Dynamic lithosphere within the Great Basin

Abstract

To place new constraints on the short-term, broad-scale lithospheric evolution of plate interiors, we utilize broadband seismic data from the Great Basin region of the Western United States to produce high-resolution images of the crust and upper mantle. Our results suggest that parts of the Great Basin lithosphere has been removed, likely via inflow of hot asthenosphere as subduction of the Farallon spreading center occurred and the region extended. In our proposed model, fragments of thermal lithosphere removed by this process were gravitationally unstable and subsequently sank into the underlying mantle, leaving behind less dense, stronger, chemically depleted lithosphere. This destabilization process promotes volcanism, deformation, and the reworking of continental lithosphere inboard from plate margins. Our results provide evidence for a new mechanism of lithospheric evolution that is likely common and significant in postsubduction tectonic settings.

Inference of the viscosity structure and mantle conditions beneath the Central Nevada Seismic Belt from combined postseismic and lake unloading studies

“…Comparison of our inferred viscosity structure with a Vs‐tomographic model [ Porter et al ., ], also shows striking correlations. Black curves in Figure b show the positions of major velocity changes in the Vs tomographic model over the region where both loading events overlap.…”

“…Thus the viscosity decrease inferred by our model may coincide with wet partial melting and an associated change to diffusion creep from dislocation creep. The seismological lithosphere‐asthenosphere boundary as suggested by Porter et al ., [] varies across the region between ∼60 and ∼80 km depth (seismic LAB curve in Figure b), in agreement with a viscosity drop at 80 km inferred in our model. However, we would not characterize this as the mechanical LAB.…”

“…(a) Calculated geothermal gradient and mantle melting curves along with a likely mantle solidus from Hirschman et al [2000]. (b) Best-fit calculated viscosity structure with the estimated Vs values[Porter et al, 2014] as a function of longitude through western Nevada. Triangles on top are representative of volcanoes that are in the region along with present-day Walker Lake and the Cedar Mountain fault.…”

Synthesizing EarthScope data to constrain the thermal evolution of the continental U.S. lithosphere

“…This suggests that the thermotectonic events within the United States may have resulted in especially high or widespread elevated temperature within the lithosphere. These high temperatures are likely due to unique conditions within the region including warming of a hydrated continental upper mantle (Dixon et al, 2004) associated with sinking of the Farallon slab and upwelling due to extension, mantle plumes, return flow from downwellings, and possible small-scale asthenospheric convection (Farmer et al, 2008;Schutt and Dueker, 2008;West et al, 2009;van Wijk et al, 2010;Hansen et al, 2013;Porter et al, 2014;Porter et al, 2017). Even though the short-term thermal effects of these processes may be substantial, the long-term (>300-500 Ma) thermal conditions should appear similar to other orogenies, as shown within our data, because cooling is characterized by progressively smaller (exponential) decay in temperature (Fig.…”

Lithospheric records of orogeny within the continental U.S.

“…However, velocity variations correlate much better with heat flow distributions [Blackwell et al, 2011], reflecting the regions that have experienced significant extension and volcanism mentioned above. Temperature alone is unlikely to be the source of the velocity contrast, but lithospheric modification through phase changes, hydration [e.g., Humphreys et al, 2003], and delamination processes [e.g., Zandt et al, 2004;Hales et al, 2005;Wells and Hoisch, 2008;West et al, 2009;Porter et al, 2014] may provide an explanation for the velocity contrast. Such downwelling processes have been argued to be occurring along the margins of the modern Colorado Plateau as delamination migrates toward its interior [Sine et al, 2008;Van Wijk et al, 2010;Levander et al, 2011] and may have occurred beneath much of the extensional provinces of the western U.S. as the lithosphere was destabilized during extension.…”