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.

In peninsular India, the Deccan Traps record massive, continental-scale volcanism in a sequence of magmatic events that mark the mass extinction at the Cretaceous-Paleogene boundary. Although the Deccan volcanism is linked with the Réunion hotspot, the origin of its periodic magmatic pulses is still debated. We develop a numerical model, replicating the geodynamic scenario of the African superplume underneath a moving Indian plate, to explore the mechanism of magmatic pulse generation during the Deccan volcanism. Our model finds a connection between the Réunion hotspot and the African large low shear-wave velocity province (LLSVP) to show pulse generation from a thermochemical plume in the lower mantle. The plume is perturbed at 660 km, and its head eventually detaches from the tail under the influence of Indian plate movement to produce four major pulses (periodicity: 5 - 8 Ma), each giving rise to multiple secondary magmatic pulses at a time interval of ~ 0.15-0.4 Ma.

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 (µ ef f ) of MC beneath MORs is recognized as the crucial factor in modulating their axial high versus flat topography. Based on a two-step viscosity calculation (suspension and solid-melt mixture rheology), we provide a theoretical estimate of µ ef f 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 µ ef f on the axial topography. Using an enthalpy-porosity-based fluid-formulation of uppermost mantle the model implements a one-way fluid-structure interaction (FSI) that transmits viscous forces of the MC region to the overlying upper crust. The limiting non-rifted topographic elevations (-0.06 km to 1.27 km) of model MORs are found to occur in the viscosity range: µ ef f = 10 12 to 10 14 Pa s. The higher-end (10 13 to 10 14 ) Pa s of this spectrum produce axial highs, which are replaced by flat or slightly negative topography as µ ef f ≤ 5 × 10 12 Pa s. We discuss a number of major natural MORs to validate the model findings.

<p>Subduction zones witness exhumation of deep crustal rocks metamorphosed under high pressure (HP) and ultra-high pressure (UHP) conditions, following burial to depths of 100 km or more. The exhumation dynamics of HP and UHP rocks still remains a lively issue of research in the Earth science community. We develop a new tectonic model based on the lubrication dynamics to show the exhumation mechanism of such deep crustal rocks in convergent tectonic settings. Our model suggests subducting plate motion produces a dynamic pressure in the subduction wedge, which supports the excess gravitational potential energy of the thicker and relatively denser overriding plate partly lying over the buoyant subduction wedge. A drop in the dynamic pressure causes the overriding plate to undergo gravitational collapse and forces the wedge materials to return to the surface. Using lubrication theory we estimate the magnitude of dynamic pressure (<em>P</em>) in the wedge as a function of subduction velocity (<em>u<sub>s</sub></em>), convergence angle (<em>α</em>) and wedge viscosity (<em>µ</em>). We also conduct thermo-mechanical numerical experiments to implement the lubrication model in subduction zones on a real scale. Our analysis suggests that drop in wedge dynamic pressure below a threshold value due to decease in <em>u</em><sub><em>s</em>  </sub>and <em>µ</em>, or by other processes, such as slab rollback and trench retreat facilitate exhumation of deep crustal rocks. Finally we discuss their implications for the exhumation of deep crustal rocks in different subduction setups such as the Himalayan continental subduction, the Mediterranean realm (Calabria–Apennine and Aegean belts) and Western Alps.</p>