Elsevier

Geochimica et Cosmochimica Acta

Volume 336, 1 November 2022, Pages 448-468
Geochimica et Cosmochimica Acta

Mineralogy, petrology, and oxygen isotopic compositions of aluminum-rich chondrules from unequilibrated ordinary and the Dar al Gani 083 (CO3.1) chondrite

https://doi.org/10.1016/j.gca.2022.08.026Get rights and content

Abstract

Understanding the genetic relationship between different chondritic components will help to decipher their origin and dynamical evolution within the protoplanetary disk. Here, we obtain insight into these processes by acquiring O-isotope data from 17 Al-rich chondrules from unequilibrated ordinary chondrites (OCs, petrologic type ≤ 3.2) and four Al-rich chondrules from the CO3.1 carbonaceous chondrite Dar al Gani (DaG) 083. These particular kinds of chondrules are of special interest, as it is suggested that their precursors may have contained refractory material related to Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs).

The four investigated Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083 consist of olivine, low-Ca pyroxene, Ca pyroxene, and spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Two chondrules have a homogeneous O-isotopic composition and two are heterogeneous in their O-isotopic composition. One chondrule contains relict spinel grains with a Δ17O value of −24.3 ± 1.3‰, indicative of 16O-rich precursor refractory material, similar to constituents of CAIs and AOAs. The presence of CAI-like precursors for the Al-rich chondrules from CO chondrites is consistent with their previously reported presence of 50Ti excesses (Ebert et al., 2018).

The Al-rich chondrules in the ordinary chondrites studied consist of olivine, low-Ca pyroxene, Ca pyroxene, and, occasionally, spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Hibonite is present in one Al-rich chondrule. The vast majority of these chondrules have heterogeneous O-isotopic compositions: Chondrule glasses are 16O-depleted compared to chondrule phenocrysts; the Δ17O values of the former approach those of aqueously formed fayalite and magnetite grains in type 3 OCs, ∼ +5‰. We infer that the chondrule glasses experienced O-isotope exchange with an aqueous fluid on the OC parent asteroids.

Chondrule phenocrysts, like spinel, olivine, low-Ca pyroxene, and Ca pyroxene, were not affected by this isotope exchange and preserved their initial O-isotope compositions. The phenocrysts within individual chondrules have similar Δ17O, whereas the inter-chondrule Δ17O values range from −4.5 to +1.4‰, i.e., they are in general 16O enriched relative to the majority of ferromagnesian type I and type II porphyritic chondrules in OCs having Δ17O of ∼ +1‰. Because no relict grains were identified in the Al-rich chondrules from ordinary chondrites, the original O-isotopic composition of the refractory precursor material remains unknown.

Additional detailed Na measurements within olivine grains show no major changes in the Na content of the chondrule melt during their crystallization. This implies either that the Na was part of the precursor material or that the Na was enriched in the chondrule melt/glass after crystallization of the olivines.

Introduction

Understanding a potential genetic link between chondrules and refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] is an important goal in cosmochemistry. Relict CAIs and AOAs found within chondrules from ordinary (OCs) and carbonaceous chondrites (CCs) indicate that CAIs were present in the chondrule-forming regions, but only some of them experienced melting during chondrule formation (e.g., Krot et al., 2002, Krot et al., 2004, Krot et al., 2006a, Krot et al., 2017a, Nagashima et al., 2020, Zhang et al., 2020). These observations are interpreted as evidence for a localized nature of chondrule-forming events (Krot, 2019).

