Terrestrial Rocks Research Articles

Dinosaur trackways from the Upper Cretaceous Nichkesai Formation near Mayluu Suu City, Southern Tien Shan Mountains, north-western Kyrgyzstan.

Trackways provide essential data on the biogeographic distribution, locomotion and behaviour of dinosaurs. Cretaceous dinosaur trackways are abundant in the Americas, Europe, North Africa and East Asia, but are less well documented in Central Asia despite extensive exposure of Cretaceous terrestrial sedimentary rocks in the region. Here we report the presence of bipedal, tridactyl dinosaur trackways near the city of Mayluu Suu, Jalal Abad Oblast, north-western Kyrgyzstan, the first discovery of dinosaur trace fossils within the country. The trackways are situated on a steep slope uncovered by a landslide around the year 2000 in a highly landslide-affected area. Photogrammetry is used to digitally analyse and conserve the trace fossils. We infer a shoreface setting for the trackways based on the locality sedimentology, discuss the identity of the track makers and highlight the potential for future trackway discovery in the area. This discovery contributes vital data to an otherwise sparse record on the spatio-temporal distribution of dinosaurs in Kyrgyzstan, and to the dinosaur trackway record of Central Asia.

The indium isotopic composition of the bulk silicate Earth

Indium (In) behaves as a moderately volatile metal during nebular and planetary processes, and its volatility depends strongly on oxygen fugacity. The In isotopic composition of the bulk silicate Earth (BSE) could provide a critical constraint on the nature of Earth’s building blocks and mechanisms that lead to its volatile depletion. However, accurately and precisely determining the isotopic composition of In of the silicate Earth is challenging due to its low abundance in igneous rocks and the presence of significant isobaric interferences on its isotopes (e.g., 113Cd+ on 113In+ and 115Sn+ on 115In+). Here, we present a purification procedure for In from rock matrices and report the first dataset of In isotopic compositions of 30 terrestrial igneous rocks, one biotite geostandard, and one carbonaceous chondrite (Allende) measured on a Nu Sapphire collision-cell equipped multi-collector inductively-coupled-plasma mass-spectrometer (CC-MC-ICP-MS) with an external reproducibility of 0.11‰ (2SD). At this level of precision, we find no statistically significant difference in the In isotopic compositions of mid-ocean-ridge basalts (MORB), oceanic island basalts (OIB), and continental flood basalts (CFB). Furthermore, Canary Islands, Iceland and Afar lavas display no analytically resolvable In isotopic variations from basalts to rhyolites. Therefore, In isotope fractionation during igneous processes is smaller than our analytical uncertainty and the In isotopic compositions of basalts are likely to be representative samples of their mantle sources. The twenty-one terrestrial basalts from diverse geological settings have an average δ115In of 0.35 ± 0.07 ‰ (2SD). This value represents the current best estimate of the In isotopic composition of the mantle as well as of the bulk silicate Earth, assuming limited In isotope fractionation during mantle partial melting, and due to the small contribution of the continental crust to the In budget (<5%). This isotopic composition provides a baseline with which to compare with chondrites and differentiated planetary bodies in future studies.

