Geodynamics of the Gulf of California from surface wave tomography
article
The Gulf of California, which forms part of the Pacific-North American plate boundary, is an ideal place to investigate upper mantle dynamics in a continental rifting area. With 19 seismic stations located around the gulf, the NARS-Baja experiment (2002-2008) was designed to image its crustal and mantle structure. Here we present results of a tomographic inversion of Love and Rayleigh interstation phase velocity measurements for a radially anisotropic shear velocity model of the Gulf of California. This study confirms the overall low shear-wave velocities in the upper 200km of the mantle found in other Rayleigh wave studies, and the presence of a positive shear-wave velocity anomaly at depths of roughly 80-160km beneath the central gulf (Zhang et al., 2009). In addition, we find that the horizontal shear velocity (VSH) is generally higher than the vertical shear velocity (VSV). For the northern gulf, however, there is strong indication for VSV>VSH in the 40-60km depth range. This region also has anomalously low shear-wave velocities down to 100km depth. Combining these observations, we suggest that the low velocity anomaly and the negative radial anisotropy (VSH<VSV) beneath the northern gulf are related to vertical flow of low velocity material in an area of a slab window, either by the vertical alignment of olivine crystals or by a fabric of vertically oriented sheets of melt. The high-velocity anomaly beneath the central gulf is interpreted as a remnant slab fragment which inhibits vertical flow from the deeper mantle. Our tomographic results indicate that the formation of the Gulf of California cannot be explained by simple models of crustal extension or dynamic upwelling. Instead, its structure and geodynamics are caused by the cessation of subduction by stalled microplates in the central and southern gulf and the presence of a slab window in the north. © 2012 Elsevier B.V.
Topics
Gulf of CaliforniaRadial anisotropySurface wavesTomographyContinental riftingCrustal extensionDepth rangeGulf of CaliforniaHigh velocityHorizontal shearLow velocitiesLow-velocity anomalyMantle structureMicroplatesOlivine crystalsPlate boundariesRadial anisotropyRadially anisotropicRayleighSeismic stationShear velocity modelsShear-wave velocitySlab windowsSurface-wave tomographyTomographicTomographic inversionUpper mantleVertical alignmentVertical flowsVertical shearAnisotropyOlivineShear wavesSurface wavesTectonicsTomographyGeodynamicscrustal structuregeodynamicsmantle structuremicroplateNorth American platePacific plateplate boundaryRayleigh waveriftingS-waveseismic anisotropyseismic tomographyslabsubductionsurface waveupper mantlewave velocityGulf of CaliforniaPacific OceanVesicular stomatitis virus
TNO Identifier
461836
ISSN
00319201
Source
Physics of the Earth and Planetary Interiors, 192-193, pp. 59-67.
Pages
59-67
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