P- and S-Wave Receiver Function Images of Crustal Imbrication beneath the Cheyenne Belt in Southeast Wyoming

Abstract

We extend the receiver function deconvolution methodology of Bostock (2004) to S-wave receiver functions and develop a method of source function spectrum estimation to constrain the crustal structure across the Archean-Proterozoic Cheyenne belt suture in southeast Wyoming using data from a dense deployment of seismic stations. S-wave receiver functions are particularly useful because freesurface reverberations do not contaminated the direct S d p arrivals, and the S-wave receiver function image is able to validate our P-wave receiver function image. P-and S-wave receiver function images and a teleseismic P-wave tomogram find a structure consistent with the imbrication of Proterozoic lower crust across the Cheyenne belt. Both P and S-wave receiver function images delineate a double Moho north of the Cheyenne belt: the Archean Moho is imaged at 41-43 km depth with a deeper velocity step at 60-62 km depth. South of the Cheyenne belt, the P-wave receiver function image finds the Proterozoic Moho dipping ∼7°northwest consistent with observed back-azimuth dependent P m s amplitudes. Given the lateral continuity with the northwest dipping Proterozoic Moho, the deeper velocity step of the double Moho is interpreted as the imbricated Proterozoic Moho. Modeling of P-wave receiver function amplitudes suggests a 6:4-7:4 km=sec velocity step across the shallower Archean Moho and a 7:4-7:9 km=sec velocity step across the deeper imbricated Proterozoic Moho. We speculate that imbrication of the Proterozoic lower crust was contemporaneous with the 1.76 Ga uplift and deformation of the 50 km-wide Palmer Canyon block immediately north of the Cheyenne belt exposed in the Laramie Mountains.

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“…In areas spanning the west coast of North America to the High Plains, these studies found specifi c tectonic provinces and terranes exhibiting structures with large variations in crustal thickness and changes in seismic velocities across the Moho (e.g., Braile et al, 1989;Prodehl and Lipman, 1989;Catchings and Mooney, 1991;Snelson et al, 1998;Bostock et al, 2002;Gorman et al, 2002;Li et al, 2002;Magnani et al, 2004;Keller et al, 2005;Frassetto et al, 2006;Lerch et al, 2007;Hansen and Dueker, 2009;Buehler and Shearer, 2010;Cox and Keller, 2010;Eagar et al, 2011;Hansen et al, 2011). Data from the Transportable Array can be used to investigate the crust across extensive distances to compare and connect the observations from these previous localized studies.…”

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

“…Finally, the receiver function spectral phase is reconstructed by exploiting the minimumphase nature of the direct-component trace. The details of this methodology are presented elsewhere [Baig et al, 2005;Bostock, 2004;Mercier et al, 2006], and the application to temporary array recording and S wave data was demonstrated by Hansen and Dueker [2009]. We note several advantages afforded by this approach.…”

“…First, the source function amplitude spectrum for each event is approximated using a rough-smooth spectral separation algorithm [Hansen and Dueker, 2009]. Second, the three-component receiver function amplitude spectrum is calculated via least-squares inversion using the source spectral estimates as constraints.…”

“…, which imaged crustal thicknesses exceeding 50 km beneath the suture zone [Crosswhite and Humphreys, 2003;Hansen and Dueker, 2009;Morozova et al, 2005;Snelson et al, 1998]. …”

The nature of the Moho in Australia from reflection profiling: A review

“…For the Capricorn Orogen (10-CP3) there is clear evidence for a doubled Moho with underthrusting of the Proterozoic domain from the north. Evidence for comparable structures comes from the work of Hanson and Dueker [14] in a receiver function study across a dense array in Wyoming that is inferred to place Proterozoic material beneath Archean with a doubled Moho.…”