Tomographic Imaging of the Upper Mantle beneath the Colorado Rocky Mountains from Simultaneous Joint Inversion of Teleseismic Body Wave Residuals and Bouguer Gravity
MACCARTHY, J.K., New Mexico Tech, Socorro, NM, firstname.lastname@example.org; ASTER, R.C., New Mexico Tech., Socorro, NM, email@example.com; HANSEN, S.M., University of Wyoming, Laramie, WY, firstname.lastname@example.org; DUEKER, K.G., University of Wyoming, Laramie, WY, email@example.com
We report on the 3D velocity structure of the uppermost mantle beneath the Colorado Rockies, derived from teleseismic travel time residuals and ground-based Bouguer gravity data. The CREST seismic network consisted of 59 broadband PASSCAL stations deployed in the central Colorado Rocky Mountains for ~15 months in 2008 and 2009. CREST was embedded in the time-coincident EarthScope Transportable Array (TA), producing a composite network of 167 stations with a mean spacing of ~24 km. An iterative nonlinear inversion is employed, where an assumed coupling relation that links the seismic and gravity data sets is encoded into the minimized objective function. We explore multiple data coupling relations and weighting schemes in order to evaluate the resolving power of the simultaneous joint inversion, and we apply the method toward inverting for a model of 3D velocity structure beneath the Colorado Rockies. Competing models for the anomaly are: 1) upwelling asthenosphere associated with flat-slab roll-back, 2) Laramide thickening and hydraulic weakening of lower lithosphere that promoted subsequent Rayleigh-Taylor instabilities of the lower lithosphere that are flanked by thinned lithosphere, 3) compositional variations due to hydration and or low-solidus material, and 4) a mini-plume or water pipe diapirs shed upwards from the 410 km low velocity zone.