Control of mush complex viscosity on mid-ocean ridge topography: A fluid–structure model analysis

Abstract

This article exploits the interaction dynamics of the elastic oceanic crust with the underlying mush complexes (MC) to constrain the axial topography of mid-ocean ridges (MORs). The effective viscosity (μeff) of MC beneath MORs is recognized as the crucial factor in modulating their axial high vs flat topography. Based on a two-step viscosity calculation (suspension and solid-melt mixture rheology), we provide a theoretical estimate of μeff as a function of melt suspension characteristics (crystal content, polymodality, polydispersity, and strain rate) and its volume fraction in the MC region. We then develop a numerical model to show the control of μeff on the axial topography. Using an enthalpy-porosity-based fluid formulation of uppermost mantle, the model implements a one-way fluid–structure interaction that transmits viscous forces of the MC region to the overlying upper crust. The limiting non-rifted topographic elevations (−0.06–1.27 km) of model MORs are found to occur in the viscosity range of μeff = 1012–1014 Pa s. The higher end (1013–1014) Pa s of this spectrum produces axial highs, which are replaced by flat or slightly negative topography as μeff≤5×1012 Pa s. We discuss a number of major natural MORs to validate the model findings.

Wall Fracturing Versus Mechanical Instability as Competing Intrusion Mechanisms of Dikes: Insights From Laboratory Experiments

“…Several studies reported the emplacement of mafic dikes in mushy regions beneath mid‐ocean ridges. Theoretical estimates suggest the mush viscosities in the order of 10 14 –10 16 Pa s (Mandal et al., 2018; Mckenzie, 1984; Sen et al., 2023), whereas crystal‐rich magma viscosities are as high as 10 10 Pa s (Mavko & Nur, 1975; Schmiedel et al., 2021; Takeuchi, 2004, 2011). In such magmatic environments, the viscosity ratio η * can be low enough (∼10 5 ), favoring the dike emplacement by purely instability mechanism, as observed in the USTG‐oil experiments (Figure 5a).…”

“… a Natural values: (Arachchige et al., 2022; Galland et al., 2014; Gerbi et al., 2004; Head et al., 2021; Mandal et al., 2018; Poppe et al., 2019; Sen et al., 2023; S. Takeuchi & Nakamura, 2001; Wang et al., 2021). …”

“…The rectangular glass box was filled with the host (USTG or gel wax) material, leaving the top surface unconfined to accommodate the liquid volume injected into the host. One of the side glass walls (XZ side: 18 cm × 14 cm) had a tiny hole, which was sealed with a soft sticking sheet at the time of model preparation that the needle of a Nature is 10 5 times stronger than the model a Natural values: (Arachchige et al, 2022;Galland et al, 2014;Gerbi et al, 2004;Head et al, 2021;Mandal et al, 2018;Poppe et al, 2019;Sen et al, 2023;S. Takeuchi & Nakamura, 2001;Wang et al, 2021).…”