Gallium isotopic constraints for the origin of the Earth-Moon system

Comparatively heavy isotopic compositions of moderately volatile elements (MVE) in lunar rocks have been advocated to reflect the loss of light isotopes during devolatilization processes from the Moon. In this study we present new gallium (Ga) isotope data for lunar highland rocks, with a focus on the Ferroan Anorthosite Suite (FAS). These are commonly thought to be direct crystallization products from the late lunar magma ocean (LMO) and should contain the majority of the Ga inventory of the Moon. As such, FAS rocks are crucial for identifying the processes that drove Ga isotope fractionation as well as for inferring the Ga isotopic composition of the bulk Moon.Our data reveal that FAS samples have a range in δ71Ga from −0.27 to 0.22‰ and are generally isotopically light in Ga compared to other lunar lithologies, but straddle values typical of terrestrial rocks. Although Ga is defined as an MVE, these Ga isotope variations do not correspond with concentrations of more volatile elements, indicating that Ga isotope variations in the FAS are not primarily controlled by devolatilization processes. Instead, the Ga isotopic compositions of bulk FAS rocks broadly correlate with the composition of plagioclase, with the calcium content of plagioclase decreasing as Ga becomes isotopically heavier. This suggests that fractionation of Ga isotopes in FAS rocks was caused by the preferential incorporation of isotopically light Ga into plagioclase during the later solidification stages of the LMO. The progressive crystallization and extraction of plagioclase forces the residual melt towards increasingly heavier Ga isotope ratios, corroborating similar conclusions derived from correlations between δ71Ga and Eu* in the mare basalt suite.Using Ga isotope partitioning calculations, we demonstrate that an isotope fractionation coefficient between plagioclase and coexisting melt of −0.3 to -0.4‰ could explain the observed range of δ71Ga values in FAS, mare basalt suite rocks, and KREEP. These calculations allow for a first order estimate of the Ga isotopic composition of the bulk silicate Moon prior to plagioclase fractionation and suggest it was close to the composition of the bulk silicate Earth. This would imply that the Moon did not lose a substantial fraction of its Ga inventory during accretion, consistent with new constraints from Rb-Sr isotope systematics that indicate the Moon's volatile deficit was primarily inherited from Theia. In conjunction with the overlap in non-mass-dependent isotope ratios, these collective observations could be reconciled if Theia and the proto-Earth formed in similar regions of the inner Solar System that were already volatile-depleted.

Relict Mesoarchean (2.99–2.94 Ga) metamorphism overprinted by late Neoarchean tectonothermal event(s) from the Sukma Group supracrustal rocks, Bastar craton, India: Evidence from new Lu-Hf and Sm-Nd garnet isochron and Th-U-total Pb monazite ages

Mesoarchean metasupracrustal successions can preserve evidence of tectonothermal reworking involving Paleoarchean felsic crust. Paleoarchean tonalite and trondhjemite of the Bastar craton, central India contain remnants of amphibolite-facies meta-supracrustal rocks of the Sukma Group, which likely represents the oldest Archean terrestrial sedimentary rocks. In order to constrain the time of metamorphic events combined garnet Lu-Hf and Sm-Nd geochronology and Th-U-total Pb dating of texturally preserved monazite from garnet-bearing metapsammite samples, representative of cover rocks overlying orthopyroxene-bearing tonalite basement, were conducted. Relics of an earlier garnet porphyroblast-forming metamorphic stage 1 (M1) developed at upper amphibolite-to granulite-facies conditions, are texturally distinct from the widespread metamorphic stage 2 (M2) marked by the garnet-breakdown to cordierite-anthophyllite symplectite. The M2-stage conditions, at ∼ 650–700 °C and ∼ 5.7 kbar, in the metasupracrustal remnants, are similar to those in garnet-amphibole-bearing quartzite and also as inferred from associated calc-silicate gneiss. Samarium-Nd chronology on whole-rock and porphyroblastic garnet fractions from three garnet-bearing quartzite samples yielded a weighted mean age of 2990 ± 10 Ma whereas Lu-Hf isotopic systematics on the same garnets from two of these quartzite samples yielded a weighted mean age of 2940 ± 31 Ma. Superposed Late Neoarchean M2 stage tectonothermal events include mylonitization of a ∼ 3.5 Ga basement tonaliteat 2525 ± 20 Ma and garnet formation within a Fe-rich quartzite at 2413 ± 21 Ma, as constrained from Sm-Nd isochron ages and similar to the in-situ weighted mean chemical age of 2367 ± 19 Ma of monazite included within M2-stage symplectitic cordierite around the older M1-stage garnet. The relict 2.99–2.94 Ga mid-crustal amphibolite-to granulite-facies M1 metamorphic assemblages stabilized within metasupracrustal rocks, formed in response to crustal thickening during Mesoarchean convergent tectonics, and were likely related to amalgamation of Paleoarchean crustal fragments.

