Agata Krzesińska¹, Jérôme Gattacceca², Jon M. Friedrich^3,4 and Pierre Rochette²

¹Institute of Geological Sciences, Polish Academy of Sciences INGPAN, Wrocław, Poland
²CEREGE UM34, CNRS, Aix-Marseille University, Aix-en-Provence, France
³Department of Chemistry, Fordham University, Bronx, New York, USA
⁴Department of Earth and Planetary Science, American Museum of Natural History, New York, USA

Petrofabrics in chondrites have the potential to yield important information on the impact evolution of chondritic parent asteroids, but studies involving chondritic petrofabrics are scarce. We undertook an analysis of the Pułtusk H chondrite regolith breccia. Measurements of anisotropy of magnetic susceptibility and quantitative tomographic examination of metal grains are presented here and the results are compared with petrographic observations. The major fabric elements are in Pułtusk shear fractures cutting the light-colored chondritic clasts as well as brittly and semibrittly deformed, cataclased fragments in dark matrix of regolith breccia. Cataclasis is accompanied by rotation of silicate grains and frictional melting. Fabric of metal grains in chondrite is well defined and coherently oriented over the breccia, both in the clasts and in the cataclastic matrix. Metal grains have prolate shapes and they are arranged into foliation plane and lineation direction, both of which are spatially related and kinematically compatible to shear-dominated deformational features. We argue that the fabric of Pułtusk was formed in response to impact-related noncoaxial shear strain. Deformation promoted brittle cataclastic processes and shearing of silicates, and, simultaneously, allowed for ductile metal to develop foliation and lineation. We suggest that plastic flow is the most probable mechanism for the deformation of metal grains in the shear-dominated strain field. The process led also to the formation of large metal nodules and bands in the dark matrix of breccia.

Reference
Krzesińska A, Gattacceca J, Friedrich JM and Rochette P (2015) Impact-related noncoaxial deformation in the Pułtusk H chondrite inferred from petrofabric analysis. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12429]

Published by arrangement with John Wiley & Sons

Paul A. Giesting^1,†, Susanne P. Schwenzer², Justin Filiberto¹, Natalie A. Starkey², Ian A. Franchi², Allan H. Treiman³, Andy G. Tindle⁴ and Monica M. Grady²

¹Department of Geology, Southern Illinois University Carbondale, Carbondale, Illinois, USA
²Department of Physical Science, Planetary and Space Sciences, The Open University, Milton Keynes, UK
³Lunar and Planetary Science Institute, Houston, Texas, USA
⁴Department of Earth Sciences, The Open University, Milton Keynes, UK
^†Department of Geography and Geology, Illinois State University, Illinois, USA

Amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma, but also shock and postshock processes. We have analyzed amphibole and other phases from NWA 2737 melt inclusions, and we evaluate these data along with published values to constrain the crystallization Cl and H2O content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains. Using a model for the Cl/OH exchange between amphibole and melt, we estimate primary crystallization OH contents of chassignite amphiboles. SIMS analysis shows that amphibole from NWA 2737 currently has 0.15 wt% H2O. It has lost ~0.6 wt% H2O from an initial 0.7–0.8 wt% H2O due to intense shock. Chassigny amphibole had on average 0.3–0.4 wt% H2O and suffered little net loss of H2O due to shock. NWA 2737 amphibole has δD ≈ +3700‰; it absorbed Martian atmosphere-derived heavy H in the aftermath of shock. Chassigny amphibole, with δD ≤ +1900‰, incorporated less heavy H. Low H2O/Cl ratios are inferred for the primitive chassignite magma, which had significant effects on melting and crystallization. Volatiles released by the degassing of Martian magma were more Cl-rich than on Earth, resulting in the high Cl content of Martian surface materials.

Reference
Giesting PA, Schwenzer SP, Filiberto J, Starkey NA, Franchi IA, Treiman AH, Tindle AG and Grady MM (2015) Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12430]

Published by arrangement with John Wiley & Sons

Gulchekhra I. Kokhirova* andPulat B. Babadzhanov

Institute of Astrophysics of the Academy of Sciences of the Republic of Tajikistan, Dushanbe, Republic of Tajikistan

Three bright fireballs belonging to the August θ-Aquillid (ATA) meteor shower were photographed by the Tajikistan fireball network in 2009. Two of them are classified as the meteorite-dropping fireballs according to the determined parameters of the atmospheric trajectories, velocities, masses, and densities. Detection of the more dense bodies among cometary meteoroids points to a heterogeneous composition of the parent comet, and supports the suggestion that some meteorites might originate in the outer solar system, in the given case from the Jupiter-family comet reservoir. A search for the stream’s parent was undertaken among the near-Earth asteroids (NEAs); as a result, the asteroid 2004MB6 was identified as a possible progenitor of the ATA meteoroid stream. Investigation of the orbital evolution of the 2004MB6 and the fireball-producing meteoroid TN170809A showed that both objects have similar secular variations in the orbital elements during 7 kyr. The comet-like orbit of the 2004MB6 and its association with the ATA shower suppose a cometary origin of the asteroid.

Reference
Kokhirova GI and Babadzhanov PB (2015) The August θ-Aquillid fireballs and possible relationship with the asteroid 2004MB6. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12431]

Published by arrangement with John Wiley & Sons