An Erratum to this paper has been published: https://doi.org/10.1134/S0016702924190017

We present the results of stepwise crushing and combustion analyses for noble gases, carbon and nitrogen in Pesyanoe aubrite pyroxene lithologies, composed of grey (Px-G) and light (Px-B) enstatites differing in the degree of impact processing and the number of inclusions. Our study identifies three main noble gas endmembers in Pesyanoe: a cosmogenic component, radiogenic 40Ar, and an endmember representing a mixture of solar wind and Q components in variable proportions. Based on petrographic and noble gas data we argue that these gases accumulated in the material during its regolith history and were later redistributed into gas inclusions/voids as the result of an impact event. During impact metamorphism, Px-G acquired its grey color and multiple gas inclusions were formed within it, more than in case of Px-B. Our study demonstrates for the first time: (1) The host phase of gases trapped during shock metamorphism are grains of rock-forming minerals, in particular Px-G, due to the formation of a large number of cracks in the direction of cleavage during brittle deformation, (2) The gas capture is associated not with the final stage of the formation of consolidated fragmental breccia, at which lithification of the fragments occurred, but with one of the intermediate impact events. High amounts of trapped and cosmogenic noble gases are released during the stepwise crushing—significantly higher than in case of any other studied aubrite. Some unusually high 36Ar/132Xe ratios (up to 54 780 versus 22 705 in the solar wind) were discovered during crushing of Px-G. Our preferable explanation of this phenomenon is a specific superposition of noble gas elemental fractionation processes related to the impact cratering of the Pesyanoe parent body. The carbon isotopic composition (δ13C = –21.2 ± 0.2‰, 1σ) is slightly heavier than that of the Bustee aubrite carbon. The combined use of different extraction methods made it possible to determine that the solar type and indigenous (δ15Nindig = –0.1 ± 3.2‰, 1σ) nitrogen components are located in the gas inclusions, whereas the extraneous nitrogen component ( +45‰) is chemically bound. The large cosmic ray exposure age variations (44 and 55 Ma in case of Px-G and Px-B, respectively) and the heterogeneous distribution of solar-type gases in Pesyanoe aubrite point to a diverse irradiation history of the material before breccia formation. Alternatively/additionally, cosmogenic gases (as well as solar and primordial) in Px-G may have became lost and/or partly redistributed into gas inclusions as a result of the impact event.

Stepwise crushing and combustion methods were applied to study the KREEP-rich lunar breccia Dhofar 1442, the clastic material of which is cemented by porous matrix. The stepwise crushing released significant amount of gases of extraterrestrial origin from gas voids. Argon, nitrogen, and carbon are simultaneously released by stepwise combustion at 1100°С. The simultaneous high-temperature degassing of these gases, as well as the coincidence of С/N ratio and nitrogen and carbon contents in high-temperature combustion steps with those of crushing indicate that the gas carriers are voids in high-temperature phases (in particular, minerals, glasses), which are decomposed/melted at these temperatures. Helium and neon are released from the same positions at lower temperatures. The isotopic composition of neon obtained by stepwise combustion and crushing corresponds to the composition of fractionated solar wind. The fraction of argon in the first crushing steps is higher than that of any other of studied gases. The 40 Ar/ 36 Ar in the trapped lunar argon is ~18, which is not consistent with empirical model implying that 40 Аr is implanted from lunar atmosphere (McKay et al., 1986; Eugster et al., 2001; Joy et al., 2011). We believe that the entrapment of volatile elements in gas voids of the meteorite Dhofar 1442 was caused by the redistribution of gases from one structural sites into others during impact events that accompanied the cratering, in particular, leading to the formation of the impact melt breccia Dhofar 1442. The trapped gases of the meteorite Dhofar 1442 contain not only typical volatile components (solar, radiogenic, cosmogenic, re-implanted 40 Ar) of lunar breccias, but also nitrogen and carbon formed through the oxidation of organic matter of metamorphosed chondrites, which are present in the breccia. With increasing number of strokes and, correspondingly, a degree of crushing, the elemental ratios change. A slight decrease of 4 He/ 20 Ne ratio during crushing is likely related to the different diffusion ability and permeability of helium relative to neon under temperature influence and/or to the heterogeneous distribution of these gases in voids of different size. The 4 He/ 36 Ar, 20 Ne/ 36 Ar, 14 N/ 36 Ar, and 12 С/ 36 Ar ratios increase by factors of 10–100 during crushing. This can be explained by the combination of dynamically different processes leading to the argon fractionation relative to other gases and uneven redistribution of gases from different positions in voids of different sizes during impact metamorphism.

The isotopic composition of noble gases, nitrogen, and carbon in two samples of the Ozerki L chondrite, which differ in the degree of impact metamorphism, analyzed by the methods of stepwise oxidation and crushing, is reported. The data obtained indicate that the meteorite contains gases trapped on the asteroid during the impact events. The isotopic composition of trapped argon, studied by the stepwise crushing method, is dominated by radiogenic 40Ar (the average 40Ar/36Ar values are 846 in the chondrite material and 1908 in the melt with fine chondrite fragments). Most of the trapped 36Ar is located in positions inaccessible for crushing. The isotopic composition of Ne is a mixture of the solar-wind neon, cosmogenic, and most likely planetary (Q) components. The elemental composition of the trapped noble gases is formed by mixing of the solar, planetary (Q), and cosmogenic components in different proportions. Diffusion processes caused by impact events most likely influenced the elemental abundance of noble gases, primarily helium. Almost all carbon and nitrogen are chemically bound in the rock. In general, their isotopic composition corresponds to that of ordinary chondrites; however, an atypically light carbon isotopic composition with a bulk value δ13C = –47.6 ± 4.8 (‰) was detected in a sample of the chondrite material. The nitrogen released during crushing is isotopically lighter than that released during oxidation. This may indicate that in the course of impact processes, solar nitrogen is more easily mobilized and redistributed into voids than organic nitrogen enriched in the heavy isotope.

