We performed high-resolution Ar-40/Ar-39 dating of a suite of lunar meteorites from hot deserts: Dhofar 025, 309, 730, 733, 1442, Northwest Africa 6888, and Sayh al Uhaymir 449. The identification of terrestrial and lunar trapped argon components via isochrons allowed us to identify in situ radiogenic argon and to obtain proper chronological information. The last total reset ages of all studied samples are in the range of 3.1 to 4.2 Ga, coeval with the intense cratering period on the Moon and mare volcanism. Only Northwest Africa 6888 was totally reset <2.5 Ga ago. The most deeply buried breccia Dhofar 733 has the oldest age of 4.23 +/- 0.04 Ga within this series of meteorites. Dhofar 733, 1442, and NWA 6888 were furthermore affected by recent impact events <= 1 Ga. All meteorites were irradiated by galactic cosmic rays on the surface of the Moon for several up to hundreds of Ma. A simple irradiation history is revealed for only one meteorite Dhofar 733 delivered to Earth within similar to 0.5 Ma. The comparison of exposure ages, solar argon abundances and partial loss of cosmogenic and radiogenic argon of lunar breccias indicates that long surface residence enhances accumulation of solar wind implanted Ar-36 but also diffusive gas loss, most likely by surface thermal effects as solar and/or impact heating. The surficial regolith breccias Dhofar 025, 1442, NWA 6888, SaU 449 contain lunar trapped argon with Ar-40/Ar-36 ratios varying from 6 to 15, while the deep-derived breccia Dhofar 730 contains argon with (Ar-40/Ar-36)(trapped) ratio of 81. This could indicate that the composition of trapped argon in lunar meteorites may depend on rock layering depth. We suggest that the final capture of gases happens during sintering and agglutination along grain boundaries caused by thermal processes accompanying shock-induced compaction. Dhofar 1442 contains two distinct lunar trapped argon components with (Ar-40/Ar-36)(trapped) ratios of 14.58 +/- 0.28 and 5.5 +/- 0.7 indicating that lunar meteorites may contain more than one extraterrestrial trapped component incorporated during different thermal events. Our new Ar-40/Ar-39 ages of lunar meteorites significantly increase the number of high- resolution plateau age spectra, providing more compelling evidence of geochronologically meaningful pre 3.9 Ga ages. The different age distribution when compared to Apollo samples that were frequently dominated by Imbrium ejecta may be related to the fact that lunar meteorites provide a more random and thus complete sampling of the lunar surface, encompassing ejecta of older large basins, thereby favoring scenarios of more continuous or episodic pre 3.9 Ga bombardments. A possible scenario leading to episodic small body disturbances and bombardments involves close stellar encounters within the massive stellar cluster in which the sun resided during the first hundreds of million years of its lifetime.

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.

The results of a study of chilled glasses sampled during the 45th cruise of the R/V Professor Logachev at the top of the submarine volcano Puy des Folles are presented. The Puy des Folles volcano is located in the axial part of the rift valley of the Mid-Atlantic Ridge (MAR) at 20°31′ N. Unlike typical volcanic axial highs which usually does not exceed several hundred meters the summit of the Puy des Folles volcano is located a depth of 1950 m and rises 1800 m above the bottom of the rift valley. The data on geochemistry and isotope composition of chilled glasses examined allow us to come to a number of conclusions that expanded existing ideas about magmatic and tectonic processes conducted in the rift valley of the slow spreading ridges. Chilled glasses sampled at the top of the Puy des Folles volcano are originated from a very depleted melt formed by partial melting of the DM reservoir. Puy des Folles volcano was formed as result of the activity of a long-lived magma chamber located below the rift valley axis. It is possible that, in addition to the DM reservoir, a mantle source enriched in incompatible elements may have participated in the formation of the parental melts for the studied chilled glasses. A weak geochemical signal of contamination of the parental melt with a hydrothermal component in chilled glasses was established. Signs of stagnation in the spreading of the oceanic crust in the rift valley segment studied in this work have been established.