Terpane Characterization of Crude Oils from Niger Delta, Nigeria: A Geochemical Appraisal

The geochemistry of crude oils from the Niger Delta, Nigeria, were evaluated using the characterization of C₁₉ to C₃₅ terpanes. Analyses of two representative crude oils from Western and Central Niger Delta showed abundances of C₁₉ to C₂₉ tricyclic terpanes constituted 12.09% and 29.74%, C₂₄ tetracyclic terpane 0.31% and 0.15% and C₂₇ to C₃₅ pentacyclic terpanes 87.61% and 70.12%, respectively. Diagnostic ratios of terpanes indicated relatively low abundances of C₂₃, C₂₈ and C₂₉ tricyclic terpanes, low abundances of homohopanes, a significantly high abundance of oleanane and that the Niger Delta crude oils were derived from terrestrial organic matter source rocks deposited in an oxic environment during the Tertiary period. Multivariate oil-oil correlation plot showed the Western and Central Niger Delta crude oils are not distinct, but moderately related (genetically). However, diagnostic ratios of C₂₄ tetracyclic terpane, which was high and moderate and gammacerane, which was low and high, revealed crude oils from Western Niger Delta were derived from predominantly terrestrial source and crude oils from Central Niger Delta were derived from terrestrial source with input from marine organic matter, respectively. Tricyclic terpanes/hopanes and isomerization ratios of C₃₂ homohopanes indicated the Niger Delta crude oils were generated at high maturity, at top of the oil generation window.

Differential hydrocarbon generation and evolution of typical terrestrial gas-prone source rocks: An example from the Kuqa foreland basin, NW China

Terrestrial gas-prone source rocks are significant for hydrocarbon gas accumulations especially in central and western basins in China. The Kuqa foreland basin in the northern margin of the Tarim Basin, NW China is rich in natural gas with recent discoveries of several large to giant gas-producing fields (e.g., the Kela-2, Dibei, Dabei-1, and Zhongqiu-1 gas fields, etc.) and a proven 3 P gas reserve of over one trillion cubic meters (TCM). This proliferous petroleum province is powered by an effective and diverse gas-prone source rock series in the basin comprising mudstone, carbonaceous mudstone, and coal seams. To date, little systematic research work has been done on the petroleum generation potential of the source rocks. This has seriously restricted the assessment of petroleum resources and further exploration in the frontier areas of the basin. A sealed gold tube pyrolysis approach was employed to simulate the oil and gas generation and cracking yields for the aforementioned three types of source rock. Compared with typical Type I and II1 kerogens, the three types of source rocks in the Kuqa foreland basin are characterized by (1) far less hydrocarbon yield (150 mg/g TOC) with comparatively larger amounts of CO2 (310 mg/g TOC), (2) a limited capacity and narrower window (0.5%–1.08% Ro) for oil generation, and (3) a much earlier secondary cracking for bulk oil to light oil and gases (>0.86% Ro for mudstone and >1.08% Ro for both carbonaceous mudstone and coal). All the source rocks are gas-prone, and significant amount of gas can still be generated during an over-mature stage. The kinetic parameters obtained allow us to model hydrocarbon generation in the Kuqa foreland basin more realistically. It is concluded that (1) two episodes of hydrocarbon generation occurred with hydrocarbon gases being mainly generated during the later stage (12–3 Ma); and (2) the depocenter of the basin is capable of supplying massive high-mature gases as late as in the Quaternary, which is crucial for the formation of giant gas fields. The findings provide new insight on the reconstruction of oil and gas accumulation processes and further hydrocarbon exploration in the basin.

Discovery of “Meteoritic” Layered Disulphides ACrS2 (A = Na, Cu, Ag) in Terrestrial Rock

