subduction—i.e., "push-together subduction."

1) Relevant concepts: subduction zones occur where one oceanic plate sinks beneath another plate, producing (a) an accretionary prism and uplift (mountain building), (b) flux melting of the mantle wedge that feeds stratovolcanoes, and (c) a Wadati‑Benioff zone of shallow-to-deep earthquakes within the descending slab. Deep "implosion" earthquakes are characteristic of stressed, sinking slabs where metamorphic phase changes and transformational faulting generate seismicity down to ~700 km.

2) Step-by-step reasoning:
- Identify regional plates: the Juan de Fuca plate is subducting eastward beneath the North American plate off the Washington coast.
- Uplift: Compression and accretion along the plate boundary build the Olympic Peninsula (accreted sediments and uplifted material).
- Volcanism: Water released from the subducting slab lowers the melting point of overlying mantle, producing magma that rises to form the Cascade stratovolcanoes, including Mt. Rainier.
- Deep earthquakes: The descending slab produces intermediate to deep seismicity (Wadati‑Benioff zone); at depth brittle failure is replaced by transformational faulting or "implosion" style quakes as minerals reorganize under high pressure.

3) Intermediate steps / mechanisms: subduction → dehydration → mantle melting → andesitic magmas → stratovolcanoes; subduction → slab flexure + phase changes → deep seismicity.

4) Why the correct answer is correct: All three phenomena (Olympic uplift, Cascade volcanoes, deep slab earthquakes) are direct consequences of compressive subduction—hence "push-together subduction."

5) Why other choices are incorrect:
- Push-together obduction: obduction places oceanic crust onto continents, not the dominant process here.
- Pull-apart: extensional rifting produces basins, not uplifted peninsulas and arc volcanism.
- Slide-past: transform faults (slide-past) cause lateral shear, not deep slab earthquakes or arc volcanoes.
- Hot-spot: intraplate hot spots produce volcanism without a Wadati‑Benioff zone or accretionary uplift.

Conclusion: The correct answer is "Push-together subduction," matching the provided answer.

What tectonic produced the Olympic Peninsula, Mt. Rainier, and deep “implosion” earthquakes? 单项选择题

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