This paper presents the new geochemical isotope (Sr–Nd system, H2O, Cl) data obtained for basalt glasses of the Mid-Atlantic Ridge (MAR) sampled from six areas of the MAR axial zone between 31° and 12° N. The data are consistent with the existing ideas about large-scale geochemical segmentation of the MAR. It is shown that samples from predominantly serpentinite segments have a narrower range of variations of strontium isotopic composition (87Sr/86Sr = 0.7027–0.7032) in comparison with samples collected from the areas where the crustal section is dominated by basalts (87Sr/86Sr = 0.7024–0.7041). The variation ranges of the neodymium isotopic composition in these two groups of samples are almost identical (εNd = +4.9 to +10.9 and +5.9 to +11.6 in serpentinite and basalt segments, respectively), although, in general, serpentinite segments have a slightly more enriched composition. The wide variations of the neodymium isotopic composition and increased contents of Cl, H2O, and U, as well as increased K2O/TiO2 and La/Sm ratios, in samples from serpentinites can most probably be related to the participation of different geochemically heterogeneous sources in the magmatism of the MAR axial zone. The influence of enriched plume-type matter cannot be excluded in some segments. The isotopic composition of noble gases may shed light on the subject.

This paper presents the new geochemical isotope (Sr–Nd system, H 2 O, Cl) data obtained for basalt glasses of the Mid-Atlantic Ridge (MAR) sampled from six areas of the MAR axial zone between 31° and 12° N. The data are consistent with the existing ideas about large-scale geochemical segmentation of the MAR. It is shown that samples from predominantly serpentinite segments have a narrower range of variations of strontium isotopic composition ( 87 Sr/ 86 Sr = 0.7027–0.7032) in comparison with samples collected from the areas where the crustal section is dominated by basalts ( 87 Sr/ 86 Sr = 0.7024–0.7041). The variation ranges of the neodymium isotopic composition in these two groups of samples are almost identical (εNd = +4.9 to +10.9 and +5.9 to +11.6 in serpentinite and basalt segments, respectively), although, in general, serpentinite segments have a slightly more enriched composition. The wide variations of the neodymium isotopic composition and increased contents of Cl, H 2 O, and U, as well as increased K 2 O/TiO 2 and La/Sm ratios, in samples from serpentinites can most probably be related to the participation of different geochemically heterogeneous sources in the magmatism of the MAR axial zone. The influence of enriched plume-type matter cannot be excluded in some segments. The isotopic composition of noble gases may shed light on the subject.

The Fernando de Noronha archipelago (southwest Atlantic, 345 km from the coast of Brazil) is considered as the result of mantle plume activity. However, data on the isotopic composition of helium and neon, which are, perhaps, the only unambiguous geochemical criterion for deep mantle plumes have not been published yet for the region. In this paper, we present the first data on the isotopic composition of helium, neon, argon, and nitrogen, obtained by stepwise crushing of mantle xenoliths from the basanites of the San José Formation. The results obtained may indicate that fluid inclusions contain the very first portions of the exsolved gases—they are ultra-depleted in helium in relation to neon and especially argon. This conclusion is also supported by He–Ar–CO2 systematics. The isotopic composition of helium (4He/3He = 31 879 ± 6796) and neon (21Ne/22Ne(mantle) = 0.0453 ± 0.0012) indicates that it was indeed a mantle plume, identical in noble gas composition to the Kerguelen plume. According to the Ar–Ne isotope systematics 40Ar/36Ar (mantle) = 7455 ± 2290. Nitrogen is characterized by a heavy isotopic composition (δ15N = +5.4 ± 0.2‰), which corresponds to the hypothesis of the subduction nature of nitrogen in deep mantle plumes.

