Geoid data and thermal structure of the oceanic lithosphere

1995 ◽  
Vol 22 (14) ◽  
pp. 1913-1916 ◽  
Author(s):  
W. Philip Richardson ◽  
Seth Stein ◽  
Carol A. Stein ◽  
Maria T. Zuber
Keyword(s):  
Thermal Structure ◽  
Oceanic Lithosphere

Mantle thermal structure at northern Mid–Atlantic ridge from improved numerical methods and boundary conditions

2019 ◽  
Author(s):  
Marco Cuffaro ◽  
Edie Miglio ◽  
Mattia Penati ◽  
Marco Viganò
Keyword(s):  
Boundary Conditions ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Geophysical Data ◽  
Mantle Flow ◽  
Viscous Forces ◽  
Versus Domain ◽  
Mid Atlantic Ridge ◽  
Velocity Constraints ◽  
New Formulation

Summary We computed mantle flow and thermal structure beneath a segment of the northern Mid-Atlantic ridge using numerical simulations adopting asymmetric spreading and ridge migration as boundary conditions. The objective is to obtain new insights on mantle processes acting at this ridge segment. We explored different lateral boundary conditions based on velocity, stress and stress-velocity constraints highlighting differences in the depth of the thermal base of the lithosphere versus domain width. Here, we propose a new formulation of lateral and bottom boundary conditions based on the choice of a proper tangential stress at the bottom and on lateral boundaries of the domain accounting for ridge migration. Moreover, dimensional analysis of governing equations suggests that heat generation due to work of the viscous forces cannot be neglected in the computations. Therefore, we included this thermal contribution into the numerical experiments providing an application to the northern Mid-Atlantic ridge at the reference latitude of 43 ○N. Results are compared with available geophysical data in the area, including also mantle tomography models. Asymmetric spreading and ridge migration in numerical modelling account for an asymmetric accretion of the oceanic lithosphere, supporting the evidence of the asymmetries described by geophysical data across the northern Mid-Atlantic ridge segments.

Linking subduction dynamics to back-arc deformation

2020 ◽  
Author(s):  
Valentina Magni ◽  
Manel Prada
Keyword(s):  
Boundary Conditions ◽  
Numerical Models ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Lau Basin ◽  
Crustal Composition ◽  
Lithospheric Extension ◽  
Back Arc ◽  
Existing Structure ◽  
Tyrrhenian Basin

<p> <span>The morphology of back-arc basins shows how complex their formation is and how pre-existing lithospheric structures, rifting and spreading processes, and subduction dynamics all have a role in shaping them. </span><span>Often, back-arc basins present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. Episodes of fast and slow trench retreat can cause rift jumps, migration of magmatism, and pulses of higher crustal production (e.g., Tyrrhenian Basin). The evolution of a back-arc basin is not only tightly linked to subduction dynamics, but it is likely that the composition and the pre-existing structure of the lithosphere play a role in shaping the basin too. </span><span>In this work, we investigate the interplay between these features with numerical models of lithospheric extension with a visco-plastic rheology. We use the finite element code ASPECT to model the rifting of continental and oceanic lithosphere with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically change key parameters such as crustal composition and thickness, initial thermal structure and rheology of the lithosphere, and rate of extension. These models aim at understanding how pre-existing lithospheric structures affect back-arc rifting and spreading and what processes control spreading centres jumps in back-arc settings. Preliminary results show that time-dependent boundary conditions that simulate episodes of fast trench retreat, thus fast extension, play an important role into the style of lithospheric back-arc deformation. Finally, we will compare our model results with the location and timing of back-arc rifting and spreading in different active and inactive back-arc basins.</span></p>

scholarly journals Origins of ultralow velocity zones through slab-derived metallic melt

2016 ◽  
Vol 113 (20) ◽  
pp. 5547-5551 ◽  
Author(s):  
Jiachao Liu ◽  
Jie Li ◽  
Rostislav Hrubiak ◽  
Jesse S. Smith
Keyword(s):  
Large Scale ◽  
Thermal Structure ◽  
Melting Curve ◽  
Oceanic Lithosphere ◽  
Earth’S Core ◽  
Eutectic Melting ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Metallic Melt

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron−carbon system crosses the current geotherm near Earth’s core−mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core−mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

Numerical simulation of subduction zone pressure-temperature-time paths: constraints on fluid production and arc magmatism

1991 ◽  
Vol 335 (1638) ◽  
pp. 341-353 ◽  
Keyword(s):  
Heat Transfer ◽  
Partial Melting ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Transfer Model ◽  
Temperature Time ◽  
Subducting Slab

The location and sequence of metamorphic devolatilization and partial melting reactions in subduction zones may be constrained by integrating fluid and rock pressure-temperature-time ( P-T-t ) paths predicted by numerical heat-transfer models with phase diagrams constructed for metasedimentary, metabasaltic, and ultramafic bulk compositions. Numerical experiments conducted using a two-dimensional heat transfer model demonstrate that the primary controls on subduction zone P-T-t paths are: (1) the initial thermal structure; (2) the amount of previously subducted lithosphere; (3) the location of the rock in the subduction zone; and (4) the vigour of mantle wedge convection induced by the subducting slab. Typical vertical fluid fluxes out of the subducting slab range from less than 0.1 to 1 (kg fluid) m -2 a -1 for a convergence rate of 3 cm a -1 . Partial melting of the subducting, amphibole-bearing oceanic crust is predicted to only occur during the early stages of subduction initiated in young (less than 50 Ma) oceanic lithosphere. In contrast, partial melting of the overlying mantle wedge occurs in many subduction zone experiments as a result of the infiltration of fluids derived from slab devolatilization reactions. Partial melting in the mantle wedge may occur by a twostage process in which amphibole is first formed by H 2 O infiltration and subsequently destroyed as the rock is dragged downward across the fluid-absent ‘hornblende-out’ partial melting reaction.

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