Formation of CV chondrules by recycling of amoeboid olivine aggregate-like precursors

Abstract

We have studied porphyritic olivine-rich chondrules of the carbonaceous chondrite Kaba (CV3) by combined highresolution X-ray mapping, quantitative electron microprobe analyses, and oxygen isotopic analyses via secondary ion mass spectrometry. These chondrules contain smaller inner-chondrule olivine grains characterized by low refractory element (Ca, Al, Ti) contents, and larger outer-chondrule olivine crystals that are enriched in refractory elements and show complex Ti and Al oscillatory zonings. Our O isotopic survey revealed that many of the inner-chondrule olivines are 16 O-richer than the relatively isotopically uniform outer-chondrule olivines. Inner-chondrule olivine crystals-only a minority of which may be derived from earlier generations of chondrules-are likely mostly inherited from nebular condensates similar to AOAs, as they share similar isotopic and chemical features and are thus interpreted as relict grains. Still, being 16 O-poorer than most AOAs, they may have experienced significant exchange with a 16 O-poor reservoir prior to chondrule formation (even if to a lesser degree than relicts in CM2 and ungrouped C2 chondrites). Subsequent incomplete melting of the relict grains produced Ca-Al-Ti-rich melts that engulfed the remaining relict olivine grains. The complex Ti and Al zoning patterns in outer chondrule (host) olivines, in particular the systematic dilution near the margin, seem to reflect gas-melt interactions (with e.g. SiO (g), Mg (g)) which also buffered the O isotopic composition of chondrule hosts. Together, these results demonstrate that important episodes of recycling of nebular condensates occurred in the solar protoplanetary disk.

An unusual compound object in Yamato 793408 (H3.2‐an): The missing link between compound chondrules and macrochondrules?

“…However, it has been shown recently that 16 O-rich relict chondrule olivine grains are rather Ca-Al-Ti poor (Marrocchi et al 2018), which is inconsistent with the previous idea that refractory-enriched grains are relicts (Pack and Palme 2003;Pack et al 2004). Furthermore, Libourel and Portail (2018) and Marrocchi et al (2018Marrocchi et al ( , 2019 suggest that RF formed together with other chondrule olivine grains by epitaxial growth during gas-melt interactions. These RF show constant D 17 O within a single chondrule and between different chondrules, thus reflecting interaction with an 16 O-poor gas in the chondrule-forming region (Marrocchi et al 2018).…”

“…A few of the free-floating olivine grains are RF and likely formed from gas-melt interaction with an 16 Opoor gas (Libourel and Portail 2018;Marrocchi et al 2018Marrocchi et al , 2019, rather than being relict olivines (e.g., Jones et al 2004).…”

“…Chondrules were open systems during their molten stage and interacted with their surrounding nebular gas (e.g., Tissandier et al 2002;Libourel et al 2006;Marrocchi and Chaussidon 2015;Friend et al 2016;Piani et al 2016;Souli e et al 2017;Ebel et al 2018; Barosch et al 2019). The open system scenario is further supported by Marrocchi et al (2018Marrocchi et al ( , 2019 and Libourel and Portail (2018), who suggested that refractory forsterites (RF)-olivines with high Ca,Aland very low Fe-concentrations-formed from crystallization and interaction with the surrounding gas. The latter, however, is in conflict with the interpretation of Pack et al (2004), who suggested that these refractory olivines originated from a common reservoir, that is, RF are basically xenolithic in chondrites.…”

An evolutionary system of mineralogy. Part III: Primary chondrule mineralogy (4566 to 4561 Ma)

“…Adding to their complex thermal histories, many chondrules display evidence for rapid heating events after their initial crystallization (Krot et al 1997a;2004a, 2018Ruzicka 2012;Baecker et al 2017). At least four lines of evidence point to multiple subsequent heating events for many, if not most, chondrules: (1) many chondrule phenocrysts nucleate on earlier generations of olivine or pyroxene relict grains with different chemical properties (Marrocchi et al 2019); 2some chondrules appear to envelop others (Wasson et al 1995;Hobart et al 2015);…”

Best practices for the use of meteorite names in publications

“…There are many more examples in the literature that could be cited in this context where meteorite specimens are provided following the recommendations given below (e.g., Bouvier et al 2015;Santos et al 2015;Jilly-Rehak et al 2017;Marrocchi et al 2019 should NOT be used in publications, except when needed to provide historical context, identify specimens (see §5), or prevent confusion by readers. Synonyms are listed in the Meteoritical Bulletin Database for the sole purpose of identifying meteorites that may have appeared in previous publications or in popular usage under different names.…”