Images of crustal variations in the intermountain west

Abstract

[1] We develop a map of crustal thickness variations across the Great Basin, Colorado Plateau, Rocky Mountain, and Great Plains Provinces of the western United States using common conversion point stacking of teleseismic receiver functions. Below the Rocky Mountains and High Plains in Colorado we find the thickest crust in the region at 45-50 km thick. Beneath the Basin and Range, thinner, between 30 and 40 km, crust is found. Thin, 30 km thick, crust is present in the northern portion of Nevada and Utah despite elevations similar to those farther south. Crustal thickness across the Colorado Plateau can be characterized as a broad transitional region between the thin crust of Basin and Range to the thicker crust of the Rocky Mountains. The impedance contrast across the Mohorovicic discontinuity decreases below the Colorado Plateau, as converted arrivals recorded in this region appear weak compared to surrounding areas. Variations in V P /V S across the region indicate higher values along the western boundary of the Basin and Range, in the Rocky Mountains, and in the western Great Plains. We are not able to characterize V P /V S in the Colorado Plateau. We find that crustal thickness does not closely correlate with surface topography within each region or across the region as a whole. Differences in crustal thickness in each tectonic province indicate the need for a mantle component to support the high elevations across the western United States.

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

“…Gilbert and Sheehan (2004) reported the crust in the Grand Junction area as ~45 km thick and noted that there is limited acoustic impedance contrast at this level, which is consistent with a layer of mafic underplating at the base of the crust. However, Bueller & Shearer (2010) reported the crustal thickness near Grand Junction as between ~35 and ~40 km (say ~37 km) using seismic tomography.…”

“…Durrheim & Mooney, 1994;Karlstrom et _ al., 2002). More recent studies (e.g., Gilbert & Sheehan, 2004;Karlstrom et _ al., 2012) Decker, 1995, andDecker et al, 1988) but without explaining the revision; on this basis a slightly thicker mobile lower-crustal layer would be predicted. We are not aware of any measurement of the heat production in this particular borehole; however the value adopted is similar to others measured in the surrounding region (e.g., Edwards et al, 1978) and the resulting basal heat flow is within the ~34±4 mW m -2 range long considered characteristic of the Great Plains (e.g., Roy et al, 1968;Decker & Smithson, 1975).…”

The Great Basin Altiplano during the middle Cenozoic ignimbrite flareup: insights from volcanic rocks

“…Another approach to the determination of the thickness of the middle Cenozoic crust is to compensate for the amount of later extensional thinning, assuming plane strain in the EW direction and using the observed province-wide crustal thickness today of a relatively uniform 30^5 km (Allmendinger et al 1987;Mooney and Braile 1989;Gilbert and Sheehan 2004). However, estimates of the amount of whole-province extensional thinning range widely, for example, from as much as 100% (Hamilton 1989) to as little as 20-30% (Stewart 1980).…”

“…Additional data include the crustal thickness determined by geophysical methods as cited in published works. For the Andean locales, crustal thicknesses are from Hildreth and Moorbath (1988) and Allmendinger et al (1997), and for the western US, from Mooney and Braile (1989), Prodehl and Lipman (1989), and Gilbert and Sheehan (2004). Nd and Pb isotopes are not listed in Table 1 as such data are not available in many publications, especially older ones.…”

Crustal structure of the northwestern Basin and Range Province and its transition to unextended volcanic plateaus

“…The best data come from the COCORP (Consortium for Continental Reflection Profiling) 40°N deep seismic reflection profiles [e.g., Allmendinger et al, 1987;Klemperer et al, 1986] and the 1986 PASSCAL Basin and Range Lithospheric Seismic Experiment [e.g., Jarchow et al, 1993;Catchings and Mooney, 1991]. The COCORP and PASSCAL data are augmented by passive imaging of the eastern Basin and Range [Gilbert and Sheehan, 2004], refraction/ reflection imaging along the Ruby Mountains [Stoerzel and Smithson, 1998], and a coarse refraction survey across western Nevada and eastern California [Louie et al, 2004]. The crust varies in thickness from 34 km in central Nevada to $30 km at 40°N in northwestern Nevada and western Utah (Figure 1), and has been interpreted to be underlain by a high-velocity (V p $ 7.4 km/s) ''rift pillow'' [e.g., Catchings and Mooney, 1991] across much of northwestern Nevada.…”