Lunar volatile depletion due to incomplete accretion within an impact-generated disk
Lunar volatile depletion due to incomplete accretion within an impact-generated disk
复制标题
DOI：
10.1038/ngeo2574
复制
发表时间：
2015-12-01
影响因子：
18.3
通讯作者：
Fegley, Bruce, Jr.
中科院分区：
文献类型：
--
作者：
Canup, Robin M.;Visscher, Channon;Fegley, Bruce, Jr.
月球可能是由巨大撞击产生的围绕地球轨道运行的蒸气和熔体盘形成的(1)。月球和地球的地幔具有相似的成分。然而，鉴于蒸发逃逸机制 (4) 似乎与预期的盘条件 (5) 不一致，目前尚不清楚为什么月球样本的挥发性元素比陆地地幔岩石 (2,3) 更贫乏。动力学模型(6,7)表明，月球最初是从最外层圆盘吸积的，但后来从内层圆盘的熔化物中获得了高达 60% 的质量。在这里，我们结合了动力学、热学和化学模型来表明，月球中挥发性物质的消耗可以通过内盘中富含挥发性物质的熔体优先吸积到地球而不是生长中的月球来解释。内盘中的熔体最初很热且挥发性较差，但随着盘的冷却，挥发物会凝结。在我们的模拟中，当引力相互作用导致月球轨道远离圆盘时，内圆盘熔化物向月球的输送实际上停止了，并且月球吸积的这种终止发生在钾和更易挥发的元素凝结之前。因此，来自内盘的月球部分预计将被挥发性耗尽。我们认为，这种机制可以解释部分或全部月球挥发性损耗，具体取决于月球内部的混合程度。
The Moon may have formed from an Earth-orbiting disk of vapour and melt produced by a giant impact(1). The mantles of the Moon and Earth have similar compositions. However, it is unclear why lunar samples are more depleted in volatile elements than terrestrial mantle rocks(2,3),given that an evaporative escape mechanism(4) seems inconsistent with expected disk conditions(5). Dynamical models(6,7) suggest that the Moon initially accreted from the outermost disk, but later acquired up to 60% of its mass from melt originating from the inner disk. Here we combine dynamical, thermal and chemical models to show that volatile depletion in the Moon can be explained by preferential accretion of volatile-rich melt in the inner disk to the Earth, rather than to the growing Moon. Melt in the inner disk is initially hot and volatile poor, but volatiles condense as the disk cools. In our simulations, the delivery of inner disk melt to the Moon effectively ceases when gravitational interactions cause the Moon's orbit to expand away from the disk, and this termination of lunar accretion occurs before condensation of potassium and more volatile elements. Thus, the portion of the Moon derived from the inner disk is expected to be volatile depleted. We suggest that this mechanism may explain part or all of the Moon's volatile depletion, depending on the degree of mixing within the lunar interior.