The geochemical peculiarities of sample collection of MORB chilled glasses obtained in six areas of the axial zone of the Mid-Atlantic Ridge (MAR), 12°–31° N have been studied. The results of this study provided information on the composition of the parental melts for these glasses and made it possible to assess the probable geochemical effects reflecting the interaction of magmatic melts with hydrothermal systems of the MAR axial zone or with altered oceanic crust (AOC). It is shown that basalts of the E-MORB family which includes most samples are localized mainly in the “cold” segments of the MAR, in the crustal section dominated by serpentinites. On the other hand, samples with depleted signatures (N-MORB) belong to MAR segments where serpentinite outcrops either are absent or play a subordinate role. The E-MORB chilled glasses from “cold” segments of the MAR show signs of contamination of basaltic melts with components assimilated either from the host serpentinites or from aqueous–saline fluids circulating in hydrothermal systems located in serpentinites (“serpentinite hosted”). Judging by the data obtained on the nature of Cl, U, and Sr variations in the studied chilled glasses ascribed to the N-MORB family, there are no signs of intracrustal contamination. It is assumed that relics of the ancient continental lithosphere preserved under axial zone of the MAR and involved in the partial melting of the shallow mantle took part in the formation of E-MORB parental melts in some MAR segments.

Here we present data on nitrogen and argon isotopic compositions and He–Ar–N–C(CO 2 ) elemental ratios obtained during stepwise crushing of fresh basaltic glasses of the N-MORB family from Mid-Atlantic ridge rift valley at 16°07′–17°11′ N. The bulk nitrogen isotopic composition in the samples varies from δ 15 N (total) = –5.2 ± 0.2‰ (i.e., typical for MORB glasses) to δ 15 N (total) = +4.6 ± 0.3‰ (pointing to the presence of organic nitrogen). The δ 15 N variations in the crushing steps are wider and range from –13.8 to +8.3‰. The 40 Ar/ 36 Ar ratios in the crushing steps vary from the value close to that in the atmosphere (~296) up to 11 100 ± 590 (the bulk values cover a range from 355 ± 11 to 2799 ± 159). Correlations between argon and nitrogen isotopic and elemental ratios imply mixing between an N-MORB type mantle component and a surface-derived component enriched in 15 N. Carbon (CO 2 )—nitrogen systematic suggests that the most plausible source for isotopically heavy nitrogen is the organic matter brought into the fluid source. Strong relationships between Ar and N isotopic compositions and Cl, H 2 O, and K, as well as Ar–N 2 , N 2 –CO 2 and Ar–He–CO 2 systematics, indicate that melt degassing and contamination with atmospheric Аr and organic nitrogen are the two dominant processes responsible for elemental and isotopic variation. The contamination of magmatic melts with surface related noble gases and organic nitrogen occurred through their interaction with high salinity hydrothermal brines. We propose that this contamination mechanism may be universal and largely responsible for the observed variations in the isotopic composition for a number of volatile elements in MORB glasses. However larger set of samples from the hydrothermal fields’ related areas has to be studied for better understanding how common is the established contamination mechanism.

Here we present summarizing of isotopic compositions and element ratios of noble gases, nitrogen, carbon and hydrogen in carbonatites of different generations of the Guli massif (West Siberia, Russia) obtained by stepwise crushing. The data point to the subcontinental lithospheric mantle (SCLM) as a primary source of the fluid phase in Guli carbonatites. However, the estimated 40Ar/36Ar ratio in the Guli mantle source of about 5400 is similar to the Kola plume value of 5000 ± 1000 (Marty et al., 1998). One explanation of such a low estimated 40Ar/36Ar ratio in the mantle end-member with SCLM type helium (4Не/3Не ~ 120000) and neon (21Nе/22Nеmantle ~ 0.7) is an admixture of atmospheric argon to the local mantle source. This assumption is supported by the Ar-Ne systematics as well as by the data for hydrogen isotopic composition. Early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotopic compositions of carbon (CO2), argon, and hydrogen (H2O). The mantle component dominated in fluids at the early formation stages of the Guli massif rocks, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon and neon, and most likely a high portion of CO2 with isotopically heavy carbon. The argon-neon-hydrogen isotope systematics suggest that the most plausible source of these late stage fluids are high temperature paleometeoric waters. The absence of a plume signature could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.

