Petrology and chemistry of the Miles IIE iron. II: Chemical characteristics of the Miles silicate inclusions

概要

論文の詳細を見る
A total of nine silicate inclusions (6 gabbroic, 3 cryptocrystalline) were isolated from slab samples of the Miles IIE iron meteorite. They were studied petrologically and then analyzed by instrumental neutron activation analysis, along with the host metal. Based on the siderophile element abundances in the host metal phase, Miles can be classified as a IIE iron but in some aspects it does not match the siderophile abundances of either IIE or anomalous IIE (IIE-An) irons. It may be a member of a third group of IIE irons, tentatively named fractionated IIE. Compared with the average H chondrite, the highly siderophile elements (Re, Os, Ir) are relatively more depleted than the less refractory siderophiles, except for Cu which is as depleted as the highly siderophile elements. This suggests that the metal phase of Miles was not simply produced by a vaporization/fractional condensation process. Rather, it was produced by the melting of H chondritic materials, followed by melt-solid segregation. At least a part of the immiscible sulfide in which Cu was distributed to a considerable degree, was removed from the metal melt. Silicate inclusions have variable amounts of siderophile elements, but their relative abundances are similar to those of the metal phase. This suggests that the siderophile elements in the silicate inclusions have the same genesis as those in the host metal. Plagiophile elements (Al, Na and K) are all enriched in the silicate inclusions, especially in the cryptocrystalline inclusions, with K being the most abundant, successively followed by Na and Al. This fractionation of the plagiophile elements must have occurred during the fractional crystallization process, when the silicate inclusions formed. Rare earth elements (REE) are fairly enriched in the silicate inclusions (especially in the gabbroic inclusions) but their concentrations are slightly lower than that expected from the degree of partial melting of H chondritic materials. A mechanical loss of Ca-phosphate in sampling is suggested for the inconsistency in the REE abundances. Based on the REE abundance variations in the silicate inclusions of several IIE irons, including Miles, we infer that the degree of differentiation of the parental liquids from which silicate inclusions formed was highly variable; it increased from Watson to Weekeroo Station, with Miles being intermediate.
国立極地研究所の論文

Petrology and chemistry of the Miles IIE iron. II: Chemical characteristics of the Miles silicate inclusions

スポンサーリンク

概要

著者

関連論文

スポンサーリンク