Crustal structure and evolution beneath the Colorado Plateau and the southern Basin and Range Province: Results from receiver function and gravity studies

Abstract

[1] Over the past several decades, contrasting models have been proposed for the physical and chemical processes responsible for the uplift and long-term stability of the Colorado Plateau (CP) and crustal thinning beneath the Basin and Range Province (BRP) in the southwestern United States. Here we provide new constraints on the models by modeling gravity anomalies and by systematically analyzing over 15,500 P-to-S receiver functions recorded at 72 USArray and other broadband seismic stations on the southwestern CP and the southern BRP. Our results reveal that the BRP is characterized by a thin crust (28.2 ± 0.5 km), a mean V p /V s of 1.761 ± 0.014 and a mean amplitude (R) of P-to-S converted wave (relative to that of the direct P wave) of 0.181 ± 0.014 that are similar to a typical continental crust, consistent with the model that the thin crust was the consequence of lithospheric stretching during the Cenozoic. The CP is characterized by the thickest crust (42.3 ± 0.8 km), largest V p /V s (1.825 ± 0.009) and smallest R (0.105 ± 0.007) values in the study area. In addition, many stations on the CP exhibit a clear arrival before the P-to-S converted phase from the Moho, corresponding to a lower crustal layer of about 12 km thick with a mafic composition. We hypothesize that the lower crustal layer, which has an anomalously large density as revealed by gravity modeling and high velocities in seismic refraction lines, contributed to the long-term stability and preuplift low elevation of the Colorado Plateau.

Physical State and Structure of the Crust Beneath the Western‐Central United States From Multiobservable Probabilistic Inversion

“…As another example, our estimates of crustal thickness are in excellent agreement with those obtained by Frassetto et al () in the CP. Likewise, our estimates beneath stations shown in Figure a (except for R17A) agree closely with the crustal thicknesses calculated by Bashir et al (). Finally, the general pattern of our crustal thickness map is similar to that estimated by Purevsuren (), particularly in the western margins of the CP where a thick crust (∼50 km) was reported by this author.…”

“…Despite some localized differences (e.g., near the Kaibab uplift, west of the Grand Canyon), the overall pattern of crustal thickness derived here is similar to that reported in numerous previous studies (e.g., Bashir et al, ; Frassetto et al, ; Gilbert & Sheehan, ; Gilbert et al, ; Gilbert, ; Hansen et al, ; Lowry & Pérez‐Gussinyé, ; Prodehl & Pakiser, ; Purevsuren, ; Sheehan et al, ; Shen et al, ; Velasco, ; Zandt et al, ), pointing towards a general agreement for the region. For example, thick crust (∼>46 km) found beneath the SRM (e.g., Bailey et al, ; Gilbert & Sheehan, ; Gilbert, ; Prodehl & Pakiser, ; Shen et al, ; Shen et al, ; Shen & Ritzwoller, ) is broadly consistent with our results.…”

“…The main aim of this work is to provide further constraints on the physical state and structure of the crust beneath western‐central United States and to use this information to elucidate evolutionary models and test hypotheses regarding the present‐day topography of the region. Although the focus is on the SRM and the GP, the crustal structure across the CP and surroundings, where some inconsistencies exist concerning their crustal structure (Bailey et al, ; Bashir et al, ; Frassetto et al, ; Gilbert & Sheehan, ; Gilbert, ; Hansen et al, ; Karlstrom et al, ; Liu et al, ; Lowry & Pérez‐Gussinyé, ; Parsons et al, ; Sheehan et al, ; Shen et al, ; Zandt et al, ), is also addressed. We take advantage of complimentary data sets to provide robust models of the temperature, density, and seismic structure of the crust at a nominal resolution of 1 degree.…”

Receiver function constraints on crustal seismic velocities and partial melting beneath the Red Sea rift and adjacent regions, Afar Depression

“…In addition, the pre-melt V p and values used in Watanabe [1993] are comparable with typical V p values used for RF stacking and the resulting values beneath continental areas such as the Limpopo belt in southern Africa [Nair et al, 2006] and the Colorado Plateau and the Basin and Range Province in North America [Bashir et al, 2011].…”

Analysis of Seismic Activity near Theodore Roosevelt Dam, Arizona, during the Occupation of the EarthScope/USArray Transportable Array

“…1). A range of datasets, including crustal structure and thickness, stress orientations, volcanism, seismicity, heat flow, and gravity, suggest that the ATZ represents a tectonic transition between the thick and relatively stable crust of the CP and the thin and highly-extended crust of the southern B&R (Brumbaugh, 1987;Hendricks and Plescia, 1991;Thompson and Zoback, 1979;Frassetto et al, 2006;Bashir et al, 2011;Gilbert, 2012). However, these transitions do not strictly occur along the physiographic boundaries, and the tectonic evolution of the region remains enigmatic (e.g., Menges and Pearthree, 1989).…”