For the first time, chromium disulphides, known from meteorites, such as caswellsilverite, NaCrS2; grokhovskyite, CuCrS2; and a potentially new mineral, AgCrS2, as well as the products of their alteration, such as schöllhornite, Na0.3CrS2∙H2O, and a potentially new mineral with the formula {Fe0.3(Ba,Ca)0.2} CrS2·0.5H2O, have been found in terrestrial rock. Layered chromium disulphides were found in unusual phosphide-bearing breccia of the pyrometamorphic Hatrurim Complex in the Negev Desert, Israel. The chromium disulphides belong to the central fragment of porous gehlenite paralava cementing altered host rock clasts. The empirical formula of caswellsilverite is (Na0.77Sr0.03Ca0.01)Σ0.81(Cr3+0.79Cr4+0.18V3+0.01 Fe3+0.01)Σ0.99S2·0.1H2O, and the end-member content of NaCrS2 is 76%. It forms single crystals in altered pyrrhotite aggregates. Grokhovskyite has the empirical formula {Cu+0.84Fe3+0.10Ca0.06 Na0.01 Sr0.01Ba0.01}Σ1.03(Cr3+0.94 Fe3+0.05 V3+0.05)Σ1.00S2·0.35H2O, and the CuCrS2 end-member content is 75–80%. A potentially new Ag-bearing chromium disulphide is characterised by the composition (Ag0.89Cu0.07)Σ0.96(Cr0.98 Fe0.03V0.01Ni0.01)Σ1.04S2. Caswellsilverite, grokhovskyite and AgCrS2 form in gehlenite paralava at high temperatures (near 1000 °C) and low pressure under reducing conditions. The structure of the layered chromium disulphides, MCrS2, is characterised by the presence of hexagonal octahedral layers (CrS2)1−, between which M-sites of the monovalent cations Ag, Cu and Na set. A low-temperature alteration of the layered chromium disulphides, when schöllhornite and {Fe0.3(Ba,Ca)0.2}CrS2·0.5H2O form, is reflected in the composition and structural modification of the layer with monovalent cations, whereas the octahedral layer (CrS2)1− remains unchanged.

On the influence of the trace element composition of regoliths on the labor safety of astronauts on the Moon

Introduction. The problem of using near-Earth space to meet various human needs, including the development of minerals, especially on the Moon, is becoming relevant, which increases the importance of research on occupational safety in these conditions. The study aims to research the trace element composition of regoliths in comparison with terrestrial rocks and its significance for the safety of astronauts on the lunar surface. Materials and methods. The researchers evaluated the trace element composition of the regolith by calculating the concentration coefficients and the quality drop coefficient. When identifying homogeneous classes of regoliths by concentrations of 38 chemical elements, we used computer technology to classify multidimensional observations under conditions of self-organization. Results. We know that the concentrations of many trace elements in regoliths significantly exceed their concentrations in terrestrial soils. Calculated for the Luna-16 and Luna-24 marine regoliths, as well as for Apollo-11 and Apollo-12, the quality reduction coefficient varies from 27 to 100, which corresponds to the "crisis" category. This indicates that the content of trace elements in the regolith ranges from weekly critical (27 for the Luna-16 regolith) to highly critical (100 for the Apollo-12 regolith). The researchers identified trace elements whose concentrations in lunar regoliths significantly exceed their concentrations in terrestrial soils: Cr, Be, Co, Sc, Ho, Se, Ni, Au, Ag, Er, Tm, Y, Sm, Gd, Tb, Dy Yb, Lu, Cd, Zr, Sr, Ce, Pr, Nd, Eu. Trace trace elements are included in the group of substances with allergenic, fibrogenic and carcinogenic effects and can have a negative impact on the health of future lunar colonists. Limitations. The authors have conducted the study for the composition of regolith on the surface of the Moon and did not cover aspects of human protection from lunar dust by space stations, structures, spacesuits and special equipment. Conclusion. When assessing the impact of environmental factors on the safety of astronauts during the colonization of the Moon, attention should be paid to the toxicological aspects of working conditions, in particular the trace element composition of regoliths and lunar dust.

Mass-independent Sn isotope fractionation and radiogenic 115Sn in chondrites and terrestrial rocks

Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In.Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures.Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth’s core.

FirstIn SituTerrestrial Osbornite (TiN) in the Pyrometamorphic Hatrurim Complex, Israel

