The role of gravitational body forces in the development of metamorphic core complexes

Abstract

Within extreme continental extension areas, ductile middle crust is exhumed at the surface as metamorphic core complexes. Sophisticated quantitative models of extreme extension predicted upward transport of ductile middle-lower crust through time. Here we develop a general model for metamorphic core complexes formation and demonstrate that they result from the collapse of a mountain belt supported by a thickened crustal root. We show that gravitational body forces generated by topography and crustal root cause an upward flow pattern of the ductile lower-middle crust, facilitated by a detachment surface evolving into low-angle normal fault. This detachment surface acquires large amounts of finite strain, consistent with thick mylonite zones found in metamorphic core complexes. Isostatic rebound exposes the detachment in a domed upwarp, while the final Moho discontinuity across the extended region relaxes to a flat geometry. This work suggests that belts of metamorphic core complexes are a fossil signature of collapsed highlands.

Oligocene‐Miocene Exhumation of the Pinaleño Metamorphic Core Complex, Southeastern Arizona: Support for Magmatism and Plate Margin Reorganization as Controls on Regional Exhumation Trends

“…Foundering of the Farallon slab may have produced a similar effect as a slab window (see discussion below). The second idea, that a change in stress conditions is a requirement for the onset of extension, is widely accepted, but whether core complex formation tracks the migration of triple junctions or is a function of other processes remains debated (e.g., Bahadori et al., 2022). Zuza and Cao (2023) noted that there was a poor correlation between core complex exhumation and triple junction migration in the central to northern U.S. Cordillera, but the role of plate reorganization in the southern U.S. and northern Mexico Cordillera were not considered.…”

“…There are additional hypotheses for core complex formation, including gravitational collapse of tectonically thickened crust (Bahadori et al, 2022;Chapman et al, 2020;Coney & Harms, 1984;Sonder & Jones, 1999;Spencer et al, 1995) that are important, but not addressed by the new data presented in this study. Regardless of the exact processes involved in the development of the Cordilleran core complexes in the southern Basin and Range province, we note that trench-parallel trends (e.g., the migration of triple junctions and changes in stress state) are equally important as trench-perpendicular trends (e.g., inboard and outboard magmatic sweeps) to consider.…”

“…These core complexes are central to many tectonic models, however, the geodynamic mechanisms and forces that generated them remain the subject of debate. End‐member hypotheses for core complex formation in North America include (a) orogenic collapse due to excess gravitational potential energy following the termination of orogenesis, (b) changes in plate boundary conditions with regional stress fields transitioning from compressional to extensional, (c) opening of a slab window in the subducting Farallon plate, (d) Farallon slab roll‐back and/or foundering, and (e) thermal weakening and viscosity decrease of the crust due to enhanced heat flow from increased asthenospheric upwelling and regional magmatism (Armstrong & Ward, 1991; Atwater, 1970; Bahadori et al., 2022; Coney, 1987; Coney & Harms, 1984; Dickinson & Snyder, 1979; Dokka & Ross, 1995; Gans et al., 1989; Glazner & Bartley, 1984; Gottardi et al., 2020; Howlett et al., 2021; Jepson et al., 2022; Konstantinou, 2022; Lund‐Snee & Miller, 2022; Rey et al., 2009; Sonder & Jones, 1999; Zuza & Cao, 2023).…”

Incorporating H‐κ Stacking With Monte Carlo Joint Inversion of Multiple Seismic Observables: A Case Study for the Northwestern US

“…The observation of reduced crustal thickness (compared with SR2016, Figure S9 in Supporting Information S1; Figure 8) beneath the Basin and Range region suggests a diminished contribution of crustal support to the topography through isostasy, indicative of greater dynamic support from the underlying mantle. Additionally, a stronger contrast in crustal thickness between Basin and Range and adjacent tectonic provinces such as Colorado Plateau, as shown in Figure 8, also predicts greater Gravitational Potential Energy (GPE) differences (e.g., Bahadori et al., 2022), which leads to a different GPE‐induced stress field.…”