Pacific-Farallon Ridge

The Pacific-Farallon Ridge was a spreading ridge during the late Cretaceous that extended 10,000 km in length and separated the Pacific Plate to the west and the Farallon Plate to the east. It ran south from the Pacific-Farallon-Kula triple junction at 51°N to the Pacific-Farallon-Antarctic triple junction at 43°S.[1] As the Farallon Plate subducted obliquely under the North American Plate, the Pacific-Farallon Ridge approached and eventually made contact with the North American Plate about 30 million years ago.[2] On average, this ridge had an equatorial spreading rate of 13.5 cm per year until its eventual collision with the North American Plate. In present day, the Pacific-Farallon Ridge no longer formally exists since the Farallon Plate has been broken up or subducted beneath the North American Plate, and the ridge has segmented, having been mostly subducted as well. The most notable remnant of the Pacific-Farallon Ridge is the 4000 km Pacific-Nazca segment of the East Pacific Rise.[3]

North America subduction1
Relative velocity vectors of Pacific, Farallon, and Kula plates 55 million years ago


As a spreading ridge, the Pacific-Farallon Ridge was a divergent plate boundary, which is where the two plates are moving away from each other. Partial mantle melting occurs beneath such ridges, which forms new oceanic crust. The Pacific-Farallon Ridge was thought to be a particularly productive spreading ridge, and there are estimates that the ridge and its remnants have formed up to 45% of all oceanic lithosphere since 83 million years ago.[4] The spreading rate of the Pacific-Farallon Ridge has varied throughout its lifetime with an acceleration of its spreading rate occurring 55 to 48 million years ago, around the same time that a significant portion of the Farallon Plate broke to form the Vancouver Plate.[5] The spreading rate decreased once the ridge made contact with the North American Plate 16 million years ago.[6]

Geologic history

San Andreas Fault Sequential Diagrams
Formation of the Juan de Fuca (including Explorer and Gorda) and Cocos plates (including Rivera) and of the San Andreas Fault from the Farallon plate

As the Farallon Plate made contact with the North American Plate and began subducting beneath it, it fragmented into the Juan de Fuca Plate and Cocos Plate, and then later fragmented further to form the Rivera Plate.[7] Once the Pacific-Farallon Ridge began subducting beneath the North American Plate, the remains of the Farallon Plate broke apart to form the Monterey, Arguello, Magdalena, and Guadelupe Microplates, and the southern portion of the ridge rotated in a clockwise manner.[8] The contact of the ridge with North America marked a transition of the Pacific-Farallon Ridge from being a globally oriented spreading ridge system to a locally oriented one. The distinction between these systems is that slab pull and gravitational gliding forces determine the characteristics of the globally oriented whereas those of the locally oriented are influenced by the contact of the ridge with the North American Plate.[9]

As the Pacific-Farallon Ridge began its subduction underneath the North American plate 30 million years ago, its southern segment, the East Pacific Rise continued spreading. The East Pacific Rise did not begin its subduction under the North American Plate until 20 million years ago, and the presently surviving portion of the East Pacific Rise is the Pacific-Nazca segment. The present-day spreading from the East Pacific Rise dominates the spreading regime in the Central and South Pacific.[10]

See also


  1. ^ The Solid Earth
  2. ^ MacLeod, C. J.; Tyler, Paul A.; Walker, C. L. (228). Tectonic, Magmatic, Hydrothermal and Biological Segmentation of Mid-ocean Ridges. Geological Society of London. ISBN 9781897799727.
  3. ^ HANDSCHUMACHER, David (2013). "Post-Eocene Plate Tectonics of the Eastern Pacific". The Geophysics of the Pacific Ocean Basin and its Margin. Geophysical Monograph Series. pp. 177–202. doi:10.1029/GM019p0177. ISBN 9781118663592.
  4. ^ Rowan, Chris (May 2014). "New Paper: Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma".
  5. ^ Rowan, Christopher; Rowley, David (June 2014). "Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma". Geophysical Journal International. 197 (3): 1273–1283. doi:10.1093/gji/ggu056.
  6. ^ Till, Alison B.; Yount, M. E.; Riehle, J. R. (1993). U.S. Geological Survey Bulletin. U.S. Government Printing Office.
  7. ^ "Farallon Plate [This Dynamic Earth, USGS]". USGS.
  8. ^ Bartolomeo, Eleanor; Longinotti, Nicole. "Chapter 2 Tectonic history of the Transverse Ranges: Rotation and deformation on the plate boundary" (PDF). Cite journal requires |journal= (help)
  9. ^ Bohannon, Robert; Parsons, Tom. "Tectonic implications of post–30 Ma Pacific and North American relative plate motions" (PDF). Cite journal requires |journal= (help)
  10. ^ "Plate Tectonics". Ocean Oasis.

