A model of lunar evolution |
| |
| Authors: | D W Strangway H N Sharpe |
| |
| Institution: | (1) Dept. of Geology, University of Toronto, Canada;(2) Institute for Aerospace Studies, University of Toronto, Canada |
| |
| Abstract: | There have been many models describing the evolution of our sister planet. As information from the intensive exploration by
the Apollo program has accumulated, more constraints on these models have emerged. We specifically consider a hypothesis in
which there is a present day asthenosphere, a heat flow between 24 and 32 ergs cm−2 s−1 and a crust which developed early in the Moon's history by melting of the outer 100 to 200 km. We have also introduced a
constraint which keeps the deep interior below the Curie point of iron for the first 1 to 1.5 b.y. so that it is able to carry
the memory of an early field which magnetized the cold interior. The magnetized mare basalts and breccias cooled in this field
from above the Curie point of iron (≈800°C.) and acquired a thermoremanent magnetization. While fully recognizing that some
of these constraints are subject to other interpretations, it is nevertheless instructive to consider the thermal history
that follows from such a model. First, the initial temperature must be high enough to cause melting in the outer 100–200 km,
while the interior temperature must be cool enough to be below the Curie point of iron. Second, the crust in this model cools
off so rapidly that the mare basalts could not be developed as late as indicated in lunar history. Rather we propose that
the mare basalts result from local remelting associated with giant impacts. Third, the Moon's deep interior must have warmed
up enough to erase the memory of the ancient magnetic field from the deep interior and to develop the asthenosphere which
has been detected seismically. Fourth, if this asthenosphere is real, the viscosity of the Moon as a function of temperature
must be high enough to have prevented convective cooling until the temperature increased to a value near the solidus temperature.
At this temperature, the Moon would then likely cool by convection in the solid state. It is, therefore, a consequence of
this model that solid body convection tool place late in lunar history. This may well have contributed to the lunar center
of figure and center of mass offset, to the low order terms in its gravity field and to, its disequilibrium moment of inertia
differences. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
