An integration to optimally constrain the thermal structure of oceanic lithosphere

Abstract

[1] The evolution through time of the oceanic lithosphere is a substantial, incompletely resolved geodynamical problem. Consensus remains elusive regarding its thermal structure, physical properties, and the best model through which to unify observational constraints. We robustly reevaluate all three of these by (i) simultaneously fitting heat flow, bathymetry, and temperatures derived from a shear velocity model of the upper mantle, (ii) using the three main thermal models (half-space, plate, and Chablis), and (iii) analyzing five depth-age curves, wherein contrasting techniques were used to exclude anomalous features from seafloor depths. The thermal models are updated to all include a temperature-dependent heat capacity, a temperature-and pressure-dependent thermal conductivity, and an initial condition of adiabatic decompression including melting. The half-space model, which lets the lithosphere thicken indefinitely, cannot accurately fit the subsidence curves and requires mantle potential temperatures, T m , that are too high. On the other hand, the models including a mechanism of basal heat supply are able to simultaneously explain all observations within two standard errors, with best-fitting parameters robust to the choice of the filtered bathymetry curve. For the plate model, which imposes a constant temperature at a fixed depth, T m varies within 1380-1390 C, the equilibrium plate thickness a within 106-110 km, and the bulk thermal expansivity a within 2.95À3.20 Á 10 À5 K À1 . For the Chablis model, which prescribes a fixed heat flow at the base of a thickening lithosphere, the best-fitting values are T m = 1320À1380 C, a = 176À268 km, a ¼ 3:05À3:60 Á 10 À5 K À1 . Driven by more accurate ocean depths, the plate model provides better joint-fittings to the observations; however, it requires values of a lower than experimentally measured, which can be explained by a reduction of the apparent expansivity due to elastic rigidity of the upper lithosphere. The Chablis model better fits the data when a is set close to or above the experimental values. Although statistically consistent within two standard errors, a tendency toward incompatibility between observed depth-age curves and seismically derived temperatures is revealed with new clarity, because the latter do not exhibit a clear steady state whereas the former flatten; further work is needed to identify the origin of this apparent discrepancy.This work opens the way to investigations fully independent of particular solutions of the heat equation.

Semi-Empirical Oceanic Depth–Age Relationship Inferred from Bathymetric Curve

“…Subsequently, for ages 147-180 Ma, depth stabilizes at 6700-6760 m (note that the reference depth of 6400 m is exceeded). The semi-empirical depth-age curve computed in this paper may be compared with other curves, produced from various data and based on various assumptions (GOUTORBE and HILLIER 2013). For simplicity, we compare our curve with a selection of others, including those reflecting PSM and GDH1 models as well as the sediment/isostasy-corrected GEBCO with digital isochrons of the oceans proposed by MÜ LLER et al (2008), denoted GEBCO-M. All these use the same depth interval 2500-6400 m. The curve derived in this paper agrees particularly well with fully empirical depth-age relationship from GEBCO-M.…”

Fractal density and singularity analysis of heat flow over ocean ridges

“…The heat flow decreases with distance from mid-ocean ridges 5 6 7 . Gravity and crustal thickness have been used to constrain thermal contraction models, but the variation of heat flow and see-floor depth with age or distance became the primary constraint on models of the thermal structure and evolution of the oceanic lithosphere 8 9 . Several possible cascade processes have been discussed to interpret the generation and evolution of heat flow, including mantle convection 10 , heat conduction 11 , circulation 12 , heat released during exothermal serpentinisation reactions 13 , heat sources in plumes and magmatic eruptions 14 15 , dike injection 16 and earthquake swarms 17 .…”

“…These functions fit the observed young age topography and observed old age heat flow well. These three models (PSM, GDH1 and CHABLIS) have been validated by many authors using various types of observed data and they have been often employed as standard models for comparisons 3 8 9 25 26 27 28 29 30 31 32 33 .…”

“…In addition, two different types of functions are usually utilized to fit the heat flow data within two separate age ranges: a square root function of age for young seafloor and an exponential function for old seafloor 20 21 25 29 . Under the assumption of hydrothermal circulation, the discrepancy between predicted and observed heat flow in young seafloor can be used to estimate the level of hydrothermal heat flux and power loss 3 9 25 27 30 31 32 . The drawback of this bi-function model is that the discontinuity of the change rate (derivatives) of heat flow versus age might be difficult for interpretation and the different choice of the cut-off age separating two age domains may cause bias in estimation of heat flux.…”

Seafloor topography and the thermal budget of Earth

“…These temperatures are all potential temperatures. 1994; Hillier and Watts, 2005;Crosby et al, 2006;Zhong et al, 2007;Goutorbe and Hillier, 2013;Hasterok, 2013). The plate model can easily explain the fl attening behavior because the thickness of an aging lithosphere converges to a prescribed value imposed by the bottom boundary condition, typically set at the depth of ~100 km.…”