Aluminum-rich (>10 wt% bulk Al2O3) chondrules, occurring in all chondrite groups, are of special interest as they have been suggested to have formed from precursors containing refractory CAI- and/or AOA-like objects (Nagahara and Kushiro, 1982, Bischoff and Keil, 1983b, Bischoff and Keil, 1983a, Bischoff and Keil, 1984, Bischoff et al., 1985, Bischoff et al., 1989, Krot and Rubin, 1994, Krot and Keil, 2002, Russell et al., 2000, MacPherson and Huss, 2005, Guan et al., 2006, Rout and Bischoff, 2008, Zhang and Hsu, 2009, Ebert and Bischoff, 2016, Ebert et al., 2018, Ebert et al., 2019, Zhang et al., 2020). However, because Al-rich chondrules are relatively common in non-carbonaceous (NCs) chondrites, which generally contain very rare refractory inclusions, it is still not clear to what extent CAIs and AOAs make up the Al-rich chondrule precursors in these meteorites (MacPherson and Huss, 2005). Based on bulk chemical compositions, Bischoff and Keil, 1983b, Bischoff and Keil, 1983a, Bischoff and Keil, 1984 defined several subtypes of Al-rich chondrules in ordinary chondrites – Na,Al-rich (Na2O ≥ 5.0 wt%), Ca,Al-rich (Na2O ≤ 5.0 wt%), Na-Cr,Al-rich (Cr2O3 ≥ 2.4 wt%) and intermediate.

A detailed study of the Na,Al-rich chondrules from ordinary, Rumuruti, and CO3.1 chondrites has shown that these chondrules typically consist of euhedral-to-subhedral mafic minerals embedded within a brownish nepheline-normative, glassy mesostasis and often have volatility-controlled rare earth element (REE) patterns – Group II, III, and ultra-refractory (Ebert and Bischoff, 2016) – similar to those commonly observed in CAIs (Mason and Martin, 1977, MacPherson et al., 1988, Davis et al., 2018) and AOAs (Grossman et al., 1979). The combination of elevated refractory element abundances (Al, Ti, and REE), as well as CAI-like group II and group III REE patterns provide strong evidence that Al-rich chondrules contained refractory precursors chemically and mineralogically similar to CAIs and AOAs, providing a link between the two major chondritic components, chondrules and refractory inclusions (Ebert and Bischoff, 2016). It has to be mentioned that this connection between Al-rich chondrules and CAIs and AOAs based on the REE patterns has been questioned by Jacquet et al., 2018, Jacquet et al., 2019.

Similar connections between Al-rich chondrules and refractory material can be drawn by considering the Ti-isotope compositions. Ca,Al-rich inclusions in CCs and OCs typically have 50Ti excesses between ∼2–16 ɛ units (e.g., Trinquier et al., 2009, Williams et al., 2016, Ebert et al., 2018, Shollenberger et al., 2018, Render et al., 2019), also linking CAIs from different chondrites to a formation in a common isotopic reservoir. As titanium isotopes are not expected to exchange with the nebular gas during chondrule formation (Niemeyer, 1988a, Gerber et al., 2017), 50Ti is a perfect tracer to constrain the role of CAI constituents as possible precursor components of Al-rich chondrules. If 50Ti-enriched refractory material was involved as a precursor, it should be still detectable in the resulting chondrules. Indeed, Na,Al-rich chondrules in CO chondrites show positive excesses of 50Ti up to 14.5 ± 0.5ε, which is best explained by the presence of CAI-like material in their precursors (Ebert et al., 2018). However, Na,Al-rich chondrules in ordinary chondrites show no evidence for 50Ti excesses (ε50Ti range from ∼−2 to 0); these Ti-isotope compositions are similar to those of ferromagnesian chondrules and bulk ordinary chondrites (Gerber et al., 2017, Ebert et al., 2018). Based on these observations, Ebert et al. (2018) concluded that an “unknown” refractory component, mineralogically and chemically similar to known CAIs but with normal Ti-isotope compositions, was among Na,Al-rich chondrule precursors in the ordinary chondrites’ chondrule-forming region. Possible explanations for such a component could be either a heterogeneous distribution of 50Ti in the CAI-forming region or a different non-CAI origin of the refractory precursors.

