Fine-grained serpentine in CM2 carbonaceous chondrites and its implications for the extent of aqueous alteration on the parent body: A review

AbstractSamples from asteroid 25143 Itokawa returned by the Hayabusa mission have been identified as LL4-6 ordinary chondrite materials and have shown it to be a rubble pile that aggregated after break-up of a parent body. Here we investigate particle RB-CV-0038 from the Itokawa regolith using scanning and transmission electron microscopy and energy dispersive spectroscopy. We identify a cubanite-chalcopyrite-troilite-pyrrhotite assemblage, the phases and structure of which are indicative of low-temperature, aqueous alteration. Cubanite is stable only at temperatures below around 250 °C and has thus far only been identified in CI carbonaceous chondrites and the comet 81P/Wild2 sample suite. Chalcopyrite is also very rare in the meteorite record and is found mostly in R chondrites and some CK chondrites. Because the Itokawa parent body experienced significant thermal alteration with little evidence of low-temperature equilibration or aqueous alteration, we propose that the assemblage we identify is most likely exogenous and represents a component of an impacting body.

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Constraints on the ice composition of carbonaceous chondrites from their magnetic mineralogy

10.31223/x5cd1b ◽

2021 ◽

Author(s):

Sanjana Sridhar ◽

James Bryson ◽

Ashley King ◽

Richard Harrison

Keyword(s):

Size Range ◽

Parent Body ◽

Carbonaceous Chondrites ◽

Magnetic Mineralogy ◽

Aqueous Alteration ◽

First Order ◽

Direct Replacement ◽

History Of ◽

Bulk Chemical ◽

Weathering Effects

Carbonaceous chondrites experienced varying degrees of aqueous alteration on their parent asteroids, which influenced their mineralogies, textures, and bulk chemical and isotopic compositions. Although this alteration was a crucial event in the history of these meteorites, their various alteration pathways are not well understood. One phase that formed during this alteration was magnetite, and its morphology and abundance vary between and within chondrite groups, providing a means of investigating chondrite aqueous alteration. We measured bulk magnetic properties and first-order reversal curve (FORC) diagrams of CM, CI, CO, and ungrouped C2 chondrites to identify the morphology and size range of magnetite present in these meteorites. We identify two predominant pathways of aqueous alteration among these meteorites that can be distinguished by the resultant morphology of magnetite. In WIS 91600, Tagish Lake, and CI chondrites, magnetite forms predominantly from Fe-sulfides as framboids and stacked plaquettes. In CM and CO chondrites, <0.1 μm single-domain (SD) magnetite and 0.1–5 μm vortex (V) state magnetite formed predominantly via the direct replacement of metal and Fe-sulfides. After ruling out differences in temperature, water:rock ratios, terrestrial weathering effects, and starting mineralogy, we hypothesise that the primary factor controlling the pathway of aqueous alteration was the composition of the ice accreted into each chondrite group’s parent body. Nebula condensation sequences predict that the most feasible method of appreciably evolving ice concentrations was the condensation of ammonia, which will have formed a more alkaline hydrous fluid upon melting, leading to fundamentally different conditions that may have caused the formation of different magnetite morphologies. As such, we suggest that WIS 91600, Tagish Lake, and the CI chondrites accreted past the ammonia ice line, supporting a more distal or younger accretion of their parent asteroids.

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Phyllosilicates and other layer-structured materials in stony meteorites

Clay Minerals ◽

10.1180/claymin.1985.020.4.01 ◽

1985 ◽

Vol 20 (4) ◽

pp. 415-454 ◽

Cited By ~ 51

Author(s):

D. J. Barber

Keyword(s):

Major Part ◽

Solar Nebula ◽

Layered Compounds ◽

Carbonaceous Chondrites ◽

Aqueous Alteration ◽

Structured Materials ◽

Fine Grained ◽

Current Thinking ◽

The Matrix ◽

Detailed Chemical

AbstractCurrent thinking regarding the possible origins and probable evolutionary histories of meteorites is summarized. Selected data concerning the composition, petrology and other characteristics of the CI and CM groups of stony meteorites in which layered minerals principally occur are then presented. Layered compounds, mainly phyllosilicates, are shown to form a major part of the fine-grained matrix of the CI and CM meteorites, which are classified as carbonaceous chondrites. The results of recent investigations of matrix mineralogy are reviewed, with particular emphasis on the findings of electron microscopy. Several forms of Fe-Mg-serpentine have been identified as the principal phyllosilicates. ‘Poorly-characterized phases’ in CM meteorites have proved to be tochilinite and intergrowths of tochilinite with serpentines. The results generally indicate that the phyllosilicates and most other matrix minerals formed by aqueous alteration in the regoliths of the CI and CM parent bodies; but there is isotopic evidence for the incorporation of components and possibly mineral grains which predate the solar nebula. It is concluded that more detailed chemical and mineralogical information about the phyllosilicates and associated minerals will enable useful constraints to be placed on the possible identities of their precursors and the environments in which both they and the matrix minerals formed.

