The origin of the IAB main group (MG) iron meteorites is explored through consideration of 182W isotopic compositions, thermal modeling of 26Al decay, and mass independent (nucleosynthetic) Mo isotopic compositions of planetesimals formed in the noncarbonaceous (NC) protosolar isotopic reservoir. A refined 182W model age for the meteorites Campo del Cielo, Canyon Diablo, and Nantan suggests that the IAB-MG parent body underwent some form of metal-silicate segregation as early as 5.3 ± 0.4 Myr after calcium-aluminum rich inclusion (CAI) formation or as late as 13.8 ± 1.4 Myr after CAI formation. If melting of the IAB-MG occurred prior to 7 Myr after CAI formation, it was likely driven by 26Al decay for a parent body radius >40 km. Otherwise, additional heat from impact is required for melting metal this late in Solar System history. If melting was partially or wholly the result of internal heating, a thermal model of 26Al decay heat production constrains the accretion age of the IAB-MG parent body to ~1.7 ± 0.4 Myr after CAI formation. If melting was, instead, dominantly caused by impact heating, thermal modeling suggests the parent body accreted more than 2 Myr after CAI formation. Comparison of Mo mass independent isotopic compositions of the IAB-MG to other NC bodies with constrained accretion ages suggests that the Mo isotopic composition of the NC reservoir changed with time, and that the IAB-MG parent body accreted between 2 to 3 Myr after CAI formation, thus requiring an origin by impact. The relationship between nucleosynthetic Mo isotopic compositions and accretion ages of planetesimals from the NC reservoir suggests that isotopic heterogeneity developed from either addition of s-process material to, or removal of coupled r-/p-process material from the NC reservoir.

中文翻译：

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IAB主族铁陨石起源和非碳质（NC）储层同位素演化的新意义


通过考虑 182W 同位素组成、26Al 衰变的热模拟以及在非碳质 (NC) 原太阳同位素库中形成的星子的质量独立（核合成）Mo 同位素组成，探索了 IAB 主族 (MG) 铁陨石的起源。 Campo del Cielo、Canyon Diablo 和 Nantan 陨石的精确 182W 模型年龄表明，IAB-MG 母体早在富钙铝夹杂物 (CAI) 形成后 5.3 ± 0.4 Myr 就经历了某种形式的金属硅酸盐偏析或最迟在 CAI 形成后 13.8 ± 1.4 Myr。如果 IAB-MG 的熔化发生在 CAI 形成后 7 Myr 之前，则可能是由母体半径 >40 km 的 26Al 衰变驱动的。否则，在太阳系历史的晚期，需要额外的撞击热量来熔化金属。如果熔化部分或全部是内部加热的结果，则 26Al 衰变热产生的热模型将 CAI 形成后 IAB-MG 母体的吸积年龄限制为 ~1.7 ± 0.4 Myr。相反，如果熔化主要是由冲击加热引起的，热模型表明在 CAI 形成后母体吸积了超过 2 Myr。 IAB-MG 的 Mo 质量独立同位素组成与其他具有受限吸积年龄的 NC 体的比较表明，NC 储层的 Mo 同位素组成随时间变化，并且 IAB-MG 母体在 CAI 后 2 至 3 Myr 之间吸积形成，因此需要撞击起源。 核合成钼同位素组成与来自NC储层的星子吸积年龄之间的关系表明，同位素异质性是由于向NC储层添加s过程材料或从NC储层中去除耦合的r/p过程材料而产生的。