Evidence of Mantle‐Based Deformation Across the Western United States. Issue 4 (21st February 2022)

• Record Type: Journal Article
• Authors: Castellanos, Jorge C.; Humphreys, Eugene; Clayton, Robert W.
• Is Part Of: Geophysical research letters. Volume 49:Issue 4(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-21
• Subjects: mantle dynamics -- crustal flow -- seismic anisotropy; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094854
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We investigate the role that upper mantle buoyancy anomalies play in determining the behavior of the crust. Recently, Castellanos et al. (2020; https://doi.org/10.1126/sciadv.abb0476 ) observed that the anisotropy of the Pacific Northwest (PNW) crust correlates with the upper‐mantle velocity structure and suggested that vertical loads in the upper mantle can displace the Moho and drive crustal flow on a regional scale. To provide further insight into this relation, we resolve the crustal anisotropy in regions where near‐surface mantle‐based deformation might have occurred or is presently occurring. Specifically, we focus on the crust around the Rocky Mountains and around California since high‐resolution tomographic images reveal the presence of mantle structures similar to the ones that are thought to be driving the crust in the PNW. Our results reveal crustal flow driven by mantle vertical loading in both regions and suggest that this mechanism may be key in maintaining crustal isostasy during an orogeny. Plain Language Summary: While it has long been hypothesized that the main forces driving tectonic deformation result from the flow in the convecting mantle, there is new evidence suggesting that mantle vertical loading also plays an important role in crustal tectonics. Here, we illuminate the deformation field of the lower crust in different regions of the United States to search for evidence of mantle forcing of crustal flow. Our findings reveal that mantle gravitational loads can uplift or downwarp the crust‐mantle boundary and create lateral pressure gradients that drive the lower crustal away from upwellings and toward downwellings, causing thinning and thickening of the crust. This mechanism differs from conventional models in which crustal thickness variations are associated with topographic variations and suggests that mantle vertical loading might be key to maintaining isostatic equilibrium and a main driver of crustal deformation. Our results bring us closer to understanding how crustal motions respond to mantle‐derived forces and how these influence tectonic evolution processes. Key Points: Crustal seismic anisotropy reveals the coupling between the crust and the mantle Mantle vertical loads drive crustal flow in much of the western United States Mantle loads can depress the Moho, thicken the crust, and cause isostatic compensation without any topographic expression