Although IVA irons have O- and Cr-isotopic compositions resembling those of equilibrated LL chondrites, the bulk composition of refractory elements (e.g., Re, Ir, Pt) in the IVA core appears to be significantly lower than LL. These compositional discrepancies suggest known IVA irons may be missing early crystallized samples. We hypothesize the bulk composition of the IVA core is LL-like, but current collections do not include early fractional-crystallization IVA products. Our fractional-crystallization modeling of element vs. Au trends suggests that extant IVA irons are products of > 40% crystallization of the core, assuming an initial 2.9 wt.% S content. The model-derived bulk (Ni-normalized) composition of the IVA core is depleted relative to LL in most moderate volatiles: S (82% depletion), Ge (99.9% depletion), Ga (95% depletion), As (50% depletion); however, Au is enriched by 10%. Because moderate volatiles with depletions > 80% relative to LL have 50%-condensation temperatures < 1,020 K, it seems likely these depletions reflect post-accretion impact-induced volatilization of the IVA asteroid. The mean Ni-normalized compositions of analyzed IVA irons yield a lesser depletion of As (30%) and greater enrichment of Au (48%) relative to LL. The IVA asteroid may have experienced a complex parent-body thermal and collisional history: (1) differentiation, (2) impact-induced mantle stripping, devolatilization, and fractional condensation, (3) rapid crystallization of the core from the outside inwards, (4) shattering of the core after ∼75% crystallization, (5) quenching of thinly insulated samples (e.g., Fuzzy Creek), (6) formation of amorphous free silica in several IVA irons after impact-induced vaporization of portions of the overlying silicate mantle, followed by fractional condensation, (7) loss of portions of the core representing the first 40% of crystallization, (8) reaccretion of some core fragments, facilitating relatively slow cooling of a few IVA irons (e.g., Duchesne, Duel Hill (1854), Chinautla), and (9) collisional resetting of the Re-Os clock 4456 ± 25 Ma ago.

尽管 IVA 铁具有与平衡的 LL 球粒陨石相似的 O 和 Cr 同位素组成，但 IVA 核心中难熔元素（例如 Re、Ir、Pt）的整体组成似乎明显低于 LL。这些成分差异表明已知的 IVA 熨斗可能缺少早期结晶样品。我们假设 IVA 核心的主体成分类似于 LL，但目前的收藏不包括早期的分级结晶 IVA 产品。我们对元素与 Au 趋势的分级结晶建模表明，假设初始 S 含量为 2.9 wt.%，现有的 IVA 铁是核心结晶 > 40% 的产物。在大多数中等挥发物中，IVA 核心的模型衍生的本体（Ni 归一化）成分相对于 LL 是耗尽的：S（82% 耗尽）、Ge（99.9% 耗尽）、Ga（95% 耗尽）、As (50% 耗尽); 然而，Au 富集了 10%。因为相对于 LL 消耗 > 80% 的中等挥发物具有 50% 的冷凝温度 < 1,020 K，这些消耗似乎很可能反映了 IVA 小行星的吸积后撞击引起的挥发。与 LL 相比，分析的 IVA 铁的平均 Ni 归一化成分产生较少的 As (30%) 消耗和较大的 Au (48%) 富集。IVA小行星可能经历了复杂的母体热和碰撞历史：（1）分化，（2）撞击引起的地幔剥离，脱挥发分和分馏，（3）核心从外向内快速结晶，（ 4) 约 75% 结晶后核心的破碎，(5) 薄绝缘样品（例如，Fuzzy Creek）的淬火，