Lithosphere-asthenosphere interaction beneath the western United States from the joint inversion of body-wave traveltimes and surface-wave phase velocities

Abstract

S U M M A R YThe relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surfacewave tomography (ballistic waves and noise correlations) informs us on the shallow structure.Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E-W extent of the USArray used in this study allows imaging the 'slab graveyard', a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

A rootless rockies—Support and lithospheric structure of the Colorado Rocky Mountains inferred from CREST and TA seismic data

“…[e.g., Schmandt and Humphreys, 2010;Obrebski et al, 2011]. However, the coarse 70 km station spacing is suboptimal for the purpose of scattered wave imaging, and the TA has been generally unable to provide robust high-resolution images above $200 km depth, leaving key questions about the evolution and lithospheric structure of the continent unresolved.…”

Interstation phase speed and amplitude measurements of surface waves with nonlinear waveform fitting: application to USArray

“…Shapiro et al 2005;Lin & Ritzwoller 2011;Obrebski et al 2011). This area encompasses a variety of complex tectonic features, including regions with eastwest extension, active volcanoes, the organic belt including Rocky Mountains and the stable cratonic region (Fig.…”

“…Shapiro et al 2005;Ekström et al 2009), body-wave tomography (e.g. Burdick et al 2010), higher-mode phase speed mapping of surface waves (Yoshizawa & Ekström 2010) and joint tomography of body and surface waves (Obrebski et al 2011).…”

Sn propagation in the Western United States from common midpoint stacks of USArray data

“…The estimates by Levander and Miller [2012] are lower at 90 km but still significantly deeper compared to their measured LAB depth of 65 km below the Basin and Range. In addition, Obrebski et al [2011] noted that their observation of high shear velocities might be consistent with a stable and relatively thick lithosphere for the northeastern part of the Colorado Plateau.…”

“…Tomographic images from body and surface wave data show very heterogeneous velocity structure in the upper mantle in the Western United States [e.g., Lin et al, 2011;Obrebski et al, 2011;Schmandt and Humphreys, 2010]. Prominent local low-velocity anomalies imaged below the Snake River Plain and the southwestern Colorado Plateau likely reflect higher temperatures due to volcanism.…”