Stepwise crushing data on nitrogen and argon isotopic compositions and He-Ar-N-C(CO 2 ) elemental ratios in fresh basaltic glasses of the N-MORB family from Mid-Atlantic ridge rift valley at 16°07'-17°11' N are discussed. The bulk nitrogen isotopic composition in the samples varies from δ 15 N (total) = -5.2±0.2 ‰ (i.e., typical for MORB glasses) to δ 15 N (total) = +4.6±0.3 ‰ (pointing to the presence of organic nitrogen). The δ 15 N variations in the crushing steps are wider and range from -13.8 to +8.3 ‰. The 40 Ar/ 36 Ar ratios in the crushing steps vary from the value close to that in the atmosphere (~296) and up to 11100±590 (the bulk values cover range from 355±11 to 2799±159). Correlations between argon and nitrogen isotopic and elemental ratios imply mixing between an N-MORB type mantle component and a surface-derived component enriched in 15 N. Carbon (CO 2 ) – nitrogen systematic suggests that the most plausible source for isotopically heavy nitrogen is the organic matter brought into the fluid source. Strong relationships between Ar and N isotopic compositions and Cl, H 2 O, and K concentrations (Silantyev et al., 2008), as well as Ar-N 2 , N 2 -CO 2 and Ar-He-CO 2 systematics, indicate that melt degassing and contamination with atmospheric А r and organic nitrogen are the two dominant processes responsible for elemental and isotopic variations. The contamination of magmatic

Aubrites are achondritic meteorites (enstatite pyroxenites) that were formed in highly reduced magmatic environments on a differentiated parent body sharing a common oxygen isotope reservoir with enstatite chondrites (EC), Earth and Moon, and could be considered as a geochemical model of the early proto-Earth. Some pyroxenes of the Pesyanoe aubrite have high abundance of gaseous inclusions, captured during the crystallization of the rocks. Investigation of the inclusions by IR spectroscopy reveals presence of OH− groups and C–H bonds. The former are assigned to protonated point defects in enstatite lattice and the latter to compounds occupying void walls. Molecular water and CO2 were not observed. Volatile components released from the samples of the Pesyanoe enstatite by stepwise crushing and heating are composed of CO2, H2O and a non-condensable phase. Hydrogen isotopic composition of volatiles extracted in form of molecular water in Px-separates varies in the range δD = −61 – −84‰ with mean value of δD = −73 ± 16‰ VSMOW and is within the ranges of ECs and Earth’s mantle. The total abundance of H2 in the pyroxene of Pesyanoe were estimated as at least 0.047 ppm that is too low in comparison with that of enstatite chondrites (≥30 ppm H2) and could indicate nearly complete degassing of the Pesyanoe primitive precursor material during the Pesyanoe parent body accretion or a mantle degassing in igneous differentiation process. In a last case a primitive precursor could have D/H ratio different from that of enstatite chondrites.

The lunar meteorite Dhofar 1436 is dominated by solar wind type noble gases. Solar argon is equilibrated with “parentless” 40 Ar commonly known as lunar orphan argon. Ar‐Ar isochron analyses determined the lunar trapped 40 Ar/ 36 Ar ratio to 2.51 ± 0.04, yielding a corrected plateau age of 4.1 ± 0.1 Ga, consistent with the lunar Late Heavy Bombardment period. Lunar trapped and radiogenic argon components are all released at high temperatures (1200–1400 °C). Surprisingly, solar noble gases and lunar trapped argon can largely be released by crushing. Initial crushing steps mainly release elementally fractionated solar wind gases, while in advanced crushing steps, cosmogenic components dominate. Cosmogenic noble gases indicate irradiation at the lunar surface; they are less fractionated than solar wind species. We favor a scenario in which both solar and a large fraction of cosmogenic gases were acquired before the 4.1 Ga event, which caused shock metamorphism and formation of the regolith breccia. Sintering and agglutination along grain boundaries resulted in mobilization of solar wind, reimplanted, radiogenic, and cosmogenic noble gases, and resulted in their partial homogenization, fractionation, and retrapping in voids and/or defects accessible by crushing. An alternative scenario would be complete reset of the K‐Ar system 4.1 Ga ago accompanied by loss of all previously accumulated solar and cosmogenic noble gases. Later, the precursor of Dhofar 1436 became lunar regolith and accumulated solar and cosmogenic noble gases and reimplanted 40 Ar before its final formation of the polymict impact breccia. The C abundance of the step‐combusted Dhofar 1436 is 555.3 ppm, with δ 13 C of −28‰ to +11‰. Nitrogen contents released by crushing and combustion are 3.2 ppm and 20.8 ppm, respectively. The lightest nitrogen composition (δ 15 N = −79‰) is likely due to release from voids of shock metamorphic phases and is rather a result of the mobilization of nitrogen components that accumulated prior to the 4.1 Ga event.

