Three Major Failed Rifts in Central North America: Similarities and Differences

Abstract

The North American craton preserves nearly two billion years of geologic history, including three major rifts that failed rather than evolving to continental breakup and seafloor spreading. The Midcontinent Rift (MCR) and Southern Oklahoma Aulacogen (SOA) show prominent gravity anomalies due to large volumes of igneous rift-filling rock. The Reelfoot Rift (RR), though obscure in gravity data, is of interest due to its seismicity. The ca. 1.1 Ga MCR records aspects of the assembly of Rodinia, whereas the ca. 560 Ma SOA and RR initiated during the later breakup of Rodinia and were inverted during the assembly of Pangea. Comparative study of these rifts using geophysical and geological data shows intriguing similarities and differences. The rifts formed in similar tectonic settings and followed similar evolutionary paths of extension, magmatism, subsidence, and inversion by later compression, leading to similar width and architecture. Differences between the rifts reflect the extent to which these processes occurred. Further study of failed rifts would give additional insight into the final stages of continental rifting and early stages of seafloor spreading.Three Major Failed Rifts in Central North America: Similarities and Differences GSA Today, v. 32, https://doi.org/GSATG518A.1. CC-BY-NC.

Ediacaran‐Ordovician Magmatism and REE Mineralization in the Wet Mountains, Colorado, USA: Implications for Failed Continental Rifting

“…These new data support a northwest‐trending failed rift model, which approximately matches the orientation of the regional gravity high over the Wet Mountains (see Pardo & Keller, 2008). The high gravity response may represent underlying, dense, mafic‐ultramafic material (i.e., underplate) that is typical in rift systems including the Southern Oklahoma Aulacogen (Elling et al., 2022; Keller & Baldridge, 1995). Ediacaran‐Ordovician alkaline magmatism and Cambrian‐Ordovician REE and thorium mineralization in the Wet Mountains is, therefore, interpreted as a continuation of the along‐strike, west‐northwest‐trending Ediacaran‐Cambrian Southern Oklahoma Aulacogen (Figure 18).…”

Joint Inversion of SPREE Receiver Functions and Surface Wave Dispersion Curves for 3‐D Crustal and Upper Mantle Structure Beneath the U.S. Midcontinent Rift

“…S. Stein et al (2018) explain the development of the MCR as a result of deformational processes during a reorganization of plate motions and the resulting evolution of plate margins, suggesting that deformation caused decompression melting and leaky transform faults that resulted in a large volume (up to a million cubic kilometers) of volcanic basalt. This model explains the asymmetric gravity anomaly and volcanic volumes of the MCR (Elling et al, 2022;Merino et al, 2013) as a consequence of the east and west arms being boundaries between a microplate and two diverging major plates. The MCR's intersection with the Superior Craton is a defining area within which to study rift inception and demise.…”

“…The gravity and magnetic highs (Figure 2) indicate layers of dense and predominantly mafic volcanic rocks flanked and overlain by nearly flat‐lying younger sedimentary rocks. After uplift of the central portion of the rift and associated erosion of these sedimentary rocks along the rift axis, the remaining marginal sedimentary rocks have relatively low densities and are essentially non‐magnetic, therefore negative gravity anomalies and subdued magnetic signatures usually flank the strongly positive signatures (Allen et al., 1997; Chandler et al., 1989; Elling et al., 2022).…”

“…Numerous geophysical studies (e.g., Foster et al., 2020; Miller & Nicholson, 2013; Van Schmus, 1992) have examined the MCR by quantifying the contrast between the rift valley and its surroundings. This contrast is seen in the composition, gravity, and magnetic signatures of the crust and mantle (Elling et al., 2022; C. A. Stein et al., 2014; S. Stein et al., 2018; Van Schmus & Hinze, 1985; Zhang et al., 2016). The prominent gravity anomalies shown in Figure 2 define the geographic extent of the MCR (Chandler & Lively, 2011).…”

“…Numerous geophysical studies (e.g., Foster et al, 2020;Miller & Nicholson, 2013;Van Schmus, 1992) have examined the MCR by quantifying the contrast between the rift valley and its surroundings. This contrast is seen in the composition, gravity, and magnetic signatures of the crust and mantle (Elling et al, 2022;C. A. Stein et al, 2014;S.…”