金属世界上的铁火山作用和钯矿的起源
Ferrovolcanism on metal worlds and the origin of pallasites
摘要：
当分化的微行星冷却时，它们的核心可以从外到内固化，这一点可以通过古地磁测量和铁陨石的冷却速率估计得到证明。由外向内凝固的细节和剩余堆芯熔体的命运知之甚少。对于主要由Fe和Ni与较轻的组成元素（如硫）合金化组成的芯，这种向内的芯生长可能通过固体FeNi枝晶的生长来实现。FeNi枝晶的生长导致残留熔体的互连袋，其随着FeNi继续固化而逐渐富含硫直至31wt%硫的共晶组合物。在这里，我们表明，区域的残留富硫FeNi熔体的核心获得足够的过剩压力，通过岩脉传播到地幔。因此，地核物质将侵入上覆的岩石地幔，甚至可能喷发到星子表面。我们把这些过程统称为铁火山作用。我们的计算表明，铁火山岩表面喷发更有可能与地幔厚度小于50公里的机构。我们发现，侵入铁岩浆活动可以产生钯，一个神秘的类陨石的橄榄石晶体夹带在矩阵的FeNi金属。铁火山喷发可以解释普绪喀的体积密度与铁陨石不一致，但仍显示出金属表面成分的证据。
英文摘要：
As differentiated planetesimals cool, their cores can solidify from the outside-in, as evidenced by paleomagnetic measurements and cooling rate estimates of iron meteorites. The details of outside-in solidification and fate of residual core melt are poorly understood. For a core primarily composed of Fe and Ni alloyed with lighter constituent elements, like sulfur, such inward core growth would likely be achieved by growth of solid FeNi dendrites. Growth of FeNi dendrites results in interconnected pockets of residual melt that become progressively enriched in sulfur up to a eutectic composition of 31 wt percent sulfur as FeNi continues to solidify. Here we show that regions of residual sulfur-enriched FeNi melt in the core attain sufficient excess pressures to propagate via dikes into the mantle. Thus, core material will intrude into the overlying rocky mantle or possibly even erupt onto the plantesimals surface. We refer to these processes collectively as ferrovolcanism. Our calculation show that ferrovolcanic surface eruptions are more likely on bodies with mantles less than 50 km thick. We show that intrusive ferromagmatism can produce pallasites, an enigmatic class of meteorites composed of olivine crystals entrained in a matrix of FeNi metal. Ferrovolcanic eruptions may explain the observations that Psyche has a bulk density inconsistent with iron metorites yet shows evidence of a metallic surface composition.
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