Figure - available from: Journal of Geophysical Research: Solid Earth
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Laboratory reference models with R = 10⁻⁵ and Ts = 0.5 cm showing the evolution of (a) Mode 1 plumes for α = 20° and (b) Mode 2 plumes for α = 40°.
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Dehydration melting in subduction zones often produces cold plumes, initiated by Rayleigh‐Taylor instabilities in the buoyant partially molten zones lying above the dipping subducting slabs. We use scaled laboratory experiments to demonstrate how the slab dip (α) can control the evolution of such plumes. For α > 0°, Rayleigh‐Taylor instabilities ev...
Citations
... Rayleigh-Taylor (RT) instability occurs at the interface between two fluids when a denser (heavier) fluid is supported or accelerated by a less dense (lighter) one 1,2 . The mixing driven by RT instability plays a pivotal role in a wide range of natural and engineering phenomena, including corona formation 3 , inertial confinement fusion 4 , supernova explosions 5, 6 , the formation of underground salt domes 7 , and the evolution of volcanic islands 8 . Acceleration is a critical factor influencing the development of RT instability. ...
Rayleigh-Taylor (RT) instability commonly arises in compressible systems with time-dependent acceleration in practical applications. To capture the complex dynamics of such systems, a two-component discrete Boltzmann method is developed to systematically investigate the compressible RT instability driven by variable acceleration. Specifically, the effects of different acceleration periods, amplitudes, and phases are systematically analyzed. The simulation results are interpreted from three key perspectives: the density gradient, which characterizes the spatial variation in density; the thermodynamic non-equilibrium strength, which quantifies the system's deviation from local thermodynamic equilibrium; and the fraction of non-equilibrium regions, which captures the spatial distribution of non-equilibrium behaviors. Notably, the fluid system exhibits rich and diverse dynamic patterns resulting from the interplay of multiple competing physical mechanisms, including time-dependent acceleration, RT instability, diffusion, and dissipation effects. These findings provide deeper insights into the evolution and regulation of compressible RT instability under complex driving conditions.
... The best-known example of the effects of rock hydration and associated partial melting on rock buoyancy is the development of so-called cold plumes (Ghosh et al., 2020), which form above a subducting plate at relatively shallow depths of up to ∼150 km as a result of the infiltration of slab-derived water-rich fluids into the mantle wedge (Gerya et al., 2006). Further subduction of the oceanic plate, which consists of serpentinites, hydrated sediments, carbonates, and carbonated basalts (Safonova et al., 2015), is often followed by stagnation at the level of the MTZ (Fukao et al., 2009). ...
Many vertical seismic velocity anomalies observed below different parts of the Eurasian plate are rooted in the transition zone between the upper and lower mantle (410–660 km), forming so-called secondary plumes. These anomalies are interpreted as the result of thermal effects of large-scale thermal upwelling (primary plume) in the lower mantle or deep dehydration of fluid-rich subducting oceanic plates. We present the results of thermo-mechanical numerical modelling to investigate the dynamics of such small-scale thermal and chemical (hydrous) anomalies rising from the lower part of the Earth's upper mantle. Our objective is to determine the conditions that allow thermo-chemical secondary plumes of moderate size (initial radius of 50 km) to penetrate the continental lithosphere, as often detected in seismo-tomographic studies. To this end, we examine the effect of the following parameters: (1) the compositional deficit of the plume density due to the presence of water and hydrous silicate melts, (2) the width of the weak zone in the overlying lithosphere formed because of plume-induced magmatic weakening and/or previous tectonic events, and (3) a tectonic regime varied from neutral to extensional. In our models, secondary plumes of purely thermal origin do not penetrate the overlying plate, but flatten at its base, forming “mushroom”-shaped structures at the level of the lithosphere-asthenosphere boundary. On the contrary, plumes with enhanced density contrast due to a chemical (hydrous) component are shown to be able to pass upwards through the lithospheric mantle to shallow depths near the Moho when (1) the compositional density contrast is ≥ 100 kg m⁻³ and (2) the width of the lithospheric weakness zone above the plume is ≥ 100 km. An extensional tectonic regime facilitates plume penetration into the lithosphere but is not mandatory. Our findings can explain observations that have long remained enigmatic, such as the “arrow”-shaped zone of low seismic velocities below the Tengchong volcano in south-western China and the columnar (“finger”-shaped) anomaly within the lithospheric mantle discovered more than two decades ago beneath the Eifel volcanic fields in north-western Germany. It appears that a chemical component is a characteristic feature not only of conventional hydrous plumes located over presently downgoing oceanic slabs, but also of upper mantle plumes in other tectonic settings.
... These subduction driven processes eventually determine the pattern (extension/contraction) of large scale deformations and their manifestation in surface topography in the overriding plate (Lallemand et al. 2005 ;Brun & Faccenna 2008 ). Slab dehydration is an influential process to facilitate mantle wedge melting, resulting in volcanic arc formation at the overriding plate edges (Ghosh et al. 2020 ;Yoo & Lee 2020 ;Lee & Kim 2021 ). Several studies have shown slab age as another important factor in subduction dynamics. ...
