Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
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13. The Thermal Conditions of Venus
13. The Thermal Conditions of Venus
Pages 174-190
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From page 174... ...
The models include the core which is capable of solidifying when the core's temperature drops below the liquidus curve, the mantle which is proposed as divided into two, independent of the convecting layers (upper and lower mantle) , and the cold crust which maintains a temperature on the surface of the convective mantle close to 1200°C.
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From page 175... ...
, we will use two Raleigh figures: R ttgp^Td3 (2) R c~gp/\Td3 `3' XrlT where ~ denotes the thermal expansion coefficient; g is the acceleration of gravity; AT is the mean superadiabatic temperature difference in the layer; d denotes layer thickness, X is the coefficient of thermal diflusivi~; and ale and AT are defined by the formulae: b Ao To = _~ exp T ; To = 0° d2 ~ Ao ~~ p )
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From page 176... ...
and the temperature of the top of the lower thermal boundary layer, To;, can be calculated from the adiabatic relationship through the temperature in the base of the upper thermal boundary layer, Tu: T = nTu; To = natty' where n and no are constants.
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From page 177... ...
is completely determined by the temperatures indicated in Figure lb. The thermal balance equations for the upper mantle, the lower mantle, and the core are written as: 31r(Rr—R32)
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From page 178... ...
Reference temperatures are indicated for: the surface Ts; lithosphere base TB; base of the upper thermal boundary layer of the upper mantle Tut; peak of the lower boundary layer of the upper mantle TL1; boundary between the upper and lower mantles T12; base of the upper boundary layer of the lower mantle TU2; peak of the lower boundary layer of the lower mantle TL2; and the boundary between the core and the mantle Tom. Thicknesses of the thennal boundary layers are given: 51 for the boundaries of the upper mantle; 52 and [c for the boundaries of the lower mantle.
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From page 179... ...
describes heat release occurring when the core solidifies after the core adiabat drops below the core liquidus curve. It is supposed that the core consists of the mixture, Fe-FeS, and as solidification begins from the center of the planet, sulfur remains in the liquid layer, reducing the solidification temperature.
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From page 180... ...
The initial value of TU2 is the most significant, since Tut, due to the low thermal inertia of the upper mantle, rapidly adapts to the thermal regime of the lower mantle (t < 0.5 billion years)
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From page 181... ...
The thermal flow to the surface is obtained lair adding ~ 11 erg cm~ls~1 to FL, generated by the radioactive elements of the crust. The dashed line indicates the thermal flow generated bar radioactive elements of the lower mantle.
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From page 182... ...
~. The time scale for thermal inertia, as compared with models based on the conventional APC (Solomatov et al.
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From page 183... ...
, at the boundary of Venus' core, with a single pure iron melting curve, Tm (P) and a single equation of the state for iron p(P)
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From page 184... ...
Complete solidification of the core would have led to the absence of a liquid layer in the core and would have made it impossible for the magnetic field to be generated. However, for this, the temperature near the boundary of Venus' core should have dropped below the eutectic value, which, according to the estimates of Anderson et al.
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From page 185... ...
The vertical segments illustrate errors in determining temperature for curves 1 and 2. The boundary labels are as follows: CM is the boundary between the core and the mantle; C denotes the center of the planet; I is the boundary of the solid inner core; and the final letter indicates Earth (E)
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From page 186... ...
The mean temperature of the convective layer of the crust has been calculated at ~ 1600K, 1700K, l900K and 2000K, respectively, for quartz diorite, anorthosite, diabase, and albite, and exceeds the melting temperature for basalts by hundreds of degrees. This means that convection does not protect the crust from melting, and heat is removed by the melted matter.
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From page 187... ...
This is three to five times greater than crust generation in the terrestrial spreading zones. Another process by which basalt material circulates is where new portions of melted basalt reach the crust from the upper mantle, and basalt returns back to the mantle in the eclogite phase.
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From page 188... ...
The melted matter may flow to the surface or form intrusions; (c3 convection in the crust which does not reach the surface or reaching the surface; (d) lifting of hot plume from the bottom of the upper mantle to the crust of Venus, taggenng enhanced heat flow, a flow of crust matenal, and the sinking of the crust; (e)
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From page 189... ...
Basalt circulation also occurs by another way: the basalt is melted out of the upper mantle and returned back in the form of eclogite masses, which sink into the lighter mantle rock. It Is possible that this process triggers the accumulation of eclogite at the boundary between the upper and lower mantles, resulting in the chemical separation of the mantle.
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From page 190... ...
190 PLANETARY SCIENCES Sobolev, S.U, and A.Yu. Babeiko.
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