Tectonic Settings of NPS Sites—Master List

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block diagram of horst and graben

Divergent Plate Boundaries

Almost all the Earth’s new crust forms at divergent boundaries, but most are not well known because they lie deep beneath the oceans. These are zones where two plates move away from each other, allowing magma from the mantle to rise up and solidify as new crust. When divergent motion occurs beneath a continental plate, rift structures and normal faults form.

Continental Rifts—Active

Continental Rifts—Ancient

Passive Continental Margins—Modern

Passive Continental Margins—Ancient

diagram of convergent plates

Convergent Plate Boundaries

The way that plates behave when they collide depends mostly on what type of lithosphere they are made of. In oceanic-contentental subduction, the oceanic plate is pulled beneath another, forming a deep trench. The long, narrow zone where the two plates meet is called a subduction zone. In continental-continental plate collision, the crusts are pushed together and faulted forming towering mountain ranges.

Subduction Zones—Active

Accreted Terranes

Subduction Zones—Ancient

Collisional Mountain Ranges—Appalachain-Ouachita-Marathon

Collisional Mountain Ranges—Northern Alaska

block diagram of transform fault

Transform Plate Boundaries

At transform plate boundaries plates grind past each other side by side. This type of boundary separates the North American plate from the Pacific plate along the San Andreas fault, a famous transform plate boundary that’s responsible for many of California’s earthquakes.

Continental

Oceanic

diagram of a hotspot

Hotspots

A hotspot is area of concentrated heat in the mantle that produces magma that rises to the Earth’s surface to form volcanic features. The volcanic activity of the Hawaiian Islands is one example. Hotspots may persist for millions of years.

Continental Hotspot

Oceanic Hotspot

diagram of accreted terrains

Growth of the North American Continent

A craton is the relatively stable nucleus of a continent. Cratons are made up of a shield-like core of Precambrian Rock and a buried extension of the shield. Accreted terrains are portions of crust that are too thick and buoyant to be subducted which are "scraped off" and become added to the over-riding tectonic plate along a convergent (collisional) plate boundary.

Continental Craton

Deformed Continental Craton

Accreted Terrains

Site Index & Credits

Plate Tectonics and Our National Parks (2020)

  • Text and Illustrations by Robert J. Lillie, Emeritus Professor of Geosciences, Oregon State University [E-mail]

  • Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute.

Last updated: October 9, 2020

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