- Award ID(s):
- 1723057
- NSF-PAR ID:
- 10389156
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 228
- Issue:
- 1
- ISSN:
- 0956-540X
- Page Range / eLocation ID:
- 631 to 663
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
The dependence of planetary tectonics on mantle thermal state: Applications to early Earth evolutionFor plate tectonics to operate on a planet, mantle convective forces must be capable of forming weak, localized shear zones in the lithosphere that act as plate boundaries. Otherwise, a planet's mantle will convect in a stagnant lid regime, where subduction and plate motions are absent. Thus, when and how plate tectonics initiated on Earth is intrinsically tied to the ability of mantle convection to form plate boundaries; however, the physics behind this process are still uncertain. Most mantle convection models have employed a simple pseudoplastic model of the lithosphere, where the lithosphere "fails" and develops a mobile lid when stresses in the lithosphere reach the prescribed yield stress. With pseudoplasticity high mantle temperatures and high rates of internal heating, conditions relevant for the early Earth, impede plate boundary formation by decreasing lithospheric stresses, and hence favor a stagnant lid for the early Earth. However, when a model for shear zone formation based on grain size reduction is used, early Earth thermal conditions do not favor a stagnant lid. While lithosphere stress drops with increasing mantle temperature or heat production rate, the deformational work, which drives grain size reduction, increases. Thus the ability of convection to form weak plate boundaries is not impeded by early Earth thermal conditions. However, mantle thermal state does change the style of subduction and lithosphere mobility; high mantle temperatures lead to a more sluggish, drip-like style of subduction. This "sluggish lid" convection may be able to explain many of the key observations of early Earth crust formation processes preserved in the geologic record. Moreover, this work highlights the importance of understanding the microphysics of plate boundary formation for assessing early Earth tectonics, as different plate boundary formation mechanisms are influenced by mantle thermal state in fundamentally different ways.more » « less
-
Abstract Rocky planets with high levels of internal heat production experience high rates of melting and extensive volcanic resurfacing in the heat pipe mode of planetary heat transport. On Earth, this took place prior to the onset of plate tectonics during the first billion or more years. The extraction of melt from a planetary mantle affects the mantle dynamics, the temperature structure of the interior, the viscosity of mantle material, and the timescales of thermal equilibration in the mantle, and therefore, developing a quantitative parameterization for heat transport by volcanism is necessary to calculate the thermal histories of terrestrial planets efficiently. In this work, we develop a quantitative parameterization of heat transport in planetary mantles including the effect of melting. The heat flux due to melting, the internal temperature of the mantle, the temperature of the lid base, the lid thickness, and the heat flux due to conduction were calculated using the parameterization for different cases of solidus gradient and surface melting temperatures, and the values were compared with the results of numerical simulations for validation. The good fit achieved (<15% relative error) over a large range of melt fluxes with no additional parameters indicates that the parameterization usefully and accurately models the process of mantle convection including melting.
-
SUMMARY Oceanic plateaus (or aseismic ridges) can be either subducted into the deep mantle, or accreted onto the overriding plate. Furthermore, some oceanic plateaus can change subduction mode from steep to flat-slab subduction. What factors control the fate of oceanic plateaus during subduction remain enigmatic. Here, we investigate the controls on these modes and their respective geological effects using 2-D thermomechanical simulations. We systematically examine the characteristics of an oceanic plateau (including crustal thickness and length), plateau-trench distance, convergence rate and eclogitization of the oceanic crust. Our models confirm that the size of the plateau and eclogitization are the main factors controlling the subduction characteristics. For the eclogite models, a relatively thin oceanic plateau (≤20 km thick) undergoes steep subduction, a moderate-scale plateau (25–30 km thick) favours flat-slab subduction and large-scale plateaus (≥35 km thick) are more susceptible to collide and accrete to the overriding upper plate. Eclogitization significantly reduces the formation chance and duration of flat-slab subduction. The switch from flat-slab to steep subduction occurs rapidly (<5 Ma), and the steepening occurs twice as fast as the flattening. The plateau-trench distance determines the location of the break-off, and shallow break-off (<300 km) of the frontal slab will significantly change the subduction pattern. Either fast convergence rates (≥8 cm yr−1) or overthrusting of the overriding plate promotes the formation of flat-slab subduction. The mode changed from flat-slab to steep subduction explains the landward migration of magmatism followed by a trenchward migration in Eastern China since the Mesozoic.
-
Abstract Recent planetary data and geophysical modeling suggest that hydrothermal activity is ongoing under the ice crust of Enceladus, one of Saturn's moons. According to these models, hydrothermal flow in the porous, rocky core of the satellite is driven by tidal deformation that induces dissipation and volumetric internal heating. Despite the effort in the modeling of Enceladus' interior, systematic understanding—and even basic scaling laws—of internally heated porous convection and hydrothermal activity are still lacking. In this article, using an idealized model of an internally heated porous medium, we explore numerically and theoretically the flows that develop close to and far from the onset of convection. In particular, we quantify heat‐transport efficiency by convective flows as well as the typical extent and intensity of heat flux anomalies created at the top of the porous layer. With our idealized model, we derive simple and general laws governing the temperature and hydrothermal velocity that can be driven in the oceans of icy moons. In the future, these laws could help better constraining models of the interior of Enceladus and other icy satellites.
-
SUMMARY Tectonic plate motions predominantly result from a balance between the potential energy change of the subducting slab and viscous dissipation in the mantle, bending lithosphere and slab–upper plate interface. A wide range of observations from active subduction zones and exhumed rocks suggest that subduction interface shear zone rheology is sensitive to the composition of subducting crustal material—for example, sediments versus mafic igneous oceanic crust. Here we use 2-D numerical models of dynamically consistent subduction to systematically investigate how subduction interface viscosity influences large-scale subduction kinematics and dynamics. Our model consists of an oceanic slab subducting beneath an overriding continental plate. The slab includes an oceanic crustal/weak layer that controls the rheology of the interface. We implement a range of slab and interface strengths and explore how the kinematics respond for an initial upper mantle slab stage, and subsequent quasi-steady-state ponding near a viscosity jump at the 660-km-discontinuity. If material properties are suitably averaged, our results confirm the effect of interface strength on plate motions as based on simplified viscous dissipation analysis: a ∼2 order of magnitude increase in interface viscosity can decrease convergence speeds by ∼1 order of magnitude. However, the full dynamic solutions show a range of interesting behaviour including an interplay between interface strength and overriding plate topography and an end-member weak interface-weak slab case that results in slab break-off/tearing. Additionally, for models with a spatially limited, weak sediment strip embedded in regular interface material, as might be expected for the subduction of different types of oceanic materials through Earth’s history, the transient response of enhanced rollback and subduction velocity is different for strong and weak slabs. Our work substantiates earlier suggestions as to the importance of the plate interface, and expands the range of quantifiable links between plate reorganizations, the nature of the incoming and overriding plate and the potential geological record.more » « less