Аннотация.Исследованы составы расплавных включений в главных минералах щелочных пород Гулинского плутона -оливиновый нефеленит, мелилитолит, ункомпагрит, якупирангит.Методом LA-ICP-MS получены данные по редкоэлементному составу расплавов в них.Анализ полученных данных позволяет сделать вывод о

RationaleThe study of multi‐isotope systematics of fluid inclusions is of great importance for understanding of the sources and evolution of fluid phases in mantle rocks and ore deposits. The most appropriate technique for such investigations is a (stepwise) crushing method that is widely used for noble gases and nitrogen. However, because of the possible influence of mechanochemical reactions and back sorption, analyses of the isotope composition of water extracted by crushing from fluid inclusions are challenging.MethodsAn isotope ratio mass spectrometry (IRMS)‐based method for hydrogen (and oxygen) isotopic analysis in sub‐microliter volumes of water extracted from fluid inclusions by crushing is presented. The verification of the possible influence of adsorption processes and mechanochemical reactions on the results of isotope analysis was performed for the first time. For that a series of parallel analyses of hydrogen isotopic ratios from water inclusions in quartz applying physically different extraction methods (crushing and thermodecrepitation) was conducted.ResultsFour series of quartz aliquots were analyzed: three series extracting water by crushing (two series for δ2H values and one for δ18O values) and one by thermodecrepitation. The mean value for the crushing results is δ2H = −85.3 ± 3.6 ‰ (1σ, n = 11), which coincides well with the thermodecrepitation data (−86.3 ± 2.0 ‰, 1σ, n = 5), suggesting that our methodological approach allows the influence of back sorption or mechanochemical reactions during the crushing experiment to be minimized. The reproducibility of the oxygen isotopic ratios is ±0.9 ‰ (1σ, n = 5).ConclusionsThe conducted experiments have shown that the influence of back sorption or mechanochemical reactions during crushing on isotopic results is not crucial for our method. The developed IRMS‐based method for hydrogen (and oxygen) isotopic analysis in sub‐microliter volumes of water is well applicable for multi‐isotope investigations of gases extracted from fluid inclusions. As an application a well‐defined 40Ar/36Ar–δ2H correlation in mantle rocks is presented for the first time.

— The first data on the isotopic composition and elemental ratios of nitrogen, carbon, and noble gases in samples from the early stages of the formation of the Guli Complex (Maimecha-Kotui igneous province, Polar Siberia), obtained using the method of stepwise crushing, are reported. The 40 Ar/ 36 Ar ratios in the crushing steps vary from the values close to atmospheric (~296) in the meimechite sample to 5000–6000 in pyroxenite and melilitolite; the latter correspond to the estimate for the mantle source of carbonatite from the Guli massif, according to the Ne–Ar systematics. The bulk nitrogen isotopic composition (δ 15 N) in the studied rocks varies from +3.7 to –5.9‰, showing a regular increase in δ 15 N with increasing nitrogen concentration; the range of δ 15 N variations in crushing steps is even wider: from +6.7‰ in pyroxenite to –15.4‰ in meimechite. The data obtained for the ultrabasic rocks of the Guli Massif suggest a significantly lower contribution of the subducted nitrogen of organic origin in comparison with the alkaline–ultramafic rocks of the Kola alkaline province and associated carbonatite, as well as with the Guli carbonatite and some Indian alkaline–ultramafic complexes with carbonatite. The N/ 36 Ar ratios in the trapped mantle component of the ultramafic rocks are 4–8 times lower than that in the associated carbonatite. This, most likely, indicates different fluid sources, or the preferred escape of nitrogen from the fluid phase at the early stages of the formation of the Guli Massif.

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.