Based on the solar-like oxygen isotopic compositions of refractory inclusions (McKeegan et al., 2011) and the presence of decay products of short-lived radionuclides 7Be and 10Be formed by solar energetic particle irradiation, CAIs are thought to have formed from a gas of approximately solar composition, possibly close to the young Sun, and were subsequently distributed into the different regions of the protoplanetary disk where chondrules formed and chondrites accreted (Shu et al., 1996, McKeegan et al., 2000, MacPherson et al., 2003, Brownlee et al., 2006, Chaussidon et al., 2006, Ciesla, 2007, Krot et al., 2009, Wielandt et al., 2012, MacPherson, 2014 and references therein). If CAIs or AOAs were present among Al-rich chondrule precursors, these chondrules may have preserved an 16O-rich signature of these precursors. In addition, O-isotope compositions of Al-rich chondrules in ordinary chondrites can be potentially used to constrain their formation region to the inner vs outer Solar System. Note that on a three-isotope oxygen diagram (δ17O vs δ18O), vast majority of chondrules in CCs plot below the terrestrial fractionation (TF) line, whereas those from NCs plot along or above it (e.g., Tenner et al., 2018 and references therein).

In this context, it is important to consider the effects of exchange and equilibration of O-isotopes during chondrule formation or during metasomatic/aqueous alteration in the solar nebula and/or on the chondrites’ parent bodies. Melted chondrules behaved as open systems (e.g., Kita et al., 2010) and appear to have experienced O-isotope exchange with the surrounding solar nebula gas (e.g., Clayton et al., 1991; Tenner et al., 2018). Oxygen isotopic compositions of most CAIs, AOAs, and chondrules (except relict grains) from most unmetamorphosed (petrologic type 2–3.0) chondrites are uniform (e.g., Makide et al., 2009, Ushikubo et al., 2017, Kööp et al., 2016, Krot et al., 2017b, Krot et al., 2019a). This O-isotope homogeneity can be subsequently modified by post-crystallization O-isotope exchange with either nebular gas or aqueous fluid on the chondrites’ parent asteroids; the latter process is consistent with the common presence of isotopically heterogeneous chondrules and refractory inclusions in metamorphosed (petrologic type > 3.0) CO and CV carbonaceous chondrites (e.g., Wasson et al., 2001, Itoh et al., 2004, Itoh et al., 2007, Rudraswami et al., 2011, Krot et al., 2019b, Krot et al., 2019a, Ebert et al., 2020). To minimize the effects of parent body alteration, in this study, we used only Al-rich chondrules from the weakly metamorphosed ordinary chondrites of petrologic type ≤ 3.2 [NWA 3358 (H3.1), Adrar 003 (L/LL3.1), Vicencia (L3.15), Krymka (LL3.2), and Vicencia (LL3.2)] and the CO3.1 chondrite Dar al Gani (DaG) 083.

Section snippets

Methods and samples

All polished thin sections and meteorite chips discussed in this work were provided by the Institut für Planetologie of the Westfälische Wilhelms-Universität Münster and by the Hawai‘i Institute of Geophysics and Planetology (HIGP), University of Hawai‘i (UH) at Mānoa.

For identification of Al-rich chondrules, a Zeiss Axiophot optical microscope was used for thin sections microscopy. Thick sections and meteorite chips were studied with a JEOL 6610-LV electron microscope (SEM) at the

NWA 3358 (H3.1)

NaC-1 is a porphyritic pyroxene (PP) chondrule, ∼150 µm in apparent diameter (Fig. 1a). It consists of low-Ca pyroxene (En94Wo5) phenocrysts rimmed by Ca pyroxene (En56Wo43) and embedded in glassy mesostasis (12.2 wt% Na2O). Oxygen-isotope compositions were measured for two low-Ca pyroxene grains in the core and rim of the chondrule, and for the mesostasis in the core. The pyroxenes and mesostasis are in O-isotope disequilibrium. Two low-Ca pyroxene grains have similar Δ17O, −4.3 ± 2.8‰ and

Al-rich chondrules from a CO-chondrite

Four Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083 were measured for O-isotope compositions (Fig. 7, Fig. 8, Fig. 10; Table 3b). The chondrule CO-Ca-Al-2 has an internally uniform O-isotope composition, with spinel, olivine, and Ca pyroxene having Δ17O values of −2, −1, and 0‰, respectively. In chondrule CO-NaC-2, only Ca pyroxene grains were measured (Δ17O ∼ −3‰). Two other chondrules, CO-Ca-Al-1 and CO-NaC-1, are isotopically heterogeneous, with Δ17O ranging from ∼−25 to ∼−4‰

Conclusions

We investigated the mineralogy, petrology, and O-isotope compositions of 17 Al-rich chondrules and/or their constituents from unequilibrated ordinary chondrites (petrologic type < 3.2) and four Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083.

