Origin of iron meteorites - the oldest materials in the Solar System

岩浆铁陨石形成的模型假设液态金属来自硅酸盐熔体的重力分离。Hf-W测年法确定了这一事件的时间，并表明铁陨石与富Ca， al包裹体（CAI）的年龄大致相同，CAI是太阳系中最古老的岩石，但比球粒陨石的主要成分球粒更古老。这种年龄关系与一般的假设相反，即分化体是球粒质母体熔化的产物。它强调了岩浆铁陨石的重要性，它代表了最古老的星子的金属核。同样古老的富含硅酸盐的物质也不存在。通过研究可能由溶出形成的非金属包裹体和直接分析金属相中的亲石元素，如Si、Al、Cr和P，可以重建铁陨石以前富含硅酸盐的地幔。这些元素的浓度在高温下与金属/硅酸盐熔体平衡不一致，但反映了低温过程。从金属中失去亲石元素的过程在IIIAB铁陨石中最有效，因为这些元素的浓度极低。铁陨石中的硅酸盐、氧化物、磷酸盐、磷化物或硫化物包裹体可能是这些元素的汇。我们将继续分析IC、IIC群，特别是IVA和IVB群岩浆铁的金属相，它们在所有研究的铁陨石中具有最高的Si和Al浓度。我们还将继续在这些陨石中寻找非金属夹杂物。此外，包裹体的氧同位素将被测量，以提供有关母体同位素特征、均匀程度和氧气来源的信息。

Models of the formation of magmatic iron meteorites assume gravitational segregation of liquid metal from a silicate melt. The Hf-W dating method determines the timing of this event and shows that iron meteorites have about the same age as Ca,Al-rich inclusions (CAI), the oldest rocks in the solar system but are older than chondrules the major component of chondrites. This age relationship is in contrast to the general assumption that differentiated bodies are the product of melting of chondritic parent bodies. It emphasizes the importance of magmatic iron meteorites which represent the metal cores of the oldest planetesimals. Similarly old silicate-rich material does not exist. The former silicate-rich mantles of the iron meteorites may be reconstructed i) by studying non metal inclusions that could have formed by exsolution and ii) by direct analyses of lithophile elements, like Si, Al, Cr, and P in metal phases. The concentrations of these elements are inconsistent with metal/silicate melt equilibrium at high temperature but reflect low temperature processes. The process responsible for loosing lithophile elements from the metal was most efficient in IIIAB iron meteorites which have extremely low concentrations of such elements. Inclusions of silicates, oxides, phosphates, phosphides or sulfides in iron meteorites may have acted as sink for these elements. We will continue to analyze metal phases of group IC, IIC and especially IVA and IVB magmatic irons which have the highest concentrations of Si and Al in all studied iron meteorites. We will also continue to search for non-metal inclusions in these meteorites. In addition, oxygen isotopes of inclusions will be measured to provide information about the isotopic signature of the parent body, degree of homogenization and origin of the oxygen.