Heat loss and tectonic style of Venus

Abstract

The tectonic style of a terrestrial planet depends strongly on the mechanisms of heat release from the mantle through the lithosphere to the surface. Three types of lithospheric heat transfer have been proposed. (1) Lithospheric conduction, (2) (hot spot) volcanism, (3) plate recycling (mainly at spreading plate margins). In the case of the Earth the total heat flow is determined by plate recycling 65%) heat conduction through the lithosphere 20%, decay of radioactive elements in the crust 15%) hot spot volcanism ~1%. Scaling the mean surface heat flow density of the Earth to venusian conditions leads to 66mWlm'. In the case of Venus plate tectonics play only a minor role. Thus, two processes remain for heat release: (hot spot) volcanism and conduction. The term "hot spot" is written in brackets because volcanism on Venus occurs globally, not necessarily associated with hot spots.The volcanic lava production has been estimated from Venera 15/16 scenes. Arecibo and Magellan images revealed that the surface character south of 30" N is very similar to the area covered by Venera. The main results of the estimation are: (i) The maximum thickness of the plain lavas is 3 km. (ii) With plain lava thicknesses larger than 200 m the lava production from central volcanoes is negligible. (iii) Two age models have been used for the mean age of the area obseved: At, = lo9 a, At, = 400 x lo6 a. At, leads to the maximum lava production rate of 3 km3/a compared to 20 to 25 km3/a of the Earth; this gives a maximum contribution of 0.75 mW/m' to the heat flow density of Venus, i.e. about 1%. This implies that either heat conduction is the only dominating process for heat release or there is a hidden reservoir of the "missing basalt" somewhere or there is another unknown tectonic process. Assuming pure conduction and correcting the surface heat flow density for radioactive elements in the crust leads to a thickness of the thermal lithosphere of 45 km. A reservoir for the "missing basalt" could be basaltic underplating to a depth of 100 km. This gives a contribution of about 20 mW/m' with the age model At2 to the heat flow density from first order calculations.While the tectonic style of the Earth can be described to be linear formed at the plate margins, the surface of Venus is characterized by global spotty volcanism. The surface is more dominated by volcanic landforms than in the case of the Earth despite the relatively low lava production rate with a maximum of 3 km3/a. As plate tectonics is a minor process on Venus, conduction through a rather thin lithosphere should play an important role for heat release.

Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two‐dimensional models

“…The amount by which crustal HPE concentration is enhanced depends on the melt fraction: for example if a parcel of mantle melts by a total of 5% to produce crust, the HPE concentration in the resulting crust is 20 times higher than it was in the source material. The globally averaged HPE concentration is the same regardless of whether it is spatially constant or undergoes melt‐solid partitioning and, based on the similarity of heat producing element concentration in Venusian basalts to those in terrestrial basalts [ Janle et al , 1992; Nimmo and McKenzie , 1997; Turcotte , 1995], is assumed to have the “bulk silicate Earth” (BSE) value of 5.2 × 10 12 W/kg (at the present day), and an average half‐life of 2.43 Ga.…”

Atmosphere/mantle coupling and feedbacks on Venus

“…Spatial variations are not considered. We use Earth‐like values for the concentration of heat‐producing elements [ Janle et al ., ; Nimmo and McKenzie , ; Turcotte , ] with a concentration of 5.2 × 10 −12 W/kg at the present day and a half‐life of 2.43 Gyr. The phase transitions in the olivine system and in the pyroxene‐garnet system are included with parameters based on mineral physics data [ Irifune and Ringwood , ; Ono et al ., ], as discussed in Xie and Tackley [].…”

Tessera terrain on Venus: A survey of the global distribution, characteristics, and relation to surrounding units from Magellan data

“…Tessera terrain has practically no morphological analogs on the terrestrial planets except for Within the area surveyed by Venera 15/16 (Figure l a), large (up to thousands of kilometers across) and small (up to hundreds of kilometers across) occurrences of tesserae comprise about 10-15% of the surface [Sukhanov, 1986]. The surfaces in intervening areas between tesserae are dominated by smooth and rolling lava plains [Sukhanov, 1986[Sukhanov, , 1992Sukhanov et al, 1989;Bindschadler and Head, 1989;Janle et al, 1992]. Tesserae within the northern high latitudes covered by Venera 15/16 are distributed nonrandomly and show a tendency to be clustered.…”