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Published March 1969 | Published
Journal Article Open

La zona de baja velocidad; The Low Velocity Zone


The low velocity zone in tectonic and oceanic regions is too pronounced to be the effect of high temperature gradients alone. Partial melting is consistent with the low velocity, low Q and abrupt boundaries of this region of the upper mantle and is also consistent with measured heat flow values. The inferred low melting temperatures seem to indicate that the water pressure is sufficiently high to lower the solidus about 200° C to 400° C below laboratory determinations of the melting point of anhydrous silicates. The mechanical instability of a partially molten layer in the upper mantle is probably an important source of tectonic energy. The top of the low-velocity zone can be considered a self-lubricated surface upon which the top of the mantle and the crust can slide with very little friction. Lateral motion of the crust and upper mantle away from oceanic rises is counterbalanced by the flow of molten material in the low-velocity layer toward the rise where it eventually emerges as new crust. If this lateral flow of molten material is not as efficient as the upward removal of magma, the regions of extrusion, such as oceanic rises, will migrate.

Additional Information

© 1969 Union Geofisica Mexicana. Monograph title Pan American symposium on the upper mantle, Mexico, D.F., 1969 Group 5, Seismology. This research was partially supported by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR contract number AF-49(638)-1337, and National Science Foundation grant GA 1003.

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