METHODS IN THE LUNAR DHOFAR 1436 METEORITE. E.V. Korochantseva 1,2 , A.I. Buikin 1 , J. Hopp 2 , A.B. Verchovsky 3 , A.V. Korochantsev 1 , M. Anand 3 , and M. Trieloff 2 , 1 Vernadsky Institute of Geochemistry, Kosygin St. 19, 119991 Moscow, Russia, 2 Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany, 3 School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK(e-mail: Mario.Trieloff@geow.uni-heidelberg.de).

M. A. Ivanova, C. A. Lorenz, M. Humayun, K. Richter, C. M. Corrigan, I. A. Franchi, A. B. Verchovsky, E. V. Korochantseva, V. V. Kozlov, S. N. Teplyakova, Kononkova N. N., and A. V. Korochantsev, Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991, Russia; meteorite2000@mail.ru, National Museum of Natural History, Smithsonian Institution, USA; National High Magnetic Field Laboratory and Department of Earth, Florida State University, USA; Planetary and Space Sciences Research Institute, Open University, UK, Mailcode XI2, NASA JSC, USA Oxford Instruments OM & Gatan Inc., Moscow, Russia .

The Ghubara meteorite contains abundant trapped gases in voids of highly retentive phases that can be released by stepwise crushing and thermal degassing. Their composition is dominated by the solar wind component and by radiogenic argon. We favor a scenario in which a large impact event on L-chondrite asteroid 470 Ma ago caused release, mobilization, fractionation and redistribution of accumulated gases on the Ghubara parent body. The Ghubara breccia was formed at that event and occluded trapped gases into the voids. The uncommonly high 20Ne/36Ar ratios of the analysed samples compared to the solar composition is considered to be due to trapping of gases released from surrounding rocks that lost light noble gases preferentially over the heavy ones. The 4He/20Ne and 4He/36Ar ratios, being as usually lower than in solar wind, gradually increase during stepped crushing, indicating non equilibrium distribution of the gases between the voids of different sizes that can be caused by the dynamics of the shock metamorphism process. The neon isotopic composition released by stepwise crushing and combustion is a mixture of two components: solar dominating trapped and cosmogenic Ne. The former component is mainly degassed in the initial crushing steps opening the large inclusions/voids, while the relative contribution of the latter, likely released from galactic cosmic ray produced tracks, increases with progressive crushing. During stepwise combustion the same trend in the release of the Ne components with increasing temperature is observed. The nitrogen and carbon abundances as well as their isotopic compositions in Ghubara are usual for ordinary chondrites. Most of nitrogen is chemically bounded and associated with carbon. The delivery time of Ghubara from the parent body asteroid to the Earth calculated from its exposure age is 9–28 Ma.

1 , E. V. Korochantseva 1,2 , J. Hopp 2 , I. Franchi 3 , M. Humayun 4 , S. N. Teplyakova 1 , N. N. Kononkova 1 , 1 Vernadsky Institute RAS, Kosygin St. 19, 119991, Moscow, Russia, c-lorenz@yandex.ru, 2 Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany, 3 Planetary & Space Sciences, Open University, Milton Keynes, UK, 4 National High Magnetic Field Laboratory, Florida State University, USA.

METEORITE DHOFAR 1436 E.V. Korochantseva 1,2 , A.I. Buikin 1 , A.B. Verchovsky 3 , J. Hopp 2 , A.V. Korochantsev 1 , M. Anand 3 , M. Trieloff 2 , 1 Vernadsky Institute of Geochemistry, Kosygin St. 19, 119991 Moscow, Russia, 2 Klaus-Tschira-Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany (e-mail: Mario.Trieloff@geow.uni-heidelberg.de), 3 Planetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK.

Here we present the first data on He, Ne, Ar isotopic and elemental composition in fluid phases of tholeiitic chilled glasses from the Bouvet Triple Junction (BTJ). The chilled glasses from several dredging stations situated at different segments of BTJ have been investigated: Spiess Ridge, Mid Atlantic Ridge (MAR) and in a valley of the Southwest Indian Ridge (SWIR). The data allow to distinguish within BTJ three segments characterized by different geochemical behavior of He, Ne and Ar. MAR and Spiess samples contain MORB-like helium and neon while SWIR is characterized by addition of plume type He and Ne. The strong atmospheric contamination is typical of all segments, but for MAR it is less pronounced. The Ne-Ar isotope systematics suggests that the atmospheric component was most probably introduced into the mantle source of the fluids with fragments of oceanic crust/sediments.

The article considers different points of view on the genesis of extraterrestrial trapped argon with a composition different from primordial/solar in meteorites and lunar rocks. An alternative hypothesis of the origin of this component is discussed.