A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

Abstract

A magma accretion model of oceanic lithosphere is proposed and its implications for understanding its thermal field examined. The new model (designated Variable Basal Accretion-VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer is considered a space dependent variable. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling models. Another noteworthy feature of the new model is its ability to account for the main features in the thermal behavior of oceanic lithosphere. The improved fits to bathymetry have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation. Also, use of VBA model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH (Global Depth Heat Flow) reference models. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

A global reference model of Curie-point depths based on EMAG2

“…Previous estimates of global heat loss based on surface heat flow range widely from ~29 TW to 47 TW 1 2 3 4 5 6 . We further exam this problem with reference to our global Curie depth model.…”

“…Our planet Earth is under constant cooling and differentiation since its origin. Its current thermal state and heat loss can be estimated from surface heat flow measurements 1 2 3 4 5 6 . However, heat flow estimates have evident drawbacks; they are often measured at sparsely and irregularly distributed sites, and they are strongly affected by shallow hydrothermal circulation and therefore are limited in inferring deep thermal structure of the lithosphere.…”

“…In one early study 1 , and in some recent calibrations minimizing the hydrothermal effects 3 4 , the global heat loss was estimated at about 40–47 TW (or 4.4–4.7 × 10 13 W). Other reappraisals of global heat flow database, however, concluded that global conductive heat loss falls in the range from 29 to 34 TW 2 5 6 . The differences between these estimates vary considerably.…”

Global distribution of the lithosphere-asthenosphere boundary: a new look

“…V. M. Hamza and F. P. Vieira: Global distribution of the lithosphere-asthenosphere boundary Hamza et al (2010) presented a model that takes into consideration the thermal consequences of variable rates of magma accretion at the lower boundary of the lithosphere. According to this model (designated VBA), the variability in the rate of magma accretion at the base of the lithosphere has a direct influence on surface heat flux and bathymetry.…”

Heat Flow in the Campos Sedimentary Basin and Thermal History of the Continental Margin of Southeast Brazil

“…There are indications that the high heat flow belt is not restricted to the Campos basin but extends to the south into the Santos basin and also to the north into the Espirito Santo basin. The existence of a major geothermal belt adjacent to the continental margin of southeast Brazil is an altogether surprising result as it departs from the usual trend of decreasing heat flow age of ocean crust [74,75]. The width of the high heat flow zone is narrow implying that the heat source is located at shallow depths in the upper crust and is relatively recent.…”