  • Precise Na measurements within olivine grains of selected Al-rich chondrules reveal no changes in the chondrule melts’ Na content during the olivine crystallization.

  • Al-rich chondrules from the CO3.1 chondrite have a heterogeneous oxygen isotopic

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank Ulla Heitmann (Münster) for sample preparation, Thorsten Grund for the technical assistance on the SEM, and Celeste Brennecka for writing support. We thank Gary Huss for the fruitful discussions. Furthermore, we thank Sarah Russell, Kohei Fukuda and one anonymous reviewer who provided very helpful reviews of the manuscript as well as Yves Marrocchi for his careful editorial handling. This work was partly supported by the German Research Foundation (DFG) within the Collaborative

References (129)

  • R.N. Clayton et al.

    Distribution of the pre-solar component in Allende and other carbonaceous chondrites

    Earth Planet Sci. Lett.

    (1977)
  • A.M. Davis et al.

    Titanium isotopes and rare earth patterns in CAIs: Evidence for thermal processing and gas-dust decoupling in the protoplanetary disk

    Geochim. Cosmochim. Acta

    (2018)
  • D.S. Ebel et al.

    Condensation in dust-enriched systems

    Geochim. Cosmochim. Acta

    (2000)
  • S. Ebert et al.

    Genetic relationship between Na-rich chondrules and Ca, Al-rich inclusions? – Formation of Na-rich chondrules by melting of refractory and volatile precursors in the solar nebula

    Geochim. Cosmochim. Acta

    (2016)
  • S. Ebert et al.

    Ti isotopic evidence for a non-CAI refractory component in the inner Solar System

    Earth Planet Sci. Lett.

    (2018)
  • S. Ebert et al.

    Oxygen-isotope heterogeneity in the Northwest Africa 3358 (H31.) refractory inclusions – fluid-assisted isotopic exchange on the H-chondritic parent body

    Geochim. Cosmochim. Acta

    (2020)
  • J.N. Grossman et al.

    ALH 85085: A unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes

    Earth Planet Sci. Lett.

    (1988)
  • L. Grossman et al.

    Trace elements in the Allende meteorite-IV. Amoeboid olivine aggregates

    Geochim. Cosmochim. Acta

    (1979)
  • W. Herbst et al.

    A new mechanism for chondrule formation: Radiative heating by hot planetesimals

    Icarus

    (2016)
  • T.R. Ireland et al.

    Hibonite-bearing microspherules: A new type of refractory inclusions with large isotopic anomalies

    Geochim. Cosmochim. Acta

    (1991)
  • S. Itoh et al.

    Petrography and oxygen isotopic compositions in refractory inclusions from CO chondrites

    Geochim. Cosmochim. Acta

    (2004)
  • N.T. Kita et al.

    A short duration of chondrule formation in the solar nebula: Evidence from 26Al in Semarkona ferromagnesian chondrules

    Geochim. Cosmochim. Acta.

    (2000)
  • L. Kööp et al.

    New constraints for the relationship between 26Al and oxygen, calcium, and titanium isotopic variation in the early Solar System from a multi-element isotopic study of Spinel-Hibonite Inclusions

    Geochim. Cosmochim. Acta

    (2016)
  • A.N. Krot et al.

    Ca,Al−rich inclusions, amoeboid olivine aggregates, and Al-rich chondrules from the unique carbonaceous chondrite Acfer 094: I. Mineralogy and petrology

    Geochim. Cosmochim. Acta

    (2004)
  • A.N. Krot et al.

    Oxygen isotopic compositions of chondrules: Implications for evolution of oxygen isotopic reservoirs in the solar nebula

    Chemie Erde

    (2006)
  • A.N. Krot et al.

    Origin and chronology of chondritic components: A review

    Geochim. Cosmochim. Acta

    (2009)
  • A.N. Krot et al.

