Crustal structure of the Ruby Mountains metamorphic core complex, Nevada, from passive seismic imaging

Abstract

We use data from a temporary passive seismic array to illuminate the deep structure of the Ruby Mountains metamorphic core complex (RMCC). Despite decades of geologic mapping and geophysical exploration, the relative importance of lateral crustal flow, diapirism, and brittle faulting in the formation of the RMCC has remained unclear. Our Ruby Mountains Seismic Experiment (RMSE) utilized 50 passive broadband stations from 2010 to 2012 spaced at 5-10 km along three ~100-km-long intersecting profiles as part of the Earthscope Flexible Array program. Common conversion point stacks of our P-wave receiver functions show a fairly flat Moho at 32 ± 2 km depth throughout most of the study area but reaching 40 km in a narrow, north-south crustal welt 20-50 km west of the exposed RMCC. Our shear-wave splitting analysis shows that fast directions of polarization rotate clockwise from west to east across our study area, broadly matching regional studies and models that placed the anisotropy below the lithosphere. However, because our north-south crustal welt coincides with WE polarizations, the observed splitting may include a component of crustal anisotropy. We integrate our observations with older magnetotelluric and seismic refraction and reflection data to support a model of asymmetric crustal flow during formation of the RMCC at the edge of a preexisting orogenic plateau.

A Middle Crustal Channel of Radial Anisotropy Beneath the Northeastern Basin and Range

“…Within the northern Basin and Range are three MCCs: the Ruby Mountains, Snake Range, and ARG Mountains (Figure 1). This study benefits from data collected by the recent Ruby Mountains Seismic Experiment (RMSE), which provides exceptionally dense,~5-10 km spacing, broadband seismograph coverage of the Ruby Mountains (Figure 1; Litherland & Klemperer, 2017). The northern Ruby Mountains expose Proterozoic to Paleozoic metasedimentary rocks of the miogeocline that were intruded by Mesozoic to early Cenozoic plutons, buried during crustal shortening of the Sevier Orogeny, and then subjected to multiple phases of exhumation beginning in the late Cretaceous (Hodges et al, 1992;MacCready et al, 1997;Sullivan & Snoke, 2007).…”

“…Continuous three-component (3-C) broadband seismic data were collected from the RMSE (Litherland & Klemperer, 2017) and surrounding permanent network stations (Figure 1; Table S1). Using interstation measurements of surface wave propagation extracted from empirical Green's functions estimated using ambient noise interferometry, we obtain Rayleigh and Love wave data (Figure 2; Bensen et al, 2007).…”

“…Each of the five inversion parameterization cases were run using three different regional crustal thickness models ( Figure 5; Buehler & Shearer, 2017;Schmandt et al, 2015;Shen & Ritzwoller, 2016) and an interpreted local crustal thickness model calculated below each station within the RMSE ( Figure 5; Litherland & Klemperer, 2017). The motivation for testing the different crustal thickness models is to determine if the strength and pattern of radial anisotropy are dependent on the choice of crust thickness model.…”

Crustal Composition Beneath Southern Idaho: Insights from Teleseismic Receiver Functions

“…The starting model is extremely important due to the non-uniqueness present in the inversion of receiver functions. Here, I use 2-km thick layers with velocities matching the standard AK135 Earth model (Kennett et al, 1995; Figure 10) with an adjusted Moho depth derived from previous studies that include the EARS database (Crotwell and Owens, 2005), Eager (2010), and Litherland and Klemperer (2017). The selection of a 2-km layer thickness will be discussed in further detail in chapter 3.…”

“…For my inversions, I use the AK135 standard Earth model with crustal thickness estimates beneath each station as a further constraint. These H-k derived estimates come from the EARS database (Crotwell and Owens, 2005), Eager (2010), and Litherland and Klemperer (2017). To explore the range of crustal velocities beneath Idaho, I select three stations with contrasting crustal lithologies; TA.I12A, located on rocks associated with the granitic Idaho Batholith; XC.Y03, located on basaltic rocks of the eastern SRP; and TA.K11A, located along the southern margin of the western SRP (Figure 13a).…”