Heat flow maintained in ocean basins of great age: investigations in the north-equatorial West Pacific

Abstract

S U M M A R YMultipenetration heat flow measurements have been made at four sites in deep basins of the west-central Pacific Ocean: the West Mariana Basin, Central Mariana Basin, Nauru Basin and Central Pacific Basin. The final heat flows are, respectively, 46.6 f 0.5, 49.4 f 0.2, 44.2 f 0.9 and 49.5 f 1.1 mW m-*. Each site was surveyed bysingle-channel seismic reflection profiling, and provided a gravity core. The instrument measured thermal conductivity in situ over the entire depth intervals used for determination of the gradients, and the reduction scheme iterated conductivity and heat-capacity changes into the fitting procedure, both of entry frictional decays and of conductivity heat pulse decays. The absolute accuracy of the instrument should approach 2 per cent and the first site would make a good intercalibration standard for heat flow measurement. The heat flow variation between the sites is real, and there is also a significant variation in the isostatically reduced depths of the sites. There is no age progression of either depth or heat flow, and, when five other good multidata points are included, the relationship between depth and heat flow conforms to that expected from simple cooling models only in an average sense for the whole group. The most plausible explanation for the variations is that heat flow and thermal elevation are dependent on different levels of deep lithosphere reheating at different times between 70 and 120Myr ago. It is suggested that additional topographic variation is caused by the different accumulations of sediment and lava flows at each site, and to errors in the isostatically reduced depths due to incomplete knowledge of the stratigraphy down to the crust-mantle interface. These explanations of the topographic variation could be tested by seismic refraction measurements.

Reservoir Definition

“…This suboceanic heat flow varies from several hundreds of milliwatts per square meter at mid-oceanic ridges to about 50 mW m −2 over oceanic lithosphere older than 80 Myr (Lister et al, 1990). When thermal effects of hydrothermal circulation are removed, this variation is well explained by the cooling plate model.…”

Constraints on plate tectonics initiation from scaling laws for single-cell convection

“…Considering the thermal evolution of terrestrial planets is beyond the scope of this study, and we use the Earth's oceanic lithosphere as a reference point and take the interior temperature T i as $1700 K and surface heat flux in the old oceanic lithosphere as 40 mW/m 2 (Parsons and Sclater, 1977;Lister et al, 1990;Stein and Stein, 1992). Since the scaling laws used in this paper are derived from calculations using Newtonian rheology, we use the activation energy of diffusion for olivine which is about 375 kJ/mol (Hirth and Kohlstedt, 2003).…”

Interprétation des données de flux de chaleur et de gravité dans le Bouclier Canadien /

“…Dans les océans, le flux est élevé près de la ride médio-océanique (une moyenne globale de 110 mW-m" 2 , Jessop, 1990), et diminue systématiquement vers les bassins et fossés océaniques (48 mW-m~2, Lister et al, 1990). L'explication généralement acceptée est que la lithosphère océanique se refroidit en s'éloignant de la ride.…”