ABBOTT


H3–6
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Found 1951
36° 18' N., 104° 17' W.

This meteorite was found in Colfax County, New Mexico and was classified (The Meteoritical Bulletin #37) as an H3–6 polymict regolith breccia, which contains impact-melt and shock-darkened clasts embedded within a solar gas-rich matrix. It has a total known weight of 9.5 kg. Abbott has been shocked to stage S3 as evidenced by olivine grains with undulose extinction and planar fractures. Similarly shocked, hydrated, dark inclusions with CM-like mineralogy and petrology have been identified in Abbott. These are thought to have accreted at low velocities with low shock and minimal heating prior to the S3 shock event (Rubin and Bottke, 2007, 2009).

One of these CM inclusions, identified as subtype of 2.3 (±0.1), contains chondrules, CAIs, and ~35 vol% "pooly characterized phases" (PCP)—now determined to be tochilinite-cronstedtite intergrowths (TCI). Another CM inclusion, with a subtype of 2.1, has a yellow-green color and contains abundant cm-sized chondrules and phyllosilicates, with ~30 vol% PCP, along with various sulfides, and carbonates. Anomalies present in some clasts have been attributed to impact heating/dehydration effects.

Prior interest in asteroid 6 Hebe as the source of H chondrites to Earth has lost favor after hydrocode model data showed inconsistencies between expected and observed CRE ages based on the scenario of direct injection into resonances. The steady delivery of H chondrite material from 6 Hebe to Earth is also unexplained. Current studies by Rubin and Bottke (2009) have led to the conclusion that family-forming events resulting in large meteoroid reservoirs, which have homogenous compositions and locations near dynamical resonances such as the Jupiter 3:1 mean motion resonance, are the likely source of the most prevalent falls including H chondrites and HED achondrites (especially howardites). As a matter of fact, a number of asteroids having H-like mineralogies have been observed near the 3:1 and 5:2 resonances at 2.82 AU (Burbine et al., 2015 and references therein). See further details on the Abbott page. Spectral comparisons conducted on the H chondrite Fayetteville and the asteroid 1270 Datura, a member of a young family less affected by space weathering processes, indicate close similarities exist between them (Mothé-Diniz and Nesvorný, 2008).

Rubin and Bottke (2009) submit three possible scenarios attempting to answer the question of why CM clast components only appear in H chondrite and HED achondrite regoliths:

  1. Perhaps the H chondrite and HED asteroid families are the only asteroid families with such ancient ages as to permit a significant accumulation of CM projectiles produced from gravitational interactions and parent body disruptions occurring in the outer asteroid belt between asteroids and/or comets during the Late Heavy Bombardment period ~3.4–4.1 b.y. ago as they migrated inwards. Hydrated clasts could reflect a similarity in orbits and low-velocity impacts. The source family of the H chondrites might be consistent with the Koronis and Eunomia families, the latter lying near the Jupiter 3:1 resonance providing efficient delivery to Earth. The Eunomia family was determined to be the result of a sub-critical cratering event by the impact of a 13–46 km projectile creating a crater with a diameter close to 238 km while ejecting 30% of its initial volume (Leliwa-Kopystyński et al., 2009).
  2. As an alternative to the scenario above, the hydrated CM clasts may have been incorporated into the regolith breccia of the large H chondrite and HED asteroids as a result of spallation during impacts of large-sized CM projectiles, creating lithification of the regolith in the process.
  3. Another possible scenario, recognizing the high prevalence of CM xenolithic clasts in only the large H chondrite and HED achondrite asteroids, in addition to the regolith of the Moon, suggests that a recent collisional fragmentation event occurred involving a CM object located close to the H chondrite and HED asteroids. Rubin and Bottke (2007) provided circumstantial evidence demonstrating that this young CM source may be an ~170-km C-complex asteroid located in the inner asteroid belt which had been disrupted ~160 m.y. ago, and which now comprises the >3000-member Baptistina asteroid family (paradoxically, excluding Baptistina itself). Rubin and Bottke (2009) conjecture that this hydrated CM material impacted at low velocity onto small, regolith-rich, H chondrite and HED fragments which had been previously impact disrupted.

    This scenario would require that the H chondrite and HED asteroids be located in the inner asteroid belt near the Baptistina family, and therefore, raises the possibility that the H chondrite asteroid may be associated with the Flora family of S-type asteroids (e.g. 8 Flora and 951 Gaspra). The Baptistina family is located near several dynamic resonances (e.g., the 7:2 and 5:9 mean motion resonances with Jupiter and Mars, respectively), and a significant flux of material has been calculated to reach multiple Earth-crossing orbits within a few to several tens of m.y. Results of a study by Bottke et al. (2007) suggest that this Baptistina family material may have also been responsible for the K–Pg (formerly K–T) boundary impact event, which is consistent with a 65 m.y. old carbonaceous chondrite fossil meteorite thought to be a portion of the impactor, and consistent also with the chemical composition of K–Pg ejecta layers. However, contradictory spectroscopic data obtained by Reddy et al. (2009), including analyses of absorption features and albedo values, suggest that 298 Baptistina is more likely an S-type asteroid similar to the LL chondrites, and is inconsistent with a carbonaceous chondrite.

Other xenolithic clasts have been identified within chondrites. In the multicomponent chondrite Study Butte, an H3–6 breccia, an igneous-textured andesitic inclusion was identified, which probably represents a xenolithic clast from a distinct, volcanic parent body (Sokol et al., 2007). No radiogenic 26Mg was observed in this clast, which is consistent with crystallization on its parent body later than 4 m.y. after CAI formation, followed by its transportation and late incorporation into the Study Butte regolith. However, due to its similar O-isotopic composition to that of H chondrites, and providing that the size of the H-chondrite parent was large enough to produce impact-generated melts, the clast may have been derived from such a melt zone on the H-chondrite parent body itself.

A search for xenolithic clasts in a diversity of regolith-bearing meteorite groups was conducted by Zolensky et al. (2009). They described fine-grained anhydrous, fine-grained hydrous, and coarse-grained hydrous xenoliths, and are trying to identify those which could have been derived from collisionally-disrupted Kuiper Belt Objects.

Further details on the thermal history of the H-chondrite parent body can be found on the Peekskill page. The photo of Abbott shown above is a 13.3 g end section exhibiting a high free metal content characteristic of this chondrite group. Below is a photo of the reverse side showing the weathered fusion crust of this meteorite.

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