Isotopic constraints on genetic relationships among group IIIF iron meteorites, Fitzwater Pass, and the Zinder pallasite

TL;DR

This study uses molybdenum isotopic analysis to clarify the genetic relationships among group IIIF iron meteorites, revealing their close genetic links and distinctions from other meteorite groups.

Contribution

The paper provides new Mo and W isotopic data for IIIF irons, Fitzwater Pass, and Zinder pallasite, enhancing understanding of their genetic relationships and origins.

Findings

IIIF irons share similar Mo isotopic compositions, indicating a common origin.

Fitzwater Pass has distinct isotopic signatures, linking it to non-magmatic IAB irons.

Zinder pallasite is unrelated to IIIF irons and shares isotopic features with main-group pallasites.

Abstract

Complex interelement trends among magmatic IIIF iron meteorites are difficult to explain by fractional crystallization and have raised uncertainty about their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a powerful tool to assess if individual IIIF irons are related to each other. However, while trace-element data are available for all nine IIIF irons, Mo isotopic data are limited to three samples. We present Mo isotopic data for all but one IIIF irons that help assess the genetic relationships among these irons, together with new Mo and W isotopic data for Fitzwater Pass (classified IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has been proposed). After correction for cosmic-ray exposure, the Mo isotopic compositions of the IIIF irons are identical within uncertainty and confirm their belonging to carbonaceous chondrite-type (CC) meteorites. The mean Mo isotopic composition of Group IIIF overlaps those Groups IIF and IID, but a common parent body for these groups is ruled out based on distinct trace element systematics. The new Mo isotopic data do not argue against a single parent body for the IIIF irons, and suggest a close genetic link among these samples. By contrast, Fitzwater Pass has distinct Mo and W isotopic compositions, identical to those of some non-magmatic IAB irons. The Mo and W isotope data for Zinder indicate that this meteorite is not related to IIIF irons, but belongs to the non-carbonaceous (NC) type and has the same Mo and W isotopic composition as main-group pallasites.