Slab pull
Encyclopedia
The Slab pull force is a tectonic plate force due to subduction. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle
at trench
es. This force and the slab suction force account for most of the overall force acting on plate tectonics
, and the ridge push force accounts for 5 to 10% of the overall force.
Carlson et al. (1983) in Lallemandet al. (2005) defines the slab
pull force as:
Where the constant K is set to 4.2 times g (gravitational acceleration = 9.81 ms−2) according to McNutt (1984), Δρ = 80 kg.m−3 is the mean density difference between the slab and the surrounding asthenosphere, L is the slab length calculated only for the part above 670 km (Upper-lower mantle boundary), and A being the slab age in Ma at the trench.
The slab pull force manifests itself between two extreme forms:
Between these two examples there is the evolution of the Farallon plate
: from the huge slab width with the Nevada, the Sevier
and Laramide orogenies
; the Mid-Tertiary ignimbrite flare-up
and later left as Juan de Fuca
and Cocos
plates, the Basin and Range Province under extension, with slab break off, smaller slab width, more edges and mantle
return flow.
Some early models of plate tectonics
envisioned the plates riding on top of convection cells like conveyor belt
s. However, most scientists working today believe that the asthenosphere
does not directly cause motion by the friction
of such basal forces. The North American Plate
, is nowhere being subducted
, yet it is in motion. Likewise the African
, Eurasian
and Antarctic Plate
s. The subducting slabs around the Pacific Ring of Fire
cool down the Earth and its Core-mantle boundary
, around the African Plate the upwelling mantle plumes from the Core-mantle boundary produce rifting. The overall driving force for plate motion and its energy source remain subjects of ongoing research.
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
at trench
Trench
A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide , and by being narrow compared to their length ....
es. This force and the slab suction force account for most of the overall force acting on plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, and the ridge push force accounts for 5 to 10% of the overall force.
Carlson et al. (1983) in Lallemandet al. (2005) defines the slab
Slab (geology)
In geology, a slab is the portion of a tectonic plate that is being subducted.Slabs constitute an important part of the global plate tectonic system. They drive plate tectonics both by pulling along the lithosphere to which they are attached in a processes known as slab pull and by inciting...
pull force as:
- Fsp = K times Δρ times L times √A
Where the constant K is set to 4.2 times g (gravitational acceleration = 9.81 ms−2) according to McNutt (1984), Δρ = 80 kg.m−3 is the mean density difference between the slab and the surrounding asthenosphere, L is the slab length calculated only for the part above 670 km (Upper-lower mantle boundary), and A being the slab age in Ma at the trench.
The slab pull force manifests itself between two extreme forms:
- The aseismic back-arcBack-arc basinBack-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces caused by oceanic trench rollback and the...
extension as in the Izu-Bonin-Mariana ArcIzu-Bonin-Mariana ArcThe Izu-Bonin-Mariana arc system is an outstanding example of a plate tectonic convergent boundary. IBM extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, Bonin Islands, and Mariana Islands; much more of the IBM arc system is submerged below sealevel...
. - And as the AleutianAleutian ArcThe Aleutian Arc is a large volcanic arc in the U.S. state of Alaska. It consists of a number of active and dormant volcanoes that have formed as a result of subduction along the Aleutian Trench...
and Chile tectonics with strong earthquakes and back-arc thrustingThrust faultA thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
.
Between these two examples there is the evolution of the Farallon plate
Farallon Plate
The Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate— then located in modern Utah— as Pangaea broke apart during the Jurassic Period...
: from the huge slab width with the Nevada, the Sevier
Sevier orogeny
The Sevier orogeny was a mountain-building event that affected western North America from Canada to the north to Mexico to the south. This orogeny was the result of convergent boundary tectonic activity between approximately 140 million years ago and 50 Ma. The Sevier River area of central Utah...
and Laramide orogenies
Laramide orogeny
The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute, as is the cause. The Laramide...
; the Mid-Tertiary ignimbrite flare-up
Mid-Tertiary ignimbrite flare-up
The Mid-Tertiary ignimbrite flare-up, as the name implies, is a dramatic period of volcanic eruptions in mid-Tertiary time, approximately 25-40 million years ago, centered in the western United States...
and later left as Juan de Fuca
Juan de Fuca Plate
The Juan de Fuca Plate, named after the explorer of the same name, is a tectonic plate, generated from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone...
and Cocos
Cocos Plate
The Cocos Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it.-Geology:...
plates, the Basin and Range Province under extension, with slab break off, smaller slab width, more edges and mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
return flow.
Some early models of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
envisioned the plates riding on top of convection cells like conveyor belt
Conveyor belt
A conveyor belt consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley...
s. However, most scientists working today believe that the asthenosphere
Asthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...
does not directly cause motion by the friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
of such basal forces. The North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
, is nowhere being subducted
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
, yet it is in motion. Likewise the African
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...
, Eurasian
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
and Antarctic Plate
Antarctic Plate
The Antarctic Plate is a tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. The Antarctic Plate has a boundary with the Nazca Plate, the South American Plate, the African Plate, the Indo-Australian Plate, the Scotia Plate and a divergent boundary...
s. The subducting slabs around the Pacific Ring of Fire
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
cool down the Earth and its Core-mantle boundary
Core-mantle boundary
The core–mantle boundary lies between the Earth's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2900 km of depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth...
, around the African Plate the upwelling mantle plumes from the Core-mantle boundary produce rifting. The overall driving force for plate motion and its energy source remain subjects of ongoing research.