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下地幔的背景:
A team of scientists, made the first laboratory study of the deformation properties of a high-pressure silicate mineral named post-perovskite. McNamara, a geophysicist, modeled the stresses the mineral would typically undergo as convection（对流）
"This the first time the deformation properties of this mineral have been studied at lower mantle temperatures and pressures," says McNamara. "The goal was to observe where the weak planes are in its crystal structure and how they are oriented." The results of the combined laboratory tests and computer models, he says, show that post-perovskite doesn't fit what is known about conditions in the lowermost mantle.
Earth's mantle is a layer that extends from the bottom of the crust, about 25 miles down, to the planet's core, 1,800 miles deep. Scientists divide the mantle into two layers separated by a wide transition zone centered around a depth of about 300 miles. The lower mantle（下地幔）lies below that zone.
Most of Earth's lower mantle is made of a magnesium silicate mineral called perovskite. In 2004, earth scientists discovered that under the conditions of the lower mantle, perovskite can change into a high-pressure form, which they dubbed post-perovskite. Since its discovery, post-perovskite has been geophysicists' favorite candidate to explain the composition of a mysterious layer that forms the bottom of Earth's lower mantle. |
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发表于 2012-10-13 08:16:06