AbstractOsbornite (TiN) is extremely rare in nature (commonly found in enstatite meteorites) and has not yet been identified correctly to form naturally in terrestrial settings. Due to its thermodynamic stability and thermal shock resistance, TiN has wide industrial applications, mainly as coatings. However, as the melting temperature of TiN is very high (~3000°С), coatings are produced at much lower temperatures via physical or chemical vapor deposition. Also, anthropogenic analogues of osbornite are often observed in pyrometallurgical slags. Therefore, it is critical to distinguish between anthropogenic and naturally occurring osbornite. A detailed petrographic study was undertaken on in situ osbornite found within unusual gehlenite-bearing breccias from wadi Zohar, Negev Desert of the pyrometamorphic Hatrurim Complex. The Hatrurim Complex, which extends through Israel, Palestine, and Jordan within the Dead Sea Rift zone, mainly comprises larnite, gehlenite, and spurrite rocks. Osbornite, in close association with iron phosphides, barringerite, and schreibersite, occurs at contacts between gehlenite, paralava, and calcinated clasts of host sedimentary rocks. Based on investigation of pseudowollastonite and Fe-P series phases, osbornite is formed at low pressure, extremely high temperatures (~1200-1500°С), and reduced conditions, following pyrolysis of organic matter contained in the sedimentary protolith. This is the first identification of in situ osbornite in terrestrial rocks and indicates that high-temperature and highly reduced conditions, which are common for meteorites, may occur at/near the Earth’s surface as a result of sustained pyrometamorphism in particular settings. Our findings also provide relevant data and criteria for comparing osbornite occurrences elsewhere and ultimately evaluating their origins.

Mercury isotope variation during organic matter maturation to petroleum

Although both sedimentary rocks and petroleum generally contain detectable levels of Hg, the characteristics of Hg isotope fractionation and its transformation from biomass to sedimentary rocks to petroleum have not been sufficiently investigated to date. Here, we report Hg contents and isotope compositions in source rocks and crude oils from the Paleogene of the Bohai Bay Basin and in source rocks from the Permian and Jurassic of the Sichuan Basin in China. Our analysis made use of an improved crude oil Hg pre-concentration system involving pyrolytic cracking and KMnO4/H2SO4 Hg trapping to analyze Hg fractionation during organic matter maturation to petroleum. Positive mass-independent fractionation (MIF) signatures of Hg isotopes were detected in the source rocks, with Δ199Hg ranging between −0.04‰ and + 0.48‰ (mean + 0.12 ± 0.12‰), which is significantly different from the negative Δ199Hg of terrestrial non-source rocks. Positive Hg-MIF signatures were detected in the crude oil, with Δ199Hg ranging between +0.04‰ and + 0.21‰ (mean + 0.13 ± 0.06‰). We propose a model of Hg isotopic fractionation related to organic matter history. From organic matter to source rock, Hg system variations are attributed to endogenic (i.e., photoreduction) and exogenic processes (i.e., terrestrial, magmatic and hydrothermal Hg inputs). From source rock to petroleum, Hg is mobilized during hydrocarbon migration, a process that occurs with MDF but without significant MIF.

Experimental study on mix proportions of similar materials to reef limestone

Reef limestone is different from conventional terrestrial rocks and is characterized by high porosity, low density, and low strength. To study similar materials applicable to model tests of reef limestone, reef limestone was classified into four types, i.e. weakly-cemented and dense (WD), strongly-cemented and dense (SD), weakly-cemented and loose (WL), and strongly-cemented and loose (SL) according to measured data. Sixteen test schemes were designed for mix proportions to prepare similar materials by using an orthogonal scheme. Therein, the foaming agent, powdered talc, sea sand, cement, gypsum powder, and air-entraining agent were used as base materials, and the cement/gypsum ratio, foaming agent/water ratio, and talc/water ratio were taken as controlling factors for the density, porosity, and uniaxial compressive strength (UCS). The physico-mechanical parameters of the similar materials were evaluated using range analysis. Results show that the foaming agent/water ratio exerts a strong controlling effect on the porosity and UCS and a certain controlling effect on the density; the cement/gypsum ratio and the talc/water ratio both have certain controlling effects on the density and UCS while do not exert obvious controlling effects on the porosity. On this basis, the mix proportions were optimized and the optimal mix proportions that separately meet similarity requirements of the above four types of reef limestone were obtained. That is, the ratios of the cement/gypsum ratio, foaming agent/water ratio, and talc/water ratio are separately 2.5:0.03:0.1, 2:0.02:0.15, 3.5:0.04:0.15, and 3:0.01:0.2.