... We have used the software package COMSOL Multiphysics R (version 5.3a), to implement the ALE driven moving mesh method. This software has been e xtensiv ely used for studying a wide range of geodynamic problems, for example mantle convection (He 2014 ), magma upwelling (Shahraki & Schmeling 2012 ), Ra yleigh-Ta ylor instabilities (Ruffino et al. 2016 ;Ghosh et al. 2020 ) and mid-ocean ridge development (Mont ési & Behn 2007 ), wedge melting (Lee & Kim 2021 ) and subduction zone modelling (Carminati & Petricca 2010 ;Rodriguez-Gonzalez et al. 2012 ). The ALE method is generally invoked in handling moving boundary problems to obtain time-dependent numerical solutions. ...
The Sunda plate has shaped itself in a complex tectonic framework, driven by the interactions of multiple subduction zones in its history. Using thermo-mechanical computational fluid dynamic models we show in this paper how the in-dip double-subduction dynamics has controlled the first-order 3D topography of this plate, currently bounded by two major N-S trending active trenches: Andaman-Sumatra-Java and Philippines on its western and eastern margins, respectively. We consider six E-W transects to account for an along-trench variation of the subduction parameters: subduction rate (Vc), shallow-depth (200–300 km) slab dip (α) and inter-trench distance (λ) in our 2D numerical experiments. The deviatoric stress fields and the topographic patterns are found to strongly depend on λ. For large inter-trench distances (λ = 2000 to 3000 km), the overriding plate develops dominantly tensile stresses in its central zone, forming low topographic elevations. Decreasing λ results in a transition from extensional to contractional deformation, and promotes topographic uplift in the southern part. We explain these effects of λ in terms of the sub-lithospheric flow vortex patterns produced by the subducting slabs. Large λ (> 2000 km) generates non-interacting flow vortices, located close to the two trenches, leaving the mantle region beneath the overriding plate weakly perturbed. In contrast, small λ results in their strong interaction to produce a single upwelling zone, which facilitates the overriding plate to gain a higher topographic elevation. The stress field predicted from our model is validated with the observed stress patterns. We also interpolate a three-dimensional topographic surface and vertical uplift rates from the serial model sections, and compare them with the observed surface topography of the Sunda plate.
... Considering an extremely slow motion in the geodynamic setting, the dynamic scaling must satisfy the following relation (Ghosh et al., 2020;Marques & Mandal, 2016), ...
The factors controlling the spatiotemporally varying deformation patterns in Tibet, a
prolonged period (∼50 to 19 ± 3 Ma) of NNE-SSW shortening, accompanied by eastward flow and orogenparallel extension in a later stage (19 ± 3 Ma to present-day), are still poorly constrained. Using viscous models, we performed scaled laboratory experiments with steady and unsteady state collision kinematics to address this issue. Our model Tibet under steady-state collision, irrespective of high (5.5 cm/yr) or low (3.5 cm/yr) indentation rates fails to produce the present-day crustal velocity fields and the deformation patterns, reported from GPS observations. An unsteady-state collision with decelerating convergence rates (5.5–3.5 cm/yr) is found to be a necessary condition for the initiation of eastward flow and ESEWNW extensional deformations. The model results also suggest that the mechanical resistance offered by the rigid Tarim block resulted in crustal uplift at faster rates in western Tibet, setting a west to east topographic gradient, existing till present-day. This topographic gradient eventually polarized the gravity controlled flow in the east direction when the convergence velocity decelerated to ∼3.5 cm/yr at around 19 ± 3 Ma. Our model shows the present-day eastward flow in central Tibet follows nearly a Poiseuille type velocity profile, bounded by the Himalaya in the south and the Tarim basin in northern Tibet. This flow kinematics allows us to explain the preferential locations of crustal-scale dextral and sinistral faults in southern and northern Tibet, respectively. Finally, the present-day model crustal-flow velocity, strain rates, and topographic variations are validated with GPS and geological field data
... Zhang et al., 2020). Mélange-diapirs are thus discrete Rayleigh-Taylor instabilities that can develop on a regular spacing as function of slab dip, which may also explain the strikingly uniform distribution of arc front volcanoes (Ghosh et al., 2020). Since the mineral assemblages in mélanges like these are different to those of a typical mantle peridotite, the trace elements can be strongly influenced by the stability of some key non-peridotitic accessory minerals. ...