Farallon (Farallón meaning cliff in the Spanish Language) may refer to:

Farallon Capital, American capital management firm

Farallon Computing later known as Netopia, known for PhoneNet networking and Timbuktu (software)

Farallon de Medinilla, small island in the Northern Mariana Islands chain

Farallon de Pajaros (Birds Rock), the northernmost island in the Northern Mariana Islands chain

Farallon de Torres, a former name of Zealandia Bank in the Northern Mariana Islands chain

Farallon Island Light, lighthouse on Southeast Farallon Island, California

Farallon Islands, group of islands and rocks in the Gulf of the Farallones, off the coast of San Francisco, California, USA

Farallon Plate, ancient oceanic plate

Farallon Steamship Disaster, wooden steamship hit Black Reef in the Farallon Islands in 1910 and sank in Alaska

Farallon Trench, ancient oceanic trench on the west coast of North America during the Late Cretaceous period

Kula-Farallon Ridge, ancient mid-ocean ridge between the Kula and Farallon plates in the Pacific Ocean during the Jurassic period

Pacific-Farallon Ridge, former mid-ocean ridge between the Pacific and Farallon plates in the Pacific Ocean during the Tertiary period

Farallon (island), Panama

Farallon Plate

The Farallon Plate was an ancient oceanic plate that began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic period. It is named for the Farallon Islands, which are located just west of San Francisco, California.

Over time, the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate. The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate.The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate.

These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.

Geology of the Pacific Ocean

The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than 2.5 cm/year (1 in/year), while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/year (6 in/year).

Gorda Ridge

The Gorda Ridge (41°36'19.6"N 127°22'03.1"W), a tectonic spreading center, is located roughly 200 kilometres (120 mi) off the northern coast of California and southern Oregon. Running NE – SW it is roughly 300 kilometres (190 mi) in length. The ridge is broken into three segments; the northern ridge, central ridge, and the southern ridge, which contains the Escanaba Trough.

Juan de Fuca Ridge

The Juan de Fuca Ridge is a mid-ocean spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America. The ridge separates the Pacific Plate to the west and the Juan de Fuca Plate to the east. It runs generally northward, with a length of approximately 500 kilometers (300 miles). The ridge is a section of what remains from the larger Pacific-Farallon Ridge which used to be the primary spreading center of this region, driving the Farallon Plate underneath the North American Plate through the process of plate tectonics. Today, the Juan de Fuca Ridge pushes the Juan de Fuca Plate underneath the North American plate, forming the Cascadia Subduction Zone.

Mid-Pacific Mountains

The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plate and rises up to 2 km (1.2 mi) (Darwin Rise) above the surrounding ocean floor and is covered with several layers of thick sedimentary sequences that differ from those of other plateaux in the North Pacific. About 50 seamounts are distributed over the MPM. Some of the highest points in the range are above sea level which include Wake Island and Marcus Island.

The ocean floor of the MPM dates back to the Jurassic-Cretaceous, some of the oldest oceanic crust on Earth.The MPM is a range of guyots with a lava composition similar to those found in Iceland and the Galapagos Islands, and they probably formed similarly at or near a rift system.

In the Cretaceous, they formed large tropical islands located closer to the Equator that began to sink in the late Mesozoic.The MPM formed in the Early Cretaceous (at c. 110 Ma) over a hotspot that uplifted the ocean floor of the still young Pacific Plate. Reefs developed on the subsiding islands and renewed volcanism in the Late Cretaceous helped maintain some of eastern islands but inevitably the guyots sank to their present depth.

It has been proposed that the MPM has crossed over several hotspots, and the MPM guyots are indeed older on the western MPM than the eastern part, but the guyots do not form chains that can be traced to any known hotspots. The MPM, nevertheless, must have originated over the South Pacific Superswell. Among the guyots in the Mid-Pacific Mountains are Allison Guyot, Horizon Guyot, Resolution Guyot and Darwin Guyot.The western half of the Easter hotspot chain, a lineament that includes the Line Islands and Tuamotu archipelago, begins near the eastern part of the MPM. The formation of the MPM thus probably occurred at the Pacific-Farallon Ridge and the Easter hotspot, or where the Easter Microplate is now located.

Mid-ocean ridge

A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of ~ 2,600 meters (8,500 ft) and rises about two kilometers above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness in the oceanic crust, and emerges as lava, creating new crust and lithosphere upon cooling. The Mid-Atlantic Ridge is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are called mid-ocean ridges. Mid-ocean ridges around the globe are linked by plate tectonic boundaries and the outline of the ridges across the ocean floor appears similar to the seam of a baseball. The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi).

Outline of oceanography

The following outline is provided as an overview of and introduction to Oceanography.

Outline of plate tectonics

This is a list of articles related to plate tectonics and tectonic plates.

Pacific-Kula Ridge

The Pacific-Kula Ridge is a former mid-ocean ridge that existed between the Pacific and Kula plates in the Pacific Ocean during the Paleogene period. Its appearance was in an east-west direction and the Hawaiian-Emperor seamount chain had its attribution with the ridge. The Pacific-Kula Ridge lay south of the Hawaii hotspot around 80 million years ago, moving northward relative to the hotspot.



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