Dynamic compressive characteristics and damage constitutive model of coral reef limestone with different cementation degrees

Reef limestone has a heterogeneous, anisotropic, porous structure. According to apparent pore characteristics, shallow reef limestone can be divided into four types: weakly-cemented porous (WP), strongly-cemented porous (P), weakly-cemented dense (WD), and strongly-cemented dense (D) types. On this basis, physical properties including the density porosity, and longitudinal wave velocity of each type of reef limestone and their intrinsic correlations were measured and discussed. The quasi-static and dynamic compression tests were conducted on the four types of reef limestone samples to estimate the correlations of physical properties of reef limestone and its dynamic and static parameters. Results show that reef limestone is different from most terrestrial rocks; its compressive strength is weakly correlated with the strain rate and its static tension–compression ratio is slightly larger than that of terrestrial rocks (about one fifth). The static tensile and compressive strengths as well as the dynamic compressive strength of dense reef limestone all linearly increase with the density; the static compressive strength of porous reef limestone is weakly related to the density while the dynamic compressive strength increases with the elastic longitudinal wave velocity as a quadratic function. The dynamic fracture mode of dense reef limestone is dominated by block failure while strip-shaped fragments are mainly formed along the coral growth line in porous reef limestone. The energy-dissipation density of the two major types of reef limestone is roughly linearly correlated with the dynamic compressive strength. Finally, a constitutive model for dynamic damage of reef limestone under impact load was established based on statistical damage theory and its effectiveness was verified experimentally.

Visible and near-infrared reflectance spectra of igneous rocks and their powders

Most solid planetary bodies in the solar system are covered by a layer of fine particles and the topic of light scattering by small particles has been thoroughly studied in the past decades. In contrast, light reflection from intact rocks has received much less attention, though the spectral features of fresh rocks are more diagnostic than that of highly space-weathered regolith grains. As high spatial-resolution spectral images obtained by modern space-borne and in-situ sensors have become available, it is important to understand the spectral feature links between rocks and powders made by crushing the rocks. In this work, we selected 13 terrestrial igneous rocks with a 1 μm absorption feature and measured the visible and near-infrared reflectance spectra of their slabs and powders in three size fractions, 0-45 μm, 90-125 μm, and 450-900 μm. We have found that the spectral characteristics of these samples can be divided into two groups. For slabs with reflectance lower than 0.1 at 0.5 μm, they have less pronounced 1 μm absorption feature. For slabs with reflectance higher than 0.1, they have pronounced 1 μm feature, consistent with that of their powdered counterparts. By using the equivalent-slab and the Hapke model, we obtained the optical constants and single scattering albedo values of the samples. The dependence of single scattering albedo on effective absorption thickness indicates that the differences between the spectral characteristics of rock slabs and powdered samples are likely controlled by the degree of weak surface scattering contributions. We reconstructed the spectrum of a powdered lunar meteorite which best matches the Chang'E-4 rock and found that the reconstructed rock spectra are very close to the rock spectrum observed in-situ by Chang'E-4.

Komatiites as Complex Adsorption Surfaces for Amino Acids in Prebiotic Environments, a Prebiotic Chemistry Essay.

Komatiites represent the oldest known terrestrial rocks, and their composition has been cataloged as the closest to that of the first terrestrial crust after the cooling of the magma ocean. These rocks could have been present in multiple environments on the early Earth and served as concentrators of organic molecules. In this study, the adsorption of five amino acids (glycine, lysine, histidine, arginine, and aspartic acid) on a natural komatiite, a simulated komatiite, and the minerals olivine, pyroxene, and plagioclase were analyzed under three different pH values: acid pH (5.5), natural pH of the aqueous solution of each amino acid and alkaline pH (11). Adsorption experiments were performed in solid-liquid suspensions and organic molecules were analyzed by spectrophotometry. The main objective of this essay was to determine if the complex surfaces could have participated as concentrators of amino acids in scenarios of the primitive Earth and if the adsorption responds to the change of charge of the molecules. The results showed that komatiite is capable of adsorbing amino acids in different amounts depending on the experimental conditions. In total, 75 systems were analyzed that show different adsorptions, which implies that different interactions are involved, particularly in relation to the type of amino acid, the type of solid material and the conditions of the medium.