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Discovery of fossil asteroidal ice in primitive meteorite Acfer 094

Science Advances ◽

10.1126/sciadv.aax5078 ◽

2019 ◽

Vol 5 (11) ◽

pp. eaax5078 ◽

Cited By ~ 1

Author(s):

Megumi Matsumoto ◽

Akira Tsuchiyama ◽

Aiko Nakato ◽

Junya Matsuno ◽

Akira Miyake ◽

...

Keyword(s):

Solar Nebula ◽

Carbonaceous Chondrite ◽

Parent Body ◽

Carbonaceous Chondrites ◽

X Ray ◽

Porous Texture ◽

Fine Grained ◽

X Ray Computed ◽

Source Materials ◽

Insight Into

Carbonaceous chondrites are meteorites believed to preserve our planet’s source materials, but the precise nature of these materials still remains uncertain. To uncover pristine planetary materials, we performed synchrotron radiation–based x-ray computed nanotomography of a primitive carbonaceous chondrite, Acfer 094, and found ultraporous lithology (UPL) widely distributed in a fine-grained matrix. UPLs are porous aggregates of amorphous and crystalline silicates, Fe─Ni sulfides, and organics. The porous texture must have been formed by removal of ice previously filling pore spaces, suggesting that UPLs represent fossils of primordial ice. The ice-bearing UPLs formed through sintering of fluffy icy dust aggregates around the H2O snow line in the solar nebula and were incorporated into the Acfer 094 parent body, providing new insight into asteroid formation by dust agglomeration.

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Unusual microstructures in the C2 carbonaceous chondrites

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100074732 ◽

1983 ◽

Vol 41 ◽

pp. 188-189

Author(s):

Kazushige Tomeoka ◽

Peter R. Buseck

Keyword(s):

Parent Body ◽

Carbonaceous Chondrites ◽

Early Solar System ◽

X Ray Diffraction ◽

Mineralogical Characterization ◽

Fine Grained ◽

Transmission Electron ◽

Diffraction Patterns ◽

O Phase

Carbonaceous chondrites are among the most primitive meteoritic samples of early solar system materials that are accessible for study. One of the characteristics of these meteorites is that their mineral constituents are extremely fine grained, and so high-resolution transmission electron microscopy (HRTEM) is a powerful method to study the mineralogy of carbonaceous chondrites.The C2 type carbonaceous chondrites contain abundant amounts of an unusual “Fe-Ni-S-O” phase, which has been termed the “poorly characterized phase” (PCP). Its identity has been one of the more difficult problems of carbonaceous chondrite mineralogy. Its puzzling composition and X-ray diffraction patterns do not fit any known mineral. It may be a) related to a primordial condensate, or b) an alteration product in a parent body regolith. Detailed mineralogical characterization of PCP potentially bears on these questions and therefore is of great interest for meteorite scientists.

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Meteorite Mineralogy

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.205 ◽

2020 ◽

Author(s):

Alan E. Rubin ◽

Chi Ma

Keyword(s):

Outer Space ◽

Matrix Material ◽

Parent Body ◽

Primary Phase ◽

Shock Metamorphism ◽

Aqueous Alteration ◽

Fine Grained ◽

Thermal Metamorphism ◽

Geochemical Properties ◽

Gaseous Envelopes

Meteorites are rocks from outer space that reach the Earth; more than 60,000 have been collected. They are derived mainly from asteroids; a few hundred each are from the Moon and Mars; some micrometeorites derive from comets. By mid 2020, about 470 minerals had been identified in meteorites. In addition to having characteristic petrologic and geochemical properties, each meteorite group has a distinctive set of pre-terrestrial minerals that reflect the myriad processes that the meteorites and their components experienced. These processes include condensation in gaseous envelopes around evolved stars, crystallization in chondrule melts, crystallization in metallic cores, parent-body aqueous alteration, and shock metamorphism. Chondrites are the most abundant meteorites; the major components within them include chondrules, refractory inclusions, opaque assemblages, and fine-grained silicate-rich matrix material. The least-metamorphosed chondrites preserve minerals inherited from the solar nebula such as olivine, enstatite, metallic Fe-Ni, and refractory phases. Other minerals in chondrites formed on their parent asteroids during thermal metamorphism (such as chromite, plagioclase and phosphate), aqueous alteration (such as magnetite and phyllosilicates) and shock metamorphism (such as ringwoodite and majorite). Differentiated meteorites contain minerals formed by crystallization from magmas; these phases include olivine, orthopyroxene, Ca-plagioclase, Ca-pyroxene, metallic Fe-Ni and sulfide. Meteorites also contain minerals formed during passage through the Earth’s atmosphere and via terrestrial weathering after reaching the surface. Whereas some minerals form only by a single process (e.g., by high-pressure shock metamorphism or terrestrial weathering of a primary phase), other meteoritic minerals can form by several different processes, including condensation, crystallization from melts, thermal metamorphism, and aqueous alteration.

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