Continents are created and destroyed at convergent margins but understanding the interconnectedness of this system—a complex interplay of subaerial and tectonic erosion, volatile exchange and metamorphism, partial fusion and melt evolution—is far from complete. Here we use geochemical data from the Mexican convergent margin to reveal a strong connectivity between subducted materials and typical orogenic andesites. We find that the along-strike isotopic variations of andesitic stratovolcanoes in Mexico are mirrored by those of riverine sediments sampled along the continental margin, which presumably represent the compositions of tectonically ablated forearc crust entering the subduction zone. Isotopic modelling further indicates that the Mexican andesites represent partial melts of subduction mélanges, constituted by mixtures of altered subducted ocean crust, forearc debris and mantle peridotite in similar proportions. Remarkably, the concentrations and ratios of incompatible trace elements in the volcanoes also correlate with the major element compositions of their corresponding forearc sediments. This suggests that the modal contents of key mineral phases in the partially molten mélanges control the trace element abundances of the andesitic magmas. These findings demonstrate that a significant proportion of tectonically eroded subducted crust is not lost to the deep mantle, but effectively reincorporated into arc magmas in a closely interlaced continental rock cycle.
The mechanisms underlying exhumation have been a topic of debate among researchers for many decades, prompting the development of numerous computational models aimed at elucidating the processes that initiate exhumation. However, a key gap in the literature lies in understanding how segments of the subducting lithospheric plate detach and subsequently exhumate after extended periods. Specifically, there has been limited investigation into whether material is stripped from the upper portion of the downgoing plate at relatively shallow depths, approximately 30 km, and, if so, whether these segments can eventually reach the Earth's surface. Furthermore, no existing model demonstrates that material can detach from the subducting plate as early as 15,000 years after the subduction is initiated. This study seeks to examine whether such a phenomenon occurs, using the subduction system of the Mediterranean Ridge as a case study. The process was simulated by extensively modifying an established thermomechanical visco-elasto-plastic code, named I2ELVIS, initially introduced by Gerya (2010). Lastly, macroscopic observations from the broader Hellenides region were employed to ascertain whether any such metamorphic rocks had indeed surfaced, thus confirming their exhumation. In conclusion, this research serves as a foundational investigation into a subject that warrants further exploration and detailed analysis in the future.
It is known that the Earth’s history is characterized by periodic activation of tectonomagmatic processes, when they are intensified without visible reasons. This is obviously related to the evolution of deep-seated petrological processes, the peculiar reflect of which are events in the external shells of the modern Earth (tectonosphere), but the nature of these processes and mechanisms of their translation in tectonosphere remain weakly studied. This problem is considered by the Late Cenozoic (Neogene–Quaternary) global activation. The modern Earth represents a cooling body with solidifying liquid iron core. This process should be accompanied by several thermodynamic, physical, and physical-chemical effects, which could lead to the internal activation of our planet. We attempted to decipher these problems using available geological, petrological, geochemical, and geophysical data on the present-day activation. It is shown that main active element in the modern Earth is uninterruptedly upward moving thin crystallization zone located between completely solidified part of the core (solid inner core) and its completely liquid part (external liquid core). Diverse phase transitions in a cooling melt passing through bifurcation points are related to this zone. The phase transitions are represented by both a change of crystallizing solid phases which built up inner core and retrograde boiling with formation of drops of “core” fluids. These drops are floated in high-Fe host melt and are accumulated at the mantle base, where they are involved in the formation of mantle plumes, which are the main carriers of deep-seated pulsed into external geosphere, and finally leave the core with them. It is suggested that in one of such points the fluid solubility in cooling high-Fe liquid of external core sharply decreases. This should lead to the simultaneous intensification of retrograde boiling of this melt over the entire zone surface of zone of the core crystallization zone, i.e., on a global scale. This could provide the influx of excess “core” fluids required for large-scale generation of mantle plumes and serve as trigger for Late Cenozoic global tectonomagmatic activation of the Earth.
It is a well-accepted hypothesis that deep-mantle primary plumes originate from a buoyant source layer at the core-mantle boundary (CMB), where Rayleigh–Taylor (RT) instabilities play a key role in the plume initiation process. Previous studies have characterized their growth rates mainly in terms of the density, viscosity and layer-thickness ratios between the denser overburden and the source layer. The RT instabilities, however, develop in the presence of global flows in the overlying mantle, which can act as an additional factor in the plume mechanics. Combining 2D computational fluid dynamic (CFD) model simulations and a linear stability analysis, this article explores the influence of a horizontal global mantle flow in the instability dynamics. Both the CFD simulation results and analytical solutions reveal that the global flow is a dampening factor in reducing the instability growth rate. At a threshold value of the normalized global flow velocity, short as well as long wavelength instabilities are completely suppressed, allowing the entire system to advect in the horizontal direction. Using a series of real-scale numerical simulations this article also investigates the growth rate as a function of the density contrast, expressed in Atwood number = (- )/ (+), and the viscosity ratio, where and are densities and viscosities of the overburden mantle and source-layer, respectively. It is found that increase in either or promotes the growth rate of a plume. In addition, the stability analysis predicts a nonlinearly increasing RT instability wavelength with increasing global flow velocity, implying that the resulting plumes widen their spacing preferentially in the flow direction of kinematically active mantle regions. The theory accounts for additional physical parameters: source-layer viscosity and thickness in the analysis of the dominant wavelengths and their corresponding growth rates. The article finally discusses the problem of unusually large inter-hotspot spacing, providing a new conceptual framework for the origin of sporadically distributed hotspots of deep-mantle sources.
