A multicomponent Isabella anomaly: Resolving the physical state of the Sierra Nevada upper mantle from Vp/Ns anisotropy tomography
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A multicomponent Isabella anomaly: Resolving the physical state of the Sierra Nevada upper mantle from Vp/Ns anisotropy tomography
  • Published Date:

    2019

  • Source:
    Geosphere ; 15 (6): 2018–2042.
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A multicomponent Isabella anomaly: Resolving the physical state of the Sierra Nevada upper mantle from Vp/Ns anisotropy tomography
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  • Description:
    The Isabella anomaly, a prominent upper-mantle high-speed P-wave anomaly located within the southern Great Valley and southwestern foothills of the Sierra Nevada, has been interpreted either as foundering sub-Sierran lithosphere or as remnant oceanic lithosphere. We used Vp/Vs anisotropy tomography to distinguish among the probable origins of the Isabella anomaly. S waveforms were rotated into the Sierran SKSFast and SKSSlow directions determined from SKS-splitting studies. Teleseismic P-, SFast-, SSlow-, SKSFast-, and SKSSlow-wave arrival times were then inverted to obtain three-dimensional (3-D) perturbations in Vp, Vp/VsMean, and percent azimuthal anisotropy using three surface wave 3-D starting models and one one-dimensional (1-D) model. We observed the highest Vp/Vs anomalies associated with slower velocities in regions marked by young volcanism, with the largest of these anomalies being the Mono anomaly under the Long Valley region, which extends to depths of at least 75 km. Peak Vp/Vs perturbations of +4% were found at 40 km depth. The low velocities and high Vp/Vs values of this anomaly could be related to partial melt.
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