geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

, a slab window is a gap that forms in a

subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

oceanic plate when a mid-ocean ridge meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted.Thorkelson, Derek J., 1996, Subduction of diverging plates and the principles of slab window formation, '' Tectonophysics'', v. 255, p. 47-63 Formation of a slab window produces an area where the crust of the over-riding plate is lacking a rigid lithospheric mantle component and thus is exposed to hot asthenospheric mantle (for a diagram of this, see the link below). This produces anomalous thermal, chemical and physical effects in the mantle that can dramatically change the over-riding plate by interrupting the established tectonic and magmatic regimes. In general, the data used to identify possible slab windows comes from

seismic tomography Seismic tomography or seismotomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on ...

and heat flow studies.van Wijk, J.W., Govers, R., Furlong, K.P., 2001, Three-dimensional thermal modeling of the California upper mantle: a slab window vs. stalled slab, ''Earth and Planetary Letters'', v. 186, p. 175-186

Effects

As a slab window develops, the mantle in that region becomes increasingly hot and dry. The decrease in hydration causes arc volcanism to diminish or stop entirely, as magma production in subduction zones generally results from hydration of the mantle wedge due to de-watering of the subducting slab. Slab-window magmatism may then replace this melting, and can be produced by multiple processes, including increased temperatures, mantle circulation producing interaction of supra- and sub-slab mantle, partial melting of subducted slab edges and extension in the upper plate. Mantle flowing upward through the slab window in order to compensate for the decreased lithospheric volume can also produce decompression melting. Slab window melts are distinguished from calc-alkaline subduction-related magmas by their different chemical compositions. The increase in temperature caused by the presence of a slab window can also produce anomalous high temperature metamorphism in the region between the trench and the volcanic arc.Groome, Wesley G., Thorkelson, Derek J., 2009, The three-dimensional thermo-mechanical signature of ridge subduction and slab window migration: Tectonophysics v. 464, p. 70-83

Geometry

The geometry of a slab window depends primarily on the angle the ridge intersects the subduction zone and the dip angle of the down-going plate. Other influential factors include the rates of divergence and subduction as well as heterogeneities found within specific systems. There are two end-member scenarios in terms of the geometry of a slab window: the first is when the subducted ridge is perpendicular to the trench, producing a V-shaped window, and the second is when the ridge is parallel to the trench, causing a rectangular window to form. Guillaume, Benjamin et al. 2010, mantle flow and dynamic topography associated with slab window openings: Insights from laboratory models: Tectonophysics v. 496, p. 83-98

Examples

The

North American Cordillera The North American Cordillera, sometimes also called the Western Cordillera of North America, the Western Cordillera or the Pacific Cordillera, is the North American portion of the American Cordillera, the mountain chain system (cordillera) alon ...

is a well-studied plate margin that provides a good example of the effects a slab window can have on an over-riding continental plate. Beginning in the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

, the fragmentation of the Farallon Plate as it subducted caused slab windows to open that then generated anomalous features in the North American Plate. These effects include distinct fore-arc volcanism and extension in the plate which may be a contributing factor to the formation of the Basin and Range Province. The northward younging of Pemberton Belt volcanism in southwestern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...

may have been related to a northward moving slab window edge under North America 29 to 6.8 million years ago. In addition to the fossil slab windows of the Cenozoic seen in North America, there are other regions along the

Pacific Rim The Pacific Rim comprises the lands around the rim of the Pacific Ocean. The ''Pacific Basin'' includes the Pacific Rim and the islands in the Pacific Ocean. The Pacific Rim roughly overlaps with the geologic Pacific Ring of Fire. List of co ...

(e.g. in California, Mexico, Costa Rica, Patagonia and the Antarctic Peninsula) that exhibit active ridge subduction producing slab windows. McCrory, P.A., Wilson, D.S., Stanley, R.G., 20 January 2009
"Continuing evolution of the Pacific-Juan de Fuca-North America slab window system - A trench-ridge-transform example from the Pacific Rim"
''Tectonophysics'' vol. 464, issues 1–4, pp. 30–42. .

References

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External links

Schematic diagram of a slab window and related effects
GSA publications

University of Colorado Western US Tectonics term project Geological processes Plate tectonics Subduction

Effects

Geometry

Examples

See also

References

External links