Origin of Iron Meteorite Groups IAB and IIICD
Origin of Iron Meteorite Groups IAB and IIICD
复制标题
铁陨石群 IAB 和 IIICD 的起源
DOI：
10.1515/zna-1980-0801
复制
发表时间：
1980
期刊：
影响因子：
--
通讯作者：
A. Kracher
中科院分区：
文献类型：
--
作者：
J. Wasson;J. Willis;C. Wai;A. Kracher
根据低Ge、Ga、W和Ir含量和高As含量，将几种以前归属于IAB组的低Ni铁陨石重新归类为IIICD; IIICD的低Ni极限值现在为62 mg/g，IAB的低Ni极限值为64 mg/g。两组中产生的分馏模式非常相似。长期以来，人们一直认为，与岩浆铁陨石群相反，IAB和IIICD并不是由金属岩浆的分离结晶形成的。其他模型也被提出，但都有严重的缺陷。提出了一个新的模型，涉及每个铁的形成在小池的影响熔体上的母体组成的材料类似于在一些IAB和IIICD铁中发现的奥氏体夹杂物，但最初不平衡。这些撞击熔体的温度范围从~ 1190 K到~ 1350 K。熔融和未熔融固体之间的平衡程度范围从最低温度下的最小到最高温度下的中等。在Ni含量为12 atom %的Fe-Ni-S体系中，熔体的最低温度在Co_2O_3附近。在冷却时，这些沉淀的金属通过平衡结晶具有~ 600 mg/g Ni。富镍熔体是富镍硫化物和金属在不平衡奥氏体基体中熔融的结果。低镍铁在高温熔体中形成，接近FeS-Fe共晶的成分或稍微富含金属。我们认为，随着Ni浓度的增加，Ge，Ga和耐火材料的丰度降低，反映了这些元素在氧化物相中的不平衡的铁磁性材料中的捕获，并且很少进入富Ni熔体母体的Oktibbeha县铁。其余元素倾向于在熔体中具有或多或少独立于温度的元素/Ni比。的显着的相关性之间的I-结晶包裹体和镍含量的主机金属的详细演变（兆）风化层中，这些群体起源的解释。最富镍的熔体只能产生从一个不平衡的球粒陨石母体;作为不断沉积的影响能量产生越来越高的变质等级，最大镍含量的影响熔体（及其随后沉淀的金属）逐渐下降。
Abstract Several low-Ni iron meteorites previously assigned to group IAB are reclassified IIICD on the basis of lower Ge, Ga, W and Ir concentrations and higher As concentrations; the low-Ni extreme of IIICD is now 62 mg/g, that of IAB is 64 mg/g. The resulting fractionation patterns in the two groups are quite similar. It has long been established that, in contrast to the magmatic iron meteorite groups, IAB and IIICD did not form by fractional crystallization of a metallic magma. Other models have been proposed, but all have serious flaws. A new model is proposed involving the formation of each iron in small pools of impact melt on a parent body consisting of material similar to the chondritic inclusions found in some IAB and IIICD irons, but initially unequilibrated. These impact melts ranged in temperatures from ~ 1190 K to ~ 1350 K. The degree of equilibration between melt and unmelted solids ranged from minimal at the lowest temperature to moderate at the highest temperature. The lowest temperature melts were near the cotectic in the Fe-Ni-S system with Ni contents of ~ 12 atom %. Upon cooling, these precipitated metal having ~ 600 mg/g Ni by equilibrium crystallization. The Ni-rich melt resulted from the melting of Ni-rich sulfides and metal in the unequilibrated chondritic parent. Low-Ni irons formed in high temperature melts near the composition of the FeS-Fe eutectic or somewhat more metal rich. We suggest that the decreasing Ge, Ga and refractory abundances with increasing Ni concentration reflect the trapping of these elements in oxide phases in the unequilibrated chondritic material, and that very little entered the Ni-rich melt parental to the Oktibbeha County iron. The remaining elements tended to have element/Ni ratios in the melts that were more or less independent of temperature. The remarkable correlation between I-Xe age of the chondritic inclusions and Ni content of the host metal is explained by a detailed evolution of (mega)regolith in which these groups originated. The most Ni-rich melts could only be generated from an unequilibrated chondrite parent; as the continuing deposition of impact energy produced increasingly higher grades of metamorphism, the maximum Ni content of the impact melts (and their subsequently precipitated metal) gradually decreased.