Continental Mid‐Lithosphere Discontinuity: A Water Collector During Craton Evolution

Abstract

Cratons are ancient and long-lived stable continental lithosphere with weak tectonism, where the crust has not undergone intense deformation since Archean time (

Strong Physical Contrasts Across Two Mid‐Lithosphere Discontinuities Beneath the Northwestern United States: Evidence for Cratonic Mantle Metasomatism

“…Previous studies have proposed many different physical mechanisms for MLDs, which can be broadly divided into four categories: (a) changes in composition, which includes the appearance of hydrous minerals (e.g., Fu et al., 2022; Krueger et al., 2021; Rader et al., 2015; Selway et al., 2015), and the decrease in depletion level (magnesium number Mg#; e.g., Yuan & Romanowicz, 2010), (b) the onset of partial melt (e.g., Thybo, 2006), (c) the onset of elastically accommodated grain‐boundary sliding, which can be due to increasing temperature or water content (e.g., Karato et al., 2015), and (d) changes in seismic anisotropy, which is usually attributed to the lattice‐preferred orientation (LPO) of olivine in unaltered peridotite (e.g., Ford et al., 2016; Yang et al., 2023; Yuan & Romanowicz, 2010). We prefer changes in composition and the presence of partial melts as the causes of our observed MLDs because they can generate significant azimuthal‐invariant velocity drops in the mantle lithosphere (e.g., Chantel et al., 2016; Saha & Dasgupta, 2019; Saha et al., 2018).…”

Lithospheric Structure of the Circum‐Pannonian Region Imaged by S‐To‐P Receiver Functions

“…A shear wave velocity drop of 2%–10% is usually associated with the presence of partial melts (Saha et al., 2018; Thybo, 2006), changes in deformation creep mechanisms (diffusion and dislocation creep, Aulbach et al., 2017; Fei et al., 2016), a high water content layer produced by fluid metasomatism (Aulbach et al., 2017). Fluids can migrate from the underlying subduction or thermo‐chemical plume sources and can accumulate in a mantle layer with low temperature and pressure, increasing water capacity at a depth shallower than 100 km (e.g., Fu et al., 2022; Karato et al., 2015). It has also been proposed that carbonated silicate melts and pargasite dehydration might be connected to intra‐lithospheric discontinuities (cf.…”

“…Despite ongoing research, the origin of the MLD and its relationship to the LAB remain a topic of current interest. The MLD is a relatively thin (from a few kilometers up to a few tens of kilometers thick), characterized by lower seismic velocity beneath the discontinuity and higher conductivity (Selway et al., 2015) and its depth is typically at ∼100 km but can vary between 60 and 160 km (Fu et al., 2022; Rader et al., 2015). The importance of MLD has been highlighted in relation with various tectonic processes such as the removal or destruction of cratonic roots (Wang & Kusky, 2019), displacement of shallow cratonic lithosphere (Wang et al., 2017), delamination of lower continental lithosphere or localized subsequent deformation events (Dunbar & Sawyer, 1988).…”

Roles of Continental Mid‐Lithosphere Discontinuity in the Craton Instability Under Variable Tectonic Regimes

“…Variable generation rates and formation time have been discussed in Fu et al. (2022). Therefore, in this study, the constant generation rate of R h = 15 km 2 /Myr and model time of 550 Myr are applied in the numerical model to simulate the formation of the MLD.…”

“…Meanwhile, the time for the formation of MLD is still controversial, which may be related to the time of global cratonization and the onset of plate tectonics. Variable generation rates and formation time have been discussed in Fu et al (2022). Therefore, in this study, the constant generation rate of R h = 15 km 2 /Myr and model time of 550 Myr are applied in the numerical model to simulate the formation of the MLD.…”