North American Plate

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The North American Plate is a tectonic plate covering most of North America, extending eastward to the Mid-Atlantic Ridge and westward to the Cherskiy Range in East Siberia. The plate includes both continental and oceanic crust. The interior of the main continental landmass includes an extensive granitic core called a craton. Along most of the edges of this craton are fragments of crustal material called terranes, accreted to the craton by tectonic actions over the long span of geologic time. It is believed that much of North America west of the Rockies is composed of such terranes.

The easterly side of the North American Plate is a divergent boundary with the Eurasian Plate to the north and the African Plate to the south forming the northern part of the Mid-Atlantic Ridge. The southerly side is a boundary with the Cocos Plate to the west and the Caribbean Plate to the east. The westerly side is a convergent boundary with the subducting Juan de Fuca Plate to the north and a transform boundary with the Pacific Plate to the south along the San Andreas Fault. On the northerly side is a continuation of the Mid-Atlantic ridge, here called the Mid-Arctic Ridge.

On its western edge the Farallon Plate has been subducting under the North American Plate since the Jurassic period. The Farallon Plate has almost completely subducted beneath the western portion of the North American Plate leaving that part of the North American Plate in contact with the Pacific Plate as the San Andreas Fault. The Juan de Fuca, Cocos, and Nazca Plates are remnants of the Farallon Plate.

The boundary along the Gulf of California has not yet been clearly described and research is ongoing. The Gulf is underlain by the northern end of the East Pacific Rise. West of the Rise is the Pacific Plate. East of the Rise, most tectonic maps show the North American Plate. It is generally accepted that a piece of the North American Plate was broken off and transported north as the East Pacific Rise propagated northward, creating the Gulf of California. The block which broke off is known geologically as the Salinian Block. However, it is as yet unclear whether the oceanic crust east of the Rise and west of the mainland coast of Mexico is actually a new plate beginning to converge with the North American Plate, consistent with the standard model of rift zone spreading centers generally.

Plate motion

For the most part, the North American Plate moves in roughly a southwest direction away from the Mid-Atlantic Ridge. The motion of the plate cannot be driven by subduction as no part of the North American Plate is being subducted, thus other mechanisms continue to be investigated. One recent study suggests that a mantle convective current is propelling the plate.

See also

• Geologic timeline of Western North America

References

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Last updated on Thursday March 13, 2008 at 15:29:23 PDT (GMT -0700)
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