Relative impact of mantle densification and eclogitization of slabs on subduction dynamics: A numerical thermodynamic/thermokinematic investigation of metamorphic density evolution

Abstract

Understanding the relationships between density and spatio-thermal variations at convergent plate boundaries is important for deciphering the present-day dynamics and evolution of subduction zones. In particular, the interaction between densification due to mineralogical phase transitions and slab pull forces is subject to ongoing investigations. We have developed a two-dimensional subduction zone model that is based on thermodynamic equilibrium assemblage calculations and includes the effects of melting processes on the density distribution in the lithosphere. Our model calculates the "metamorphic density" of rocks as a function of pressure, temperature, and chemical composition in a subduction zone down to 250 km. We have used this model to show how the hydration, dehydration, partial melting and fractionation processes of rocks all influence the metamorphic density and greatly depend on the temperature field within the subduction system. These processes are largely neglected by other approaches that reproduce the density distribution within this complex tectonic setting. Our model demonstrates that the initiation of eclogitization (i.e., when crustal rocks reach higher densities than the ambient mantle) of the slab is not the only significant process that makes the descending slab denser and generates the slab pull force. Instead, the densification of the lithospheric mantle of the sinking slab starts earlier than eclogitization and contributes significantly to slab pull in the early stages of subduction. Accordingly, the complex metamorphic structure of the slab and the mantle wedge has an important impact on the development of subduction zones.

The evolution of the Bangong–Nujiang Neo-Tethys ocean: Evidence from zircon U–Pb and Lu–Hf isotopic analyses of Early Cretaceous oceanic islands and ophiolites

“…In our zircon dating results, the peak of 162-168 Ma may represent the initial subduction of the BangongNujiang suture zone, because numerous models and observations have shown that old and cold oceanic lithosphere becomes denser than the underlying asthenosphere (Capitanio et al, 2010;Duesterhoeft et al, 2014;Marques et al, 2013;Oxburgh and Parmentier, 1977;Uyeda and Kanamori, 1979), and when the oceanic crust is first subducted, the additional dragging force associated with the cold and dense oceanic plate will decrease the pressure of the magma chambers in the mid ocean ridge, which in turn product larger amounts of mafic magma than usual. This inference is also supported by regional geological data.…”

Controls of inherited lithospheric heterogeneity on rift linkage: Numerical and analog models of interaction between the Kenyan and Ethiopian rifts across the Turkana depression

“…The deformation of materials is accommodated via an elastoviscoplastic rheology, which self‐consistently reproduces diverse deformation processes like faulting, flexure, and lower crustal flow. SLIM3D has been extensively benchmarked and applied to model lithospheric‐scale processes in divergent [ Brune et al , , ; Brune and Autin , ; Brune , ; Heine and Brune , ; Koopmann et al , ; Clift et al , ; Brune et al , , ], convergent [ Quinteros et al , ; Quinteros and Sobolev , ; Duesterhoeft et al , ], and transform [ Popov et al , ; Brune , ] plate boundaries and in a centimeter‐scale study of localization dynamics [ Cyprych et al , ].…”

Stochastic Inversion of P‐to‐S Converted Waves for Mantle Composition and Thermal Structure: Methodology and Application

“…The free-energy minimization can be carried out in two ways: by dynamic or by static implementation. Dynamic implementation means minimizing the Gibbs free-energy of the system at a particular value of pressure, temperature, and composition during the 10.1029/2018JB016032 inversion process (e.g., Afonso et al, 2013;Chust et al, 2017;Duesterhoeft & Capitani, 2013;Duesterhoeft et al, 2014;Khan et al, 2006). Alternatively in the static implementation, physical properties are calculated for a certain range of pressure-temperature conditions and stored in tables prior to the solution of the inverse problem (e.g., Zunino et al, 2011).…”