Abstract
AbstractWe investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter's Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in 17O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in 17O and significantly depleted in 18O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced 18O/16O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca2Mg[Si2O7]) or a an åkermanite‐diopside (MgCaSi2O6) intergrowth.
Highlights
Primitive meteorites, micrometeorites, interplanetary dust particles (IDPs), and cometary material contain small amounts of refractory dust grains which predate the formation of the Sun and our planetary system and are characterized by highly anomalous isotopic compositions that cannot be explained by chemical or physical processes within the solar system (e.g., Zinner 2014)
We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine-grained chondrule rims in six Mighei-type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray, and Yamato 791198), and the CM-related carbonaceous chondrite Sutter’s Mill
We conducted an investigation of the presolar grain inventories in the fine-grained dust rims (FGRs) of a set of CM chondrites and the CM-related carbonaceous chondrite Sutter’s Mill
Summary
Micrometeorites, interplanetary dust particles (IDPs), and cometary material contain small amounts of refractory dust grains which predate the formation of the Sun and our planetary system and are characterized by highly anomalous isotopic compositions that cannot be explained by chemical or physical processes within the solar system (e.g., Zinner 2014). Instead, they possess nucleosynthetic signatures of their stellar parents. These presolar or “stardust” grains condensed in the ejecta of evolved stars or stellar explosions (novae and supernovae) They became part of the interstellar medium (ISM) where they were exposed to high-energetic irradiation, exposure to shockwaves from nearby supernova. Determining the abundances and distributions of the different types of presolar dust allows for the study of parent body alteration processes, and potential heterogeneities in the distribution of presolar circumstellar matter within the nascent solar system (Zinner 2014; Floss and Haenecour 2016)
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