Vesicular Olivines and Pyroxenes in Shocked Kamargaon L6 Chondrite: Implications for Primary Volatiles and Its Multiple Impacts History

AbstractAbundant vesicles are found in terrestrial rocks, basaltic meteorites, and carbonaceous chondrites which testify to the presence of significant quantities of volatiles and favorable conditions for vesiculation. Furthermore, vesicular olivine has been reported in terrestrial rocks and carbonaceous chondrites. However, vesicles in the ordinary chondrites are rare due to their low volatile content and obliteration by the late impact events. Here, we report the first evidence of vesicular olivine (Fo76) and pyroxene (En73–81Fs17–26Wo01–02) in an ordinary chondrite. The vesicular texture in the shocked Kamargaon L6 chondrite possibly formed due to localized melting during a shock event and subsequent degassing of volatiles after decompression. We propose three possible mechanisms for vesicle formation in the Kamargaon meteorite: (a) liberation of S2 vapor, (b) evaporation of moderately volatile elements (MVEs) like Na and Mn, and (c) vaporization of olivine and pyroxene, by constraining the primary abundance of volatiles based on the observed volume of vesicles. We suggest that all three or any combination of these mechanisms could be responsible for vesicle formation. Segmented texture in olivine is also observed in the shock vein (SV) of the Kamargaon chondrite. The segmentation has developed due to the formation of sub‐grain boundaries during the recovery process when grains were subjected to localized shear stress. Average shock pressure and temperature conditions in the SV are ∼24–25 GPa and ∼2310–2633K, respectively. The thermal model of the SV cooling gives the crystallization time of ∼50 ms and shock pulse duration of ∼2s.

Geochemistry of apatite individuals in Zhijin phosphorites, South China: Insight into the REY sources and diagenetic enrichment

Marine sedimentary phosphorites are rich in rare earth elements (REE) and yttrium (REY) which primarily hosted in collophanite composed of closely-packed apatite nanocrystals. Limited by small particle diameters, the fine metallogenic process of apatite crystals and REY enrichment remains unknown. To address this, using early Cambrian REY-rich phosphorite from Zhijin, South China as an example, mineralogical and in situ geochemical characteristics of apatite individuals were analyzed and compared with collophanites. Our study found that: (1) the apatite individuals, with diameters between 40 and 100 μm, were divided into authigenic/diagenetic apatites, terrigenous clastic apatites, and hydrothermally altered apatites; (2) Terrigenous clastic apatites have highest ∑REY levels (4673–12232 ppm) and lowest Y/Ho (23–28), in addition, Y/Ho showed negative relationships with ∑REY in all apatite monominerals, as well as bulk phosphorites; (3) Compared with collophanites and old phosphorite, authigenic/diagenetic apatite individuals showed similar REY patterns, in addition, diagenetic apatites have higher ∑REY, Ce/Ce* and Eu/Eu* ratios but lower (La/Yb)N and (La/Sm)N (>0.5) ratios relative to authigenic apatite individuals and collophanites. This dataset indicated that weathering of terrestrial magmatic rocks provided not only clastic apatites but also REY into the South China ocean during the early Cambrian, mixed with REY derived from deep seawater. Authigenic apatite individuals form similarly to apatite nanocrystals in collophanites, with diagenetic modification playing vital role. During this process, apatite individuals grew up and underwent stronger diagenesis than apatite nanocrystals in collophanites, absorbing REY from porewater, which resulted in higher REY concentrations in apatite individuals. This study provides new data and insight into the formation of authigenic/diagenetic apatite individuals and improves our understanding of REY sources and diagenetic effects on REY enrichment.

Ermakovite (NH4)(As2O3)2Br, a new exhalative arsenite bromide mineral from the Fan-Yagnob coal deposit, Tajikistan