    Evidence for oxygen-isotope exchange in refractory inclusions from Kaba (CV3.1) carbonaceous chondrite during fluid-rock interaction on the CV parent asteroid

    Geochim. Cosmochim. Acta

    (2019)
  • A.N. Krot et al.

    Calcium-aluminum-rich inclusions recycled during formation of porphyritic chondrules from CH carbonaceous chondrites

    Geochim. Cosmochim. Acta

    (2017)
  • A.N. Krot et al.

    High-temperature rims around calcium-aluminum-rich inclusions from the CR, CB and CH carbonaceous chondrites

    Geochim. Cosmochim. Acta

    (2017)
  • G.J. MacPherson

    Calcium–aluminum-rich inclusions in chondritic meteorites

  • G.J. MacPherson et al.

    Petrogenesis of Al-rich chondrules: Evidence from bulk compositions and phase equilibria

    Geochim. Cosmochim. Acta

    (2005)
  • G.J. MacPherson et al.

    Extinct 10Be in Type A calcium-aluminum-rich inclusions from CV chondrites

    Geochim. Cosmochim. Acta

    (2003)
  • K. Makide et al.

    Oxygen- and magnesium-isotope compositions of calcium-aluminum-rich inclusions from CR2 carbonaceous chondrites

    Geochim. Cosmochim. Acta

    (2009)
  • Y. Marrocchi et al.

    Oxygen isotopic diversity of chondrule precursors and the nebular origin of chondrules

    Earth Planet Sci. Lett.

    (2018)
  • Y. Marrocchi et al.

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

    Geochim. Cosmochim. Acta

    (2019)
  • R. Mathieu et al.

    Na2O solubility in CaO-MgO-SiO2 melts

    Geochim. Cosmochim. Acta

    (2011)
  • H. Nagahara et al.

    Condensation of major elements during chondrule formation and its implication to the origin of chondrules

    Geochim. Cosmochim. Acta

    (2008)
  • K. Nagashima et al.

    Oxygen-isotope composition of chondrules phenocryst and matrix grains in Kakangari K-grouplet chondrite: Implications to a chondrule-matrix genetic relationship

    Geochim. Cosmochim. Acta

    (2015)
  • J.A.M. Nanne et al.

    Origin of the non-carbonaceous–carbonaceous meteorite dichotomy

    Earth Planet Sci. Lett.

    (2019)
  • F.R. Niederer et al.

    The isotopic composition of titanium in the Allende and Leoville meteorites

    Geochim. Cosmochim. Acta

    (1981)
  • S. Niemeyer

    Titanium isotopic anomalies in chondrules from carbonaceous chondrites

    Geochim. Cosmochim. Acta

    (1988)
  • S. Niemeyer

    Isotopic diversity in nebular dust: The distribution of Ti isotopic anomalies in carbonaceous chondrites

    Geochim. Cosmochim. Acta

    (1988)
  • S. Niemeyer et al.

    Ubiquitous isotopic anomalies in Ti from normal Allende inclusions

    Earth Planet Sci. Lett.

    (1981)
  • J. Pape et al.

    Time and duration of chondrule formation: Constraints from 26Al-26Mg ages of individual chondrules

    Geochim. Cosmochim. Acta

    (2019)
  • M. Piralla et al.

    Conditions of chondrule formation in ordinary chondrites

    Geochim. Cosmochim. Acta

    (2021)
  • C.M.O’D. Alexander et al.

    The formation conditions of chondrules and chondrites

    Science

    (2008)
  • J.T. Armstrong

    Quantitative elemental analysis of individual microparticles with electron beam instruments

    (1991)
  • V. Batanvoa et al.

    New olivine reference material for in situ microanalysis

    Geostand. Geoanal. Res.

    (2019)
  • A. Bischoff et al.

    Ca–Al–rich chondrules and inclusions in ordinary chondrites

    Nature

    (1983)
  • A. Bischoff et al.

    Catalog of Al-rich chondrules, inclusions and fragments in ordinary chondrites

  • Cited by (2)

    • Subtype 3.0 chondrites: Petrologic classification criteria

      2024, Meteoritics and Planetary Science
    View full text