Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites

Rubin, Alan E.

doi:10.1016/j.gca.2012.05.016

Cited by 97 publications

(129 citation statements)

References 83 publications

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“…Petrofabrics were analysed using the technique of Rubin (2012), which is consistent with earlier studies (e.g., Tomeoka et al, 1999). The orientations of the long axes of all of the chondrules in the thin sections, and on the three faces of the Murchison block, were measured relative to the horizontal on the SEM monitor.…”

Section: Aspect Ratios and Petrofabric Analysesmentioning

confidence: 90%

“…The aim of the present study is to reconcile this contradiction between the evidence for compaction of the CMs (i.e., presence of petrofabrics) and their low shock stage, and we test three possible explanations: (i) the petrofabrics formed by lithostatic compaction rather than by hypervelocity impacts (Table 1); (ii) the petrofabrics formed by low shock pressures, which themselves may be due to attenuation of a higher magnitude shock wave by the porous meteorite matrix (Rubin, 2012); (iii) the petrofabrics formed by multiple episodes of low intensity shock, rather than by a single higher intensity event. In order to evaluate these possibilities we have sought to understand better the degree and mechanism(s) of compaction of carbonaceous chondrite parent bodies by quantification of chondrule deformation and associated petrofabrics of eight CMs.…”

Section: Impacts and Parent Body Evolutionmentioning

confidence: 93%

“…However, compactional petrofabrics are commonplace in CM meteorites (Table 1), and have been attributed to either impact or lithostatic processes. The importance of distinguishing between these two agents of compaction has been recently highlighted by Rubin (2012), who suggested that impacts had generated the aqueous solutions that mediated alteration of the CMs (e.g., by melting of H 2 O-rich ice and/or dehydration of phyllosilicates) and facilitated their movement within the parent body (i.e., by generating high permeability fracture networks). ALH 88045 is one example of a highly altered CM meteorite with flattened chondrules, but that shows no other evidence of shock deformation (Zolensky et al, 1997).…”

Section: Impacts and Parent Body Evolutionmentioning

confidence: 99%

“…It is one of the least aqueously altered CMs known (i.e., CM2.5; Rubin et al, 2007) and so according to the model of Rubin (2012) it should be unshocked; indeed he found that it lacks a petrofabric and most of its olivine grains belong to S1. Scott et al (1992), however, classified Murchison as S1-S2 breccia, indicating that some regions or clasts had been shocked to >5 GPa.…”

Section: The Murchison Paradoxmentioning

confidence: 99%

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The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Lindgren

Hanna

Dobson

et al. 2015

Geochimica et Cosmochimica Acta

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Petrographic analysis of eight CM carbonaceous chondrites (EET 96029, LAP 031166, LON 94101, MET 01072, Murchison, Murray, SCO 06043, QUE 93005) by electron imaging and diffraction, and X-ray computed tomography, reveals that six of them have a petrofabric defined by shock flattened chondrules. With the exception of Murchison, those CMs that have a strong petrofabric also contain open or mineralized fractures, indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix. The CMs studied span a wide range of petrologic subtypes, and in common with Rubin (2012) we find that the strength of their petrofabrics increases with their degree of aqueous alteration. This correspondence suggests that impacts were responsible for enhancing alteration, probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body. Two meteorites that do not fit this pattern are MET 01072 and Murchison; both have a strong petrofabric but are relatively unaltered. In the case of MET 01072, impact deformation is likely to have postdated parent body aqueous activity. The same may also be true for Murchison, but as this meteorite also lacks fractures and veins, its chondrules were most likely flattened by multiple low intensity impacts. Multiphase deformation of Murchison is also revealed by the microstructures of calcite grains, and chondrule-defined petrofabrics as revealed by X-ray computed tomography. The contradiction between the commonplace evidence for impact-deformation of CMs and their low shock stages (most belong to S1) can be explained by most if not all having been exposed to multiple low intensity (i.e., <5 GPa) shock events. Aqueous alteration was enhanced by those impacts that were of sufficient intensity to open high permeability fracture networks that could connect to fluid reservoirs.

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Section: Aspect Ratios and Petrofabric Analysesmentioning

confidence: 90%

Section: Impacts and Parent Body Evolutionmentioning

confidence: 93%

Section: Impacts and Parent Body Evolutionmentioning

confidence: 99%

Section: The Murchison Paradoxmentioning

confidence: 99%

See 2 more Smart Citations

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Lindgren

Hanna

Dobson

et al. 2015

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

show abstract

“…This lithology provides evidence of temperature elevations above the freezing point of water as a result of highly energetic impacts 24 and/or the decay heat of radiogenic aluminium-26 (ref. 25).…”

Section: Discussionmentioning

confidence: 99%

Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid

et al. 2013

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The majority of water has vanished from modern meteorites, yet there remain signatures of water on ancient asteroids. How and when water disappeared from the asteroids is important, because the final fluid-concentrated chemical species played critical roles in the early evolution of organics and in the final minerals in meteorites. Here we show evidence of vestigial traces of water based on a nanometre-scale palaeomagnetic method, applying electron holography to the framboids in the Tagish Lake meteorite. The framboids are colloidal crystals composed of three-dimensionally ordered magnetite nanoparticles and therefore are only able to form against the repulsive force induced by the surface charge of the magnetite as a water droplet parches in microgravity. We demonstrate that the magnetites have a flux closure vortex structure, a unique magnetic configuration in nature that permits the formation of colloidal crystals just before exhaustion of water from a local system within a hydrous asteroid.

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Size‐frequency distributions and physical properties of chondrules from x‐ray computed microtomography and digital data extraction

Friedrich

Chen

Giordano

et al. 2021

Microscopy Res & Technique

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Within this work, we present the first true three‐dimensional (3D) analysis of chondrule size. Knowledge about the physical properties of chondrules is important for validating astrophysical theories concerning chondrule formation and their aggregation into the chondritic meteorites (known as chondrites) that contain them. The classification of chondrites into chemical groups also relies on chondrule properties, including their dimensions. Within this work, we quantify the diameters of chondrules in five ordinary chondrites (OCs; comprised of the H, L, and LL chondrites) and one low‐iron enstatite (EL) chondrite. To extract the chondrule size data, we use x‐ray computed microtomography to image small (~1–2 cm3) chondrite samples followed by manual digital segmentation to isolate chondrules within the volumes or subvolumes. Our data yield true 3D results without stereographic corrections necessary for two‐dimensional (2D) or petrographic thin section‐based determinations of chondrule sizes. Our results are completely novel, but are consistent with previous surface analysis (2D) data for OCs. Within our OC chondrule diameter data, we find the trend of mean chondrule diameters increasing in the order H < L < LL. We also present the first detailed EL chondrite chondrule size‐frequency distribution. Finally, we examine the shapes and collective orientations of the chondrules within the chondrites and show that chondrite petrofabrics can be explored with our methodology. Chondrule shape‐preferred orientations are identical to the orientations of the metal and sulfide grains in the chondrites and this is likely due to impact‐related compaction. Highlights We present a first true three‐dimensional analysis of chondrule size. Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites. We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution. We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology.

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Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites

Cited by 97 publications

References 83 publications

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid

Size‐frequency distributions and physical properties of chondrules from x‐ray computed microtomography and digital data extraction

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