AbstractIn terrestrial rocks, Br minerals are extremely rare with only nine minerals known where Br is a dominant component. A new arsenite bromide mineral ermakovite, (NH4)(As2O3)2Br, was discovered at the tract of Kukhi-Malik, Fan-Yagnob coal deposit, ca. 75 km N of Dushanbe, Tajikistan. Ermakovite is a fumarolic mineral formed directly from gas from a natural underground coal fire. Associated minerals are sulfur, realgar, amorphous As-sulfides, salammoniac, alacránite, bonazziite and thermessaite-(NH4). In addition, there are amorphous As2S3 intergrowths associated with ermakovite. The mineral typically occurs as tabular or prismatic hexagonal crystals up to 200 μm with the following forms: c (001), m (010) and p (014). Spherulites and multi-twinned intergrowths are very common. The mineral is optically uniaxial (–), ω = 1.960 (5) and ɛ = 1.716(3) (589 nm). The measured density is 3.64(2) g/cm3. The mineral is insoluble in water, HCl, HNO3 and organic solvents. The empirical formula calculated on the basis of (As+Sb) = 4 atoms per formula unit is [(NH4)0.92Na0.01]0.93(As3.94Sb0.06)4.00O6.02(Br0.97Cl0.08I0.01)1.06. The strongest lines in the powder X-ray diffraction pattern are [d, Å (I, %) (hkl)]: 9.160 (80)(001); 4.560(90)(002); 3.228(100) (102); 2.629(80)(110); and 2.522(60)(103). Ermakovite is hexagonal, P6/mmm, a = 5.271(3), c = 9.157(6) Å, V = 220.3(3) Å3 and Z = 1. The sandwich-type structure of ermakovite is based on three types of layers: (1) a honeycomb [As2O3] arsenite layer; (2) an NH4+ layer; and (3) a Br layer. The layer stacking sequence is ⋅⋅⋅NH4–As2O3–Br–As2O3–NH4⋅⋅⋅. Ermakovite has a synthetic analogue. Infrared and Raman spectra are also reported.An overview of the processes that give rise to high concentrations of Br, leading to the formation of exotic Br minerals, is given.

Radon Measurement and Radiological Dose Assessment From Terrestrial Rocks Using Solid-State Nuclear Track Detectors

Radon Measurement and Radiological Dose Assessment From Terrestrial Rocks Using Solid-State Nuclear Track Detectors

The cadmium and zinc isotope compositions of the silicate Earth – Implications for terrestrial volatile accretion

Zinc and Cd isotope compositions are presented for a comprehensive suite of terrestrial rocks to constrain the extent of Zn and Cd isotope fractionation during igneous processes and better define the δ66Zn and δ114Cd values of the silicate Earth (the δ values denote per mille deviations of 66Zn/64Zn from JMC Lyon Zn and of 114Cd/110Cd from NIST SRM 3108 Cd). Analyses of spinel lherzolites provide a bulk silicate Earth (BSE) δ114CdBSE value of –0.06 ± 0.03 ‰ (2SD). For Zn, the peridotite data of the current and previous studies define a mean δ66ZnBSE = 0.20 ± 0.05 ‰ (2SD). Komatiite analyses of this and published investigations yield similar mean values, which suggests that the Zn and Cd isotope compositions of the mantle remained fairly constant since the Archean. Data for loess provide upper continental crust compositions of δ114Cd = 0.03 ± 0.10 ‰ and δ66Zn = 0.23 ± 0.07 ‰. The Zn isotope and abundance data for peridotites and oceanic basalts are in accord with the previous observation of a mantle array, with basalts having higher Zn concentrations and δ66Zn values than the peridotites. To a first order, this reflects slightly incompatible behaviour of Zn during mantle melting and melt differentiation with associated enrichment of heavy Zn isotopes in the melt phase. Cadmium is marginally more incompatible than Zn during igneous processes and the oceanic basalts also display a minor enrichment of heavy Cd isotopes relative to peridotites. However, secondary processes produce significant Cd isotope variability in both mantle melts and peridotites, obscuring the primary igneous array. The δ66ZnBSE estimates of this and previous studies resemble the Zn isotope compositions of CV and CO carbonaceous and some enstatite chondrites. In contrast, the BSE has a lower δ114CdBSE value than enstatite and carbonaceous chondrites. This implies that the Cd isotope composition of the BSE was either fractionated during accretion or that Earth’s Cd inventory was not exclusively acquired from material related to carbonaceous and enstatite chondrites. Importantly, delivery of Zn and Cd to the BSE solely by CI and CM chondrites is not in accord with the meteorite and terrestrial stable isotope data of these elements.