z-logo
Premium
Plate deformation at depth under northern California: Slab gap or stretched slab?
Author(s) -
ten Brink Uri S.,
Shimizu Nobumichi,
Molzer Philipp C.
Publication year - 1999
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/1999tc900050
Subject(s) - geology , slab , slab window , subduction , lithosphere , upwelling , triple junction , plate tectonics , geothermal gradient , north american plate , convergent boundary , seismology , oceanic crust , geophysics , tectonics , oceanography
Plate kinematic interpretations for northern California predict a gap in the underlying subducted slab caused by the northward migration of the Pacific‐North America‐Juan de Fuca triple junction. However, large‐scale decompression melting and asthenospheric upwelling to the base of the overlying plate within the postulated gap are not supported by geophysical and geochemical observations. We suggest a model for the interaction between the three plates which is compatible with the observations. In this “slab stretch” model the Juan de Fuca plate under coastal northern California deforms by stretching and thinning to fill the geometrical gap formed in the wake of the northward migrating Mendocino triple junction. The stretching is in response to boundary forces acting on the plate. The thinning results in an elevated geothermal gradient, which may be roughly equivalent to a 4 Ma oceanic lithosphere, still much cooler than that inferred by the slab gap model. We show that reequilibration of this geothermal gradient under 20–30 km thick overlying plate can explain the minor Neogene volcanic activity, its chemical composition, and the heat flow. In contrast to northern California, geochemical and geophysical consequences of a “true” slab gap can be observed in the California Inner Continental Borderland offshore Los Angeles, where local asthenospheric upwelling probably took place during the Miocene as a result of horizontal extension and rotation of the overlying plate. The elevated heat flow in central California can be explained by thermal reequilibration of the stalled Monterey microplate under the Coast Ranges, rather than by a slab gap or viscous shear heating in the mantle.

This content is not available in your region!

Continue researching here.

Having issues? You can contact us here